CODEWITHSUNDEEP
javamultithreading
srock
srock

Reputation: 413

why does the main thread wait

In the below code, why does the main thread wait until the child thread is finished.

Driver.java

public class Driver {
public static void main(String[] args) throws InterruptedException {
    Thread t = new Thread(new ThreadRunner());
    t.start();
}
}

ThreadRunner.java

public class ThreadRunner implements Runnable {
@Override
public void run() {
    for (int i = 0; i < 10; i++) {
        System.out.println("Child thread" + i);
    }
}
}

Here in the Driver class after calling 't.start()' shouldn't the program quit? I'm not using join but still the main thread waits until the newly spun 'ThreadRunner' run is running. Is it because in java the main thread (which is started by main method) always waits until all the threads are shut?

Upvotes: 1

Views: 162

Answers (3)

jevely
jevely

Reputation: 172

you can add 'System.out.println("main thread");' below 't.start()'

then you can see main thread is the first.

Upvotes: -1

John Vint
John Vint

Reputation: 40256

The main thread doesn't actually wait. The main thread completes. The program does not quit because you create a Thread that is non-daemon. The JVM will shut down when only daemon threads remain.

Upvotes: 2

Aasmund Eldhuset
Aasmund Eldhuset

Reputation: 37950

The main thread exits immediately after having started the other thread, but the Java program as a whole continues running as long as there are non-daemon threads alive (and unless you specifically request it, new threads will be non-daemon).

Making the thread a daemon thread is easy: simply call t.setDaemon(true); before starting it.

Upvotes: 5

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