Java多線程和並發（四），線程返回值獲取方式和Callable接口

目錄

1.主線程等待法

2.使用Thread類的join()阻塞當前線程，等待子線程執行完畢

3.通過Callable接口實現：通過FutureTask Or線程池獲取

四、線程返回值獲取方式和Callable接口

1.主線程等待法

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類的join()阻塞當前線程，等待子線程執行完畢 

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);
    }
}

缺點很明顯，不夠精准，只能等子線程結束才能繼續主線程

3.通過Callable接口實現：通過FutureTask Or線程池獲取

（1）使用FutureTask獲取返回值

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）通過線程池獲取返回值

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();
        }
    }
}