JAVA多线程编程——1.9线程让步-1.11守护线程

1.9线程让步（yield方法）

yield()方法的作用是当前线程放弃CPU资源，然后重新选择运行哪个线程。

public class Thread_191 {    static  class  MyThread extends Thread{        public void run(){        long  beginTime = System.currentTimeMillis();        int count =0;        for(int i=0;i<5000000;i++){            //Thread.yield();            count+=i+1;        }        long endTime = System.currentTimeMillis();        System.out.println("用了： "+(endTime-beginTime)+"毫秒！ ");    }}public static void main(String[] args) {        MyThread myThread= new MyThread();        myThread.start();}

}

1.10线程优先级

1.线程优先级是可以继承的。

/** * Created by Senliang-Ying on 2017/11/28. */public class Thread_1101 {    static class MyThread1 extends Thread{    public void run(){        System.out.println("MyThread1 run priority =" + this.getPriority());        MyThread2 myThread2 = new MyThread2();        myThread2.start();    }}static class MyThread2 extends Thread{    public void run(){        System.out.println("MyThread2 run priority =" + this.getPriority());    }}public static void main(String[] args) {    System.out.println("main thread begin priority = "+ Thread.currentThread().getPriority());    Thread.currentThread().setPriority(6);    System.out.println("main end priority= "+Thread.currentThread().getPriority());    MyThread1 myThread1 = new MyThread1();    myThread1.start();}}

2.设置优先级（setPriority）

import java.util.Random;public class Thread_1102 {static class MyThread1 extends Thread {    public void run() {//            System.out.println("MyThread1 run priority =" +    this.getPriority());        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));    }}static class MyThread2 extends Thread {    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 static void main(String[] args) {    for (int i = 0; i < 5; i++) {MyThread1 thread1= new MyThread1();thread1.setPriority(10);thread1.start();MyThread2 thread2 = new MyThread2();thread2.setPriority(4);thread2.start();    }}}

多次运行后，可以发现优先级高的线程大多数情况下优先执行。

1.11守护线程

JAVA中有两种线程，一种是用户线程，一种是守护线程（Daemon），守护线程就是一种陪伴用户线程的线程，只有当一个用户线程都没有的情况下，守护线程才会停止，垃圾回收机制就是一个典型的守护线程。可以用setDeamon()方法对线程对象进行设置。代码如下

/** * Created by Senliang-Ying on 2017/12/4. * 守护线程 */public class Thread_1103 {static class MyThread extends Thread {    private int i = 0;    @Override    public void run() {        try {            while (true) {                i++;                System.out.println("i= " + i);                Thread.sleep(1000);            }        } catch (InterruptedException e) {            e.printStackTrace();        }    }}public static void main(String[] args) {    try{        MyThread thread = new MyThread();        thread.setDaemon(true);//设置为守护线程        thread.start();        Thread.sleep(5000);        System.out.println("我离开thread对象也不再打印了，也就是停止了");    }catch(InterruptedException e){        e.printStackTrace();    }}

}

输出如下：
i= 1
i= 2
i= 3
i= 4
i= 5
我离开thread对象也不再打印了，也就是停止了