實現的方式主要有三種

1、構造函數傳參

2、成員變量傳參

3、回調函數傳參

問題：如何實現處理線程的返回值？

1、主線程等待法（優點：實現起來簡單，缺點：需要等待的變量一多的話，代碼就變的非常臃腫。而且不能精準控制時間）

public class CycleWait implements Runnable{
    private String value;
    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);
//        }
        t.join();
        System.out.println("value : " + cw.value);
    }
}

2、使用Thread類的join()阻塞當前線程以等待子線程處理完畢（缺點：精準度不夠）

3、通過Callable接口實現：通過FutureTask Or 線程池獲取

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;
    }
}

FutureTask 實現方式

public class FutureTaskDemo {
    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());
    }
}

線程池實現方式

public class ThreadPoolDemo {
    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 (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        } finally {
            newCachedThreadPool.shutdown();
        }
    }
}

如何給run()方法傳參數