Java - How to tell all subthreads are done

Question

I want to run a few tasks simultaneously so I have a code that looks like this:

for(final Task task : tasks){
    (new Thread(){public void run(){
        task.run(args);
}}).start();

How can I know when all of the tasks are done (the amount of tasks can vary) so that I can run something only after everything is done?

System.out.println("All tasks are finished");

Answer 1

A shorter version is to use a parallelStream

tasks.parallelStream().forEach(t -> t.run(args));

This will run all the tasks, using all the CPUs you have (if you have enough tasks) and wait for the all to finish.