JAVA中的图形用户界面示例

【例9.24】综合鼠标事件和键盘事件处理的程序，模拟一个电子白板，可以用鼠标在上面绘画，可用键盘在上面写字。 import javax.swing.*; import java.awt.*; import java.awt.event.*; public class MouseAndKeyDemo extends JApplet { protected int lastX = 0, lastY = 0; public void init() { setBackground(Color.white); setForeground(Color.blue); addMouseListener(new PositionRecorder()); addMouseMotionListener(new LineDrawer()); addKeyListener(new CharDrawer()); } protected void record(int x, int y) { lastX = x; lastY = y; } private class PositionRecorder extends MouseAdapter{ public void mouseEntered(MouseEvent e) { requestFocus(); record(e.getX(), e.getY()); } public void mousePressed(MouseEvent e) { record(e.getX(), e.getY()); } } private class LineDrawer extends MouseMotionAdapter { public void mouseDragged(MouseEvent e) { int x = e.getX()，y = e.getY(); Graphics g = getGraphics(); g.drawLine(lastX, lastY, x, y); record(x, y); } } private class CharDrawer extends KeyAdapter { public void keyTyped(KeyEvent event) { String s = String.valueOf(event.getKeyChar()); getGraphics().drawString(s, lastX, lastY); record(lastX + 11, lastY); } } } 程序中，在类MouseAndKeyDemo中定义了三个私有嵌套类，两个类对鼠标事件进行处理，一个类对键盘事件进行处理。 程序的运行情况如下图所示。图中的线用鼠标随手画出，文字用键盘输入