Lecture 4- Introduction to Classes and Objects in Java and Paradigms of OOP

[Music] [Music] so welcome to lecture four introduction to object oriented programming so in the last few lectures so we talked about the classes and objects in C++ so we have run several codes and now what is the syntax in Java all right another objectoriented programming called Java so we are going to see the syntax as I already Define when you define a class the only difference is in C++ you have a semicolon right so if I'm writing the C++ same the class I have to put a semicolon over here all right so whereas you should not put a semicolon in Java so that is the first difference in the class rest of them almost similar so you can see I have imported several functions utility Lang and input output all right so here you have class car car is the name of the class all right so under this you have two data member all right so here you have a data member one is brand Under string another one is year under integer all right so you have two data members one is brand another one is year one is string another one is integer all right so here we call this as a method right so this is a method in C++ we call it is member function so in Java it is nothing but a method right so this display info is a method whereas in the last few lectures in C++ we call this as a member function both are equivalent so I call this in C++ all right so here you have a method called display info more or less similar all right so syntax is C out we used to write C out in C++ and in Java it is system.out.println Ln stands for new line right system.out.print Ln so there you use C out the same syntax in C++ if we write like this C+ C out brand and then you put endl all right exactly the same syntax this is the similar syntax in C++ similar syntax in C++ and in Java you have system. out. print this is like quote you are writing we can write in C C++ also that's understood I did not write it in the code you are writing whatever you are writing in the code will be printed and then you have plus symbol and brand all right so exactly similar we have already seen several C++ syntax so you are now familiar so see out brand andl equalent and similarly we are Printing system.out.print and here right system. out. printer L year and what is the year correct so we have two member data and you have one member function the class is over the class is called car right the car class has two member data in fact I have to call data member in Java and Method display info which is equivalent to member function in C++ so now this is the driver class right which is having main whenever you are having a main in Java you call this as a driver class all right so you can find the main all right so you can find the main correct so this main is name of the class capital M and here like a void main or int main when you're writing in C++ all right so here you have void main rest of the thing we'll see in the due course right now no need to worry because our focus is on class and object all right so here in Java because it is d dynamic in nature so when you're are creating an object right when you are creating an object so my car is an object and then dynamically we have to allocate a memory or automatically it will be allocated when you write new and the next one is slowly I'm introducing this Constructor all right so here my car is object all right and here you have class the new operator we'll take one example in the case of array right and here this is first time we are seeing this is called Constructor anyway we will Define Constructor extensively right suppose I declare let us assume in C++ in a of 10 right array of 10 elements static array so what about a dynamic array if I ask you to create a dynamic array what will you do in Star a all right a equal to new an of 10 all right so you might have used this new operator while creating a dynamic array this is a dynamic array in C++ all right so this is a static array so in the case of java everything is dynamic suppose I want to write the same code so this is a C++ code so in Java what you will do you use like this in Array notation instead of pointer I'll put this in a and then you are writing a equal to new in of 10 same almost the same code except the star right so this is in the case of java so in Java everything we have to talk in terms of dynamic right this is ruled out I cannot declare like this in Java all right so similarly when I have this the object my car you have object and car is the class now I have given some example of new in C++ so dynamically create a memory the new will dynamically create a memory so my car y capital c here so object so this object will be located in some address right so here in Java we call that is a identity Ash map I'll write completely identity Ash map you call it as address in C++ right so here is a identity Ash map so some address let us say 0x 732 EF something like that so in this address your my car object right will be stored right and line number 27 and 28 we have the data members brand my car. brand so I give some brand name and my car. year 2024 so now my car is invoking display info my car object which is invoking so dot operator same exactly same what we have studied in C++ my car do operator display info right so when it calls so you can see that brand is Kia and year is 2024 right so that will be prined system. out. printer learn we want to print these two values brand and year so when when I run the code I will get this as a output all right so car brand is Kia and here is 2024 so we will see now I introduce I'll use Escape I'll go to the eclipse program if you open Eclipse right so Java this is called Java eclipse this environment is called Java Eclipse so here you go the same program that I have written so here you you have class car right so here you have class car class car has two member data or data member brand and year right and then you have a method called display info all right line number 15 to 18 then when you come to the main program we call it as main one all right so we have car car is the class and my car is the object right so we are creating we are instantiating an object called my car under class car and a new operator and you have a Constructor so line number 28 and 29 the my car which is having two data member is getting the value right my car. brand is Kia and my car. ear is 2024 so now in line number 32 my car is invoking display info right my car is invoking display info when it is invoking display info it goes line number 15 and there are two print out statement right two print statement system.out.print and car brand so brand value what is the brand name Kia and system. out. print and year is 2024 so when I run this code all right so here you have you can go here and then run this code you can see the output in the bottom car brand is here and here is 2024 so this is under Java Eclipse so you can install Java Eclipse all right and then it's a good compiler for Java compiler so you can run the code so this is in housee you can install this in your machine or in your computer and then you start running this code right so more or less we had seen the objects and classes extensively we saw in C++ I have introduced Java so you can write the basic programs in Java as well all right so at one point of time I'll introduce all the programs right or all the concepts with the help of both C++ and Java and at what point of time right so we will follow only C++ so it is understood both are almost same all right so once you get that feeling so you can start writing the code only in C++ but whenever there is a difference or some of the functionalities available only in C++ not in Java or vice versa so that point of time I will talk about that right so now the next concept is inheritance in C++ so extensively I talked about the code reusability in the last few class class ES right so that means somebody has written Class A all right and I am the new user I have written Class B so can I use some properties of Class A yes you can do that that is called as a inheritance that means B is taking the properties of a right so one of the key feature in op inheritance is one of the key feature in oop so in this case a will be called as a Base Class A will be called as a base class and B will be called as a derived class so B is using all the properties of a right unless otherwise I talked about this access modifier right when we I mean slowly I introduce the private and public when everything is public assume that all the member data and member functions are public B can use if it is private only a can use right so you cannot do the derivation all right so those things we'll talk once I introduce the access modifiers right like public private protected Etc right so right now we know what is meant by inheritance so B can use all the properties of a all right if it is publicly available so one you call it as a base class another one is the derived class so that means B can reuse the code that means that may contain a member function that may contain a member data so you are establishing a relationship between the classes all right so also you might have studied function overloading right in the basic programming like a procedural oriented programming function overloading when I introduce the class class on objects so we have another concept called function overriding so this can be achieved with the help of inheritance so these are all the basic features of inheritance in C++ so what are all the different types of inheritance in C++ so this I have told right so Class B is using the property of Class A Class A and Class B Class B is using the property of Class A this is a notation you have a arrow so that means Class B is using let us say the data member and member functions or member data and member functions so that inheritance is termed as single inheritance or you can also call it as a simple inheritance now you are extending so so can I have three classes can Class B inherit Class A and Class C inherit Class B the answer is yes you can do you call this as a multi-level inheritance you can have a b CDE e f up to that right so here B is inheriting Class A and Class C is inheriting Class B you call this as this concept as multi-level inheritance and similarly now assume that you have three classes Class A Class B and Class C all right so Class C can use the properties of Class A and Class B right Class C they can use the properties of Class A and Class B two classes all right you call it as multiple inheritance this is a concept of multiple inheritance we have a notation we'll see all right so this is called the multiple inheritance and similarly you have hierarchical inheritance Class B is using the property of Class A and Class C can also use the properties of class all right or other words Class B can be derived from class A and Class C can also be derived from Class A in the previous case multiple inheritance Class C is derived from both class A and Class B that is the meaning right so you can say other way around it can use the properties otherwise when I talk in terms of Base Class and derived class the multiple inance Class A and Class B are the based classes and Class C is the derived class all right so Class C can be derived from class A and Class B and you call this as a multiple inheritance right here Class A is the base class and Class B and Class C are the derived classes so that is also possible Right Class B and Class C are derived from class A you call this as a hierarchical and the last one is you have this we call it as Hybrid inheritance right this is called Hybrid inheritance all right so you can see both hierarchical and multiple the combination of hierarchical and multiple right the multiple Plus archical you call this as a Hybrid inheritance all right so for example here Class B and Class C they are derived from class A so Class A is the base class all right so these are all I put D1 and D2 dered classes D1 is a derived class one and D2 is a derived class two all right and now class D all right I'll put D12 so now this will become derived class which are all the base classes Class B and Class C so when you do all together whatever inheritance that we had seen in the previous slide that are nothing but multiple inheritance and hierarchical inheritance so the combination is hybrid all right so in C++ we have all these features in the case of inheritance so you may have single inheritance like this you may have multi-level inheritance like this you have multiple inheritance you have hierarchical the combination of multiple plus hierarchical you will have right multiple plus hierarchical you have have Hybrid inheritance so these are all five different inheritances which is available in C++ whereas when I am comparing with Java Java does not have this multiple inheritance right C++ you can see all are there C++ you have all are there whereas in Java you don't have multiple inheritance the moment you don't have multiple inheritance we know multiple plus hierarchical is hybrid right so which obviously hybrid also will not be available right naturally all right so we have seen the last diagram of in C++ in C++ all the inheritance are available whereas in Java we don't have multiple inheritance in terms of class so right now we have class only so in Java we have a concept called interface right so once we study in in fact we are going to study interface so when I introduce interface we will have the concept of multiple inheritance all right so right now in terms of class we don't have the concept of multiple inheritance in Java so naturally you don't have Hybrid inheritance also in Java so C++ point of view we have all these five inheritant so now we'll see an example in both C++ and Java all right so you have in the Base Class you have W right we call it as a base class W is a base class so we call it as a right because we discuss about A and B right so this class has one member data right we are in C++ now one member data called brand and we have one member function called so brand right the Show brand is just displaying see out brand brand all right so this is under vehicle so this contains brand that is a member data and it has another one that is called member function which is called Show brand so you can write like this so one is brand another one is Show brand one is a data member another one is a fun function member function right so what is the derived class we'll see another class so another class is car class car so this is the syntax now how we are going to derive class car we are going to publicly derive still I am not introduce this access modifier we will see slightly later so right now we have to worry about how it is being inherited all right so vehicle now it is a base class this is this is a way Class Car colon right you put public private or protected these are all the access modifier right now without loss of generality we put public we'll see the meaning slightly later all right so this is how the syntax go for inheritance so car is the derived class vehicle is the base class so I'll just go back to the previous slide I'll write carer right so that is B so since I put the syntax like this so now I am eligible to draw an arrow that means car can inherit the properties of vehicle right so that means it can use brand because it is in public it can use brand it can use Show brand suppose you are right under car you have an object let to say car C1 so this C1 can use right so or can access brand and Show brand that is a meaning right anyway we'll see that how we are going to do that so right now the diagram is clear all right a is the base class and B is the derived Class A is a vehicle car is the derived Class B is the derived class that means car is the derived class so that means car can access both brand and Show brand right so now this car class that itself is having one member data which is called Model right whereas here you have brand here you are naming as model all right so string model so model that belongs to car right this member data belong to car and you have one more member function right that is under car we have used a member function under vehicle one more member function line number 19 it is under car you have show model so show model will display model right what is the model right number all right so here you have model is a string model is a string line number 17 you have model so string will be displayed so we will go to the main program so main program you have my car which is an object right my car is an object so this is coming under object car right so my car is an object this is coming under class car all right so I will go back again The Inheritance scenario car is the derived class which is the base class vehicle right so under this class car I have an object called my car right so now my car. brand right so my car. brand where is brand is available in Base Class yes this can access so now under this I have an object called my car so this my car can access both brand and Show brand right so that is why you have line number 28 so this is a valid statement there won't be any error my car. brand brand is available in Base Class yes and next one is my car. model model is already available in derived class so it's not a problem the usual class and object that we had seen right so this is also clear that's a usual one now my car. show Brand Show brand is available in base class all right so this can access your my car the object my car under car can access Show brand no problem because it's concept of inheritance right so Show brand and the next one is my car. show model is already available in the derived class right so now so I have my car. brand is toyoto my car. model is Cora all right so now what will happen if I invoke I mean to say my car the object my car is invoking Show brand right what is happening Show brand you will go to the Show brand all right so that will display brand see out brand so what is brand I passed so brand is nothing but Toyota my car. brand as Toyota so the Toyota will be printed as a first input right under line number 31 if you look at at line number 32 my car. show model right so show model model what is model Corolla right so when you go over here the show model function because it is invoking if you look at line number 32 it is invoking my car object is invoking show model so show model when you look over here model will be displayed what is your model Cora so Corolla will be displayed right so both Toyota and Corolla will be displayed as output and if you look at if you run the code right so you have to get these two as a output so we will see the C++ code right for whatever we have written we'll see the C++ code now go to the CPP code code 7. CPP all right the same code that I have written all right so here you can have class vehicle which is a base class line number five you have class vehicle which is a base class all right so you have string brand and void Show brand right and similarly you have class car which is a derived class line number 15 you have derived class right so under line number 15 again you have right one string called model and you have one member function all right so Base Class is also having one data member and member function so here also you're are having one member data and member function right so these things we had already seen so now if you go to the main program my car is an object and and car is the class so my car. brand is Toyota and my car. model is Corolla and my car is invoking Show brand and my car is invoking show model right which is possible right so those things we have seen in the theory and now if I run the code compile and run right so you can see the output so we are getting brand Toyota and model Cora right so this is how your CPP program is running for for the single inheritance all right so this is the output in fact we got the same output you can see in the program also so now in the next class the same single inheritance program we will run in Java okay so with this I am concluding this lecture thank you very [Music] much o [Music]