long startTime = System.currentTimeMillis();
List<Callable<String>> callables = new ArrayList<Callable<String>>();
ExecutorService executor = Executors.newCachedThreadPool();
callables.add(new Callable<String>() {
        public String call() {
            for (int i=0; i<100000; i++) {
                System.out.println("i "+i);
            }
            return "Task 1";
        }
    }
);

callables.add(new Callable<String>() {
        public String call() {
            for (int j=0; j<100000; j++) {
                System.out.println("j "+j);
            }
            return "Task 2";
        }
    }
);

callables.add(new Callable<String>() {
     public String call() {
          for (int k=0; k<100000; k++) {
              System.out.println("k "+k);
          }
          return "Task 3";
      }
  }
);
try {
    List<Future<String>> futureLst = executor.invokeAll(callables);
    for (Future future : futureLst) {
        try {
            System.out.println(future.get());
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
executor.shutdown();
System.out.println("Time Taken - "+ (System.currentTimeMillis() - startTime));

long startTime = System.currentTimeMillis();
for (int i=0; i<100000; i++) {
    System.out.println("i "+i);
}
for (int j=0; j<100000; j++) {
    System.out.println("j "+j);
}
for (int k=0; k<100000; k++) {
    System.out.println("k "+k);
}
System.out.println("Time Taken - "+ (System.currentTimeMillis() - startTime));