第18章 多线程----线程的优先级

每个线程都具有各自的优先级，线程的优先级可以表明在程序中该线程的重要性，如果有很多线程处于就绪状态，系统会根据优先级来决定使哪个线程进入运行状态。每个新产生的线程都继承了父线程的优先级。

例如：在项目中创建PriorityTest类，该类实现了Runnable接口。创建4个进度条，分别由4个线程来控制，并且为这4个线程设置不同的优先级。

import java.awt.*;

import javax.swing.*;

public class PriorityTest extends JFrame {
    private static final long serialVersionUID = 1L;
    private Thread threadA;
    private Thread threadB;
    private Thread threadC;
    private Thread threadD;
    
    public PriorityTest() {
        getContentPane().setLayout(new GridLayout(4, 1));
        // 分别实例化4个线程
        final JProgressBar progressBar = new JProgressBar();
        final JProgressBar progressBar2 = new JProgressBar();
        final JProgressBar progressBar3 = new JProgressBar();
        final JProgressBar progressBar4 = new JProgressBar();
        getContentPane().add(progressBar);
        getContentPane().add(progressBar2);
        getContentPane().add(progressBar3);
        getContentPane().add(progressBar4);
        progressBar.setStringPainted(true);
        progressBar2.setStringPainted(true);
        progressBar3.setStringPainted(true);
        progressBar4.setStringPainted(true);
        threadA = new Thread(new MyThread(progressBar));
        threadB = new Thread(new MyThread(progressBar2));
        threadC = new Thread(new MyThread(progressBar3));
        threadD = new Thread(new MyThread(progressBar4));
        setPriority("threadA", 5, threadA);
        setPriority("threadB", 5, threadB);
        setPriority("threadC", 4, threadC);
        setPriority("threadD", 3, threadD);
    }
    
    // 定义设置线程的名称、优先级的方法
    public static void setPriority(String threadName, int priority,
            Thread t) {
        t.setPriority(priority); // 设置线程的优先级
        t.setName(threadName); // 设置线程的名称
        t.start(); // 启动线程
    }
    
    public static void main(String[] args) {
        init(new PriorityTest(), 100, 100);
    }
    
    public static void init(JFrame frame, int width, int height) {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(width, height);
        frame.setVisible(true);
    }
    
    private final class MyThread implements Runnable { // 定义一个实现Runnable接口的类
        private final JProgressBar bar;
        int count = 0;
        
        private MyThread(JProgressBar bar) {
            this.bar = bar;
        }
        
        public void run() { // 重写run()方法
            while (true) {
                bar.setValue(count += 10); // 设置滚动条的值每次自增10
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    System.out.println("当前线程序被中断");
                }
            }
        }
    }
    
}