WaitForMultipleThreadsToComplete

WaitForMultipleThreadsToComplete.java

import java.util.LinkedList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

/**
 * Created by Alex on 10/28/2015.
 */
public class WaitForMultipleThreadsToComplete {

    public static void main(String[] args) {
//        startJoinExample();
        startExecutorExample();
    }

    private static void startExecutorExample() {
        List<Callable<Object>> callables = new LinkedList<>();

        for (int i = 0; i< 10; i++) {
            callables.add(new Callable<Object>() {
                @Override
                public Object call() throws Exception {
                    int time = new Random().nextInt(5000);
                    System.out.println("Thread will run for " + time + " ms");
                    Thread.sleep(time);
                    return null;
                }
            });
        }

        ExecutorService executor = Executors.newCachedThreadPool();
        long t0 = System.currentTimeMillis();
        try {
            List<Future<Object>> results = executor.invokeAll(callables);
        } catch (InterruptedException e) {
        }
        long t1 = System.currentTimeMillis();
        System.out.println("---------- Total work time " + (t1 - t0) + " ms");
    }

    private static void startJoinExample() {
        List<Thread> threads = new LinkedList<>();

        for (int i = 0; i < 10 ; i++) {
            Thread t = new Thread() {
                @Override
                public void run() {
                    try {
                        int time = new Random().nextInt(5000);
                        System.out.println("Thread will run for " + time + " ms");
                        Thread.sleep(time);
                    } catch (InterruptedException e) {
                    }
                }
            };
            threads.add(t);
            t.start();
        }

        long t0 = System.currentTimeMillis();
        for (Thread t : threads) {
            try {
                t.join();
            } catch (InterruptedException e) {
            }
        }
        long t1 = System.currentTimeMillis();
        System.out.println("---------- Total work time " + (t1 - t0) + " ms");
    }
}