Java 虚拟机在调度各线程运行时,并非每个线程的运行机会相同,调度机制根据各线程的优先级调度各线程。因而,优先级高的线程获得的运行时间就多,优先级低的线程获得的运行时间就少。本例演示了不同优先级的线程在完成同一个任务时的不同进度,来验证上面的结论。高优先级的线程获得运行的机会多。同时开始的两个不同优先级的线程,在做同一个任务时的不同进度如图所示: 实现思路:Java 的线程类java.lang.Thread 提供了三个级别的线程优先级,即Thread.MIN_PRIORITY、Thread.NORM_PRIORITY 和Thread.MAX_PRIORITY 。并且提供了设置线程优先级的方法setPriority(int priority)。本例中,当程序运行时,两个优先级分别为Thread.MIN_PRIORITY 和Thread.MAX_PRIORITY的线程,分别使各自的进度条值增加。为此,编写一个继承Thread 类的ProgressThread 来完成计算并刷新显示进度条值的功能。程序代码: public class MainFrame extends JFrame { private JPanel contentPane; private BorderLayout borderLayout1 = new BorderLayout(); //实例化组件 private JLabel jLabel1 = new JLabel(); private JProgressBar jProgressBar1 = new JProgressBar(); private JProgressBar jProgressBar2 = new JProgressBar(); private JButton jButton1 = new JButton(); //申明两个线程类的对象 private ProgressThread pThread1=null; private ProgressThread pThread2=null; …… } 4.编写MainFrame 类的初始化方法jbInit()。 private void jbInit() throws Exception { //setIconImage(Toolkit.getDefaultToolkit().createImage(MainFrame.class.getResource("[Your Icon]"))); contentPane = (JPanel) this.getContentPane(); //设置组件属性 jLabel1.setFont(new java.awt.Font("Dialog", 0, 14)); jLabel1.setToolTipText(""); jLabel1.setHorizontalAlignment(SwingConstants.CENTER); jLabel1.setText("线程赛马演示(右边的高优先级、左边的低优先级)"); contentPane.setLayout(borderLayout1); this.setSize(new Dimension(333, 222)); this.setTitle("JThreadRace"); jProgressBar1.setOrientation(JProgressBar.VERTICAL); jProgressBar1.setFont(new java.awt.Font("Dialog", 0, 14)); jProgressBar1.setMaximumSize(new Dimension(84, 32767)); jProgressBar1.setPreferredSize(new Dimension(120, 148)); jProgressBar1.setStringPainted(true); jProgressBar2.setOrientation(JProgressBar.VERTICAL); jProgressBar2.setFont(new java.awt.Font("Dialog", 0, 14)); jProgressBar2.setPreferredSize(new Dimension(120, 148)); jProgressBar2.setStringPainted(true); jButton1.setFont(new java.awt.Font("Dialog", 0, 14)); jButton1.setToolTipText(""); jButton1.setText("Start"); jButton1.addActionListener(new java.awt.event.ActionListener() {//添加按钮的事件监听器 public void actionPerformed(ActionEvent e) { jButton1_actionPerformed(e); } }); contentPane.add(jLabel1, BorderLayout.NORTH); contentPane.add(jProgressBar1, BorderLayout.WEST); contentPane.add(jProgressBar2, BorderLayout.EAST); contentPane.add(jButton1, BorderLayout.SOUTH); } 5.处理按钮的事件方法,创建两个不同优先级的比赛线程并开始运行。 void jButton1_actionPerformed(ActionEvent e) { if(((JButton)e.getSource()).getText().equals("Start")){ //当单击时按钮文字是“Start“,则单击后设为”Stop“,并且创建两个ProgressThread 的实例,但两个 //线程的优先级不同,然后运行线程 this.jButton1.setText("Stop"); pThread1=new ProgressThread(this.jProgressBar1,Thread.MAX_PRIORITY); pThread1.start(); ProgressThread pThread2=new ProgressThread(this.jProgressBar2,Thread.MIN_PRIORITY); pThread2.start(); //否则,停止两个线程 }else{ this.jButton1.setText("Start"); this.pThread1.stopped=true; } } 6.新建一个Class,取名为ProgressThread,继承java.lang.Thread 类。编写ProgressThread类,用来完成任务并将任务进度显示在JProgressBar 对象上,代码如下: public class ProgressThread extends Thread { JProgressBar pbar; static boolean stopped; public ProgressThread(JProgressBar pbar,int priority) { try{ this.pbar=pbar; //获得MainFrame 中JProgressBar 对象的引用 this.stopped=false; this.setPriority(priority); //设置线程优先级 }catch(Exception err){ err.printStackTrace(); } } public void run() { int min=0; int max=1000; //初始化进度条的属性设置 this.pbar.setMinimum(min); this.pbar.setMaximum(max/10); this.pbar.setValue(min); //开始循环 for(int i=min; i<=max; i++){ if(stopped) break; else{ //在进度条上显示进度信息 this.pbar.setValue((int)(i/10)); this.pbar.setString(String.valueOf(i)); try{ Thread.sleep(10);//等待10ms,使得任务不至于还没看清就结束 }catch(Exception err){ err.printStackTrace(); } } } } } 完整源码包:Java线程优先级“赛马” |
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