主题：程序代码——显示按键信息

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Font;
import javax.microedition.lcdui.Graphics;
import javax.microedition.midlet.MIDlet;

public class Exec extends MIDlet {
        private Display display;

        public Exec() {
                display = Display.getDisplay(this);
        }

        public void startApp() {

                display.setCurrent(new DrawPanel());
        }

        public void pauseApp() {
        }

        public void destroyApp(boolean unconditional) {
        }
}

class DrawPanel extends Canvas {
        String str = "请按键！";

        public void paint(Graphics g) {
                g.setColor(255, 255, 255);
                g.fillRect(0, 0, getWidth(), getHeight());
                g.setColor(0, 0, 0);
                Font font = Font.getFont(Font.FACE_SYSTEM, Font.STYLE_BOLD,
                                Font.SIZE_LARGE);
                g.setFont(font);
                int fontWidth = font.stringWidth(str);
                int fontHeight = font.getHeight();
                g.drawString(str, getWidth() / 2 - fontWidth / 2, getHeight() / 2
                                - fontHeight / 2, Graphics.TOP | Graphics.LEFT);
        }

        protected void keyPressed(int keyCode) {
                if (keyCode > Canvas.KEY_POUND && keyCode < Canvas.KEY_NUM9)
                        str = "按动的键为：" + (char) keyCode;
                else {
                        switch (getGameAction(keyCode)) {
                        case Canvas.UP:
                                str = "按动的键为：向上";
                                break;
                        case Canvas.DOWN:
                                str = "按动的键为：向下";
                                break;
                        case Canvas.LEFT:
                                str = "按动的键为：向左";
                                break;
                        case Canvas.RIGHT:
                                str = "按动的键为：向右";
                                break;
                        case Canvas.FIRE:
                                str = "按动的键为：开火";
                                break;
                        case Canvas.GAME_A:
                                str = "按动的键为：GAME_A";
                                break;
                        case Canvas.GAME_B:
                                str = "按动的键为：GAME_B";
                                break;
                        case Canvas.GAME_C:
                                str = "按动的键为：GAME_C";
                                break;
                        case Canvas.GAME_D:
                                str = "按动的键为：GAME_D";
                                break;
                        default:
                                str = "其他的键";
                        }
                }
                repaint();
        }

        protected void keyReleased(int keyCode) {
        }
}