SY-4-c Implementation of abstract class in Java in easy way

import java.util.*;
abstract class BaseClass
{
    public abstract void disp();
}

class DerivedClass_1 extends BaseClass
{
    public void disp()
    {
        System.out.println("This is Derived Class 1");
    }
}

class DerivedClass_2 extends BaseClass
{
    public void disp()
    {
        System.out.println("This is Derived Class 2");
    }
}

class Demo
{
    public static void main(String[] args)
    {
        DerivedClass_1 d1 = new DerivedClass_1();
        DerivedClass_2 d2 = new DerivedClass_2();

        d1.disp();
        d2.disp();
    }
}