abstract sub-class

[feniger]

is this possible in java?
abstract class A extends B () {...}

[sukatoa]

Yep,

Here is an example,

public class test extends B{

	public test(){
		this.printA();
		this.printB();
	}

	public static void main(String args[]){
		new test().printA();
	}
}

abstract class B extends A{
	public void printA(){
		System.out.println("class B");
	}		
}

abstract class A{
	public void printB(){
		System.out.println("class A");
	}
}

Guess the output....

[Eranga]

feniger got a nice example. :)

As that example, you have keep in mind two things.

1. Abstract class can be subclassed, as you can see.

2. Abstract classes cannot instantiate. If you do such a things, in compile time, got an error that abstract class cannot be instantiate.

[danielstoner]

At any level in the class hierarchy you can declare an abstract class.

package jf.acls;

public class Concrete {
    @Override
    public String toString() {
        return "Concrete";
    }
}

package jf.acls;

public abstract class Abstract extends Concrete {
    @Override
    public String toString() {
        return "Abstract extends Concrete";
    }

    public abstract int getTheNumber();
}

[Eranga]

At any level in the class hierarchy you can declare an abstract class.

package jf.acls;

public class Concrete {
    @Override
    public String toString() {
        return "Concrete";
    }
}

package jf.acls;

public abstract class Abstract extends Concrete {
    @Override
    public String toString() {
        return "Abstract extends Concrete";
    }

    public abstract int getTheNumber();
}

Nice explanation though. I have one confusion here. What you mean any level of class hierarchy. I'm confusing it with your code. :)

[danielstoner]

I think his question was if it is possible to extend a concrete class (non-abstract) with an abstract class. And I said yes :) Abstract extends Concrete. I just wanted to make it clear that an abstract class can exist lower in the hierarchy, not only at the top. I hope it is clear now :) because if I continue to explain it will become really messy and unclear. LOL

[Eranga]

Sure, I got the point. Thanks.