JAVA：Thread与join、daemon

时间 2019-11-19

标签 java thread join daemon 栏目 Java 繁體版

原文原文链接

##不带join，不带daemon：java

package hellojava;

import java.util.logging.Level;
import java.util.logging.Logger;

public class HelloJava {

    static class TestTask implements Runnable {
        private String taskName;
        
        public TestTask(String taskName) {
            this.taskName = taskName;
        }

        @Override
        public void run() {
            for (int i=0; i<4; i++) {
                System.out.println(taskName + ": " + i);
                try {
                    Thread.currentThread().sleep(1*1000);
                } catch (InterruptedException ex) {
                    Logger.getLogger(HelloJava.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        
    }
    public static void main(String[] args) {
        System.out.println("main thread start!");
        Thread t1 = new Thread(new HelloJava.TestTask("a"));
        Thread t2 = new Thread(new HelloJava.TestTask("b"));
        t1.start();
        t2.start();
        System.out.println("main thread end!");
    }
    
}

运行输出：jvm

main thread start!
a: 0
main thread end!
b: 0
a: 1
b: 1
a: 2
b: 2
a: 3
b: 3

能够看到，t1和t2交替运行，再main线程结束后，t1和、t2仍在运行。ide

##jointhis

package hellojava;

import java.util.logging.Level;
import java.util.logging.Logger;

public class HelloJava {

    static class TestTask implements Runnable {
        private String taskName;
        
        public TestTask(String taskName) {
            this.taskName = taskName;
        }

        @Override
        public void run() {
            for (int i=0; i<4; i++) {
                System.out.println(taskName + ": " + i);
                try {
                    Thread.currentThread().sleep(1*1000);
                } catch (InterruptedException ex) {
                    Logger.getLogger(HelloJava.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        
    }
    public static void main(String[] args){
        System.out.println("main thread start!");
        Thread t1 = new Thread(new HelloJava.TestTask("a"));
        Thread t2 = new Thread(new HelloJava.TestTask("b"));
        // t1.setDaemon(true);  // 这句注不注释都不影响结果
        t1.start();
        try {
            t1.join();
        } catch (InterruptedException ex) {
            Logger.getLogger(HelloJava.class.getName()).log(Level.SEVERE, null, ex);
        }
        t2.start();
        System.out.println("main thread end!");
    }
    
}

输出：线程

main thread start!
a: 0
a: 1
a: 2
a: 3
main thread end!
b: 0
b: 1
b: 2
b: 3

t1运行结束后，t2和main线程才继续运行。注意，只要线程调用join()了，设不设daemon都不影响。code

##daemonget

package hellojava;

import java.util.logging.Level;
import java.util.logging.Logger;

public class HelloJava {

    static class TestTask implements Runnable {
        private String taskName;
        
        public TestTask(String taskName) {
            this.taskName = taskName;
        }

        @Override
        public void run() {
            for (int i=0; i<4; i++) {
                System.out.println(taskName + ": " + i);
                try {
                    Thread.sleep(1*1000);
                } catch (InterruptedException ex) {
                    Logger.getLogger(HelloJava.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        
    }
    public static void main(String[] args){
        System.out.println("main thread start!");
        Thread t1 = new Thread(new HelloJava.TestTask("a"));
        Thread t2 = new Thread(new HelloJava.TestTask("b"));
        t1.setDaemon(true);
        t2.setDaemon(true);
        t1.start();
        t2.start();
        try {
            Thread.sleep(2*1000);
        } catch (InterruptedException ex) {
            Logger.getLogger(HelloJava.class.getName()).log(Level.SEVERE, null, ex);
        }
        System.out.println("main thread end!");
    }
    
}

输出：it

main thread start!
a: 0
b: 0
a: 1
b: 1
main thread end!
b: 2
a: 2

设置daemon后，main线程结束后，daemon线程自动结束并释放。io

下面是关于daemon的两个讨论，值得一看：class