Inheritance

Inheritance is a concept which allows to create an "is-a relationship" in between two classes. It's similar to partent-child relationship. As example think of a student. Every Student is a Person. So Student inherits every behaviour and attribute which a person have. (this depends on access specifier. As example if the access specifier is private then those fields or methods cannot be inherited by its sub classes.)

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Code: public class TestInheritance{

public static void main(String []args){

Person p1 = new Person("John",20);
p1.eat();
p1.sleep();
Student s1= new Student("Merry",16);
s1.eat();
s1.sleep();
s1.study();

}

}

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class Person{

String name; int age;

Person(String name,int age){

this.name=name;
this.age=age;
System.out.println(this.name+":"+"I'm a Person");

}

void eat(){

System.out.println(this.name+":"+"Eating...");

}

void sleep(){

System.out.println(this.name+":"+"Sleeping...");

}

}

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class Student extends Person{

Student(String name,int age){

super(name,age);
System.out.println(this.name+":"+"I'm a Student");

}

void study(){

System.out.println(this.name+":"+"Studying..");

}

}

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When the above code is executed we will be able to get the following output

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Output:

John:I'm a Person

John:Eating...

John:Sleeping...

Merry:I'm a Person

Merry:I'm a Student

Merry:Eating...

Merry:Sleeping...

Merry:Studying..

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Code Explanation:

I roughly numbered the lines to show how it's going to execute the above code
01-->public class TestInheritance{
02-->public static void main(String []args){
03-->Person p1 = new Person("John",20); //making a Person object called p1
12-->p1.eat(); //calling eat method which is implemented inside the person class using p1 object
16-->p1.sleep(); //calling eat method which is implemented inside the person class using p1 object 20-->Student s1= new Student("Merry",16);// making a Student object called s1
31-->s1.eat(); /*Though a method called eat is not implemented in student class, since student is a Person it inherits eat method from its super class*/
35-->s1.sleep(); /*As mentioned above sleep method is also inherits from person class*/
39-->s1.study(); /*rather than eating and sleeping student also can study (Student class is the specialized class while Person class is the generalized class )*/
 43-->}

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44-->}
04-->class Person{ //Super class (Parent class /Generalized class) 
05-->String name;
06-->int age;
7,24-->Person(String name,int age){
8,25-->this.name=name;
9,26-->this.age=age;
10,27-->System.out.println(this.name+":"+"I'm a Person");
11,28-->}
13,31-->void eat(){
14,33-->System.out.println(this.name+":"+"Eating...");
15,34-->}
17,36-->void sleep(){
18,37-->System.out.println(this.name+":"+"Sleeping...");
19,38-->}
 }

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21-->class Student extends Person{ //sub class(child class/Specialized class)
22-->Student(String name,int age){
23-->super(name,age); /*using the super keyword we can call the constructor in Person class which expect string and an int parameter. (super is a keyword which we used to invoke super class constructors and also to access super class members. It is a must to call the super class constructor in the first line of the subclass constructor. if we havent mentioned it then it calls the default constructor which accept no parameters.)*/
29-->System.out.println(this.name+":"+"I'm a Student");
30-->}
40-->void study(){
41-->System.out.println(this.name+":"+"Studying..");
42-->}
 }

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