JAVA多線程編程——1.9線程讓步-1.11守護線程

1.9線程讓步（yield方法）

yield()方法的作用是當前線程放棄CPU資源，然後重新選擇運行哪個線程。

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線程優先級

1.線程優先級是可以繼承的。

/**
 * 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.設置優先級（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();
    }

}
}

多次運行後，可以發現優先級高的線程大多數情況下優先執行。

1.11守護線程

JAVA中有兩種線程，一種是用戶線程，一種是守護線程（Daemon），守護線程就是一種陪伴用戶線程的線程，只有當一個用戶線程都沒有的情況下，守護線程纔會停止，垃圾回收機制就是一個典型的守護線程。可以用setDeamon()方法對線程對象進行設置。代碼如下

/**
 * Created by Senliang-Ying on 2017/12/4.
 * 守護線程
 */
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);//設置爲守護線程
        thread.start();
        Thread.sleep(5000);
        System.out.println("我離開thread對象也不再打印了，也就是停止了");

    }catch(InterruptedException e){
        e.printStackTrace();
    }
}

}

輸出如下：
i= 1
i= 2
i= 3
i= 4
i= 5
我離開thread對象也不再打印了，也就是停止了