Java 多线程（Java.Thread）-----线程状态观测（Thread.State）、线程优先级和守护线程（daemon）

线程状态观测（Thread.State）

• new、runnable、blocked、waiting、timed waiting、terminated

package www.bh.c.threadtest;

public class StateTest {
    
    
    public static void main(String[] args) {
    
    
        Thread thread=new Thread(()->{
    
    
                try {
    
    
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
    
    
                    e.printStackTrace();
                }
                System.out.println("=======");
        });
        //状态一
        Thread.State state = thread.getState();
        System.out.println(state);//NEW
        //观察启动后
        thread.start();
        state=thread.getState();
        System.out.println(state);//RUNNABLE
        while (state!=thread.getState().TERMINATED){
    
    //线程不停止，会一直输出状态
            try {
    
    
                Thread.sleep(100);
            } catch (InterruptedException e) {
    
    
                e.printStackTrace();
            }
            state=thread.getState();//更新线程状态
            System.out.println(state);//输出状态TERMINATED
        }
        //thread.start();//停止后再开启会报错
    }
}

线程优先级

• Java提供了一个线程调度器来监控程序中启动后进入就绪状态后的所有线程，线程调度器按照优先级决定应该调度那个线程来执行
• 线程的优先级用数字表示，范围从1~10
  • Thread.MIN_PRIORITY=1;
  • Thread.MAX_PRIORITY=10;
  • Thread.NORM_PRIORITY=5;(默认为5)
• 使用以下方法可以改变或获取优先级
  • getPriority().setPriority(int xxx)

package www.bh.c.threadtest;

public class PriorityTest implements Runnable{
    
    
    @Override
    public void run() {
    
    
        System.out.println(Thread.currentThread().getName()+"--->"+Thread.currentThread().getPriority());
    }

    public static void main(String[] args) {
    
    
        //主线程默认优先级：5
        System.out.println(Thread.currentThread().getName()+"--->"+Thread.currentThread().getPriority());

        PriorityTest priorityTest = new PriorityTest();
        Thread t1 = new Thread(priorityTest);
        Thread t2 = new Thread(priorityTest);
        Thread t3 = new Thread(priorityTest);
        Thread t4 = new Thread(priorityTest);
        Thread t5 = new Thread(priorityTest);
        Thread t6 = new Thread(priorityTest);
//先设置优先级，再启动
        t1.start();

        t2.setPriority(1);
        t2.start();

        t3.setPriority(3);
        t3.start();

        t4.setPriority(Thread.MAX_PRIORITY);//10
        t4.start();

        t5.setPriority(7);
        t5.start();

        t6.setPriority(8);
        t6.start();
    }
}
/*
main--->5
Thread-4--->7
Thread-3--->10
Thread-5--->8
Thread-0--->5
Thread-2--->3
Thread-1--->1
 */
//注：优先级低只是意味着获得调度的低概率，并不是优先级低就不会被调用了，这都是看CPU的调度

守护线程（daemon）

• 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
• 虚拟机不用等待守护线程执行完毕
• 如：后台记录操作日志、监控内存、垃圾回收等

package www.bh.c.threadtest;
//测试守护线程
//老师守护学生
public class DaemonTest {
    
    
    public static void main(String[] args) {
    
    
        Teacher teacher = new Teacher();
        Student student = new Student();

        Thread thread = new Thread(teacher);
        thread.setDaemon(true);//默认false表示用户线程，正常的线程都是用户线程

        thread.start();//启动老师线程
        new Thread(student).start();//启动学生线程
    }
}
//老师类
class Teacher implements Runnable{
    
    
    @Override
    public void run() {
    
    
        while (true){
    
    
            System.out.println("老师守护着学生");
        }
    }
}
//学生类
class Student implements Runnable{
    
    
    @Override
    public void run() {
    
    
        for (int i = 0; i < 100; i++) {
    
    
            System.out.println("快乐学习100年");
        }
    }
}