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

Question

这是一个示例中的示例代码.我需要知道的是什么时候call()调用可调用的？触发它的是什么？

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);
  }
}

Answer 1

一旦有了submittedcallable,执行程序就会调度callable来执行.根据执行程序的不同,这可能会直接发生,也可能在线程可用后发生.

get另一方面,调用只等待检索计算结果.

所以准确地说:在submit调用和调用get返回之间的某个地方调用callable.