Session 15- Java OOPS Concepts - Method Overriding, final & super keywords in java

all right so in the last class uh 

we have seen uh inheritance which is one of the most important objectoriented 

programming concept so today we will see some more Concepts which are also related to 

inheritance so the mainly the topic is Method overriding method overwriting so this concept is 

uh related to inheritance so let us see what is Method overriding and after that we will also 

compare this with method of overloading okay there are two concepts method of overloading we 

already discussed earlier which is related to polymorphism right method overloading related 

to polymorphism means one thing can have many forms so the polymorphism we can achieve through 

overloading and this overriding is related Rel to inheritance concept okay so what is overriding so 

the overriding means whatever method we created in the class parent class the same method if you 

again recreate in child class which is called overwriting suppose this is my parent class in 

the parent class there is a method called M1 and there is some implementation and there are some 

parameters and if you extend this parent class into child class this is my child class what will 

happen normally this M1 method is also belongs to CH class right so the whatever the method is 

implemented same method is also belongs to child class because after extending through inheritance 

after extending whatever methods and variables are belongs to parent class and same variables 

and methods also belongs to CH class same M1 one method is the same implementation right but 

sometimes suppose after extending uh everything from parent to child class if you do not like 

the implementation of this method so whatever the implementation they have done in the parent class 

method if do not like this method implementation then what you can do is you can write the same 

method again in the child class without changing any definition without changing syntax means what 

type you should not change name of the method you should not change number of parameters you 

should not change order of parameters data type of parameter everything should be same this 

part is exactly the same okay so whatever method you already there in the parent class if you 

recreate the same method in the child class but you should change the implementation part 

only implementation the body of the method you will change so this process is called method 

overriding so whatever me method we already there in the parent class if you rewrite the same 

method again in the child class just by changing the implementation part which is called method 

overwriting okay so in inheritance concept it will not be duplicated because if you write the 

same method two times in the same class then it is duplicated okay for example same class if you 

write M1 M1 with the same definition this these two are the duplicated but what we are doing now 

is we are extending the C1 into C2 and in the C2 we are writing the same method with a different 

type of implementation so that is the reason which is called over ring it cannot be duplicated so 

writing means whatever the method which we already created in the parent classes after extending 

into jail class if you recreate same method without changing the definition just by changing 

the implementation part is called overwriting okay which is called overwriting so why this concept is 

required in inheritance sometimes we may not like the implementation whatever implementation they 

have already done the parent class maybe that a old implementation old logic so after extending it 

if you want to change that logic or if you want to recreate this method according to your requirement 

your own requirement you can do some change in the child class okay that will not impact again in 

the parent class parent class method is Still Remains the Same only in the child class you are 

changing the implementation of the same method this is called overwriting but what are the rules 

of overriding here is in the overriding concept we should not change the Declaration part this 

is called declaration suppose when I say void M1 here parameters and here the implementation so we 

should not change this particular part so return type should be same method name should be same 

number of parameters order of parameters data type parameters everything should be same only the 

implementation should be changed then it is called as over raing okay simple example I'll tell you to 

understand about the overrating in the real real example let's say parent is having some house 

right and after parents have gone so the same property same house will come to the child so 

after so many days or after so many years then what this child will do he will renovate the same 

house that called renovation here so what exactly he is doing he's doing some customization or some 

modification right because this becomes very old same thing overriding whatever methods are there 

in the parent class we will just try to modify them modification in the sense the definition 

we should not modify only implementation we have to modify in the CH class which is called as 

overwriting concept okay so let me tell you with example we will try to understand where exactly we 

this overring concept is required and how we can Implement along with the inheritance and this 

overring is Possible only with inheritance at least we should have two classes one parent and 

one jail class then only overing is possible if you have a single class if you create a method 

with the same definition that will be duplicated these are duplicate methods but if you create 

same method in the parent another method in the child class this is called overwriting so if 

you want to achieve method overwriting at least two classes should be there one parent class one 

child class without inheritance we cannot achieve overwriting so this concept is purely belongs 

to inheritance purely belongs to inheritance with without inheritance without having at 

least two classes you cannot achieve writing concept okay so is overriding done for a method 

only in parent class yes so whatever methods are there in the parent class you can override 

all the parents all the methods into chain class so whatever is there in the parent class 

we can over into child class it can be method or it can be variable also suppose in the parent 

class I created variable and I have and some data like this now same variable you can create 

in the child class also you can change the data this is also variable overriding and if 

you have a method in the parent class if you recreate the same method in jail class just by 

change the implementation this is called writing concept okay yes so if you extend this child 

class to another class yes suppose here there is a C1 and here C2 class here it is C3 class here 

you can create one M1 method you can rewrite here and again you can rewrite here if you want so 

you can rewrite you can overwrite this method n number of times in child classes anywhere 

okay as suppose here you don't want to re re overrate here you can overwrite and the grand 

you can override so in this hierarchy you can override this method anywhere okay this is a 

concept simple concept you can you don't need to have only two classes more than two classes 

also you can have but at least two classes we should have to achieve overring concept one 

parent and one child should be there even if you have a more number of childs no problem if 

you create a method here and this method we can override in the grand CH classes because this 

method is belongs to every class right once you have here you can override it if you do not like 

the implementation everybody's understood what is overrating so this third c will inherit which 

method same method see until unless you change the implementation the method will be the same 

don't confuse again this is again previous class concept see again I'm repeating just listen very 

carefully so let's say have four classes here who created M1 method okay and this M1 method after 

extending same M1 method will be there in C2 and again after extending same M1 method is C3 again 

after extending again same M1 method will be in the C4 so here we were overring here we are 

overring okay until unless you override this method the method implementation will be same 

in C2 C3 everywhere it is same but here you're overring got my point same method one method 

only so here this will not split into multiple classes same method is belongs to C2 same method 

is belongs to C1 same method is belongs to C3 same method is belongs to C4 but once you overwrite 

this okay the implementation will be changed okay the same method but implementation will be changed 

so here this implementation will be changed so but when you create an object of C1 class and 

access M1 method the old implementation will be executed if you create an object of C4 class 

and then call M1 method the new implementation will be executed this is the concept okay now 

let us see how can we achieve this overriding and where exactly it will be useful with 

some example so go to eclipse and create new package and today is think day 15 now in this I'm going to create uh one new class 

I will name it as over ring demo listen this carefully very important concept overriding demo 

even in automation also it is most important I'm taking main method also in the same class if 

you want you can take main method in another class no problem so this is the main class which 

contains a main method and then I will keep this one side later I will use this for creating 

objects and everything right so here I'm going to create one new class called Bank okay and 

in this I'm creating One V one method return of rate of interest Roi and it will return double 

so initially I'm rning zero this is the method I created in the bank class and when you call this 

method it will return zero rate of interest and the return return type I say double decimal 

number it will return you can put anything whatever method you want can just I'm creating 

sample method so now I will create another class called ICI ICI this extends okay extends bank 

so now I have inherited Bank class into is now is this method belongs to ICC or not yes so this 

method is belongs to ISA class also right so now I will create another class another class let's 

say SBI this is also extends Bank class now the same method is belongs to SBI also right SBA also 

having same kind of a method now what I will do is in the parent class implementation is not suitable 

for every bank if I look at here here rate of interest is zero but the rate of interest of 

this bank and this bank will be different so this implementation is not exactly the same for ICC and 

SBI so now what I will do I will again recreate the same method in the child class here and just I 

will change implementation part here I will return 10.5 and again the SBI again I'm recreating the 

same method but according to SBI I'm changing rate of interest if I look at here the same parent 

class method I'm again recreating in the child classes just by changing the implementation so 

definition it should be exactly the same it should not change but implementation you can change okay 

so this is called overring so whatever method we created in the parent class same method again we 

recreated in the child classes and IC and sbas are totally different classes there is no relation 

between these two now what type of inheritance it is can anyone tell what type of inheritance 

it is yesterday we discussed about four types of inheritances single multi-level hierarchy 

and multiple which type of inheritance it is why it is multi what is multi- 

level guys have you listen the session yesterday what is multi- level see multi- level means this is the one right 

if I look at this structure is it seems like this no right so bank is a class which is extended into 

icci and which is also extended into SBI what type of inheritance it is one parent can have multiple 

Childs hierarchy inheritance it is not multi level okay multi-level means parent to child again this 

child becomes a parent of another class here it is not like that IC SB there is no connection 

both are having same parent so it is hierarchy inheritance simple question they have not able 

to answer okay so we have override this method into child classes now come to the main class 

main methods now here if you create object of this bank and you call this Roi method it will 

return zero and if you create an object of IC and through that object if you call this Roi that 

will return 10.5 and if you create an object of SBI class then if you call R then it returns 

11.5 so whichever implementation you like you can create an object of that particular class and 

you can call that method so if you just observe here I'm just creating an object of I I equal 

to new I I now by using this object I'm calling Roi okay is it enough just calling method is 

enough if you want to capture the data or if you want to get the return return value we 

have to store it in another variable or we can directly print it here because this method 

will not print it will just return the output system Pinel and i. Roi okay and similarly if 

you if you execute this what is an output of this method you can say 10.5 why it is 10.5 

because we created object of IC and through that object we have invoked R method so whichever 

R method we recreated or we overrided inside this IC the new method will be executed the overed 

method is executed always now if you create an object of SBI this particular overrided method 

will be executed so I can say SBI SB equal to new SBI another object I created now sb. r i so this 

will also the output s sp. Ry right so now when I call this Ry method from SB this will implement 

or this will execute this is a method which is also overrided method 11. file as jav application 

okay so 11.5 so this is simple concept of writing remember what is overwriting whatever method we 

already created in the the parent class in the child classes wherever you want you want to 

change the method not only immediate parent class you can change this in whichever class 

you want after extending this class you can recreate this method in whichever class you want 

in the CH classes okay and once you've overrided this method the implementation is got changed 

so whenever you create an object of the class the new implementation will be executed okay 

so this is called overriding concept and this concept is purely related to inheritance concept 

inheritance means what there is only one parent at least one parent and child should be there 

then only we can a overring concept even if you have multiple jail classes no problem you can 

implement the method in multiple jail classes also wherever you want to recreate you can do 

it but at least two classes we should have at least one parent and one jail class we should have 

this is called overriding concept clear everyone but what are the rules we have to follow here we 

should not change the definition part declaration we should this is called declaration this is 

called implementation or we can say the body of the method okay the body of the method only we 

should change in writing we should not change the Declaration part return type name of the method 

number of parameters data type of parameters should be exactly the same you should not change 

it as per overrating yes same definition different implementation okay understood everyone 

so definition means exactly the same again parameters order of parameters data type 

everything is part of the definition so definition should not change means what even the 

parameters also you should not change here if you take two parameters in the CH class also should 

take two parameters and here it is taking two integers here also it should take two integers 

that's called overriding concept okay now let us compare writing and overloading very very 

important and very confusing topics there is a lot of difference between overwriting and 

overloading in the previous class we have seen overloading right what are the rules applicable 

in overloading can we do overloading in single class can we do overloading with single class 

yes can we do overloading with multiple classes in inheritance yes or no overring we already seen 

in the inheritance can we do overloading here okay so we'll see with practical example overriding 

along with overloading with inheritance okay with inheritance you will see overriding and 

overloading so I will write some P of code here you guys can guess and uh tell me the answer 

for that okay so let's create a new class and here I will name it as W uh loading versus 

over tring I'm taking main method also just observe it's very simple concept right so I will just have this method in one 

side overloading versus over loading now here I'm creating one new class just 

observe very carefully creating a new class called ABC my class name is ABC so here I'm creating 

one method called what M1 and here I'm taking one parameter okay one single parameter I'm taking 

and inside this I'm just printing the value of a so this is a method which is belongs to class 

ABC M1 is a method one integer parameter it is accepting no written value it is just printing 

the value of a whatever parameter we are passing value same thing it is got printing I'm creating 

another method void M2 this will also take one single parameter and this will print the value 

of B so now I have created two methods M1 with single parameter M2 with single parameter both are 

belongs to class ABC now I'll create another class called xyg and this xyg extends from from ABC 

okay now how many methods are there in XYZ how many methods are there in XY Z two methods M1 and 

M2 so whatever methods are belongs to parent same methods are belongs to XY Z also okay now what I 

will do is I will just create a same method again in the child class I don't change the Declaration 

or but I will just change only implementation here instead of printing just a I will print a star 

value this a square value a into a a into a so whatever method we created in the parent class 

same method again I recreated in the child class just by changing the implementation so what is the 

concept it is over ring or over loading overriding or overloading this is overriding it is clear 

overriding it's very clear so whatever method we created in the parent class same method we 

recreated without changing the Declaration just by changing the implementation okay now in the 

same class I will create another method with M2 M2 method and M2 is already there in the parent 

class also now again I'm creating M2 here this time I will take two parameters in a comma int B 

two parameters I'm taking and here I will print a into b or a plus b some operation I have taken 

now just observe is there any difference between the parent M2 method and CH class M2 method yes 

yes there is a difference now if I look at this how many methods are there in XY Z totally how 

many methods are there in XY Z how many methods are there in XY Z total number of methods in XY Z 

three two or four multiple options two methods or three methods or four methods how many methods are 

there in XY Z total number of methods okay let us count so the parent class M1 which is already be 

overrided okay this is one method and uh from the parent class M2 method is also belongs to XY Z but 

again we again created another M2 method so if you recreate this method if you override this method 

in the child class there will be only one method but we have not done over over in here so we have 

done overloading M2 method is overloaded in the CH class okay so M2 method as it is it is belongs to 

XY Z M2 is also belongs to XY Z M2 with one single parameter M2 with two parameters so there are two 

M2 methods are there one M1 method is there so totally how many methods are there in XY Z three 

methods are there okay so M1 method is only single one because we are overrided overriding means 

old method is gone the new implementation only will be there so this is one method but this is 

one M2 with two parameters another M2 one with single parameters comes from the parent class so 

now is there any difference between this M2 and this M2 yes and now what is the difference you 

have noticed between over riding and overloading the overriding we are not changing the decaration 

we are just changing only implementation but in overloading we are changing the Declaration 

okay so in overloading concept what are those rules only method name is same in overriding and 

overloading what is the common point in overriding and overloading what is a common Point only the 

method name is same that's it that's only one common point in writing we should not change the 

Declaration we change only the implementation in overloading we should change the Declaration 

same thing we again should not write right we will change the Declaration implementation is ours 

implementation you can have same implementation or different type of implementation according to 

the definition you can change the implementation so this is a overloading with inheritance So 

within inheritance we can achieve overriding and also overloading both the concepts we can 

achieve using inheritance now overriding is purely belongs to inheritance without inheritance 

we cannot achieve overring but without inheritance we can achieve overloading right in the last 

classes we already seen with single class we can create a number of methods with the same name 

so over ring we can achieve only with inheritance overloading we can achieve with or without 

inheritance with single or multiple classes also we can achieve overloading concept now 

you understood the difference overriding is a inheritance concept overloading is a polymorphism 

concept overriding we can achieve only if you have a two classes at least two classes or more 

than two also fine with single class we cannot achieve overing but overloading we can achieve 

with single class and also multiple class now come to the main class here I will create uh the 

object of XY J just observe XY J equal to new XY J okay so is this clear uh is this okay can we 

give XY Z lowercase characters as an object is it correct or not yeah because case sensitive 

language right uppercase XY Z and lower case XY Z will treat differently so this is XY Z obj XY 

Z obj now I'm calling XY Z obj just observe see there are three methods M1 with single variable 

M2 with single variable M2 with two variables three methods it is populating M1 M2 uh one M1 M2 

come from XY Z and M2 with single parameters come from ABC class now I'm calling first M1 method 

if I pass one single parameter I'm passing then XY Z obj Dot and again I'm calling M1 M2 with 

single parameter 200 or you can say two here can say 10 here can say 20 now from XY Z obj 

dot again I'm calling M2 method with the two parameters 10 comma 20 okay so M1 is overrided 

M2 is overloaded M1 is overrated same thing we declared and M2 is overloaded means there are 

two M2 methods are there these two M2 methods are not same so we are able to call M2 methods by 

passing different type of parameters so when you run this you will get the output like this 

so here M1 method what M1 method we do here observe very carefully M1 method from ABC will 

just print only a value but M1 method from XY G will print the square a star a into a so if 

you look at 100 we are passing we are passing 10 here but we are getting 100 is an output 

what does it mean which M1 is got executed M1 from XY Z class is executed that means overed 

method is executed always whichever method is overrided the overrided method will be executed 

suppose if you create an object of ABC class then you call M1 method which implementation 

will be executed the old implementation will be executed if you create an object of XY Z and 

if you call M1 method then overrided method is exec uted and now we call M2 method it is got 

printed 20 as it is then we pass 10 and 20 it is added two numbers 10 + 20 30 so this is how 

we can Implement over ring and overloading with inheritance okay so this is a concept so now 

the question is can we overload one method in two CL classes without extending 

these classes okay so let me tell you this so what you are saying is there are two 

different classes you are seeing there is no connection between two classes so this is 

a different class and this is a different class no inheritance right no extension means 

no inheritance and here you created one M1 method with some parameters two parameters 

here you create overloading is nothing but what you should change the Implement should 

change the Declaration but here you can have three or four parameters so if there is no 

connection between these two classes this is not called as a overloaded or overrided this is 

not called as a overloading you can create same method or you can create a different parameter 

same method with the different parameters we cannot call it as a overloading when we will 

call overloading within the same class if you create another method with the same name 

with a different declaration which is called overloading which is called overloading and if 

you have a two classes and there is a extend connection and if you create a same method with 

a different declaration that is also overloading but if there is no connection between these 

two if you create a same method again or if you change the parameters we cannot say that is 

overloading or overriding first of all there is no connection between these two classes right 

so we cannot call it as a overloading or we cannot call it as a over reading first 

of all because both are two different classes okay so we haven't changed implementation 

of M2 with single parameter in XY Z class that means does it consider as overloading method yeah 

see observe here we have override M1 method only M1 method we have overrided here M2 method we 

have not overrided M2 is not overrided M2 is just overloaded if we still want to override M2 

you can still do that can just copy this M2 one more time without changing the Declaration and 

here you can change you can call B into B okay now here this M2 is wried Method here this M2 

is overloaded method you understood now so this time we've overrided M1 and M2 also but we have 

created another M2 with two parameters now this is overrided Method over M2 method this is overloaded 

M2 method you can have both no problem everyone is understood this point there is no rule like 

if you override we cannot overload like if you overload we cannot override there is no rule like 

this depends on your requirement you can override and you can also overload same method just like 

M2 here M2 method we overrided and also overloaded okay so this is how we can achieve this 

overloaded and overring so now let us compare the points so I will put some points here and based 

on that we will try to understand what is Method overloading what is Method overloading comparison 

and interview perspective which is very very important what is the thing override and 

overloading again you are asking the basic question in introduction I have told I 

already told you what is overloading and why we need and what is overring and 

why we need with the scenarios I have explained both are not same both are not same both are not same how both are same 

see these are the differences listen this so method overriding Possible only in multiple 

classes with inheritance we can achieve and method overloading is possible both single 

and multiple classes major difference okay and method of overriding is related to what 

inherent and overloading is related to what polymorphism and in the method overring we should 

not change the signature of the method signature means what the Declaration part written type 

name of the method order of parameters all those things but body we should change but in 

overloading we should change the signature of the method major difference how come you 

say there is no difference both are same thing no only one similarity is Method names 

are same in overwriting in overloading the method names are same okay and the third thing 

belongs to inheritance and this is a belongs to polymar okay remember this so everyone is understood what is the 

difference between method overriding and method overloading in inter if anybody ask 

you should able to answer that question what is overring what is overloading what are 

the differences because many people will have confusion here a lot of people will confuse 

between overriding and overloading overloading is belongs to polymorphism overriding is 

belongs to inheritance but still we can achieve overloading with inheritance combination 

and overing means same method again we recreate and change the body overriding means we should 

change the Declaration of the method that is called overloading one thing can have many 

forms but in overwriting we are not writing many forms only same thing we are rewriting 

again and again we are not changing the form but in overloading we are changing the form 

of the method form means the Declaration part can we access child class method from 

parent class object no that is possible only with interface concept but here no if you create 

a child class object you can access methods from only child class objects whatever methods and 

whenever you say child class that is already extended method from the parent class itself 

right parent class method already acquired into the child class so whenever you call 

child class method obviously indirectly we are calling the parent class method only 

the question itself is wrong you can just observe this is a parent class M1 method 

we created now we create another CH class this M1 method is also belongs to here right 

after extending so now if you create a child class object call M1 method this will able to 

execute with the same object again if you call M1 method what does it mean actually from where 

this M1 method is coming into CH class from the parent only right so when you call M1 method 

this is got executing indirectly parent method only okay so the question is not correct 

actually so the method is actually comes from parent class only so you can execute 

the same method by using child class object or parent class object anything is fine but when 

you do overriding concept you have to carefully do it when you override M1 into CH class if 

you need new implementation then you have to create an object of jail class and then call 

this M1 method if you want old implementation then you have to create an object of parent 

class and then call M1 method if you have overrided otherwise you can create an object 

of any of these classes and you can invoke M1 method okay Arjun are you clear about this point is it possible in multi-level inheritance 

for overloading what we have seen is multile inheritance only multi- Lev inhance everything 

possible everything is possible it is what type of inheritance doesn't matter in all kinds of 

inheritances overloading is possible overriding is also possible in all kinds of inheritances it 

is possible in single multi level higher Archy multiple everywhere overloading and overring 

is possible so if you create a method M1 with one parameter here and if you create same M1 

method two parameters here and if you create same M1 me three parameters here what's wrong in 

this you can create n number of methods you can create but here we are changing the Declaration 

so what type of concept it is overloading and if you create the same method no no change of 

Declaration same method again multiple classes multiple definitions multiple declarations 

we have given right multiple implementations we have given that's called overriding in every 

class we can override if you want or the method M1 from this parent you can override in the 

grandchild also directly you can over from here to here you don't need to touch anything in the 

middle classes in all the things it is possible everywhere it is possible in every type of 

inheritance overloading and overring is possible okay clear everyone so please confirm in 

the chat box before moving to the next concept okay so remember this overwriting and overloading we finished now so we 

will discuss one important keyword uh final okay uh before final let me tell one more 

keyword uh just a second Super keyword okay super okay so let us start with the final so 

then we will discuss super so final keyword so the final keyword we can apply for for variables 

uh class variables and also methods all three levels so final keyword we can apply for variables 

methods and also class can apply for variables we can apply for methods and we can also apply 

for classes all three levels normally class contains what variables and methods right class 

is a collection of variables and methods so the final keyword we can apply for variables 

methods and class so we we can have final variables final methods final class but when you 

apply final keyword what will happen what is an advantage of final keyword so basically the 

final keyword uh is especially for uh if you want to apply some kind of a security or privacy 

on the variables or methods in the class you can go with the final keybord okay so we'll see one 

by one so first we will apply final keyword for the variable and then we will see the difference 

and then we will apply on methods then we will apply on the class Final keyword first thing 

uh let's create a new class so as I said final keyword we can apply on variables methods and 

also classes create uh new class I can just name it as test okay take this or okay final keyboard 

This is my class name and taking main method and say finish just observe very carefully so this 

is a main class and main method and in this I will create a new class class called test and in 

this I will create one variable in some x equal to 100 I'm hardcoding this data x equal to 100 

right so now you guys can answer this question I'm creating object of test class test t equal 

to new test create an object of test class can we access this variable directly from the 

CL directly from the object yes or no can we access this variable X variable directly from 

the object from the object yes obviously what's wrong in this we can access everything from 

the class using an object right so simply we can object because this is a non-static variable 

we have to access only through object there is no other way so I'm ask I'm accessing t.x okay 

when I access t.x I'm just printing the value of t.x okay and uh this will print 100 as an 

output okay this is clear we created an object of the test class and we have accessed 

the value of x that means we are able to access this variable and we are able to print that 

value of the variable can we change the value of this variable here initial value of x is 

100 we are able to access it we are able to print it similarly can we change the value of 

x can we change it or not so before printing t.x can we change why not we can simply change 

if you're able to access you can change now I can change t.x equal to 200 here I'm changing 

okay by using t.x equal to 200 and after that I'm printing t.x so observe here before changing 

we got 100 now we got a 200 what is that mean we are able to access this variable and also we 

are able to change the value of the variable through object we able to change the value of that 

variable using object at any time we can change no problem because they are simply variable ables 

the variable means what the value of the variable we can change at any time whenever you want okay 

this is a default Behavior we can just create an object of the class through object we access 

the variable and change the value now suppose when you create this variable as a final I'm 

applying final keyword for this variable now here it is giving an error what it is an error 

the final field test dox cannot be assigned and it is giving one suggestion also remove final 

modifier of X it is asking us to remove final modifier of X what does it mean when you create 

a variable with the final keyword that value is fixed we cannot change that value so before 

applying the final we are able to change the value here it is working fine but after applying 

the final keyword when you're trying to change the value it is not accepting so that is the reason 

it is asking remove final modifier first remove final modifier and then you can make the change 

but if you have a final keyword you cannot change the value got my point so the final keyword we can 

apply on the variable if you apply final keyword on the variable we cannot change the value of 

the variable that is always constant this is incorrect why it is incorrect because X is final 

variable X is final variable so we cannot change the value of variable that's the first point so 

when you apply final keyword for for the variables the value of the variable is constant we cannot 

change the value of the variable is this clear everyone yes final keyword makes 

mutable to immutable yes okay the value of the variable is fixed you cannot 

change it anywhere else if you're trying to change this will give an error so 

here it is giving an error the final field has cannot be assigned means 

you cannot assign the value to the X forget about static I'm not discussing 

static here later I will compare there is lot of difference every keyword is having lot 

of difference guys don't compare the keywords you can always compare Apple with apple 

orange with orange but you cannot compare with apple with orange okay so similarly there 

are different keywords are there and static is totally different concept concept here final 

is a totally different concept there is no relation between these two once you understand 

the final keyword then we will try to compare okay don't uh introduce static keyword here 

in in the in between final keyword okay so you will be confused so when explaining about 

final just focus only on the finals don't uh again remember other type of keywords so final 

variable means what the value of the variable cannot be changed that's it now let us apply 

final keyword for the method the first point I hope everybody is clear we cannot change 

the value of the variable which is constant now the second Point let us apply final keyword 

for the methods then what will happen we will see okay so so what I will 

do is I will create another class in Java there are so many keywords are there 

five to 10 keywords are there so we can't compare them so see here uh I'm creating another class 

uh say final keyword two taking main method and say finish okay observe first and you guys can 

tell me the answer for that question so here I'm creating one new class test we already created 

now I'm calling as a test one class okay in the test one I'm creating one method called void 

y one method simple simple method I say so I just created some method let's say this is m 

method from test test one class this is the implementation okay so in the test one class I 

have created one method normal method now I will create a child class of test one class test two 

which extends from test one okay now the method m is belongs to test two or not m is belongs to test 

two or not yes obviously because we are extended test two from test one so whatever method is 

belongs to test one which is also belongs to test two that is clear now can we override this 

method in the test two or not can we override yes obviously we can override so let us try to 

override this method vo M same declaration the body I will change so what I will change it here 

this is is m method from test two class okay this is overed Method M1 we successfully overrated 

from parent to child class we have overr fine now I will apply final keyword for this method 

in the parent class I will apply final keyword for this method so as soon as you apply final 

keyword here it is G giving an error in the child class what it is saying cannot override 

the final method from test one and what is a suggestion is giving remove final modifier of test 

1. Y what does it mean if you create a method with the final keyword we cannot override that method 

in the jail class restricted okay if you don't want to override this method in the child classes 

you can make that method as a final if you don't want to allow anyone to override your own method 

you can just make it as a final that's it okay so if you make that method as a final method you 

cannot override that method in the child classes so here this is incorrect why it is incorrect 

because because m is final method m is a final method clear everyone so when I apply final 

keyword for the variable the value of the variable is constant we cannot change when you 

create when I apply final keyword for the method we cannot override those methods in the child 

class we have restricted so we cannot override that method in the child class here it is given 

giving an error if you remove final keyword we can override this method when you apply final keyword 

we cannot override this method this is a second point so when you apply final keyword for the 

methods we cannot override those methods in the child class this is the second point now we will 

apply final keyword for the class then we will see so here I have a test one class here we have a 

test two class and we are able to extend test one into test two there is no problem we are able to 

extend when you make the class is final we cannot extend this class into child class if you don't 

want to use this class as part of inheritance you can make it as a final so now here it is started 

giving an error what it is saying the type test two cannot subclass the final class test test one 

means we cannot make test two as a sub class of test one subass in the sense child class so we 

cannot use test one as a parent that means once your class is created with a final keyword that 

class we cannot extend into child classes any other child class we cannot extend this is also 

restricted if you don't want to allow anyone to extend this class into their classes you you can 

make it as a final so final classes we cannot extend into child classes this is another point 

so this is also here it is incorrect why because why because test one test one is final class 

if it is a final we cannot extend that class into child class this is a third point so when 

you apply final keyword for the class we cannot extend that class into any other classes that is 

called final keyword now you understood when I apply final keyword for the variables the values 

of the variables are constant we cannot change when I apply final keyword for the methods those 

methods we cannot override in the child classes when you apply final keyword for the class class 

we cannot extend that class into child class simple okay overloading works as it is because 

overloading we are creating the different methods right we are not recreating there so overloading 

works as it is only overriding specifically I'm saying overriding did they say overloading here no 

right so specifically over we cannot override the methods overloading will work as it is no problem 

with the overloading and other things so when you apply variables when I apply final keyword with 

the variable the values are same we cannot change the value of the variable and if you apply final 

keyword for the methods we cannot override that method still we can do overload overload is a 

totally different method we are creating all together right overloading and over raing in over 

raing same method we are creating in overloading we are creating a different method as soon as to 

change the parameters and data type of parameters order obviously that is a totally different method 

so it is allowed so the methods we cannot override class means when I apply final keyword for the 

class we cannot extend that class into child class simple okay so this is all about final keyword 

different than so what is the context of static method static variables and static method so I'm 

repeating this concept what is the context where we have to use static and non-static non-static 

everything by default everything is non-static but when you create a static variables and static 

methods what is a context where we will create static methods and static variables yes when 

you find a variables or common the values of the variables are common across multiple objects 

okay and the method implementations are same for almost every object then you can make them as a 

static static means that is not fixed remember this see I have a static variable called x equal 

to 100 I have a final variable x equal to 100 what is the difference between these two what 

is the difference so static xal 100 means the x value default value is what 100 and even if 

you create multiple objects in all objects the value of x is what 100 only in all the objects 

x value is 100 only if you want to change this value you can change in the class level you 

can change or by object you can access the x value and you can change by object two also you 

can change by using object three also you can change this is always you can change but when 

you say x equal to 100 you can even though if you create multiple objects you cannot change 

the value this is fixed value that is a major difference okay this is a major difference 

for the variables I'm talking okay static variable value we can change at any time 

but final value we cannot change this is constant okay now compare with method suppose 

I have method M1 which is static method and I have another M1 method which is just a final 

method the context is totally different when we will apply static keyword for method again same if 

the method implementation is same across multiple objects implementation again across objects we can 

make it as a static and this implementation we can always change by using any of this object we can 

change the implementation of this method whenever you want and you can also override this method you 

can also overload this method in the CH classes wherever you want you can overload this method 

you can also override this method static M1 you have created in the parent class same strategy M1 

you can create in the child class also wading is also possible over loading is also possible every 

time but final method is not like this overriding is not possible but overloading other things 

are possible only overriding is not possible in the child classes but stating methods overriding 

overloading everything is possible is there any difference or not please respond guys is there any 

difference you noticed or not between static and final okay now we do not have a static class 

static keyword can be used only for variables and methods we cannot apply for the class 

but final keyword we can app for the class when you apply final keyword for the class 

we cannot extend the class into child class okay static classes we do not have in the 

Java static keyword is applicable only for variables and methods so now everybody is clear 

the difference between static and final so both keywords are used in the two different context 

so they are not comparable actually okay yes how can we static methods can be overden what can 

do what's wrong in this whatever static method you created in the parent class see this 

is our parent class you created M1 which is a static method right so after extending this 

into child class so same static method is belongs to child class also right same static method 

so you can just create again same method and change the implementation what is wrong in that 

implementation you can change because the method implementations we can change wherever you want 

through the object also you can change directly you can change the class or you can directly 

extend it and change the implementation in the CH class everywhere it is possible even though it 

is static method we can change implementation in the child class we can override you guys can try 

all these combinations because everything is not possible to show in the sessions so you guys 

can explore all these things it is possible invoke we use class. method name but there is yes 

observe this at the time of invoking uh okay just observe this is our parent class in the parent 

class there is M1 method which is a static now we have overrided this method in the child class 

child class is also having same M1 method same static and there is new implementation this 

is old implementation okay now what is the context here if it is a static method we can 

directly call by using a class name without creating an object by using a class name we 

can directly call M1 method right now if you call M1 with a parent like parent class name do 

M1 then it will invoke the parent class method and if you say child class do M1 then it will 

invoke the child class method okay here also we can invoke this this methods directly 

by using a class name and by using object also we can access the methods we can change 

the implementation of the methods just like a class name we are directly accessing right 

because these are the common across all the objects so by using class name directly we can 

access or by using object also we can directly access okay Arjun are you clear now so static methods also we can 

override static methods also we can overload only final method 

we cannot override that's only restriction for overloading there 

is no restrictions every method we can overload okay so one last keyword 

we will discuss and then we will finish so next keyword is is super keyword super 

and this super keyword always we will use only in inheritance there is no other place you won't use 

it only inheritance super keyword will work okay so what is the super keyword this is again related 

to overriding concept and listen very carefully you have to uh pay you have to focus okay and 

pay attention on this otherwise it will leads to confusion because we are discussing many things 

almost similar topics but slight differences will be there just observe I'm telling the scenario 

first and then we will see what is a super and also I will ask a question here you have to 

answer this I have one parent class this is our parent class in the parent class I say xal 

to 100 I extended this parent class into child class this is our child class in the child class 

can we change x value here in the child class yes we can also override variable value I can make 

it as a 200 okay so this is a scenario now I will create object of parent class through the 

object if I get x value what is the value you will get parent. X means when I create an object 

of parent class and accessing x value then you will get 100 that is clear now when I create an 

object of child class and through that object if I access x what is the value will get 200 means 

when you create an object of child class when you access x value obviously you will get the latest 

value because X is 100 is already overrided in the child class so when you create an object of 

child class through the object if you access x value you are getting the latest value by default 

you will get the latest value overrided value but my requirement is even though I created an object 

of child class instead of latest value I want to get the P immediate parent class value object is 

what child class object only okay I will create an object for the child class but when you say objx 

by default which value you will get 200 you will get by default but instead of 200 I want to get 

the parent class value parent class value I want to capture but we should not change the object 

object is referring to child only if you create an object of parent class obviously you will get 

the x value 100 but here my requirement is what I want to create an object for only child class but 

still I want to get parent value okay this is one scenario remember same thing I have a parent 

class and in the parent class I will create one method called M1 and some implementation 

is there again in the child class this is my child class I extended in the parent class 

into child class here again I overrided this method with new implementation same method I 

recreated overrided this method now when you create an object for parent class and call M1 

method the old implementation will be executed when you create an object of child class and call 

M1 method the new implementation will be executed but my requirement is I will create an object of 

Ja class I will call M1 method but I would get the output from the parent class class immediate 

parent class method I want to invoke through child class object this is my requirement how is 

possible how it is possible so the by default the latest variable value we can access by default 

the latest method implementation we can access if you create a child class object there is 

a default Behavior but still I want to use child class object only but I want to get the old 

implementation old variable Value Old in the sense the immediate parent class method implementation 

immediate parent class variable value I want to get so this is possible by using super keyword 

so super is always representing immediate parent class okay super keyword is representing immediate 

parent class so by using super keyword you can access so you guys understand the scenario first 

because once you clear about the scenario just a second hold on okay very simple guys if you create 

object for parent class okay I can access only parent class variable and 

parent class method if you create object of child class I can access child class 

variables and child class methods right but what is my requirement is I will 

create an object of child class through the topet I want to access variables and 

methods from the parent class that is a context now you understood when you create an 

object of parent class I can access everything from the parent class parent class variables and 

parent class methods when you create an object of child class I can access child class variables 

and child class methods but my requirement is if you create an object of child class through 

the top I should want to invoke parent class variables and parent class methods means the 

world implementation the world value of the variables that is a context okay so with 

this ex with the example we will try to understand okay so same thing I will uh 

replicate here you will understand by seeing the example so I'm creating 

new class okay I'll name it as uh animal I'll name it as animal class so now my voice is clear everyone okay so I'm creating a new class called animal 

and here I'm not taking any main method just click on finish so this is animal class in 

this I will create one variable called string color equal to White okay I'm just creating one 

variable called color and I'm giving some value called White also I will uh this is a class now 

I will create one child class of this I can say class dog which extends from animal Now dog is 

another class which is extend from animal so in animal class we have only one variable the 

value of the variable is what white now here I will try to change the value of the variable 

is it possible or not string color equal to Black is it is it possible or not yes because 

we just overrided the variable value whatever value we have given in the parent class I don't 

like that value so I can just change the value in the P child class now also I will try to print 

the value of the color so I can say void display color and here I will just print the value of 

the color okay now this is the implementation of the CH class observe now I'm creating another 

main class I call it as a test super here I'm taking main method you can take the same class 

no problem but I'm just taking another class okay just observe this we created Animal class 

which is having one variable and the value of the variable is white next I extended the dog class 

from animal and I changed the color of variable and just I created another new method which will 

display the value of the color okay now come to the main class here I'm creating an object of 

dog class just observe so dog D equal to new dog so dog D equal to new dog this 

is a new class which we created dog D equal to new dog now by using 

this D I'm calling display just a second okay so by using this D object 

I'm calling display color now what is an output of this code when I run this 

program what is an output you will get when I run this you will get a black 

so obviously just a second you will get a black this is what we are expected right we are 

created object of dog class and we are invoking the display color method and this will print 

the value of the color so whichever the latest value we have assigned that is got printed fine 

because the value is already overrided here so the new value we got it here now my requirement 

is I still want to use same object I still want to call same display color method but display 

color method is printing the latest value here right but instead of this latest value still I 

want to get my V value from the parent class how it is possible when you call this method it is 

just printing the latest value but still after overriding also I want to get my old value even 

though we have done overriding still I want to get my old value value then what we can do we can 

simply say super dot e like this we have to say so when you simply say only color the latest value 

you will get when you say super do color you will get the parent class value okay what does Super 

will do here is super keyword will invoke the parent class variable instead of the latest it 

will invoke the parent class variable okay now if you run this as Java application see this time 

you got white understood everyone so when I use super keyword for this variable it will get the 

value from the parent class not overrided value if you just print print only color it will give 

you the latest value this is the usage of super keyword for the variable we can also apply for 

the method I will show you that now so is this clear everyone please confirm in the chart window 

before going to the next so super keyword will be used to invoke the immediate parent class variable 

that's the first point super keyword will be used to invoke the immediate parent class variable 

now in the parent class I will create one method okay one method I say void eat eat and here I 

will Implement something here I can say eating nothing I'm not specifying just eating this is a 

method same method I will again recreate in the CH class is it overloading or overriding here 

I'm changing eating bread eating bread is it overloading or overriding which concept it is 

overriding right we have override this method into CH glass fine now let me call D do eat okay 

now which method will be invoked D do eat I call eat method from the D object child class method 

will execute so whichever new method we created whichever method we have overrided here this 

is got executed by default right so when you run this you can see eating bread so the latest 

implementation you will get by default okay but my requirement is I don't want to change the 

object I will still call eat method but instead of the new implementation I want to execute my 

world implementation I want to execute my old implementation then what we can do just comment 

the statement and inside the same method you can just say super do e what we are doing here we 

are calling Child method only but in the child method we are invoking parent class method we 

are invoking parent class method okay now if you execute this will call child class method 

only but it will try to invoke the parent class now you can see you will get the output from the 

parent class method even though if you commented here uncomment you'll get both because by default 

it is calling Child class method so eating bread is coming from here and super do e is invoked 

parent class method so that is an output we are getting okay so you can just comment this 

so the eat method sorry the super keyword can also be used to invoke the immediate parent class 

method that is the second point the super keyword will be used to invoke the immediate parent class 

variable the super keyword will be used to invoke the immediate parent class method immediate parent 

class method so this is the purpose of using super keyword even though you created an object for 

the child class still you are able to invoke the variables and methods from the parent class 

that is possible by using super keyword super keyword is always representing immediate parent 

class this this point is very very very important immediate ping class means what will it work 

multi-level inheritance in multi-level inhance how many immediate appearent classes we will have 

so this point is very important I'm not saying in every parent it will work immediate parent means 

what if you look at multiple if you look at multi- level in a tense let's say this is one class this 

is another class this is another class this is another this is multi level inheritance right 

suppose you created variable here okay and here 100 and this variable here you have overrided here 

you have overrided this variable now you created an object for this class and by using this object 

you can obviously invoke this variable by default but if you look at here through this object if you 

want to get this value will you able to get will you able to get no you will will not able to get 

why because this is not immediate parent class of this one but which one is immediate parent class 

of this one this is a immediate parent okay if you have a value here 100 then instead of this 

you will able to get this value because this is the immediate parent but you will not get this 

one or if you have here you will not get this one these two are not immediate parent classes 

okay understood every one so in multi- level inheritance also it will work but you have to 

take either these two or either these two or you take these two then it will work okay immediate 

parent class variables immediate parent class method only you will able to invoke otherwise not 

okay for example if you create an object of this class this class you can invoke variables and 

methods from the immediate parent so you will able to get from here similarly if you create an 

object of this class then you able to invoke the variables and Method from the immediate parent 

from here okay so this is a concept in case of multiple there will be multiple parent classes see 

there will not be multiple parents only one type of inheritance multiple parents will be there 

that is that is what type of inheritance multip inheritance see only in the multiple inheritance 

there is multiple parents like this no one will be immediate see here in multiple okay in case of 

multiple there will be multiple parent classes okay here there are multiple classes multiple 

parents and no one will be immediate so it will be not uh so it will not be applicable see all 

three classes are immediate parents this one is immediate parent this is also immediate parent 

this this is also immediate parent now you have some variable here a equal to 100 you have 

another variable e equal to 100 here another variable a equal to 100 so first of all by using 

a class we cannot create multiple parents in the last classes we have discussed this okay using a 

class concept we cannot create multiple parents only in inheritance it is possible sorry only with 

interface it is possible only with interfaces you can create multiple parents but in interfaces 

we cannot use super keyword okay we cannot use super keyword with the interfaces super keyword 

is always represent class not but interface okay if you have a multiple parents definitely they 

are the interfaces there should not be classes okay so the super keyword is not applicable 

for multiple inheritance if you have multiple parents if you have multiple immediate parents 

not applicable only for class it is applicable okay so these are all Concepts which are related 

to inheritance we have discussed so many things and practice it multiple times and get familiar 

and understand all the concepts even in automation also these concepts are most important inheritance 

is is very very important concept we cannot avoid in even on Automation and over raing over loading 

is also most important okay and super final keywords final keyword is not that much important 

because a development perspective these are all important interv perspective you have to know what 

are all those things okay so practice these things multiple times understand the concepts and we will 

continue in the next class so interfaces is the next session okay in the next session we will talk 

about abstract class interface how can we achieve multiple inheritance by using interface so all 

those things we will discuss in the next class okay yes so I'll stop here for today's session 

and tomorrow or next class we will continue