Java多线程编程（二）

在 Java多线程编程（一） 中的多线程并没有返回值，本文将介绍带返回值的多线程。

要想有返回值，则需要实现新的接口Callable而不再是Runnable接口，实现的方法也改为call()方法，执行器也不再是调用execute()，而是submit()

【程序实例】

 public class TaskWithResult implements Callable<String> {

     private int id;

     public TaskWithResult(int id) {
         this.id = id;
     }

     @Override
     public String call() throws Exception {
         return "result of TaskWithResult " + id + " : sum() = " + Sum(id);
     }

     private int Sum(int id) {
         return (id * (id + 1)) / 2;
     }

 }

 public class Main {

     public static void main(String[] args) {
         ExecutorService exec = Executors.newCachedThreadPool();
         ArrayList<Future<String>> results = new ArrayList<Future<String>>();
         for (int i = 0; i < 10; i++)
             results.add(exec.submit(new TaskWithResult(i)));
         for (Future<String> fs : results)
             try {
                 System.out.println(fs.get());
             } catch (InterruptedException e) {
                 System.out.println(e);
                 return;
             } catch (ExecutionException e) {
                 System.out.println(e);
             } finally {
                 exec.shutdown();
             }
     }

 }

【运行结果】

 result of TaskWithResult 0 : sum() = 0
 result of TaskWithResult 1 : sum() = 1
 result of TaskWithResult 2 : sum() = 3
 result of TaskWithResult 3 : sum() = 6
 result of TaskWithResult 4 : sum() = 10
 result of TaskWithResult 5 : sum() = 15
 result of TaskWithResult 6 : sum() = 21
 result of TaskWithResult 7 : sum() = 28
 result of TaskWithResult 8 : sum() = 36
 result of TaskWithResult 9 : sum() = 45