Nested Classes and Event Handling - Learning Java Through Games - page 227

Going back to our drawing code, the mouse motion listener checks if the left mouse
button is pressed. If it is, it gets the current coordinates of the cursor and adds the point
to the current shape. The last line redraws the panel so that we can see the new shape.
When we draw too much on a sheet of paper, it may become cluttered and we may want to
clear it. We will fix this problem by allowing the panel to be cleared when the right mouse
button is pressed. Here is our complete code.

import java .awt . ∗ ;
import java .awt. event . ∗ ;
import java .awt.geom. ∗ ;
import java . util . ∗ ;
import javax . swing . ∗ ;

public class DrawingGame {

public static void main(String [] args)

{

MyFrame f = new MyFrame ( ) ;
f . setVisible( true );

}

}

class MyFrame extends JFrame {

public MyFrame ( ) {
setSize (300 , 300) ;
MyPanel p = new MyPanel () ;
add(p) ;

}

}

class MyPanel extends JPanel {
ArrayList < MyShape > shapes = new ArrayList <> () ;
public MyPanel () {
addMouseListener( new MouseAdapter () {
public void mousePressed (MouseEvent e ) {
if (e . getButton() == 1) { // left mouse button
shapes .add( new MyShape( e . getPoint ( ) ) ) ;
repaint () ;
if (e . getButton() == 3)

{ // right mouse button

shapes = new ArrayList <> () ;

repaint () ;

}

}
} );

addMouseMotionListener( new MouseMotionAdapter () {

public void mouseDragged(MouseEvent e) {
if ((e. getModifiersEx() & MouseEvent.BUTTON1DOWN MASK) ! = 0 ) {

shapes . get(shapes . size () − 1) . addPoint(e . getPoint () ) ;
repaint () ;

}

}
} );

}

public void paintComponent(Graphics g) {