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Question

Hello I'm a new java programmer. I have a problem:
I have to create a thread of processes, say 5 threads.
but only 2 at time should execute. After one of those 2 finishes, then the next thread should be started, and so on.. until all the threads will be finished.
Is this possible? how am I gonna do this?

Answer 1

I you only need 2 threads running at a time, why don't you "reuse" a thread when it is done with a task.
And by reuse, I don't mean calling Thread.start again, because that won't work, but something like this:
public class TaskManager {
  class Task extends Thread {
    boolean running = true;
    public void kill() { running = false; }
    public void run() {
      while (running) {
        Runnable task = TaskManager.this.getTask();
        if (task == null)
          break;  // no more tasks to process
        task.run();
  private int index = 0;
  private Runnable[] tasks;
  public TaskManager() {
    // create tasks to be run:
    tasks = new Runnable[5];
    tasks[0] = new Runnable() {
      public void run() {
        int result;
        for (int i = 0; i < 10; i++)
          result += i;
        System.out.println(result);
    // and the next 4 tasks has to be created as well
    // start two threads
    Thread thread1 = new Task();
    Thread thread2 = new Task();
    thread1.start();
    thread2.start();
  public synchonized Runnable getTask() {
    if (index < tasks.size())
      return null;
    return tasks[index++]; // return the next task to the thread that called this method
}I think this will work, perhaps there are some bugs in it, but it gives you an idea.