invokeAll via ExecutorService

Syntax of this method is like this(in java 6):

<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) 
                                    throws InterruptedException

In traditional Java – If we have to release multiple threads- we have to create Thread objects and call
Start method one by one.
In Java 5.0 and above – If we can put all callable objects in a collection object and pass the collection objects to ExecutorService to release.

The invokeAll() method invokes all of the Callable objects you pass to it in the collection passed as parameter. The invokeAll() returns a list of Future objects via which you can obtain the results of the executions of each Callable. invokeAll is a blocking method. It means – JVM won’t proceed to next line until all the threads are complete.


Keep in mind that a task might finish due to an exception, so it may not have "succeeded". There is no way on a Future to tell the difference.

Example:

ExecutorService executorService = Executors.newFixedThreadPool();

List<Callable<String>> callables = new ArrayList<Callable<String>>();

callables.add(new Callable<String>() {
    public String call() throws Exception {
        return "Task 1";
    }
});
callables.add(new Callable<String>() {
    public String call() throws Exception {
        return "Task 2";
    }
});
callables.add(new Callable<String>() {
    public String call() throws Exception {
        return "Task 3";
    }
});

List<Future<String>> futures = executorService.invokeAll(callables);

for(Future<String> future : futures){
    System.out.println("future.get = " + future.get());
}

executorService.shutdown();