Java中的Future获取任务返回值详解

// 提交Runnable任务
Future<?> submit(Runnable task);
// 提交Callable任务
<T> Future<T> submit(Callable<T> task);
// 提交Runnable任务及结果引用  
<T> Future<T> submit(Runnable task, T result);

// 任务取消操作 参数是允许中断正在运行的线程
boolean cancel(boolean mayInterruptIfRunning);
// 判断任务是否取消
boolean isCancelled();
// 判断任务是否结束
boolean isDone();
// 阻塞式的获取任务返回结果
V get() throws InterruptedException, ExecutionException;
// 支持超时功能
V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;

public class Test4 {
    public static void main(String[] args) throws Exception {
        ExecutorService executor = Executors.newFixedThreadPool(2);
        Apple apple = new Apple("red apple",5999.9);
        System.out.println("调用前==" +apple);
        Task task = new Task(apple);
        Future<Apple> submit = executor.submit(task, apple);
        // 阻塞式获取
        Apple result = submit.get();
        System.out.println("调用前==" + result);
    }
}
// 实现线程方法
class Task implements Runnable{
    // 非常重要的一般 相当于是参数传递的形式，可以到线程中修改
    Apple apple;
    public Task(Apple apple){
        this.apple = apple;
    }
    @Override
    public void run() {
        // 在线程中可以操作传入的对象
        apple.setName("green apple");
        System.out.println("操作Apple");
    }
}
class Apple{
    private String name;
    private double price;
    public Apple(String name,double price){
        this.name = name;
        this.price = price;
    }
	// 省略get set方法 以及toString方法
}

public FutureTask(Callable<V> callable)
public FutureTask(Runnable runnable, V result)

// 定义对象
FutureTask<Integer> task = new FutureTask(()->{
    return 1+2;
});
// 定义线程池
ExecutorService executorService = Executors.newFixedThreadPool(3);
// 不要使用这里的返回值，就算是FutureTask实现了Future对象，
// 但是Future也现实了Runnable接口返回值为空
Future<?> submit = executorService.submit(task);
// 返回值获取
System.out.println(task.get());
executorService.shutdown();

// 定义对象
FutureTask<Integer> task = new FutureTask(()->{
    return 1+2;
});
// 线程构造方法，传入Runnable的子类
Thread thread = new Thread(task);
thread.start();
System.out.println(task.get());

public class UseFutureTask {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        // 定义线程B的执行
        FutureTask<String> futureTaskB = new FutureTask<>(new ThreadB());
        // 定义线程A的执行
        FutureTask futureTaskA = new FutureTask(new ThreadA(futureTaskB),null);
        // 线程执行
        Thread threadA = new Thread(futureTaskA);
        Thread threadB = new Thread(futureTaskB);
        threadA.start();
        threadB.start();
        futureTaskA.get();
    }
}
// 用于线程A 完成洗水壶 烧水
class ThreadA implements Runnable {
    FutureTask<String> futureTask;
    public ThreadA(FutureTask<String> futureTask){
        this.futureTask = futureTask;
    }
    @Override
    public void run() {
        try {
            System.out.println("ThreadA 洗水壶");
            TimeUnit.SECONDS.sleep(1);
            System.out.println("ThreadA 烧水");
            TimeUnit.SECONDS.sleep(15);
            // 需要获取线程B的茶叶
            String teaName = futureTask.get();
            System.out.println("ThreadA 泡茶===="+teaName);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
// 用于线程B 完成洗茶壶 洗茶杯 拿茶叶 需要返回茶叶的
class ThreadB implements Callable<String> {
    @Override
    public String call() throws Exception {
        System.out.println("ThreadB 洗茶壶");
        TimeUnit.SECONDS.sleep(1);
        System.out.println("ThreadB 洗茶杯");
        TimeUnit.SECONDS.sleep(2);
        System.out.println("ThreadB 拿茶叶");
        TimeUnit.SECONDS.sleep(1);
        return "铁观音";
    }
}