Java – Topic 30

(Drag & Drop)

LESSON NOTE

MULTIPLE LISTENERS/INTERFACES

A class can implement more than one interface at a time. You simply need to list the interfaces separated by a comma.

For example:

public class FunApplet extends Applet implements KeyListener, MouseListener

Inside such a class, you will need both statements:

addKeyListener(this);

addMouseListener(this);

And of course, you will have to implement all methods from both interfaces.

MOUSEMOVEMENTLISTENER INTERFACE

You may think that you are currently able to watch for any type of event on the mouse or keyboard right now. You’re wrong. There are some mouse events for which you need to use a different listener.

The MouseMovementListener interface provides the following event-related methods:

void mouseDragged(MouseEvent e)
void mouseMoved(MouseEvent e)

The mouseDragged method is executed when the mouse is dragged (moved while button is down). The mouseMoved method is executed when the mouse is moved with button up.

EXAMPLE

The following applet will allow you to click on a circle and drag it around as you wish. When you release the click, the circle will no longer be dragged around. The technique we will use will combine the use of the mouseClicked and mouseReleased events from the MouseListener interface along with the mouseMoved event from the MouseMotionListener.

Click here to see the applet. Click here to see the code.