abstract class hello //abstract class declaration
    {
    void leo() {}
    }


    abstract class test {} //2'nd abstract class


    class dudu {  //main class

    public static void main(String args[])
    {
    hello d = new test() ;  // tried here
    }

    }

public abstract class A {
    private int a;
    public A(int a) {
       this.a = a;
    }
    ...
}

public B extends A {
    public B() {
        super(42);
    }
    ...
}

B b = new B();    // This is an indirect instantiation of A

A a = new A(99);  // This is a compilation error.  You cannot
                  // instantiate an abstract class directly.

abstract class hello //abstract class declaration
{
    void leo() {}
}

class test extends hello
{
    void leo() {} // Custom test's implementation of leo method
}

public abstract class Human {
         // This class can't be instantiated, there can't be an object called Human
         }

  public Male extends Human {
         // This class can be instantiated, getting common features through extension from Human class
   }

  public Female extends Human {
        // This class can be instantiated, getting common features through extension from Human class

   }