Question

I am confused about the concept of interface when dealing with anonymous inner class. As far as I know that you can’t instantiate an interface in Java, so the following statement would have a compile error

     ActionListener action = new ActionListener();  // compile error

What happen when it deals with anonymous class? why does it allow to use new? For example:

     JButton button = new JButton("A");
     button.addActionListener(new ActionListener(){    //this is fine
           @Override
           public void actionPerformed(ActionEvent e){

           }
     };

Does the compiler just make a class and implement ActionListener behind the scene? How does it work?

Answer 1

It allows you to create a new anonymous class that implements ActionListener because you’re providing the implementation, you’re just not giving it a class name.