day 25- 线程的礼让，优先级，守护线程

线程的礼让

利用Thread.yield()使线程进行礼让

礼让的概念：

礼让线程，让当前正在执行的线程暂停，但并不是阻塞
将线程从运行状态转化为就绪状态
线程礼让是由cpu调度，并不一定成功

 1 public class TestYield {
 2  
 3      public static void main(String[] args) {
 4          MyYield myYield = new MyYield();
 5          new Thread(myYield,"a").start();
 6          new Thread(myYield,"b").start();
 7      }
 8  }
 9  
10  class MyYield implements Runnable{
11  
12      @Override
13      public void run() {
14          System.out.println(Thread.currentThread().getName()+ "线程开始执行");
15          Thread.yield();//礼让
16          System.out.println(Thread.currentThread().getName()+ "线程停止执行");
17      }
18  }

线程的优先级

设置线程的优先级

更改线程的优先级

其中main线程的优先级默认为5

 1 public class TestPriority {
 2      public static void main(String[] args) {
 3          //主线程优先级
 4          System.out.println(Thread.currentThread().getName()+"->"+Thread.currentThread().getPriority());
 5          MyPriority myPriority = new MyPriority();
 6          Thread t1 = new Thread(myPriority);
 7          Thread t2 = new Thread(myPriority);
 8          Thread t3 = new Thread(myPriority);
 9          Thread t4 = new Thread(myPriority);
10          Thread t5 = new Thread(myPriority);
11          Thread t6 = new Thread(myPriority);
12          Thread t7 = new Thread(myPriority);
13  
14          //设置优先级，在启动
15          t1.start();
16  
17          t2.setPriority(1);
18          t2.start();
19  
20          t3.setPriority(4);
21          t3.start();
22  
23          t4.setPriority(Thread.MAX_PRIORITY);
24          t4.start();
25  
26  //        t5.setPriority(-1);
27  //        t5.start();
28  //
29  //        t6.setPriority(11);
30  //        t6.start();
31      }
32  }
33  class MyPriority implements Runnable{
34  
35      @Override
36      public void run() {
37          System.out.println(Thread.currentThread().getName()+"->"+Thread.currentThread().getPriority());
38  
39      }
40  }

守护线程

线程分为用户线程和守护线程

虚拟机必须确保用户线程执行完毕

但虚拟机不用等待守护线程执行完毕

守护线程一般包括：后台记录日志，监控内存，垃圾回收等待等等

 1  //测试守护线程
 2  public class TestDaemon {
 3      public static void main(String[] args) {
 4          God god = new God();
 5          You you = new You();
 6  
 7  
 8          Thread thread = new Thread(god);
 9          thread.setDaemon(true);//默认是false，正常线程都是用户线程
10          thread.start();//god线程启动
11          new Thread(you).start();//you启动
12      }
13  }
14  //GOD
15  class God implements Runnable{
16      @Override
17      public void run() {
18          while (true){
19              System.out.println("god bless you");
20          }
21      }
22  }
23  
24  //YOU
25  class You implements Runnable{
26      @Override
27      public void run() {
28          for (int i = 0; i < 36500; i++) {
29              System.out.println("alive");
30          }
31          System.out.println("=====goodbye world====");
32      }
33  }