多线程编程之Runnable与Callable区别

Runnable

@FunctionalInterface

public interface Runnable {

    /**

     * When an object implementing interface <code>Runnable</code> is used

     * to create a thread, starting the thread causes the object's

     * <code>run</code> method to be called in that separately executing

     * thread.

     * <p>

     * The general contract of the method <code>run</code> is that it may

     * take any action whatsoever.

     *

     * @see     java.lang.Thread#run()

     */

    public abstract void run();

}

Callable

@FunctionalInterface

public interface Callable<V> {

    /**

     * Computes a result, or throws an exception if unable to do so.

     *

     * @return computed result

     * @throws Exception if unable to compute a result

     */

    V call() throws Exception;

}

相同点：

1.都是接口，都能够实现多线程编程，都需要Thread.start()来启动线程。

不同点：

1.Callable接口支持返回执行结果，此时需要调用FutureTask.get()方法实现，此方法会阻塞主线程直到获取‘将来’结果；当不调用此方法时，主线程不会阻塞！

Callable使用

/**

 * CallableImpl 简要描述

 * <p> TODO:描述该类职责 </p>

 *

 * @author ckmike

 * @version 1.0

 * @date 18-12-6 下午8:53

 * @copyright ckmike

 **/

public class CallableImpl implements Callable<String> {

    private String accept;

    public CallableImpl(String accept) {

        this.accept = accept;

    }

    @Override

    public String call() throws Exception {

        // 休眠

        TimeUnit.SECONDS.sleep(3);

        return this.accept;

    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {

        Callable<String> callable = new CallableImpl("my callable test!");

        FutureTask<String> task = new FutureTask<>(callable);

        long beginTime = System.currentTimeMillis();

        // 创建线程

        new Thread(task).start();

        // 调用get()阻塞主线程，反之，线程不会阻塞

        String result = task.get();

        long endTime = System.currentTimeMillis();

        System.out.println("hello : " + result);

        System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!");

    }

}

Runnable使用

/**

 * RunnableImpl 简要描述

 * <p> TODO:描述该类职责 </p>

 *

 * @author ckmike

 * @version 1.0

 * @date 18-12-6 下午9:03

 * @copyright ckmike

 **/

public class RunnableImpl implements Runnable {

    public RunnableImpl(String accept) {

        this.accept = accept;

    }

    private String accept;

    @Override

    public void run() {

        // 线程阻塞 1 秒，此时有异常产生，只能在方法内部消化，无法上抛

        try {

            TimeUnit.SECONDS.sleep(1);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

        // 最终处理结果无法返回

        System.out.println("hello : " + this.accept);

    }

    public static void main(String[] args) {

        Runnable runnable = new RunnableImpl("my runable test!");

        long beginTime = System.currentTimeMillis();

        new Thread(runnable).start();

        long endTime = System.currentTimeMillis();

        System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!");

    }

}

写这篇文章的原因是：面试时问道Runnable与Callable的区别，平时也就用Runnable比较多，基本上没有用过Callable，所以就挂了，哈哈哈，也总结给有需要的朋友。有知道Callable接口的使用场景吗？有的话可以留意分享给我吗？谢谢了！

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