Abstract class in java

 program to illustrate the concept of abstract class

package com.company;
abstract class base2{// you must use abstract keyword to create an abstract class
    public base2(){
        System.out.println("im constructor");
    }
    public void fun(){
        System.out.println("hy");
    }
    abstract public void greet();// this method which must be initialize in chlid classes
}
class derived2 extends base2{
    public void greet(){
        System.out.println("heloo");
    }
}
abstract class derived3 extends base2{ //if you don't want to create abstract method
    public void fun1(){                 //you have to make child class abstract
        System.out.println("hy world");
    }
}
public class abstractClass {
    public static void main(String[] args) {
        derived2 d=new derived2();
        d.greet();
        d.fun();
       //base2 b= new base2(); your cannot define object for this
       /* derived3 r= new derived3();
        r.fun1();   you cannot call this since it is inside abstract class  */
    }
}