三、java多线程核心技术（笔记）——线程的优先级

概论：在操作系统中，线程可以划分优先级，优先级高的获得的CPU资源较多，也就是CPU优先执行优先级较高的线程。在JAVA中线程的优先级

分1~~10个10个等级。大于或者小于会报异常。

一、线程优先级具有继承性

A 线程启动 B线程，则线程B的优先级与A的是一样的。。

public class MyThread1 extends Thread {
    @Override
    public void run() {
        System.out.println("MyThread1 run priority=" + this.getPriority());
        MyThread2 thread2 = new MyThread2();
        thread2.start();
    }
}

public class MyThread2 extends Thread {
    @Override
    public void run() {
        System.out.println("MyThread2 run priority=" + this.getPriority());
    }
}

public class Run {
    public static void main(String[] args) {
        System.out.println("main thread begin priority="
                + Thread.currentThread().getPriority());  \\获取线程的优先级
        //Thread.currentThread().setPriority(6);           \\设置线程的优先级
        System.out.println("main thread end   priority="
                + Thread.currentThread().getPriority());
        MyThread1 thread1 = new MyThread1();
        thread1.start();
    }
}

结果：

二、线程优先级具规则性

public class MyThread1 extends Thread {
    @Override
    public void run() {
        long beginTime = System.currentTimeMillis();
        long addResult = 0;
        for (int j = 0; j < 10; j++) {
            for (int i = 0; i < 50000; i++) {
                Random random = new Random();
                random.nextInt();
                addResult = addResult + i;
            }
        }
        long endTime = System.currentTimeMillis();
        System.out.println("★★★★★thread 1 use time=" + (endTime - beginTime));
    }
}

public class MyThread2 extends Thread {
    @Override
    public void run() {
        long beginTime = System.currentTimeMillis();
        long addResult = 0;
        for (int j = 0; j < 10; j++) {
            for (int i = 0; i < 50000; i++) {
                Random random = new Random();
                random.nextInt();
                addResult = addResult + i;
            }
        }
        long endTime = System.currentTimeMillis();
        System.out.println("☆☆☆☆☆thread 2 use time=" + (endTime - beginTime));
    }
}

public class Run {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            MyThread1 thread1 = new MyThread1();
            thread1.setPriority(1);
            thread1.start();            MyThread2 thread2 = new MyThread2();
            thread2.setPriority(10);
            thread2.start();
        }
    }
}