Java多线程和并发（四），线程返回值获取方式和Callable接口

目录

1.主线程等待法

2.使用Thread类的join()阻塞当前线程，等待子线程执行完毕

3.通过Callable接口实现：通过FutureTask Or线程池获取

四、线程返回值获取方式和Callable接口

1.主线程等待法

public class CycleWait implements Runnable{
    private String value;
    @Override
    public void run() {
        try {
            Thread.currentThread().sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        value = "we have data now";
    }
    public static void main(String[] args) throws InterruptedException {
        CycleWait cw = new CycleWait();
        Thread t = new Thread(cw);
        t.start();
        while (cw.value == null){
            Thread.currentThread().sleep(100);
        }
        System.out.println("value : " + cw.value);
    }
}

2.使用Thread类的join()阻塞当前线程，等待子线程执行完毕 

public class CycleWait implements Runnable{
    private String value;
    @Override
    public void run() {
        try {
            Thread.currentThread().sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        value = "we have data now";
    }

    public static void main(String[] args) throws InterruptedException {
        CycleWait cw = new CycleWait();
        Thread t = new Thread(cw);
        t.start();
        t.join();
        System.out.println("value : " + cw.value);
    }
}

缺点很明显，不够精准，只能等子线程结束才能继续主线程

3.通过Callable接口实现：通过FutureTask Or线程池获取

（1）使用FutureTask获取返回值

public class MyCallable implements Callable<String> {
    @Override
    public String call() throws Exception{
        String value="test";
        System.out.println("Ready to work");
        Thread.currentThread().sleep(5000);
        System.out.println("task done");
        return  value;
    }
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        FutureTask<String> task = new FutureTask<String>(new MyCallable());
        new Thread(task).start();
        if(!task.isDone()){
            System.out.println("task has not finished, please wait!");
        }
        System.out.println("task return: " + task.get());
    }
}

（2）通过线程池获取返回值

public class MyCallable implements Callable<String> {
    @Override
    public String call() throws Exception{
        String value="test";
        System.out.println("Ready to work");
        Thread.currentThread().sleep(5000);
        System.out.println("task done");
        return  value;
    }
    public static void main(String[] args) {
        ExecutorService newCachedThreadPool = Executors.newCachedThreadPool();
        Future<String> future = newCachedThreadPool.submit(new MyCallable());
        if(!future.isDone()){
            System.out.println("task has not finished, please wait!");
        }
        try {
            System.out.println(future.get());
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            newCachedThreadPool.shutdown();
        }
    }
}