什么时候使用Callable对象在Java Executor中调用call()方法？

public class CallableExample {

public static class WordLengthCallable
    implements Callable {
    private String word;
    public WordLengthCallable(String word) {
      this.word = word;
    }
    public Integer call() {
      return Integer.valueOf(word.length());
    }
}

public static void main(String args[]) throws Exception {
    ExecutorService pool = Executors.newFixedThreadPool(3);
    Set<Future<Integer>> set = new HashSet<Future<Integer>>();
    for (String word: args) {
      Callable<Integer> callable = new WordLengthCallable(word);
      Future<Integer> future = pool.submit(callable); //**DOES THIS CALL call()?**
      set.add(future);
    }
    int sum = 0;
    for (Future<Integer> future : set) {
      sum += future.get();//**OR DOES THIS CALL call()?**
    }
    System.out.printf("The sum of lengths is %s%n",sum);
    System.exit(sum);
  }
}