书的第十一章到十四章
以一个MIDI音乐播放器的例子
穿插了异常处理，图形用户接口，和文件输入输出流的知识
异常处理：
当你调用了有风险的方法时，需要用try/catch来处理
如果自己编写的程序中可能有风险，就要用throw来抛出异常，并且可以抛出多个
try中存放调用方法的语句，然后用catch块做异常处理/恢复程序
有多个catch时，要从继承最底层开始
final语句为无论如何都会执行的部分
一个异常处理代码块中，catch与try中间不能有程序
try一定要含有catch或者final，但只有final要继续抛出异常
如果不想处理异常，暴力的一直throw给java虚拟机，会通过编译，但会产生问题
JAVA的图形界面，awt，swing似乎用的并不多。毕竟是主要用于服务器端语言
大致了解了一些基本方法
还是直接开始实例吧，回顾代码，加上注释
这是运行后的大概样子
这个小程序还是很好玩的，可以自己创作乐器伴奏
下面是我自己敲的源码
public class BeatBox {
JPanel mainPanel;
ArrayList<JCheckBox> checkboxList;
Sequencer sequencer;
Sequence sequence;
Track track;
JFrame theFrame;
//存放16种乐器的数组
String [] instrumentNames = {
"Bass Drum","Closed Hi-Hat","Open Hi-Hat","Acoustic Snare",
"Crash Cymbal","Hand Clap","High Tom","Hi Bongo","Maracas",
"Whistle","Low Conga","Cowbell","Vibraslap","Low-mid Tom",
"High Agogo","Open Hi Conga"
};
//存放各乐器在MIDI中对应的序号
int[] instruments = {
35,42,46,38,49,39,50,60,70,72,64,56,58,47,67,63
};
//主方法启动播放器
public static void main(String[] args) {
// TODO Auto-generated method stub
BeatBox beatbox = new BeatBox();
beatbox.buildGUI();
}
//建立用户界面
public void buildGUI() {
//主界面的几个模块和初始属性
theFrame = new JFrame("BeatBox by Yshen");
theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
BorderLayout layout = new BorderLayout();
JPanel background = new JPanel(layout);
background.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
checkboxList = new ArrayList<JCheckBox>();
//按钮块，给每个按钮添加监听，下面有对应的监听器代码
Box buttonBox = new Box(BoxLayout.Y_AXIS);
JButton start = new JButton("Start");
start.addActionListener(new MyStartListener());
buttonBox.add(start);
JButton stop = new JButton("Stop");
stop.addActionListener(new MyStopListener());
buttonBox.add(stop);
JButton upTempo = new JButton("Tempo Up");
upTempo.addActionListener(new MyUpTempoListener());
buttonBox.add(upTempo);
JButton downTempo = new JButton("Tempo Down");
downTempo.addActionListener(new MyDownTempoListener());
buttonBox.add(downTempo);
JButton save = new JButton("Save");
save.addActionListener(new MySendListener());
buttonBox.add(save);
JButton load = new JButton("Load");
load.addActionListener(new MyReadInListener());
buttonBox.add(load);
//乐器列表
Box nameBox = new Box(BoxLayout.Y_AXIS);
for (int i = 0; i < 16; i++) {
nameBox.add(new Label(instrumentNames[i]));
}
//整体布局
background.add(BorderLayout.EAST, buttonBox);
background.add(BorderLayout.WEST, nameBox);
theFrame.getContentPane().add(background);
GridLayout grid = new GridLayout(16,16);
grid.setVgap(1);
grid.setHgap(2);
mainPanel = new JPanel(grid);
background.add(BorderLayout.CENTER, mainPanel);
//256个checkbox生成
for (int i = 0; i < 256; i++) {
JCheckBox c = new JCheckBox();
c.setSelected(false);
checkboxList.add(c);
mainPanel.add(c);
}
setUpMidi();
//设置主界面尺寸并设置为可见
theFrame.setBounds(50,50,300,300);
theFrame.pack();
theFrame.setVisible(true);
}
//建立MIDI播放器，记得try
public void setUpMidi () {
try {
sequencer = MidiSystem.getSequencer();
sequencer.open();
sequence = new Sequence(Sequence.PPQ,4);
track = sequence.createTrack();
sequencer.setTempoInBPM(120);
} catch (Exception e) {
e.printStackTrace();
}
}
//track就像歌曲信息
public void buildTrackAndStart () {
int[] trackList = null;
sequence.deleteTrack(track);
track = sequence.createTrack();
for (int i = 0; i < 16; i++) {
trackList = new int[16];
int key = instruments[i];
for (int j = 0; j < 16; j++) {
JCheckBox jc = (JCheckBox) checkboxList.get(j + (16 * i));
if (jc.isSelected()) {
trackList[j] = key;
} else {
trackList[j] = 0;
}
}
makeTracks(trackList);
track.add(makeEvent(176, 1, 127, 0, 16));
}
//192为乐器频道
track.add(makeEvent(192, 9, 1, 0, 15));
try {
sequencer.setSequence(sequence);
sequencer.setLoopCount(sequencer.LOOP_CONTINUOUSLY);
sequencer.start();
sequencer.setTempoInBPM(120);
} catch (Exception e) {
e.printStackTrace();
}
}
//144和128频道分别表示开始和结束
public void makeTracks (int[] list) {
for (int i = 0; i < 16; i++) {
int key = list[i];
if(key != 0) {
track.add(makeEvent(144,9,key,100,i));
track.add(makeEvent(128,9,key,100,i+1));
}
}
}
//MIDIEvent就像乐谱，前四个参数是类型，频道，音符，音量
public MidiEvent makeEvent (int comd,int chan,int one,int two,int tick) {
MidiEvent event = null;
try {
ShortMessage a = new ShortMessage();
a.setMessage(comd,chan,one,two);
event = new MidiEvent(a,tick);
} catch (Exception e) {
e.printStackTrace();
}
return event;
}
//几个按钮的监听器
public class MyStartListener implements ActionListener {
public void actionPerformed (ActionEvent a) {
buildTrackAndStart();
}
}
public class MyStopListener implements ActionListener {
public void actionPerformed (ActionEvent a) {
sequencer.stop();
}
}
public class MyUpTempoListener implements ActionListener {
public void actionPerformed (ActionEvent a) {
float tempoFactor = sequencer.getTempoFactor();
sequencer.setTempoFactor((float)(tempoFactor * 1.03));
}
}
public class MyDownTempoListener implements ActionListener {
public void actionPerformed (ActionEvent a) {
float tempoFactor = sequencer.getTempoFactor();
sequencer.setTempoFactor((float)(tempoFactor * 0.97));
}
}
//这里往下是存取的监听，将256个checkbox序列化存取
public class MySendListener implements ActionListener {
public void actionPerformed (ActionEvent a) {
boolean[] checkboxState = new boolean[256];
for (int i = 0; i < 256; i++) {
JCheckBox check = (JCheckBox) checkboxList.get(i);
if (check.isSelected()) {
checkboxState[i] = true;
}
}
try {
FileOutputStream fileStream = new FileOutputStream(new File("Checkbox.ser"));
ObjectOutputStream os = new ObjectOutputStream(fileStream);
os.writeObject(checkboxState);
os.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
public class MyReadInListener implements ActionListener {
public void actionPerformed (ActionEvent a) {
boolean[] checkboxState = null;
try {
FileInputStream fileIn = new FileInputStream(new File("Checkbox.ser"));
ObjectInputStream is = new ObjectInputStream(fileIn);
checkboxState = (boolean[]) is.readObject();
is.close();
} catch (Exception e) {
e.printStackTrace();
}
for (int i = 0; i < 256; i++) {
JCheckBox check = (JCheckBox) checkboxList.get(i);
if (checkboxState[i]) {
check.setSelected(true);
} else {
check.setSelected(false);
}
}
sequencer.stop();
buildTrackAndStart();
}
}
}
可以用这个尝试发布成jar包后转为exe给朋友玩玩。