守护进程线程未按预期工作

Question

package main.components;

import java.io.Serializable;
import java.util.Scanner;
import java.util.concurrent.TimeUnit;

public class MainSnoozerx implements Runnable, Serializable {

    private static final long serialVersionUID = 1L;
    private static int min = 0;
    static Thread mnz = new Thread(new MainSnoozerx());
    private long convertedToMiliSec = 0l;
    private Scanner scn = new Scanner(System.in);

    @Override
    public void run() {
        // TODO Auto-generated method stub
        try{
            do{
            System.out.println("Enter minutes to snooze..");
            min = scn.nextInt();
            }while(min<0);

        convertedToMiliSec = TimeUnit.MINUTES.toMillis(min);
        try {
            Thread.sleep(convertedToMiliSec);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("Alarm Now!!!");
        }catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        mnz.setDaemon(true);
        mnz.start();
    }

}

Can anyone tell me what am I doing wrong/missing? My program just terminates when I run it without printing the syso even once. I expect the code to run endlessly being a daemon thread and the user just sets the mins once and the snooze goes on forever...

Answer 1

You've got it the wrong way around, the JVM will keep running while there is at least one non-daemon thread alive. The main thread is not a daemon thread and if no other non-daemon threads are created before the main thread exits the JVM will exit.

If you want the JVM to keep running, remove the setDaemon call

Answer 2

You fired the thread without ever tell Java that you want the work done back. You need to add a mnz.join() after your start ;)

With that fix, your thread run one time for sure. If you decide to put all your run() code inside of a while loop and change your loop, you got the behaviour that you want.

Like this

@Override
public void run() {
    while (true) {
        // TODO Auto-generated method stub
        try {
            while (min == 0) {
                System.out.println("Enter minutes to snooze..");
                min = scn.nextInt();
            }

            convertedToMiliSec = TimeUnit.MINUTES.toMillis(min);
            try {
                Thread.sleep(convertedToMiliSec);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            System.out.println("Alarm Now!!!");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}
public static void main(String[] args) throws InterruptedException {
    // TODO Auto-generated method stub
    mnz.setDaemon(true);
    mnz.start();
    mnz.join();
}