java - Inner class within Interface

Question

Is it possible to create an inner class within an interface?
If it is possible why would we want to create an inner class like that since we are not going to create any interface objects?

Do these inner classes help in any development process?

Answer 1

Yes, we can have classes inside interfaces. One example of usage could be

public interface Input
{
    public static class KeyEvent {
         public static final int KEY_DOWN = 0;
         public static final int KEY_UP = 1;
         public int type;
         public int keyCode;
         public char keyChar;
    }
    public static class TouchEvent {
         public static final int TOUCH_DOWN = 0;
         public static final int TOUCH_UP = 1;
         public static final int TOUCH_DRAGGED = 2;
         public int type;
         public int x, y;
         public int pointer;
    }
    public boolean isKeyPressed(int keyCode);
    public boolean isTouchDown(int pointer);
    public int getTouchX(int pointer);
    public int getTouchY(int pointer);
    public float getAccelX();
    public float getAccelY();
    public float getAccelZ();
    public List<KeyEvent> getKeyEvents();
    public List<TouchEvent> getTouchEvents();
}

Here the code has two nested classes which are for encapsulating information about event objects which are later used in method definitions like getKeyEvents(). Having them inside the Input interface improves cohesion.