Thread printing extra lines in Java-CodePudding

I am running a program with threads, sleeping them for a random amount of time and then waking them up. When it reaches the end, it prints that the last thread is now awake 6 different times. It does not do this on any of the other ones. Does anyone know why it is doing this?

sampleThread.java


import java.util.Random;

public class sampleThread extends Thread{
    sampleThread thread;
    Random rand = new Random();

    public void run() {

        thread = new sampleThread();
        int randSleep = rand.nextInt(1000);

        System.out.println(thread.getName()   " is sleeping for "   randSleep   " milliseconds");

        try {
            Thread.sleep(randSleep);
            System.out.println(thread.getName()   " is NOW AWAKE");

        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

    }

}

driver.java


public class driver {

    public static void main(String[] args) throws ExecutionException, InterruptedException {


        List<Future<?>> futArray = new ArrayList<>();
        ExecutorService es = Executors.newFixedThreadPool(6);

        sampleThread temp = new sampleThread();
        for (int i=0; i<120; i  ) {
            Future<?> future = es.submit(temp);
            futArray.add(future);
        }

output:

Thread-117 is sleeping for 547 milliseconds
Thread-117 is NOW AWAKE
Thread-118 is sleeping for 442 milliseconds
Thread-118 is NOW AWAKE
Thread-119 is sleeping for 182 milliseconds
Thread-119 is NOW AWAKE
Thread-120 is sleeping for 487 milliseconds
Thread-120 is NOW AWAKE
Thread-120 is NOW AWAKE
Thread-120 is NOW AWAKE
Thread-120 is NOW AWAKE
Thread-120 is NOW AWAKE
Thread-120 is NOW AWAKE

I expected it to just run through and print when each was sleeping and done. Instead, it prints the last thread several times.

EDIT:

If anyone was wondering, I changed

public class sampleThread extends Thread{
sampleThread thread;
Random rand = new Random();

public void run() {

    thread = new sampleThread();

Instead of putting sampleThread thread; outside of run() and thread = new sampleThread(); inside of run(), I simply combined them into one statement of sampleThread thread = new sampleThread(); and put the whole line into run. This seems to have fixed the issue.

CodePudding user response：

You are duplicating effort. The fact that you had 120 threads should have been a hint. You created a thread pool but then ran code that created an extra thread on each submission.

Simple solution:

Don't extend Thread, implement Runnable, that's all you need.
To get the thread name use Thread.currentThread().getName()

Like so:

public static class sampleThread implements Runnable {
     Random rand = new Random();

    public void run() {

         int randSleep = rand.nextInt(1000);

        System.out.println(Thread.currentThread().getName()   " is sleeping for "   randSleep   " milliseconds");

        try {
            Thread.sleep(randSleep);
            System.out.println(Thread.currentThread().getName()   " is NOW AWAKE");

        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

    }

}

Now the output is

pool-1-thread-1 is sleeping for 526 milliseconds
pool-1-thread-6 is sleeping for 497 milliseconds
pool-1-thread-4 is sleeping for 565 milliseconds
pool-1-thread-5 is sleeping for 978 milliseconds
pool-1-thread-2 is sleeping for 917 milliseconds
pool-1-thread-3 is sleeping for 641 milliseconds
pool-1-thread-6 is NOW AWAKE
pool-1-thread-6 is sleeping for 847 milliseconds
pool-1-thread-1 is NOW AWAKE
pool-1-thread-1 is sleeping for 125 milliseconds
pool-1-thread-4 is NOW AWAKE
pool-1-thread-4 is sleeping for 884 milliseconds
pool-1-thread-3 is NOW AWAKE
pool-1-thread-3 is sleeping for 245 milliseconds
pool-1-thread-1 is NOW AWAKE
.
.
.
pool-1-thread-3 is NOW AWAKE
pool-1-thread-3 is sleeping for 863 milliseconds
pool-1-thread-5 is NOW AWAKE
pool-1-thread-6 is NOW AWAKE
pool-1-thread-4 is NOW AWAKE
pool-1-thread-1 is NOW AWAKE
pool-1-thread-2 is NOW AWAKE
pool-1-thread-3 is NOW AWAKE

Showing that you used only the 6 threads you ordered.