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