从头认识java-17.6 Callable、Future和FutureTask

这一章节我们来讨论一下Callable、Future和FutureTask的用法与关系。
1.关系
（1）Callable是Runnable的封装的异步运算任务
（2）Future用来保存Callable异步运算的结果
（3）FutureTask封装Future的实体类

2.Future
我们在这里详细介绍一下Future，因为它比较复杂，首先看看他的源代码：

public interface Future<V> { 
    boolean cancel(boolean mayInterruptIfRunning); 
    boolean isCancelled(); 
    boolean isDone(); 
    V get() throws InterruptedException, ExecutionException; 
    V get(long timeout, TimeUnit unit) 
        throws InterruptedException, ExecutionException, TimeoutException; 
}

它里面包含了几个方法
get：得到结果
get（timeout，unit）计算是否超时得到结果
cancle：取消任务
isDone、isCancle：判断任务状态

3.例子：
Callable和FutureTask

package com.ray.ch17;

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

public class Test {

	public static void main(String[] args) throws InterruptedException,
			ExecutionException {
		Callable<Integer> callable = new MyCall();
		FutureTask<Integer> futureTask = new FutureTask<Integer>(callable);
		Thread thread = new Thread(futureTask);
		thread.start();
		Thread.sleep(100);
		if (!futureTask.isDone()) {
			System.out.println(futureTask.get());
		}
		if (!futureTask.isCancelled()) {
			futureTask.cancel(true);
			System.out.println("cancelled");
		}

	}
}

class MyCall implements Callable<Integer> {

	@Override
	public Integer call() throws Exception {
		System.out.println("doing something...");
		Thread.sleep(1000);
		return new Random().nextInt(50);
	}
}

我们只需要将上面main方法里面的两个if互换就可以得出不同的结果。

Callable和Future

package com.ray.ch17;

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class Test {

	public static void main(String[] args) throws InterruptedException,
			ExecutionException {
		ExecutorService executors = Executors.newCachedThreadPool();
		Callable<Integer> callable = new MyCall();
		Future<Integer> future = executors.submit(callable);
		System.out.println(future.get());
	}
}

class MyCall implements Callable<Integer> {

	@Override
	public Integer call() throws Exception {
		System.out.println("doing something...");
		Thread.sleep(1000);
		return new Random().nextInt(50);
	}
}

总结：这一章节主要介绍了Callable、Future和FutureTask的用法与关系。


这一章节就到这里，谢谢。-----------------------------------目录