我们可以为接口和抽象类创建 object 吗？

Question

f.addMouseMotionListener(new MouseAdapter() {
    public void mouseDragged(MouseEvent e) 
    {
        String s="Mouse dragging :X = "+e.getX()+" Y= "+e.getY();
        tf.setText(s);
    }
    });

i read that we cannot instantiate objects for Abstract classes...but here we are creating new MouseAdapter() ..can someone explain how is it done with these anonymous classes..thank u.

Answer 1

You're not creating an instance of MouseAdapter , you are creating an instance of an anonymous class inheriting from MouseAdapter .

More verbosely, this could have been written:

class Goo extends MouseAdapter { public void mouseDragged(){...} };

f.addMouseMotionListener(new Goo());

Answer 2

You don't see it doesn't mean it won't happen. Just from the code, you use new MouseAdapter() to construct an object. However, if you try to read the content in.class file, you will find that the inner class has name, the usual case is,

class MouseAdapter$1 extends MouseAdapter

Till this, you should clear about everything. :)