Question

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How to wait for a set of threads to complete?

I want to run three threads, each thread calls different classes. These classes do some processing and return a Boolean value, I want to wait until all three threads return their output. I want to know how it’s possible to implement this using Java.

Thanks

Answer 1

You can use Thread.join() to do that:

Thread[] threads = new Thread[numOfThreads];
for (int i = 0; i < threads.length; i++) {
    threads[i] = new Thread(new Runnable() {
        public void run() {
            System.out.println("xxx");
        }
    });
    threads[i].start();
}

for (int i = 0; i < threads.length; i++) {
    try {
        threads[i].join();
    } catch (InterruptedException e) {
    }
}

For your solution

Thread[] threads = new Thread[3];
threads[i] = new Thread(new Runnable() {
        ...
}).start();
threads[i] = new Thread(new Runnable() {
        ...
}).start();
threads[i] = new Thread(new Runnable() {
        ...
}).start();

for (int i = 0; i < threads.length; i++) {
    try {
        threads[i].join();
    } catch (InterruptedException e) {
    }
}