Chapter 11 Java AWT Part I: Mouse Events (Optional)

1. Chapter 11Java AWT Part I: Mouse Events(Optional) Lecture Slides to Accompany An Introduction to Computer Science Using Java (2nd Edition) by S.N. Kamin, D. Mickunas, E. Reingold

2. Chapter Preview In this chapter we will: • introduce event driven programming • show how a program can respond to mouse events (e.g. clicks and mouse movements) • demonstrate how to implement a listener interface • show how mouse events can be used to build highly interactive programs

3. Abstract Windowing Toolkit (AWT) • Part of the Java distribution, but not part of the Java language itself • AWT is library of classes and methods used by Java programmers that supported are by the basic Java runtime libraries • Even though this chapter is labeled optional, it is not possible to be a complete Java programmer without understanding the AWT

4. Java Events • Events are occurrences outside of the program to which the program must respond (e.g. user key press) • Event managers are methods that first catch the event • Listener classes send messages to an event manager requesting to be notified when a particular message occurs • Event managers send messages to listeners notifying them when a particular event occurs

5. Creating Mouse Click Listeners • Import the java.awt.event package • In the class header, add the words implements MouseListener • Send the addMouseListerner(this) message to the mouse event manager (should be done in the constructor method) • Define methods mouseClicked, mousePressed, mouseReleased, mouseEntered, mouseExited

6. Mouse Click Listener Template import java.awt.event.*; … public class classname implements MouseListener { … // include manager.addMouseListener(this); // in some initialization method … public void mouseClicked (MouseEvent e) { … } public void mousePressed (MouseEvent e) { … } public void mouseReleased (MouseEvent e) { … } public void mouseEntereded (MouseEvent e) { … } public void mouseExited (MouseEvent e) { … } }

7. Finding Mouse Location • Inside mouseClicked the argument e of type MouseEvent can be used to find the location of the mouse cursor • The call e.getX( ) returns the value of the horizontal coordinate of the mouse cursor position • The call e.getY( ) returns the value of the vertical coordinate of the mouse cursor position

8. Creating Mouse Motion Listeners • Import the java.awt.event package • In the class header, add the words implements MouseMotionListener • Send the message addMouseMotionListerner(this) to the mouse event manager (should be done in the constructor method) • Define methods mouseMoved and mouseDragged

9. Mouse Motion Listener Template import java.awt.event.*; … public class classname implements MouseMotionListener { … // include manager.addMouseListener(this); // in some initialization method … public void mouseMoved (MouseEvent e) { … } public void mouseDragged (MouseEvent e) { … } }

10. Mouse Motion • mouseMoved will be called each time the mouse makes a significantly large movement • mouseDragged will be called instead if thre mouse button is pressed and the mouse makes a significantly large movement

11. Listening to All Mouse Events • Two catch all seven mouse events use the following class header public class classname implements MouseListener, MouseMotionListener { • You then need to define all seven mouse methods mouseMoved, mouseDragged, mouseClicked, mousePressed, mouseReleased, mouseEntered, mouseExited