Can an abstract class be instantiated? [duplicate]

Question

abstract class A {
    public void disp() {
        System.out.print("Abstract");
    }
}

public class B {
    public static void main(String args[]) {
        A object = new A(){ };
        object.disp();
    }
} 

I am aware that Abstract classes cannot be instantiated, but confused on this code. Actually what this code mean ?

Answer 1

The subtlety here is in the "{}". It means you explicitly provide an anonymous implementation for the missing parts (the missing parts are abstract methods) of the abstract class A allowing you to instantiate it.

But there's no abstract method in A, therefore the anonymous implementation is empty.

Example showing the behaviour with at least one abstract method:

public abstract class A {
    public abstract void bar();
    public void disp() { System.out.print("Abstract"); } 
}

public class B { 
    public static void main(String args[]) { 
        A object = new A() { 
            @Override public void bar() { System.out.print("bar"); } 
        }; 
        object.disp(); //prints "Abstract" 
        object.bar(); //prints "bar"
    } 
} 

Answer 2

This is called an anonymous inner class. You are not instantiating the abstract class, you are instantiating the concrete anonymous inner class which extends the abstract class. Of course, in order for this to be allowed, the anonymous inner class must provide implementations for all the abstract members of the abstract superclass … which it does in this case, because the abstract superclass has no abstract members.