Ordering threads to run in the order they were created/started

Here's a way to do it without having a master thread that waits for each result. Instead, have the worker threads share an object which orders the results.

import java.util.*;

public class OrderThreads {
    public static void main(String... args) {
        Results results = new Results();
        new Thread(new Task(0, "red", results)).start();
        new Thread(new Task(1, "orange", results)).start();
        new Thread(new Task(2, "yellow", results)).start();
        new Thread(new Task(3, "green", results)).start();
        new Thread(new Task(4, "blue", results)).start();
        new Thread(new Task(5, "indigo", results)).start();
        new Thread(new Task(6, "violet", results)).start();
    }
}

class Results {
    private List<String> results = new ArrayList<String>();
    private int i = 0;

    public synchronized void submit(int order, String result) {
        while (results.size() <= order) results.add(null);
        results.set(order, result);
        while ((i < results.size()) && (results.get(i) != null)) {
            System.out.println("result delivered: " + i + " " + results.get(i));
            ++i;
        }
    }
}


class Task implements Runnable {
    private final int order;
    private final String result;
    private final Results results;

    public Task(int order, String result, Results results) {
        this.order = order;
        this.result = result;
        this.results = results;
    }

    public void run() {
        try {
            Thread.sleep(Math.abs(result.hashCode() % 1000)); // simulate a long-running computation
        }
        catch (InterruptedException e) {} // you'd want to think about what to do if interrupted
        System.out.println("task finished: " + order + " " + result);
        results.submit(order, result);
    }
}