Java's Principle of Inheritance

 One of the highlights of object - oriented programming is its ability to reuse objects. In Java, a parent and child relationship can exist and this is done through the keyword extends.

With the relationship, a child can access the parent's methods and fields with the child's class ability to create its own methods and attributes.

See the program below for the sample program. 
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import javax.swing.*;
public class SampleInheritance{
public static void main (String args[]){
String numstring1=JOptionPane.showInputDialog("Input a number");
int mynum1=Integer.parseInt(numstring1);

Parent1 obj1=new Parent1();
obj1.setnum(mynum1);
obj1.square();
obj1.cube();
System.out.println("Last number result from parent methods: "+obj1.getnum());

String numstring2=JOptionPane.showInputDialog("Input a number");
int mynum2=Integer.parseInt(numstring2);

Child1 obj2=new Child1();
obj2.setnum(mynum2);

obj2.square();
obj2.cube();
obj2.nth();

System.out.println("Last number result with parent and child methods: "+obj2.getnum());


}

}


class Parent1{
int num;
void setnum(int x)
{num=x;}

void square()
{num=num*num;

}

void cube()
{num =num*num*num;

}

int getnum()
{return num;}
}

class Child1 extends Parent1{
void nth()
{ num=num/2;}

}