java user thread and thread guard

The main contents

• When the user exits the thread of all, the program will terminate, even then there is still a daemon thread running.
• java.util.concurrent following the thread pool thread created by default all users, including the timing of the scheduled task. In the actual programming, if there are some statistics class, the class monitor thread timer operation, the threads are preferably provided as a daemon thread.
• How to create a thread pool thread guard timing of execution

Once all users thread exits, even without a daemon thread runs out, it will terminate

public class Test {
    public static void main(String[] args) {
        //创建一个用户线程
        Thread userThread=new Thread(){
            public void run(){
                for(int i=1;i<=5;i++){
                    try {
                        Thread.sleep(200);
                        System.out.println("用户线程第"+i+"次运行.....");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("用户线程退出.....");
            }
        };
        //创建一个用户模拟守护线程的线程
        Thread daemonThread=new Thread(){
            public void run(){
                for(int i=1;i<=99999;i++){
                    try {
                        Thread.sleep(50);
                        System.out.println("守护线程第"+i+"次运行.....");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("守护线程退出.....");
            }
        };
        //让daemonThread成为守护线程
        daemonThread.setDaemon(true);//这里必须在启动前设置，如果不设置，默认人是用户线程
        userThread.start();
        daemonThread.start();
        System.out.println("Main exit");
    }
}

Program output

Main exit
守护线程第1次运行.....
守护线程第2次运行.....
守护线程第3次运行.....
用户线程第1次运行.....
守护线程第4次运行.....
守护线程第5次运行.....
守护线程第6次运行.....
守护线程第7次运行.....
用户线程第2次运行.....
守护线程第8次运行.....
守护线程第9次运行.....
守护线程第10次运行.....
守护线程第11次运行.....
用户线程第3次运行.....
守护线程第12次运行.....
守护线程第13次运行.....
守护线程第14次运行.....
守护线程第15次运行.....
用户线程第4次运行.....
守护线程第16次运行.....
守护线程第17次运行.....
守护线程第18次运行.....
守护线程第19次运行.....
用户线程第5次运行.....
用户线程退出.....

The timing of the use of Java thread pool

Conclusion: the Java thread pool is created by default user thread, after the main thread exits, the program will continue to run

import java.time.LocalDateTime;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        ScheduledExecutorService executorService = Executors.newScheduledThreadPool(10);

        executorService.scheduleWithFixedDelay(() -> {
            LocalDateTime localDateTime = LocalDateTime.now();
            System.out.println(localDateTime);
        },1, 1, TimeUnit.SECONDS);

        Thread.sleep(3000);
        System.out.println("Main Exit");
    }
}

Program output

2019-12-21T13:47:58.590
2019-12-21T13:47:59.592
Main Exit
2019-12-21T13:48:00.596
2019-12-21T13:48:01.601
2019-12-21T13:48:02.605
2019-12-21T13:48:03.610
2019-12-21T13:48:04.612
2019-12-21T13:48:05.615

Use daemon thread pool thread

import java.time.LocalDateTime;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        ScheduledExecutorService executorService = Executors.newScheduledThreadPool(10, new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread t = new Thread(r);
                t.setDaemon(true);
                return t;
            }
        });

        executorService.scheduleWithFixedDelay(() -> {
            LocalDateTime localDateTime = LocalDateTime.now();
            System.out.println(localDateTime);
        },1, 1, TimeUnit.SECONDS);

        Thread.sleep(10000);
        System.out.println("Main Exit");
    }
}

2019-12-21T13:45:53.966
2019-12-21T13:45:54.972
2019-12-21T13:45:55.975
2019-12-21T13:45:56.980
2019-12-21T13:45:57.985
2019-12-21T13:45:58.988
2019-12-21T13:45:59.993
2019-12-21T13:46:00.998
2019-12-21T13:46:02.003
Main Exit

Process finished with exit code 0