本例使用Canvas绘制钢琴的界面，同时使用了MIDP 2.0 media子系统来播放钢琴按键触发的声音效果。是个不错的图形用户界面和音效结合的范例。

/*

* PianoMIDlet.java * * Created on 2005年12月6日, 下午2:02 */

package com.j2medev.piano;

import javax.microedition.media.*;

import javax.microedition.lcdui.*;

import javax.microedition.midlet.*;

public class PianoMIDlet extends MIDlet {

public void startApp() { Displayable d = new PianoCanvas(); d.addCommand(new Command("Exit", Command.EXIT, 0)); d.setCommandListener(new CommandListener() { public void commandAction(Command c, Displayable s) { notifyDestroyed(); } }); Display.getDisplay(this).setCurrent(d); } public void pauseApp() {} public void destroyApp(boolean unconditional) {}}

class PianoCanvas extends Canvas {

private static final int[] kNoteX = { 0, 11, 16, 29, 32, 48, 59, 64, 76, 80, 93, 96 }; private static final int[] kNoteWidth = { 16, 8, 16, 8, 16, 16, 8, 16, 8, 16, 8, 16 }; private static final int[] kNoteHeight = { 96, 64, 96, 64, 96, 96, 64, 96, 64, 96, 64, 96 }; private static final boolean[] kBlack = { false, true, false, true, false, false, true, false, true, false, true, false }; private int mMiddleCX, mMiddleCY; private int mCurrentNote; public PianoCanvas() { int w = getWidth(); int h = getHeight(); int fullWidth = kNoteWidth[0] * 8; mMiddleCX = (w - fullWidth) / 2; mMiddleCY = (h - kNoteHeight[0]) / 2; mCurrentNote = 60; } public void paint(Graphics g) { int w = getWidth(); int h = getHeight(); g.setColor(0xffffff); g.fillRect(0, 0, w, h); g.setColor(0x000000); for (int i = 60; i <= 72; i++) drawNote(g, i); drawSelection(g, mCurrentNote); } private void drawNote(Graphics g, int note) { int n = note % 12; int octaveOffset = ((note - n) / 12 - 5) * 7 * kNoteWidth[0]; int x = mMiddleCX + octaveOffset + kNoteX[n]; int y = mMiddleCY; int w = kNoteWidth[n]; int h = kNoteHeight[n]; if (isBlack(n)) g.fillRect(x, y, w, h); else g.drawRect(x, y, w, h); } private void drawSelection(Graphics g, int note) { int n = note % 12; int octaveOffset = ((note - n) / 12 - 5) * 7 * kNoteWidth[0]; int x = mMiddleCX + octaveOffset + kNoteX[n]; int y = mMiddleCY; int w = kNoteWidth[n]; int h = kNoteHeight[n]; int sw = 6; int sx = x + (w - sw) / 2; int sy = y + h - 8; g.setColor(0xffffff); g.fillRect(sx, sy, sw, sw); g.setColor(0x000000); g.drawRect(sx, sy, sw, sw); g.drawLine(sx, sy, sx + sw, sy + sw); g.drawLine(sx, sy + sw, sx + sw, sy); } private boolean isBlack(int note) { return kBlack[note]; } public void keyPressed(int keyCode) { int action = getGameAction(keyCode); switch (action) { case LEFT: mCurrentNote--; if (mCurrentNote < 60) mCurrentNote = 60; repaint(); break; case RIGHT: mCurrentNote++; if (mCurrentNote > 72) mCurrentNote = 72; repaint(); break; case FIRE: try { Manager.playTone(mCurrentNote, 1000, 100); } catch (MediaException me) { } break; default: break; } }}

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