Session 20 - Collections in Java | ArrayList | HashSet | HashMap

okay we'll see one concept uh collections collections in Java so first of all 

what is the generic meaning of uh collection so English meaning collection so when we will 

use a collection the word collection means a group of element right whenever you want to 

represent something some group of elements we will say collection let's say collection of 

books or collection of pens or collection of some items so whenever you want to represent 

some group of items or group of elements or group of objects we call it as a collection of 

elements or collection of books or collection of items something like this so collection is a 

word which is representing a group of uh objects or a group of items or something basically it's 

a it representing a particular group which is called collection right collection is a English 

uh word and in Java collection collection is an interface predefined interface in Java there is 

an interface called collection Java there is an interface called collection and this collection 

is having set a number of methods and variables and this collection interface is implemented 

by n number of classes there are many classes are there uh uh sorry so collection is a basical 

interface and this is again extended into two more interfaces list interface and set interface so 

let me show you the hierarchy of interfaces just a yeah yes look at this so this is the structure 

in Java we have a collection interface which is a root interface of all the collections and this 

collection interface again exted into two more interfaces list and set interfaces list is one 

interface set is another interface so this is the first one and this is second one and here they 

have extended not implemented so one interface we can extend into another interface right one 

parent interface one ja interface so collection interface is extended to list interface and also 

set interface now way in further list interface is implemented by ARR list class and set interface is 

implemented by hash set class so whenever there is an interface that should be implemented by using a 

class so class must be there so the list interface is implemented by array list class set interface 

is implemented by hash set class similarly there are some more interfaces are there some more 

classes are implemented those interfaces and we call all of them called collections collections 

means these interfaces or these classes we can use to represent a group of objects we can represent 

group of objects object or group of elements or group of item whatever it is whenever you're 

representing some group of items we go for either array list class or we can go for either 

hash set class or anything like we have a link list okay and hash set hash link list so many 

collections are there up to 10 to 15 collections are there and majorly we use this list collection 

and set collection there is another one is called ashap that is totally different we will discuss 

that later so majorly collection is is a root interface which is implemented which is extended 

into again list interface and set interface list interface is implemented by ARR list set 

interface is implemented by hashit just remember this hierarchy okay now I have one question here 

let us say in the collection there are certain number of methods and uh list interface and set 

interfaces extends The Collection so is there any possibility to have common methods in list 

and set interfaces is there any possibility to have common methods yes similarly do you have any 

possibility to have common methods in Array list and haset Har list is implemented list collection 

and list interface hash set is also implemented set interface now do we have any common methods in 

Array list and hash any possibility yes so array list and has a set are two different classes there 

is no connection between these two why because ARR list is implemented list collection list 

interface hash set is implemented set interface so there could be some common methods are there 

apart from those common methods y list can have some additional methods haset is also having 

some more additional methods which are not commonly available in both the classes possibility 

is there right because some methods will Implement from list interface and let us say there are five 

methods are coming from list interface and a list can have another five methods totally 10 methods 

possibility is there similarly few methods coming from the set interface hash set is also can have 

their own methods possibility is there so array list specific methods may not be available in 

hash set interface sry hash set class hash set specific methods cannot be available able in aist 

class okay so this is a basic understanding which we need to have so why we need the interfaces 

and collection uh classes because we need this to representing group of object especially the 

collections all kinds of collections it can be list ARR list haset hash any type of collection 

if you take basically the collections can hold objects not primitive types remember this 

okay we cannot store primitive types of data in collections so list is one collection set is 

a collection hash map is a collection all these things are called collections why because they 

can hold group of objects they can hold group of objects or group of elements or group of items 

so whenever I say object that should not be a primitive okay whenever I say object that should 

not be a primitive primitive is in the sense what in float double okay and these are all primitive 

types so this type of data we cannot store but still if you want to store in numbers right 

in a collection then what we can do we have to use something called wrapper classes because 

wrapper classes are basically what we can create an objects right for integer class we can have 

integer object for double class we have a double object something like this so if you still want 

to store numbers right or Boolean or some uh data so we have to use wrapper classes instead of 

primitive type so string we can directly use no problem because string itself is a class so 

we can directly store them in the collection okay so primitive data is not allowed string 

is not a primitive okay this is nonprimitive data type string is a class basically right 

so strings we can store no problem strings are allowed other than strings we can store 

any type of objects in collections remember one Point collections allows only object type of 

data objects only allowed it can be predefined or user defined whatever it is only object type 

of data we can store primitive data not allowed in collections okay and collections especially 

designed for only objects for object oriented programming only the collections we have to 

use so all objects a group of objects we can represent in collection and colle collection 

means what collection is representing a group of elements or group of objects that's a general 

meaning but in Java collection is an interface of all the collection root interface of all the 

collection and this interface is again extended into list interface and set interface list is a 

parent of array list set is a parent of hash set and both are totally different having their own 

behavior their own nature okay we will see what what are the differences where we have to use 

a list where we have to ask it and when it is applicable when it is not applicable so we'll 

try to understand all the scenarios one by one okay now let me start with the first list 

then we will discuss it and hashmap is totally different hashmap is a again class which is 

implemented class of map interface and there is no con connection between collection interface 

and map interface the map is also there is another type of interface okay we will discuss map later 

first we will start with collection list and set collections let me minimize it first listen 

then ask the questions okay I will take all the questions at the end of the session even if you 

type now I I'm not going to address them because there are a lot of things we need to First discuss 

and once you understand then ask the questions most of the questions will be clarified okay right 

so now go to the package and you can just take new package and uh I name it this is day 20 okay yeah 

so whatever we are discussing Java everything we are using in automation there is no question about 

it okay so let's say few Concepts we are using automation few Concepts not not using automation 

it's not like that the entire automation will use all the concepts from java whatever we discussed 

so far somewhere in some scenarios we will use everything so otherwise why we should discuss 

why I should teach the Java sessions and why you should teach all the concepts unnecessarily if 

you're not using in automation right so whatever topic even it is small topic we are discussed in 

Java including collections we are going to use in automation okay there is no second question on 

that everything we are going to use in automation but when you will know that once you start 

automation once you start using the Java Concepts in automation then you will understand okay how 

we can use these Concepts in automation where exactly these Concepts will fit into and where 

it is applicable so once you start automation you will aware of it okay but before that we are 

learning all the concepts so there is no secondary question everything every concept whatever we 

discuss in Java we are going to use in automation okay all right now go to package now I'm going 

to create new class and first we'll start with the array list so yeah array list listen very 

carefully very important concept and I'll show you multiple things in one example and there 

are lot of differences also there and we need to understand them even interor perspective also 

these collections are very very important right so array list demo and uh I'm taking main method 

of also click on the Finish okay so first of all let us first understand what is an array list and 

where it is applicable and what we can achieve by using array list class so in Java as I told 

you collection is basically uh a terminology in Java collection is an interface so collection to 

representing group of elements objects data into single entity we use collection and collection 

is an interface available in java.util package in Java we have a package called java.util in this 

package all the collections are available so now let us discuss something about erray list so what 

are the properties of error list when to use why we need to use all these things so array list is 

basically what it is a class remember array list is a a class which is implemented class of list 

interface so as we have seen uh in hierarchy The Collection is an interface root interface which is 

implemented by many many again which is extended into many interfaces list is one of the interface 

and list is again implemented by erray list right overall the collection and list interfaces are 

implemented by what err list okay so err list is a class which is implemented class of what list 

interface okay so list interface is implemented by array list class so array list is a class which 

is implemented list interface which is implemented list interface these are all predefined which 

is already there in java. U package okay so the first point in Array list is heterogeneous data 

is allowed heterogeneous data is allowed in Array list what does mean what is mean heterogeneous 

data meaning is what heterogeneous homogeneous data heterogeneous data we have a two kinds 

of data homo genous data means same type of data heterogeneous means different type of data 

or different type of objects different type of elements is called heterogeneous data so array 

list allows to store heterogeneous data that means it doesn't mean homogeneous data we cannot 

store no homogeneous data also we can store along with that heterogeneous data also allowed we 

can store different type of objects okay so for example I have EMP employee type of objects 

student type of objects so all kinds of objects we can store heterogeneous data is allowed second 

Point insertion order is preserved that means it will follow index just like a normal arrays 

concept array list is also followed the array list is also follow the indexing concept index 

will start from zero 0 1 2 3 4 like this just like there are some similarities are there between 

arrays and array list but major difference is in arrays normally we prefer to use for primitive 

data types but ARR list we will prefer to use objects okay whenever you're working with objects 

we prefer to use array list when you're working with the Primitive types we use normal arrays and 

another difference is in the normal arrays if you declare an array with some size we cannot store 

more than those elements when I say array size is five that is a fixed we cannot store more than 

five elements but AIS is a dynamic there is no specific size we don't need to specify any size 

we can keep adding more number of objects okay so that's the reason we can also call this array list 

is a dynamic array means we can have n number of objects how many objects you want to store you can 

store there is no limit for that and we know need to specify the size also okay according to the 

number of object it keep increasing dynamically so the array list is also called as Dynamic array 

so array list allows to store heterogeneous data all kinds of data we can store means all the 

data means what there should be again objects type of data not primitive data now insertion 

order is also preserved index concept it will follow zero index start from zero and 1 2 3 

4 something like this even the data which is there in the ARR list also we will represent 

by using index concept so indexing is followed whenever indexing is followed that can store the 

data in order insertion order is preserved means in whichever order we have added the data the 

data is also provided in the same order that's called insertion order preserved so observe very 

carefully first understand the points then we will try to implement practically insert order 

preserved indexing is nothing but what suppose you have created a list like this and uh let's 

say you added some data like say 10 20 30 like this right in whichever order you specify the data 

in the same order the data will be stored in the memory I said this is zero element first element 

second element so 10 20 30 so same order it will maintain because indexing is possible here it will 

support indexing concept so index is a something called is a kind of algorithm to store the data 

so to store the data in the memory there are two kinds of algorithms are there one is indexing 

second one is hashing indexing hashing okay indexing is nothing but the data will be stored 

in the same place in particular order let's say suppose if I take array list or arrays concept we 

are giving some indexes right so let's say this is entire memory and suppose if you create an array 

okay and uh let's say is some memory wherever it is got free it will go there and it will create 

an array like this and the memory location 0 1 2 3 in the same position it will store all the 

elements we can find in one single place and those elements we can represent by using Index this 

is indexing technique indexing it will store in particular order okay hashing is nothing but what 

elements will be stored in the different places in the memory there is no proper order maintained 

hashing technique in hashing technique there is no proper order maintained wherever the memory is 

got free it will go and store that object objects will store in the different different places in 

the memory whereas in indexing technique objects will be stored in the sequential of memory like 

this okay so here insertion order is preserved means in whichever order we have stored the 

elements in the same order it will maintain but in hashing it will not maintain the same order 

so in whichever order we have added the data same order it will not maintain in hashing technique 

okay so remember this these are two kinds of in algorithms are there I'm not going to deep in this 

because that is not much important for us just for understanding the point inser order preserved 

means what index follows if index is supported insertion order is preserved but index is not 

supported means what it will support hashing technique if it support hashing technique of 

algorithm then it will not preserve the insertion order just remember only these two points don't 

go go beyond that okay so some collections will use indexing some collections will use hashing for 

example uh hash set hash map so these collections will use hashing technique of algorithm array 

index or array list we use indexing concept okay so some collections we use use hashing 

technique some collections will use indexing technique okay right so as of now array list will 

follow indexing algorithm so insertion order is preserved insertion order is preserved first point 

heterogeneous data is allowed insertion order is preserved third Point duplicate elements also 

allowed that means a duplicate objects also we can store duplicates are allowed and multiple 

nulls also allowed suppose sometimes I am not aware of the value unknown values are there or 

unknown objects are there still we can store them by using null so nulls also allowed multiple nulls 

also allowed heterogeneous data allowed insertion order is preserved indexing is followed index 

will start from zero and duplicate objects also allowed or duplicate elements are allowed multiple 

nulls also allowed these are the four points we have to remember before using array list so how 

we will know when you use ARR list when we have to use array list based upon the points we have 

to decide or based upon the data which we have to define suppose you have some data or suppose 

you have some objects and you want to store these objects in the collection and how we will know 

which collection should be preferred you need to understand this point okay if your objects are 

different then you can go with the ARR list and if you want to store the objects in the proper 

order and at the time of adding at the time of retrieving if you want to use IND indexing then 

you can go with the array list and if you have a duplicate objects also you have to go with the 

array list and if you have a multiple nulls in the data then also we can go with the array list 

so if all the points are satisfied if your data is satisfied all these points then go with the 

error list concept okay if your objects or if you have some data which is satisfying all these 

points then go with the error list concept and similarly have set is having different properties 

hashmap is having different properties So based upon the data or based upon the availability of 

the data and type of data we have to choose the right type of collection in your automation or in 

your programming multiple nulls in the sense if the data value is unknown for example this is an 

array list and have some objects already stored but in this location I don't know which object 

I want to store but in future I will store some object here as of now I don't know what kind of 

object I should have in this so simply you can put null okay simply you can put null and later you 

can add this if you want so null is nothing but unknown null is nothing but not an empty value it 

is unknown means as of now I put a null and later I will add this object okay so multiple nulls 

are allowed so duplicate elements also allowed insertion order is preserved heterogeneous data 

is also allow so these are the four points which you have to remember when you're working with 

the array list concept and at the end I will also compare with other collections we'll compare 

has hashmap and everything first individually we will try to understand and also practically we do 

different type of operations and finally we will summarize it okay now let's see the Practical 

part so how we can use array list what are the methods are there as I said array list is a class 

err list is a class means what which contains so many methods right and what are those methods and 

how we can use those methods to perform different type of operations okay I have defined some array 

list I have put some objects in the array list what is the use we have to perform certain type of 

operations right on the data and those operations we can do by using methods which are available 

in the ARR list class because whenever I say class that means what which contains some 

methods predefined class means predefined methods are available now we'll discuss what are 

those methods are available how we can use those methods to perform different type of operations on 

array list okay now go to eclipse and we already created one class called array list demo and when 

you're giving the class names don't give existing class names like suppose array list array list is 

already the class which is already available so we should not use the same name to the class which 

we have created so you can just add something like a list Dem or aist example something like this 

but don't give the same name okay right so now I created one new class and there is a main method 

available now we'll see how we can use this arist first thing uh how to declare the array list 

declaration part how to create a variable for the array list declaration there are many ways to 

declare the array list variable so I will show you all the ways here you guys can tell me whether 

the Declaration is valid or not okay the first declaration array list is a class so we can create 

an object for the class right so I say array list array list okay and I'll say my list equal 

to new array list okay array list is a external class which is coming from java.util package so 

that we have to import so when you place the when you place the cursor here it will show you the 

import package you can see Java AR list comes from java. util package so import this right so 

now tell me is the syntax correct or not can we create an object for the class or not yes so if 

you look at the here object we created for the child class and reference variable is also child 

class if I look at here array list class right for this array list we created object as well as we 

created a reference variable so both we have done so this is exactly perfect syntax so we created 

an object for what a list class that object is referred by my list variable this is perfect now 

can I do like this list my list equal to new erray list new error list and the list is an interface 

which we have to import again from java. so now tell me is the syntax correct correct or not yes 

obviously why because child class object can hold in the parent class variable child class object 

we can hold in the parent class variable right everything so we can access everything from by 

using this object so this is also the correct notation this is one type of Declaration okay so 

if I use these two types of declarations either first one or second one the array list allows 

to store heterogeneous data we can store any type of objects all kinds of types we can store 

suppose sometimes I want to restrict a realist to store homogeneous data suppose I don't have 

requirement to store different type of data I want to store same type of data then what we can 

do we can do like this array list my list equal to new ARR list this is normal definition right 

so it will allow all erogeneous data now I want to store only homogeneous data suppose I want 

to store only integer type of numbers then in the angular bracket you have to specify rapper 

class here and here both the sides and here okay now this particular ARR list allows to store 

only integer type of data integer in the sense again they are the integer type of objects not 

primitive types okay integer type of data it is allowed for example instead of integer if I 

say string then this arist can store it allows to store only string type of data both the sides 

we have to put string so this array list can hold only string type of data only string type of data 

we can store okay suppose if I create a list like this suppose I have something called employee 

class okay now here you can specify employee and here also you can specify employee so then 

what type of objects it can store what type of objects it can store employee type of object 

suppose you have already employ class and I have created multiple objects of that class let's 

say emp1 emp2 emp3 and you want to store all those objects into single entity okay so then you can 

specify that let's say you have an employee class okay in the employee class you created and you 

have multiple objects emp1 emp2 and so on now I want to represent all these objects into a single 

entity or single variable then you can put here and here employee then this array list can hold 

multiple EMP objects okay so ultimately the AR list can hold only objects type of data it can 

be predefined objects or it can be user defined objects anything even the numbers also can we put 

here int and int no because primitive types are not allowed but still if you want to store numbers 

we have to specify corresponding rapper class that's the reason rapper class are introduced okay 

rapper class we can use remember this so these are the many ways we can declare the array list so if 

you want to store heterogeneous data you can go with these two definitions declarations both are 

correct and if you want to store only homogeneous data then go with this kind of a syntax and this 

will store only strings and if you want to store you can specify integer wer class or double wer 

class or any type of object we can specify okay so these are the different type of declarations 

we can do it all are correct now I want to store heterogeneous data is my requirement so you can 

use this one or you can use this one anything is okay now I'm enabling the first one okay 

this is the Declaration part how to declare the are list variable now the next item once you 

created this array list there is no specific size for that okay we can store any number of objects 

now in this array list how to add data so I want to add multiple objects right so next thing is 

adding data into ARR list adding data into into array list so how we can add data into this array 

list so whenever I create an object of this array list class this object can have certain number of 

methods right so there is a method called my list dot add this is the method and by using this 

add method we can add data into the array list so how we can add suppose I want to add numbers 

right so I can still add number but it will store as a integer rapper class it will not store as a 

primitive type similarly I can add some more data in the array list by using add method so I want 

to add homogeneous data s heterogeneous data so what I will do is I will put let's say 10.5 is a 

decimal number and here I will add string and here I will add one character okay all are taking 

as a wrapper classes so even though if you're not passing some primitive type it will it will 

convert into rapper class type so we can also add okay a is a character then I can add Boolean value 

which is true or false Boolean and duplicates also allowed right so as per the array list definition 

duplicates allowed so same 100 value again I will assign one more time I will add 100 and multiple 

nulls also allowed so my list do add null okay and multiple nulls also allowed I will add one more 

null so my list do add null okay so heterogeneous data I have added all kinds of data I have covered 

so this is a way we can add data into array list now we use add method add is a method through 

which we can add data into array list fine now if you want to find size of an array list size size 

means what how many how much of data we have added to the array list so if you want to find the size 

of an array list we have a method called size okay size of array list so to find the size of array 

list we have a method called my list object dot size in case of arrays what is a how we can find 

the length of an array size of an array array length array dot length length is a keyword here 

we have a method called size so this will give you exactly how much of data we have in this array 

list okay so here you can say size of an array list size of an array list okay so how much of 

data we have stored this will give you that number and again if you want to print this array list the 

data I want to print so you can simply print also you can say printing array list there are many 

ways to print array list but straightforward is you can just specify the name of the object that's 

it so here I can say printing data from ARR list okay I'm just added some data in the array list 

then what I have done I have printed the size of the array list and then I have printed the data 

from the array list so when I execute it this will give the same thing so if you just observe 

size of the list what how many values are there eight total eight are there 1 2 3 4 5 6 7 8 which 

is also calculated duplications so totally eight data we have added and size is eight so this is 

returning eight and now you can see the uh data is also got printed in the form of list so this is 

a data which is created inside the array list okay now let us see some more operations what else we 

can do in the AR list data after printing suppose uh as of now I have these elements in the array 

list so we also added duplic Ates so duplicates data is also added you can see duplicates are 

allowed and multiple nulls also allowed or duplicate nulls also allowed erogeneous data is 

allowed and also insertion order is preserved if I look at here in whichever order I have added the 

data at the printing also done in the same order that means insertion is order also followed it 

means indexing concept is followed so all points are satisfied now we'll see some more operations 

on this array list suppose I want to remove some object from this array list there are multiple 

items are there I want to remove one of the item or one of the element so how we can do is we can 

call them as objects elements items and whatever you want it's basically representing some group 

okay so now I want to remove some object from the array list remove or element from array list so 

to remove some particular element from the AR list how we can remove it currently these are the items 

I have eight items now I want to remove some item or I want to remove some element so then how can 

we remove for example let's say based on the index we have to remove the element so we have to know 

the index number so for example if I look at here this is 0o 1 2 okay 3 4 5 and so on now what I 

want to do is I have found out two duplicates here 100 is repeated two times now I don't want to have 

duplicate now I just want to remove this one okay the 100 I want to remove so second time when it 

comes in which position it is there so 0o one 2 3 4 and five in the fifth position 100 is there that 

I want to remove so what I can do is simply can say my list dot remove my list do do remove and 

here we specify the index number let's say five that's it so this method will remove the value 

or object which is there in the fifth position so after removing again I'm trying to print the 

error list so this is a copy statement I'm again copying this so after removing Fifth Element 

I'm again printing so here I'm writing after removing after removing I'm printing the 

array list so you need to calculate from 0 1 2 3 4 something like this how to calculate 

the index 0 it will start 0 1 2 3 4 okay now Java application now we can see this is a new list 

after removing The Fifth Element so if you want to remove particular object from the ARR list you 

have to know the index okay you cannot know the index based on the value you have to see the data 

if you know what exactly the data is then only you can find the index okay so here we don't have 

any formula like length length is not there first of all for array list so don't compare the things 

guys if you learn something just learn that only individually don't compare with other things so 

whenever you want to compare you need to compare with the similar things right for example you can 

compare one apple with another type of apple but you cannot compare Apple with orange right so 

the concepts are like that basically what you are doing is you are comparing apple with orange 

no comparision possible array is different array list is different whatever options are there for 

array they are not there in Array list whatever options are there for array list they are not 

there for array so length is a related to array concept length meth is there that is related to 

Strings concept here we have a size okay size is different size is related to array list so 

there is no they are not comparable basically right so after removing the element from the 

array list this is the latest list so now we can see 100 is 100 repeated only one time so 

this is the latest list okay so 100 is once come only comes once and fifth position 100 is 

got removed after applying this remove method so if you want to remove any element from the array 

list we can directly call the remove method just by passing index and here five is index five is 

a index of element particular element whichever element you want to remove you can specify that 

index and index you need to count from zero 0 1 2 3 4 You need to count so this is a zero element 

this is a one element this is a second element third element fourth element and Fifth Element 

so we say five here that's the reason 100 is got removed okay now suppose I want to insert a new 

element in the middle of somewhere in the middle of somewhere I want to insert let us say I want 

to put some value uh before welcome and a between these two or between these two or between these 

two somewhere in the middle of something I want to insert some value then how we can do it insert 

element in the array list insertion is different adding is different okay remember this adding 

means what nothing but what suppose here we have called method called add so add means what 

these elements will be added one after another one after another I will tell you the difference 

here listen carefully adding and insertion suppose you already have some objects in the releas like 

this these elements already there and if you call add method of some value here okay and this will 

be added at the end of the list and again if you call one more add method and allue add one more 

value this will be added at the end of the list so whenever you call this add method along with 

some value it will keep adding the values at the end of the list at the end of the list but my 

requirement is I want to add value in the middle of the list somewhere in the middle of the list 

then how we can add we use same add method but additionally we have to follow we have to provide 

index so how to use this add method just we pass only value right but if you want inser the data 

then what we can do is we say my list. ADD of a method overloaded method is available this 

add method take only one parameter another add method will take two parameters the first 

parameter should be an index second parameter should be a value now what happens this value will 

insert exactly in this particular index or in this particular position so that's how we can insert 

the value in the array list insertion is nothing but in the middle of the array list somewhere 

we can insert the value okay suppose you have inserted a value then what happens to the rest 

of the values for example let's say currently this is my array list okay suppose here x y j 1 2 

some elements are there 0 1 2 3 4 these are these are the indexes right now in the second position I 

have written method like this add second position and put some a I have written statement like 

this in the second position I want to insert a then how to after executing the statement how 

this array list becomes how this array list becomes so X is same same position y first 

position same 0 1 2 3 4 5 and uh second position earlier we have a Jed in the second 

position we have a j but in the second position which value we have inserted a now it becomes a 

second position it will come a but rest of the three values will be move to the next positions 

or will occupy the next positions that means J 1 2 these Valu Still Remains the Same the value 

will not be deleted okay existing value Still Remains the Same just what happens between these 

two so exactly in the second position we have added a here then what happens it will create 

a new memory location here rest of the values will move next locations okay so after insertion 

you will get the latest array list like this so insertion is nothing but what we can insert the 

value in the middle of the list adding is nothing but what we can add values at the end of the list 

okay you understand the difference between adding and insertion adding means at the end of the list 

we can add insertion means at the middle of the list we can insert and what is the difference if 

you provide only value here that will be added at the end of the list if you provide value along 

with the index then the value will be inserted in appropriate index insertion will happen 

Okay index will automatically update updated in the sense rest of the value will move to the 

next positions and it will make free the second position and the new value will be inserted in 

the second position so this is how it will work insertion okay now we'll see so as of now this 

is my array list right now let us try to insert something in the middle of the list so I said 

my list dot add this is overloaded method Okay add two parameters we have to pass and in which 

position I want to add let's say second position uh I want to add something called Java okay 

after insertion again I'm printing the list after insertion okay after insertion here this is 

after removing this is a final list then after insertion again I'm printing the list just 

observe yes now we can see this is the latest one now you just compare first element exactly 

same no change second 10.5 10.5 same now we can see in the second position Java is occupied and 

these values are moved to the next positions next positions are occupied so that's the reason it 

is more Dynamic according to the data it will keep adding keep reducing the sizes so this is 

how we can insert an element in the list adding insertion add means we can add data in the at 

the end of the list insert means we can add data in the middle of the list this is one method of 

suppose I want to modify the value modification change the value for example here I have added 

Java now I don't want to have Java here instead of I want to make it as a python now I want to 

change this data or modify the data then how we can do it modify element how to modify element in 

the arror list just modification yeah it is not uh yeah it is we can also call it as replacement 

yes replacement or modification or change whatever you want that's all are correct modification 

in the sense what we can call it as a modify or replace or change okay now how we can do this 

as of now these are the elements I have new list in this Java is in the second position that I 

want to replace with the python or I want to modify this with the python then what you can do 

is my list dot my list dot set is a method set and here we have to specify index and value so which 

value you want to change Java what is the index of java two is an index and what is the new value 

you want to replace with new value is python that I can specify okay so in the same second position 

whatever existing value which we want to replace with the new value now after replacing again I'm 

printing after modification or after replacing again I'm printing my list after replacing now 

just observe this is the new list we got after replacing okay now we can see Java is 

replaced with the python this is called replacement modification or change anything 

you can call okay suppose I have these many elements as of now in my err now I want to 

access specific object I want to retrieve the specific spefic object let's say I want 

to extract this part I want to extract 10. or I want to extract python specific object how 

to extract or specific element how to extract or access access specific element from array 

list specific element so for example I want to access welcome then what is an index of 

Welcome index number of Welcome is what 0 1 1 2 and three three is an index of Welcome three 

is a index of welcome you need to count from zero 0 1 2 3 so my list dot there is a method 

called get get and this will accept index number so we need to just pass the index number 

index number so what is an index of this 0o 1 2 three so what is the problem guys can you see 

my screen everyone okay fine so video lagging means your internet connection is slow you can 

just check some from your side okay all right so my list do get off three so what is this 

three three is a index number so what is what is the value which we have in the third place 

0 1 2 3 welcome is there so the get method will return the object get method will return that 

object so that I can print my list dot get of three you can print like this so get is a method 

through which we can extract or we can access or we can retrieve the value or element from the 

array list so we need to pass index so here three is index three is a index let's execute now 

so this will give you the element which is there in the third position so this is return welcome 

so how to access the value from the list by using get method specific value we can access that is 

using get method and get method will accept index so if you know index then only we can extract 

the value by using index we can extract the value okay if array is too long you can find 

the size right dot size will give you total number how many number of indexes are there so 

that's the only way we can count total number of index okay now after accessing now the next 

thing is how to read all the values so there are multiple objects are there in my array list now 

I want to read all of them then how we can read reading all the elements from arist so this is 

the most important stuff there are many ways to read the data from the array list we can use a 

normal classic for Loop we can use enhanced for Loop or for each Loop or we also have something 

called iterator iterator is something new which is especially designed for collections okay by 

using iterator iterator is basically called as a cursor and by using that iterator also we 

can read the data from the collections all collections are supported so there are three 

different ways to read the data from array list now I'll show you one by one listen very 

carefully so the first approach reading all the data from the array list I'm not going to print 

reading in a sense not like this when you put my list it will just print all the data but not 

like this I want to get individual values all of them so the first approach using normal for 

Loop using normal for Loop so what I can do is using normal for Loop how to read the data by 

using normal for Loop so a list anyway follow the indexing concept right so what we can do is 

we need to know starting point ending point and the condition how much value we have to increment 

it is just like a simple normal array concept so how we will read the array by using normal for 

loops similar way we can also read data from array list suppose this is my array list I have 

some data 0 1 2 3 so we have to start from zero then we have to stop here and every time we have 

to increase I value by one so let us see how to read the data from the array list simple for I'm 

using for Loop directly and what is the starting point in I equal to 0 index start from zero and 

where we should stop suppose if you don't know size of an array list so how we can get size of an 

array list using size method so I less than I less than my list do size I less than my list dot size 

because index is starting from zero you just say only less than is okay suppose if you still want 

to put less than or equal to then what you should say you should say minus one here okay minus one 

so why we have to do like this already explained in the array concept just you have to remember 

this and if you don't specify minus one say only less than because we have to take from zero and 

last index you start from one the last index will be n minus one so this is a mest do size and 

how much value have to increment every time by one so I ++ okay now let us retrieve the data 

from the err list so my list Dot get is a method available right we already seen what is the get 

method will do get method will retrieve the data by using index so my list. getet I'm passing I as 

an index and then semicolon that's it one single statement and that I'm going to print so system 

print Ln and list.get we can put inside the print method and here inside this you can put my Lister 

do get offi so this will retrieve the values one by one based upon the index and then it will print 

by using print Ln right now execute yes now we can see we got all the values individually right 100 

is a starting value so this is a value so we will able to read the data from ARR list using normal 

Fun Loop this is one approach now let me show you another one we can also read data from ARR list 

using for each Loop or enhanced for Loop using enhanced for Loop or for each Loop okay it is 

very simpler than the first one here we don't need to use any indexing or nothing directly 

write one for Loop and what is the name of the array list my list so from the my list I will 

extract each individual value into a variable let me take some variable called X now tell 

me what is a type of this x variable what is a type what is the type of X yes so if I look at 

this from this array list we have different type of objects right heterogeneous data we have 

so at the run time we don't know what type of data we are getting into X sometimes you will get 

integers sometimes you will get decimal sometimes you will get Boolean different type of data you're 

getting into the X in every iteration so X should be an object type then only it can hold all kinds 

of data right and then I'll print the value of x simple so this is the way we can print the data 

from the array list so if I look at here this is the data which we have got so from here it is 

red so this is a data so by using enhanced for Loop we can also read the data from the array 

list now the third approach is completely new for us so these two approaches we already know 

earlier because we already work with arrays concept same thing we followed here also now the 

third approach is this is specific to collections iterator by using iterator we can also read 

the data from the error list next option using iterator yes I is a index number in the first Loop 

we have read the data by using indexing so we need to follow the index here in the for each Loop we 

don't need to do any index because for each Loop will automatically get the values 1 by one into 

variable and then we are able to print it okay now now come to the iterator iterator is a Something 

New Concept so far we have not learned because this iterator is purely related to collections 

it will not work for any other concept only for collections all kinds of collections will support 

we can use the seator for a releas hash map hash set for all kinds of collections we can use the 

seator to retrieve the data from the collections now let us try to understand how to use this 

iterator concept for array list how we can read the data from array list using iterator okay 

so basically the iterator is a cursor in we say okay we can create one iterator variable like this 

iterator it equal to my list dot we have a method called iterator so iterator is a method which is 

already there in the array list okay iterator is a method which is already there in the error list 

we can call that method so when you call this iterator method what this will return is this will 

return something called iterator type of an object it will return something called iterator type of 

an object so here we have to Define some variable let's say it and the type of the variable is what 

iterator type okay the type of this variable is what iterator type and this iterator we have 

to import from java.util package there are multiple packages are there you need to carefully 

import only java.util okay now in this particular statement from the my list. iterator I just call 

this iterator method and what this iterator method will return is iterator type of object so I have 

created this variable with the iterator okay now we need to write something called while loop 

whenever you are using iterator we prefer to use while loop okay why suppose if you know exactly 

how much of data you have in a list okay then you can go with for each Loop or you can go with the 

normal for Loop suppose if you don't know how much of data you have in Array list you don't know how 

much of data you have in err list so what I can do is first I will check the data exist or not 

if exist then I will get it and take and check another data is exist or not if exists then I will 

take it so before getting the data I will check the data is exist or not okay so what we can do in 

this we have to write one while loop okay in this from it object I will call one method called hash 

has next has next what this method will do is this method will check the element is present or not 

it will not follow indexing remember this iterator also will not follow any indexing this will also 

itate the list one by one just like a for each Lo okay so has next is a method this will check 

the first element is present or not if the first element is present then this will become true this 

will return return true conditional statement if it is written true then from the same iterator we 

will get the value by calling next method next so this method will get the exact value from the 

list that I am going to print by using system do do print Ln I can go the print so has next and 

has sorry has next and next these are the only two methods we have to remember so system. pelm it. 

next so has a next method we'll check the next element is present or not if it is present then 

get it value then again it will go up next again it will check the next element is there not yes if 

it is exist then get the element how many times it will repeat till it reaches the end of the list 

and after it reaches end of the list if it could not find any more elements then this condition 

become false then it will automatically exit so when you run this just observe it will also 

read all the data from The Collection can just see here so we got this data so by using iterate 

also we can read the data from The Collection I will repeat once again listen very carefully there 

is no break nothing it will automatically repeat everything till end of the array list as soon as 

the elements are not found then this condition become false it will exist from the while loop 

okay so why we prefer this while loop here because we do not know how much of data we have in this 

array list that's the reason dynamically we are checking each and every element exist istance then 

we are reading whenever it found no value in the ARR list then it will stop executing okay so has 

next is a method through which we can check the element exist or not id. next is a method this 

will get that particular element from the array list so before doing this we need to call one 

method called iterator from the array list and that will return iterator type of variable so 

we need to create this variable using iterator object these are again predefined so from this we 

can access as next method e next okay so when you run this you will get all the data fine so now for 

example I'm not writing any y Loop okay just what I will do is it. next it. nextt I'm just printing 

it I'm not using any looping statement now tell me what is an output of the statement will it execute 

first if it execute what is an output of the statement so what is an output of ID do next okay 

so here we have not used any looping statement we are not checking existence or not has a next 

method we are not doing anything so if you're not doing anything it will just return the first 

value in the array list the first value in the array list which is 100 so which is retaining the 

first value in the array list next time I want to get the second element third element fourth 

element Fifth Element right so for that reason we have to use has next so has next method will 

do two task one is it will go to the next element in each every iteration and check the existing 

element or not that's how has next method will work for example first time I'm using it do has 

next what it will do in the first round it will focus on the first element and if it is exist 

or not if it is exist then it will become true and it will come inside and get this element 

and next iteration has next method will check the next element present or not if it is present 

the next method will retrieve that value in the next round of iteration again has the next method 

we check the next element is present or not if it is present the next method will retrieve another 

value now in the next iteration again has next method will check the next element is present or 

not if it is present return that value so this is how has next method will work has next method will 

repeat every iteration go to the next element in each and every round and after going it will 

check the element existing or not so once it is reached end even this is also done now after 

that it will check has an next it will go to the next position so no value is available then this 

condition Falls and it will automatically exit so this is how we need to use iterator to get the 

data from the array list is it clear everyone how to read the data by using iterator concept so 

we need to First create first we need to call the method called iterator from the list Object 

Store into variable the variable type is iterator and then by using while loop by putting has next 

and next these are the two methods which we need to remember okay so has next and next by using 

these two methods we can get the data so next me if I use next method alone it will return return 

always first value okay but when I use next method inside the loop right then what happens this has 

next method will go to each and every element one by one right so whichever element the has next 

is focused that element will be written by the next method you understood the point so whichever 

the element is focused by has next method that element will be returned by the next because has 

next will navigate through array list that is a point here any confusion guys it is simple topic 

actually unnecessarily are making complication so has the next method will go to each and every 

element one by one now navigation is happened through the has next method next method will 

capture the element whichever is there in that position so the com by combining has next and next 

methods we will able to retrieve the data from the hash okay so array do not have values see simple 

logic guys in Array I have stored some values this is the first value this is the last value right 

so has next method first Focus here then here then here then here then here then after completion 

of that is there any location is available no no right after completion of the value no no 

element no location is there so obviously has next method will return false if the value is 

present then only it will return true if the value is not present return false got my point so 

here there is no question of uh having location or having element nothing as soon as you found 

the last element the next no no element right so has next method will go to the next and check 

no value so it will exit automatically it will exit yes it is just like a it is not similar to 

the object actually iterator method we are calling from the my list my list is what a list object 

from from the array list object we are calling iterator method so iterator method will return 

the iterator type of variable okay iterator will return return iterator type of variable that's 

the reason this variable which we created in iterator type iterator type so methods will return 

something it's very simple concept guys observe very carefully suppose if I create one method 

suppose M1 method I created if this method is returning string for example if this method is 

returning string so when I call M1 method and I created one variable called X now tell me what is 

the type of X what is the type of X string right why X is a string why X is a string because M1 

method is returning string output string outcome that's the reason this variable the holding 

variable should be string right this is clear everyone similarly in arror list we have a method 

called iterator and this iter Ator method do something here and finally it will return iterator 

type of object so this iterator is a written type so when you call this iterator method when 

you call this iterator method from the my list array list object so what is the written type of 

iterator method what is the type of this iterator method iterator is a type so this variable should 

be iterator so are we Crea any object here are we creating any object no we are not creating 

whenever you see new keyword that is a creating an object okay there is a difference storing the 

object in a variable is different creating an object is different when I use new keyword that 

will create an object here we are not creating any object we are storing the output in a variable 

that variable type is iterator you understood now everyone all right so this is how we can specify 

the iterator okay sometimes for example the my list is having homogeneous data homogeneous data 

suppose my list having only strings only strings so then here we can specify some rapper class 

called string if the iterator contains only strings suppose if the array list contains only 

strings then you can specify rapper class as a string suppose my ARR list contains only integers 

then we need to specify integer wrapper class if my collection contains only employee objects then 

you have to specify the employee class if your collection contains heterogeneous data integers 

strings booleans everything then it should be object okay so this is optional so specifying 

this angular bracket is optional even though if you're not specifying still it works but even 

though if you specify that there is no problem you understood my point so based upon the data 

we have to specify proper uh type in the angular bracket so this is how we can use iterator to 

read the data from the array list okay so yes this is depends upon the what type of objects 

you have in the array list so when I object here it will allow us to store all kinds of data 

so better to go with object itself okay now next item suppose I have some items in my array list 

as of now what are the items I have so these are the elements or I have in my AR list so I want 

to check my array list contains items or not is my array list is empty or not I want to check 

okay so how we can check but before reading we will normally check right if the array contains 

then we will read it so based on the condition we can do it so checking array list is empty or 

not checking array list is empty or not how we can check my list dot is empty there is a method 

called is empty so this will return true if it is empty returns true if it is not empty return 

false now tell me the output of this true or false true or false so this will return array 

list is empty or not is array list empty it will return yes yes or no it will return true or 

false it will will it return false or true it will return false why because currently we have some 

elements already present in Array list right so if there are no elements in Array list then only 

it will return true so if I look at here it is written false because error list contains some 

data okay now I want to remove I want to remove all the data from array list remove see earlier 

we have seen how to remove specific value right by using remove method so by using remove method 

we can remove specific value from the array list but if we want to remove all the objects from list 

all the elements I want to remove then how we can remove remove all the elements from array list 

how to remove all the elements at the same time at time I want to remove everything very simple 

my list dot remove all remove all that's it here we can specify something called list so remove 

all method we cannot remove all elements at a time but remove all method directly won't work 

we need to pass some parameter here I'll tell you how to remove all the elements at a time so with 

single statement it is not possible okay remove all method we remove all the stuff but before 

that we need to do something so what we need to do is remove all method cannot remove all the 

elements if you want to remove all the elements if you want to clear everything you have to call 

clear method there is a method called clear that will remove but if you want to remove multiple 

elements specific elements there are multiple things are there let me show you let's say this 

is my array list and I have some elements a b c x y z so these are the Ms currently I have 

suppose if you want to this is 0 1 2 3 4 and five now I want to remove specific element what 

you will do remove and specify the index so index of C is what two and this will remove C this will 

remove this particular element particular object suppose if you call clear method just so here my 

list. remove my list. clear so when I say my list do clear all the elements will be cleared so it 

will return empty nothing but my requirement is different my requirement is I want to remove 

multiple values randomly for example I want to remove a b c or I want to remove a and X or 

I want to remove B and Y how it is possible I don't want to write remove methods multiple times 

okay I don't want to remove this method I want I don't want to repeat this remove method multiple 

times if I want to remove a and C you can write two times mest do remove of zero mest do remove of 

two two statements you can write two elements will be removed but I want to remove multiple elements 

with the single shot then how it is possible okay first what you need to do is we have to create 

a separate list okay I say my list two I will create a separate list my list and in the my list 

what we need to do is we what are the elements we want to remove we have to put those elements in 

that new list let me show you practically then you can understand so here I'm going to create 

a new array list variable array list my list two equal to new array list and I created a new array 

list variable just observe no remove method cannot allow two parameters only one parameter is allowed 

that is index okay now ARR list my list to equal to this is a new array list I have created and in 

this array list okay my list 2 do add so what are the elements you want to remove from the ARR 

list those elements we need to to add to the new ARR list suppose I want to remove a so that 

I can specify here a I want to remove my list to do add and what else you want to remove I want to 

remove B also B you can specify and what else you want to remove my list 2. add X also I want to 

remove so I can say x okay so what are elements you want to remove pick those elements and uh 

create a new array list my list is different my list is already I created earlier and my list 

contains these elements now my list two contains three elements okay my list two contains a b and X 

now I want to remove a b x from the verginal list so what I can do now here is take the verginal 

list my list dot remove all remove all because remove all will allows another type of colle as 

a parameter that's the reason we have to pass this mileage to two here this is the statement so 

what exactly Happening Here is from the my list my list is what this is the one original list from 

this remove all what are all we have to remove whatever the elements are there in the my list two 

those elements should be removed so what are the elements are there in the my list two a b x so 

these three El elements will be removed from my list you understood the point this is an example 

okay so what are all elements we have to remove we need to keep those elements in another array 

list separate array list variable and that array list variable we have to pass now in our context 

so what I will do is I will pass our data let's say 100 I want to remove from my array list and 

then welcome also I want to remove from my array list these are the two values I want to remove 

from my array list okay now let us understand this yeah there is no shortcut way this is the 

only way we can remove all the elements at a time or else you can use Clear three scenarios I 

told you right three scenarios I'm repeating the same thing again and again you have to focusly 

listen see this is my array list I have multiple elements if you want to remove specific element 

one element then what you should do remove method you can use remove of you can pass index 

whichever element you want to remove you can pass index that will remove single element if 

you want to remove all the elements every element then you can call clear method and this will 

remove all the elements but these are not my requirement my requirement is what randomly 

I want to remove here and there some element few elements not every element then you need 

to follow this approach this approach is for what removing multiple elements randomly if you 

want to remove all the elements straightforward clear method is available if you want to remove 

single element then remove method is available if you want to remove multiple elements randomly then 

you can go with this support no direct method is available got my point everyone understood these 

are the three scenarios now in this scenario what I'm doing I have added these two elements in 

the new array list variable that array list I passing as a parameter into remove all method 

so after removing now let us print my list so after removing multiple elements I'm printing 

my list okay now this iterator also I'm just commenting for now okay now just observe how 

it is going to remove multiple elements okay now we can see after replacing these are the 

latest list now after removing how many elements we remove two elements see 100 and welcome now 

we can see in this list we cannot find 100 and welcome that means two elements are got removed 

at a time so this is how we can remove multiple elements randomly so this is a workaround for 

us there is no strip method available okay there is no Direct method available so this 

is the work for us so in the line number 81 what we exactly we doing from the my list I'm 

removing all which are there in the my list two so whatever we have added to the my list 

two those elements we are removing from the my list right so whatever elements are there in the 

my list to only those elements will be removed from the my list whatever elements we are there 

in the my list to only those elements will be removed from the my list okay is this clear 

everyone this is more than enough actually all right so if you want to remove all elements 

for example then what you can do remove all the element remove all the elements or clear what 

you can do simple my list dot clear that's it so after clearing right after clearing uh I'm 

checking array list is empty or not so for that what you can do this statement I can use after 

clearing I'm executing this now tell me what is an output of this statement now this time what's 

an output of the statement true or false true this time it will return true because array list is 

cleaned up so is array list is empty yes or no is the is empty true or false yes true so when 

I execute it this will return true yes okay so these are all different type of operations we 

can do with the array list everything is clear so far so that's it for array list concept 

array list is a collection in which we can store heterogeneous data insertion order is 

preserved duplicate elements are Al allowed multiple NS also allowed and we can do we can 

add elements we can insert elements we can remove single element we can remove multiple elements 

we can remove all the elements we can find size of an array list we can find array list array 

list is empty or not so all these things we can check so once it is clear we cannot get back 

okay all the elements are got cleared that's it once it is removed or once it is got 

cleared we cannot get back those elements okay so can you please guys confirm in the chat 

box is it clear to everyone how to work with a list it is very easy concept actually there is no 

objectoriented programming nothing no conditions nothing it's very simple and straightforward 

okay now let us move on to the next collection called hash set so if I look at here 

the collection interface again extend into set collection and this the set 

collection again implemented by what hash set class okay now let us understand 

about hash set or set collection go back so what are the properties of 

hash set let me put some points here hash set yeah so hash set is a class which is 

implemented set interface hash set is a class which is implemented set interface so 

what is the first point heterogeneous data allowed homogeneous data is also allowed this 

is a common point between har list and hashmap hash set sorry hashmap is different okay this 

is Hash set insertion order is not preserved in Array list insertion order is preserved 

because it will follow indexing technique but here insertion order is not preserved because 

it will not follow indexing technique it will follow hashing techniques that's the reason it 

is starting with hash whenever you say hash the keyword that is following hashing technique okay 

so insertion order not preserved that means what there is no indexing Concept in hash set so data 

is represented with a different thing but 0 1 2 3 4 that kind of index is not there in the hash 

set or collection index is not there that the reason in such order is not preserved means 

what in whichever order you have inserted the data it will not store the data in the same 

order that is the meaning of insertion order not pres we'll see practically duplicate 

elements also not allowed but in Array list duplicate elements are allowed but in hash set 

duplicate elements are not allowed that's the reason even multiple NS also not allowed only 

one single null is allowed if you add one more null again it become duplicate nulls so duplicate 

elements are not allowed so single null value is allowed heterogeneous data is allowed insertion 

order is not preserved duplicate elements also not allowed multiple nulls also not allowed so 

these are the attributes of has set collection okay now we'll see what are all operations we 

can do in hash set and don't compare aist and hash set has set is having different methods 

there are certain things are possible in has set but they are not possible in Array 

list similarly there are certain things are possible in Array list but they are not 

possible in haset remember yeah it is also Dynamic heterogeneous data you can keep adding 

more data there is no limit for this yeah now let us see the Practical part has set is a class 

which is implemented set collection remember the set interface inter perspective all these 

concepts are most important hash set demo right so first part 

declaration how to declare hash set declaration how to declare the hash set again 

there are multiple ways we can do it so directly if you want to do using hash set my set equ Al 

to new hash set this is the direct approach so object we created for hash set and reference 

variable is also hash set you can import this hash set from java. util package this is one 

so this will allow us to store heterogeneous data all kinds of data we can store and set my 

set equal to new hash set is it correct or not set my set equ Al to new hash set is it correct or 

not so set also interface we have to import from java. yes because this is a child class object 

so we can store child class object in the parent class variable so this is also right notation 

perfectly fine suppose these two notations will allow us to store heterogeneous data all kinds 

of data we can store but now I want to restrict it to specific data homogeneous data I want to 

store only homogeneous data then how we can do it we can do like this we can do Hash a set here 

in the angular bracket you have to specify so what kind of data you want to have suppose I want to 

have only strings then you can say string here and one more time here also before the bracket 

also we have to specify string like this okay and even hash set also allows to create only 

objects primitive types are not allowed in any of the collections okay collections I'm talking 

about collections means primitive data is not at all allowed only object type of data so this is 

another type of notation so there are multiple ways we can declare the has set variable depends 

upon your requirement now I'm trying to enable the first one hash set myet equal to new hash set so 

this will allow all kinds of data heterogeneous data is allow now so once we declare this hash 

set how we can add the data into hash set so adding elements into hash set how to add same 

method is available add method is available why because has set AR list comes from what list and 

set list and set comes from what collection so there may be some common methods available right 

chance is there so add method is available in the both the classes so by using add method we we 

can add elements to the hash set now let me add something so add my set do add here I'm adding 

100 similarly I will try to add some more values just observe very carefully most important point 

I'm going to discuss here according to the has set duplicates not allowed multiple nulls also 

not allowed duplicate number duplicate values are not allowed multiple NS also not allowed but 

intentionally I'm giving some duplicate numbers and nulls also then what will happen we will 

see so here I'll say decimal number and here I will see string variable here I will put a Boolean 

variable because this is a heterogeneous data here I will put character type of data then here again 

I'm doing duplication see observe so duplication so whatever value I have given here same value 

I'm repeating but actually has a set not allowed duplicates but still I'm trying to add duplicate 

we'll see what will happen and multiple nulls also not allowed but still I'm trying to give multiple 

nulls this is one null there is another null okay see all kinds of data have added even duplicate 

values also have added multiple nulls also added but now if you trying to print my set then what 

will happen observe very carefully this this is most important see these are the elements I 

have so with this we need to understand three points three point we need to understand see in 

which order we have added the data what the first element 100 second element 10.5 but here what 

is the first element null second element a that means what in whichever order we have added the 

data it is not preserved in such an order it is not preserved in the same order it's not printed 

we have added in different order it is printed in the different order that means insertion order 

is not preserved second Point insertion order is not preserved next Point duplicate elements not 

allowed null also not allowed multiple nulls not allowed if I look at here even though I'm trying 

to add duplicate value or duplicate nulls but finally it is taken only one null and one value 

100 see duplicates are automatically eliminated so this is the final set set collection so at 

the time of adding even though if you added some duplicates duplicate nulls it will automatically 

remove the duplicates and it will keep only the orinal values so this is how it will work okay 

so three points we understood insertion order is Not presed Duplicate elements allowed duplicate 

element not allowed multiple NS also not this is a default behavior of hash set collection insertion 

order will not present in whichever order we have added same order you will not get okay so that is 

a default Behavior set collection so now tell me when you will prefer set set collection when 

you will prefer again depends upon the data suppose you have some data which is homogeneous 

okay and which is also not having any duplicates and you do not have any nulls duplicate and 

you no need to maintain the insertion order then you can prefer the hash set so depends upon 

the nature of data we have to choose the right and appropriate collection type okay now tell me 

you if you want to maintain the insertion order and which collection you will select you want to 

maintain the insertion order in whichever order you have inserted in the same order I want to 

maintain and which one you will prefer has set or array list array list is preferred now I have 

I don't have any duplicates data I don't have any nulls then which one you will prefer has set 

okay so depends upon the nature of data you have to choose the right type of collection either 

ARR list or haset both are not preferable at the same time sometimes we prefer haset sometimes 

we prefer haset AR list okay so now we'll see different type of operations on hash asset 

so this is how just for printing has a setup okay no at the time of adding it will 

not give you any error at the time of adding duplicates also it will not give 

you an error but ultimately it will not take those values at the run time it will not 

take those values because this value is a old value this is a new value so values are same 

so it will keep only one it will compare both and will keep only one that's the automatic 

mechanism okay now suppose this is my hash set I want to remove specific value from the 

hash set I want to remove specific value from the hash set how we can remove it can anyone 

guess how to remove the element from the set removing removing element how to 

remove specific element from the haset is it possible or not how we have done in 

Array list how we have done in Array list by using Remo method right remove and we pass 

index number there by passing index we removed it but here we do not have a remove indexing 

concept here we cannot count the values from 0 1 2 3 4 no indexing is not at all supported 

here but then how we can remove the data myet do remove we directly specify the value not 

an index okay suppose 10.5 is there I want to remove 10.5 so you can directly specify 

that Direct Value have to specify okay so here 10.5 is the value not an index okay 

it is not an index but in case of ARR list we pass index number according to the index 

the values got removed but here we don't have indexing concept so we have to directly pass 

the value in the remove method so this will remove the 10.5 then after removing again I'm 

printing the data so this is after removing I will come to each and every point just have some 

patience okay so I'm just printing my set just observe see now 10.5 is got removed so this 

is the latest value in the set collection so we have to pass the value directly 

not an index index is not supported now suppose I want to insert value in the 

middle of something insertion inserting element inserting element is it possible or not 

insertion is possible or not inserting is not possible in the hashing hashing if any collection 

is using hashing technique in that insertion is not possible why it is not possible is there any 

specific reason why insertion is not possible see if you have stor the values in the proper order 

then insertion is possible if the elements are storing in the random order where you want to 

insert right there is it's not possible so if the elements are there simple example I'll give 

you guys few persons standing like this in the order in the particular order like this and the 

new person can come and stand in between any of them right here here here suppose one person is 

here another person is here another person here so the next person will come he can stand anywhere 

there is no specific area and specific order right so that is the reason insertion is not possible 

in the set collection insertion element is not possible not possible insertion is not only we 

can add the elements at the end of the set but not possible to add inser retrieving the specific 

value or access specific element accessing specific element how to access specific element 

from the set collection accessing specific value from the set collection or retrieving the value 

from the set collection so in Array list how we have done in Array list array list dot get method 

we have used in the get method what we have passed index number right get method accept index number 

based on the index it will capture the value but here we do not have indexing concept right so we 

cannot extract specific value from the hash set so accessing specific element is also not possible 

okay it is also not possible inserting element is not possible but accessing specific element 

is also not possible but there is a alternative way is available indirectly or it is we can call 

it as a workaround if you want to retrieve the values from 1 by one or if you want to retrieve 

the specific value from the set we have another approach I'll tell you there is no direct approach 

available so directly it's not possible if anybody ask you in interiew is there any is it possible 

to access specific value from the hasch set no not at all possible but is there any workaround 

available yes workaround is available let me show you that without using Loop only I'm not using any 

looping looping statement anyway we can access but without looping statement how we can access let me 

tell you direct element we cannot directly access okay that is sure but after converting this set 

into ARR list we can access we can convert a set collection into array list collection array list 

is a totally different collection we can convert a set collection to array list collection once you 

converted we can access the values from array list easily right yes so let us see how to convert so 

first part convert has set to array list let us do how to convert so to do this what we need to do 

is we need to First create array list variable so I'm creating array list variable first array list 

Al equal to new array list I have created an array list object in this we have to pass has set object 

that's it so this array list we have to from java now what exactly we are doing is we are converting 

the set collection into array list collection we are converting the set collection into ARR list 

array list so how we can do it we just create an array list object and just pass set collection 

object whatever set we created that object we need to pass now the AL is having same content or not 

whatever is there in my set the same content is having in Al also right now if you just print Al 

and see what it contains so when I write Al when I print array list now you can see these are the 

elements so in Array list index possible or not in Array list indexing is possible or not yes so 

obviously we can retrieve the specific value Al off which value you want to retrieve 100 I want 

to retrieve so what's the index of 100 0 1 2 two is a index of 100 so Al do get of two because we 

don't have we have a get method so a. get of two this is a work around for us so now we can extract 

the specific value but we cannot directly access value directly from the set collection once you 

convert it into array list then we can extra okay clear everyone so this is the alternative approach 

if you're not able to retrieve the specific value from set collection is not possible that is sure 

but once you convert this into array list we can get it this is indirect process and we haven't 

used any looping statement also okay remember this fine now the next thing suppose uh I want to 

read all the values using looping statement then how we can do this looping statement read all the 

elements using looping statement again there are multiple ways we can use normal for Loop okay so 

normal for Loop is not possible here let me tell you why read all the elements using enhanced for 

Loop only for each Loop it is possible so why it is not not possible by using normal for Loop can 

anyone tell me see I want to read all the data from the set collection using looping statement 

what I'm saying is normal for Loop through the normal for Loop we cannot read the data from the 

set why because there is no index in the normal for Loop we specify an index number right I equal 

to z i less than or equal to size i++ basically what we are doing there we are referring the index 

right but here we do not have an index so normal for Loop we cannot use when you read data from 

the set collection and another two approaches are possible so by using for each Loop we can read 

the data from the set collection now let me show you how we get very simple so we can just specify 

my set and from the myet get each and every value in the variable create this as an object and just 

print it that's it so this will print or this will read all the values from has set so this will 

print all the values individually from has set you understood my point so so why classic for 

Loop is not possible because classic for Loop in the sense we have to follow indexing starting 

point ending point condition everything we have to specify but here we are not following any 

indexing set collection doesn't support index so that is not possible okay so this is how we 

can read data from set collection using for each Lo yes once you converted into array list in 

the previous concept so once you converted set into array list once you have this array 

list you can insert also once you get an array list you can put all the you can do 

all the operations whatever operations we have done earlier in the array list all kinds 

of operations you can do in Array list because I already converted but in the scri collection 

directly we cannot do okay now let me show you another for Loop okay not for Loop by using 

iterator how we can read the data from the set collection using iterator yeah now tell me 

what is the first point how we can do iterator using iterator so what we need to do in the set 

collection also we have an iterator method in the set collection also we have a iterator method we 

have to call it now what type of variable it will return what type of variable it should be it 

should be iterator type of variable okay and if the DAT contains if set contains a different 

type of data that also you can specify in the angular bracket you can say object optional okay 

and this iterator again we have to import from java. in right now by using this it we can get 

the data and we need to write a one while loop again same process and what is a method available 

in it ID dot has a next then ID dot next it will get the value system do do pintel and id. next 

it do next that's it so this will get all the data from the hash set so by using iterator also 

we can read the data from the hasset only thing is indexing because of indexing not possible 

for Loop normal for Loop we cannot use okay this is how we can read the data from the set 

collection and in the set collection we cannot remove multiple values okay we cannot remove 

multiple values so that is the reason if you want to remove single value you can remove 

directly by specifying the value but if you want to remove multiple values you need to write 

multiple methods there is no shortcut way but you can clear all the values at a time so clearing 

all the elements in hash set how we can do this simple myet dot clear so after clearing you can 

just check elements are there or not I'm just printing my set after clearing I'm printing my 

set now just If You observe there is no values in the set empty bracket it is returning and also 

you can use e mty method also myet do e Mt it will return return true or false e empty yes or no 

yes because we already removed all the values e empty method will return true so there are no 

values in the has set so this is how we can work with the has set ARR list and has set so these 

are all have uh some kind of similarities like heterogeneous data is allowed okay and methods 

also some common methods are there add method is common remove method is a common okay get method 

is not there in err list we have a get method but in has set we don't have a get method but some 

similarities are there some different methods also there in the both the collection okay 

so can we find size of an hash set hash set size size myet dot size so this 

will give you size of an ass set okay this will give you the size of a hash set 

how many values are there in the hash set will be return so this is the six elements are there clear everyone so this is all about hash 

set ARR list and hash set so now we have another concept called hash map we'll discuss about 

this now so before going to hashmap both are clear everyone list and set collections what 

is list collection what is set collection when to use list when to use set what are 

the differences what are the similarities and what is possible in the list collection 

what is possible in set collection so you have to be more clear about these topics 

okay now let us move on to the next one hashmap so let's finish this concept guys just 

another 10 minutes I will take and we'll finish the hashmap so we cannot split this only one 

Topic in the next session okay because we'll finish the Java today itself so this is one 

small topic another 10 minutes I will finish it hashmap so hashmap is a totally different type 

of thing so we cannot compare hashmap with list and set collection because hashmap will derived 

from or implemented class of map interface map is an independent interface but other than map 

and hashmap rest of all type of collections are derived from the collection interface but only 

the hashmap is D from the map interface okay so in the map interface or map H map collection we 

can store data in the form of key and value pairs key and value pairs the combination of key and 

value is called as a pair okay the key uh and value combination is called as a pair so now 

we'll see what kind of data you can store in the hashmap just try to observe this let's say 

I have an employee ID and name let's say 101 ID some name 102 x 103 J so if you have data like 

this these are the IDS of employee these are the names of employee so if you have this data 

so this is combination of one single set ID and his name so these IDs are called keys and the 

names are called values and the combination of one key and value is called as one where okay the 

combination of the ID and the name the combination of one key and value is called one pair okay and 

uh this is one pair of data this is another pair of data this is another pair of dat if you want 

to store this kind of data we have to use hashm let me give another thing suppose I have a name or 

I have a phone number and the name of the person phone number and person phone number and person 

so this type of data also we can store in hashmap same thing again these are all keys and these 

are all values and the combination of key and value is called one pair so this type of data we 

can store in the hashmap another example let us say country and capital so so there are multiple 

countries each country is having some Capital so key and value pair so country names are the keys 

and capitals are the values okay these kind of data we can store in hashmap and one condition is 

there whatever I'm calling as a keys those keys should not be duplicated that means one1 should 

not be repeat again one2 should not repeat again the phone number of one person should not repeat 

again the country here should not repeat again so the keys should not repeat again but the values 

can be repeated the values can be duplicated yeah the username and passwords also we can store in 

hash multiple usernames multiple passwords but you need to make sure Keys should be different 

but the values can be duplicated so the X name can again repeat another employees also can have 

same name right but IDs cannot be same IDs can be different the values can be duplicated 

but but ID should be different the values can be duplicated so this is the rule we have to 

remember when you're working with the hashmap so hashmap in the hashm we can store data in the 

form of key and value pairs only key and value tily Associated we cannot insert only key or we 

cannot add only key we cannot add only value if you want to add data in the hashmap we should 

add key and value along with them similarly if you want to remove the data from hashmap Key and 

value together it will remove and at the time of printing the hashmap also it will print together 

key and value we cannot split them into two so this type of data we can store in the hash map 

only key and value it is not table format it is not table table in the sense we have n number of 

columns but here we don't have rows and columns one key associated with one single value another 

key associated with one single value so this type of data we can store in the hashmap so when do 

you use hashmap if your data is having key value page this kind of data you have then you need to 

prefer hashmap so now let us see the some of the attributes of the hashmap how hashmap will work 

what are the attributes so the first point hashmap is a class which is implemented map interface 

hashmap is implemented map interface and data can be stored in the form of key and value pirs in 

the hashmap data can be stored in the form of key and value PS and the key is always unique but we 

can have duplicate values and because it is also following hashing technique insertion order is not 

preserved indexing is not allowed okay so these are the points you need to remember and when you 

come to the duplicates values can be duplicated but the keys cannot be duplicated okay these are 

the points so now let us try to implement M this practically next class and here this is hashmap demo hashmap demo so first of all 

declaration part how to declare the hashmap Declaration so declare the hashmap 

we can simply do like asmap hashmap hm equal to new hashmap I'm just taking one variable 

hm is a object variable so hashmap we have to import from java.util package okay now 

observe very carefully so hashmap hm equal to new hashmap what is giving an error 

here type java. do map cannot be resolved it is indirectly referenced from required 

type java. do hashmap so what what I will do is hashmap hm equal to new hashmap let me 

save it and try to import hashmap first from java.util okay so whenever you create an ash 

normally this syntax should allow why it is not allowed okay uh the type java. u. map cannot be resolved 

it is indirectly referenced from required type java. okay let me check this later so let me just 

create hashmap like this hashmap hm equal to new hashmap okay so one thing we have to specify 

guys whenever you create an ash map first we will identify the data right keys and values so 

for example I have some data like this so I have some data like this employee ID and the name is 

called employee ID some other name employee ID some other name I have data something like this 

now if you look at here these are the keys and these are the values so what is the type of 

all the keys what is the type number integer right so what we have to do is first we need to 

identify the type of the the keys so here we have to put angular bracket and specify integer so the 

type of the keys are integer now what is the type of the values type of the values are string so 

comma string we have to put like this and same thing we have to put at the time of object 

creation also this is mandatory step okay so this is how we need to specify it is giving 

something called build path error let me fix [Music] this just a second Library yeah just a second guys I don't see any issue here uh new hashmap integer string bracket so just try to import the packages properly so 

at run time my eclipse is not recognizing these packages properly okay so you can declare the 

hashmap uh by using like this directly and it is allowed all types of keys all types of values 

okay different type of keys different type of values allowed and if your data is very specific 

like all the keys are integers all the values are string then you can explicitly specify specify 

the integer and string and inte is what what keys type string is what values type same thing you can 

specify here okay these are the multiple options which we have and here also in this declaration 

also we can specify if you want so instead of hashmap you can simply say map also so for example 

because map is a parent interface of hashmap right so simply you can say only map map equal to my 

map map my map equal to new hashmap or you can say hashmap hm any variable name is fine so these 

are all corrected definitions you can use any of the definitions okay so this is my declaration I 

have created because I know what are the types of keys what are the types of the values integer 

and string I'm taking so now let us see how to add pairs so here we have to call them as a pairs 

pair is nothing but a combination of key and value adding PIR P so how to add PS to the hashmap so 

take this hm and we have a method called put okay we don't have ADD method in the hashmap so we have 

only put method so hm. putut and here two values we need to add one is key another one is value 

let's say I'm adding one1 and here I'll say John so one is a Val one is a key first one is a key 

second one is a value so similarly I will try to add some more PS in the hashmap so 102 103 104 I'm 

also trying to add duplicate key so what I said at the first point duplicate keys are not allowed 

unique key is a unique it's not duplicated values can be duplicated so what I'm doing here is I'm 

trying to make keys a duplicate okay we will see what will happen so this is the way we can add 

page now how we can print this let us print h hm let's say hm now we'll see how it is going to put 

the values in the hashmap just observe see 101 is John 102 is a David 103 is Mary 104 is a squad 

sometimes you may not get the same order because insertion order is not preserved in hashmap but as 

of now we got the same order but sometimes we may get the same order so if I look at here this is an 

output I got so what about the duplicate key see initially one1 value is what John one2 value 

is what Scott and here one2 value is what to David what exactly we are doing initially one2 

value is a Scot but here we are replacing one2 value to David so the old value is replaced with 

the new value but here you have only one one Z2 entry there is only one one Z to entry so that's 

the reason duplicate keys are not allowed if you put duplicate key the old value of is got replaced 

with the new value so that's how it will work okay now if you want to find size of a hashmap how we 

can find size so we can say size of hashmap sorry yeah hashmap so we can simply say size method is 

available hm do size so this will give you size of a hashmap that means how many paids are there 

totally four paids are there one because one is duplicated right so if I look at here 1 2 3 4 so 

totally four pairs are there four pairs are there okay and suppose I want to remove one pair I want 

to remove one pair one of the pair so how we can remove this so remove pair we can remove only pair 

we cannot remove one key specific key one specific value if you want to remove the entire page should 

be removed so hm dot remove of here we have to specify key based on the key the entire pair will 

be removed okay for example uh let us say I want to remove Mary this this pair I want to remove 

so if you want to remove this pair then I have to specify the key of that pair based on the key 

everything is operated so this is a remove so here 103 is key of the pair and after removing again 

I'm printing the hash map after removing pair sorry after removing pair I'm just printing 

hm so when I want to remove the pair we have to pass the key so based on the key the pair will 

be removed now we can see this is the latest pair in the hashmap so we can remove it suppose I want 

to retrieve the I want to retrieve the value from the key value of the key how we can retrieve 

access value of the particular key then how can we access hm. get method is there get off 

here we have to specify again key suppose here David I want to access so here we have to pass 

one Z 2 so here one2 is also a key one is also a key now after accessing we have to print this 

right system do print Ln hm. get of12 so in 102 what is the value which we have is David so 

when you run this it will give you David is an output so if you want to extract the specific 

value we can pass the key in the get option okay and the next one suppose uh if you want to get 

all the key Keys all the keys not only single key so when you pass key it will get the value 

of the key now I want to retrieve all the keys from the hashmap only Keys get all the keys from 

hashmap get all the keys from the hashmap how we can get system do pin hm dot there is a method 

called key set key set so key set is a method it will return return all the keys in the form of 

set so let me just print so you can see these are the keys so it will print all it will capture all 

the keys in the form of set and similarly can we get all the values all the values from hashmap 

hm dot values this is the method available so this will return only values from the hashmap 

see we got only values so key set is a method which will return return only keys from the 

hashmap values is a method which will return return only values from the hash now I want to 

retrieve key and value both how we can retrieve I want to retrieve key and value in the key set 

method return only Keys values method written only values now I want to get keys along with 

values how we can get HM dot key set is a method okay sorry not key set entry set dot entry set 

key set means it will return return only Keys values means it will return return only values 

entry set means what it will return return Keys along with the values so when I execute this will 

return everything see here this is an output Keys along with the values everything is got returned 

okay these are the few operations we can do it REM operation we can do we can access a specific 

value by using key and we can access all the keys as a list we can access all the values and 

we can also all access keys and values by using entry set okay if you want to change the value 

of the specific key then you can change by using put method itself see you already one2 Squad we 

already put this into hashmap then if you want to change the how we can change again you have 

to write one more put specify the same key and change the value so you will keep the latest value 

that means it is basically called replacement is happening okay can we use different data type in 

place key no here whatever the data we specified all the keys should have integer all the data all 

the values should be string okay suppose if you create a hashmap like this you are not specified 

any specific type for keys and values then you can store any type of data you can store okay 

31 and 39 31 what we are doing after removing the pair we are just printing here but here we are 

just uh getting the data so there is a difference actually here it is printing everything as a list 

and here it is printing everything as a set there is a difference actually you can just notice here 

curly bracet are representing this uh list this bracket is representing the set so there is a 

difference okay now by using looping statement how we can retrieve the data from the hashmap So 

reading data from hashmap and here normal F will not work because there is no indexing supported 

in hashmap also so normal F will not work so there are only two ways we have one is by using 

enhanced for Loop other one is by using iterator so now we'll see by using for each Loop how we can 

read the data from the hashmap observe carefully most important see in the hashmap we have a key 

and value pairs both just observe this is the data I have so this is one pair this is another 

pair this is another pair now what we need to do is we have to read each and every individual pair 

so let me put some something here hm do key set hm dot key set method what the key set method will 

return key set it will return only keys right if you know the key can we get the value by using 

that key yes or no yes if you know the key we can get the value from the key so what I'm doing 

is hm. key set will return these values now now I will read each individual key into a variable 

here I'm taking one variable called int and k k is a some variable name what exactly we are 

doing here from the key set key set in the sense these are the keys I'm reading each individual key 

let's say one1 first that will store in K the next iteration one2 will store in K next iteration 

one4 will store in K right now by using this key can I get the value and just printing the key 

here K and just give some space concatenation and hm dot get off K I'm passing see K means what key 

hm. get of K means what value so get method will return the value by using this K right so now when 

I execute this it will print key keys and values like this okay all the keys and all the values so 

this is the approach we follow using for each Loop so if you want to read the data by using for each 

Loop this is the approach this is more simpler and this is preferable approach but we can also use 

iterator but it is little complicated let me show you because we need to use so many classes I'll 

tell you using iterator so using iterator how we can do this so first of all we need to declare it 

we need to declare the iterator so how to declare the iterator HM is my hashmap right hm dot so 

we cannot directly call iterator method from hm okay we cannot call iterator 

method directly from hm so what we can do is we can get only keys from 

the HM how to extract only keys from hm key set only values if you want to extract 

what is the method dot values now if you want to extract keys and values then entry set told 

you three methods right so here key set means it will return return only Keys values means it 

will return return only values entry set means it will return entry set this is one entry this 

is another entry it is under form of set so so what I'm doing is first I'm getting the entry set 

from the hashmap so this entry set is nothing but what we will get this one and on the entry set we 

can apply iterator so here I'm calling iterator method basically I'm getting all the entry sets 

and on the entry sets are in the set format so on that I can apply the iterator here now what 

this will return what is the type of this return you can just check it here if you put the cursor 

on iterator it will show you the return return type is what iterator of Entry integer string 

this is a return type this is a return type so that you have to specify this is a return 

return type so here you have to specify like this so now we need to in import this iterator 

from java.util and uh then entry also we need to import entry also predefined class that 

also we need to import java. map okay this is a return return type iterator of Entry integer 

and a string this is a return return type okay so now we got an iterator so from this iterator 

we can capture the page so now which Loop we have to use when I use iterator always we have to 

prefer while loop okay remember so while and in this I will specify it do next again methods 

are same it do has next if the next record is available then what we need to do we need to 

extract that record by using which method which method next method right so here I'm using it dot 

next so now tell me what is this ID do next will return this will return entry set this will 

return an entry set so let me explain this let's start from this okay so currently hm. entry 

set what is hm. entry set contains one1 some X one2 some y one3 something right so this is a how 

we have data so entry set is nothing but this one this one this one all three things are there now 

I'm calling it and everything is a form of set so set means this is one record second record and 

third record and iterator this are first iteration second third now when is storing this into it 

what is the type of this it iterator and what this iterator contains of integer string right 

we have two values so that's the reason entry of integer integer okay now come here while loop 

what is this ID contains ID contains this one this is it has next is nothing but first it will 

focus on the first pair first pair and again it will come here when I it do next what this will 

return it will return one entry single entry it will return and the next round second entry 

will return third round next entry will be return every time the it. next will return the 

entry entry is nothing but what the combination of key and value is called entry so what we 

need to do now here we have to store this in a variable we can call it as a entry and the type 

of this variable is entry entry this is the type of this variable okay again the data is fixed 

right so the First Data is integer format the second one is a string format that is optional 

again if you want to keep this you can keep or us no so it do next first it will check it do has 

next the first is there or not yes available so it will get that pair the pair contains again two 

values that's the reason the entry type should be entry now from this entry we have to extract key 

and value how to extract key and value from this entry object simple entry dot get key is the 

method this will get the key of the entry and concatenated concatenated I'm just saying plus 

concatenated here from the same entry I'm getting the value from the same entry get value that's 

it so has an next it will check the p is exist or not yes then it will extract the pair entry 

is representing one pair so one that from that pair we are extracting the key from the same 

pair we are extracting the value in the next round it will check another pair then again get 

that pair then again extract the key and value so this will repeat multiple times till it completes 

all the pairs from the hashmap now let us execute see this is the data we got so through iterator 

also we can iterate the hash map this is another approach normal for Loop is not possible either 

we can use enhanced for Loop or iterator okay so now the last option suppose if we want to clear 

everything from the hashmap simply you can say hm do clear so this will clear everything so again if 

you want to check whether it is empty or not you can say hm dot is empty so will it return return 

true or false true or false true because already we cleared the hashmap here so simple we can 

execute and we can true it so this is how we can work with the hash map so most important concept 

do multiple rounds of practice in automation also we will try to use this concept especially when 

you do data driven testing we use this concept and when you read the data from Excel sheet and 

put that into hashmap and then hashmap data we will parameters to the automation script so there 

are different scenarios are there we will see as part of automation testing okay so do practicing 

array list hash set hashmap so these are the major collections most of the times widely using your 

Automation and apart from there there are so many other type of collections also there and at this 

point of time you don't need to learn all types of collection so if you learn and familiar with these 

three collections are more than enough and if you are still interested to learn all other types of 

collections I have created one new playlist or in my YouTube channel you can just go to this link 

and you can find all types of collections okay so you can just go to this playlist and you can find 

all the different type of collection so this is the playlist I have created almost 10 videos are 

there and other type of collections also I have covered in this so if you're interested you can 

go through this this is optional not mandatory okay so that's all for today's session I will 

stop here we will continue in the next session