Java中的RunnableCallableFutureFutureTask的区别与示例
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Java中存在Runnable、Callable、Future、FutureTask这几个与线程相关的类或者接口,在Java中也是比较重要的几个概念,我们通过下面的简单示例来了解一下它们的作用于区别。
Runnable
其中Runnable应该是我们最熟悉的接口,它只有一个run()函数,用于将耗时操作写在其中,该函数没有返回值。然后使用某个线程去执行该runnable即可实现多线程,Thread类在调用start()函数后就是执行的是Runnable的run()函数。Runnable的声明如下 :
public interface Runnable
/**
* When an object implementing interface <code>Runnable</code> is used
* to create a thread, starting the thread causes the object's
* <code>run</code> method to be called in that separately executing
* thread.
* <p>
*
* @see java.lang.Thread#run()
*/
public abstract void run();
Callable
Callable与Runnable的功能大致相似,Callable中有一个call()函数,但是call()函数有返回值,而Runnable的run()函数不能将结果返回给客户程序。Callable的声明如下 :
public interface Callable<V>
/**
* Computes a result, or throws an exception if unable to do so.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
V call() throws Exception;
可以看到,这是一个泛型接口,call()函数返回的类型就是客户程序传递进来的V类型。
Future
Executor就是Runnable和Callable的调度容器,Future就是对于具体的Runnable或者Callable任务的执行结果进行
取消、查询是否完成、获取结果、设置结果操作。get方法会阻塞,直到任务返回结果(Future简介)。Future声明如下 :
/**
* @see FutureTask
* @see Executor
* @since 1.5
* @author Doug Lea
* @param <V> The result type returned by this Future's <tt>get</tt> method
*/
public interface Future<V>
/**
* Attempts to cancel execution of this task. This attempt will
* fail if the task has already completed, has already been cancelled,
* or could not be cancelled for some other reason. If successful,
* and this task has not started when <tt>cancel</tt> is called,
* this task should never run. If the task has already started,
* then the <tt>mayInterruptIfRunning</tt> parameter determines
* whether the thread executing this task should be interrupted in
* an attempt to stop the task. *
*/
boolean cancel(boolean mayInterruptIfRunning);
/**
* Returns <tt>true</tt> if this task was cancelled before it completed
* normally.
*/
boolean isCancelled();
/**
* Returns <tt>true</tt> if this task completed.
*
*/
boolean isDone();
/**
* Waits if necessary for the computation to complete, and then
* retrieves its result.
*
* @return the computed result
*/
V get() throws InterruptedException, ExecutionException;
/**
* Waits if necessary for at most the given time for the computation
* to complete, and then retrieves its result, if available.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @return the computed result
*/
V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
FutureTask
FutureTask则是一个RunnableFuture<V>,而RunnableFuture实现了Runnbale又实现了Futrue<V>这两个接口,
public class FutureTask<V> implements RunnableFuture<V>
RunnableFuture
public interface RunnableFuture<V> extends Runnable, Future<V>
/**
* Sets this Future to the result of its computation
* unless it has been cancelled.
*/
void run();
另外它还可以包装Runnable和Callable<V>, 由构造函数注入依赖。
public FutureTask(Callable<V> callable)
if (callable == null)
throw new NullPointerException();
this.callable = callable;
this.state = NEW; // ensure visibility of callable
public FutureTask(Runnable runnable, V result)
this.callable = Executors.callable(runnable, result);
this.state = NEW; // ensure visibility of callable
可以看到,Runnable注入会被Executors.callable()函数转换为Callable类型,即FutureTask最终都是执行Callable类型的任务。该适配函数的实现如下 :
public static <T> Callable<T> callable(Runnable task, T result)
if (task == null)
throw new NullPointerException();
return new RunnableAdapter<T>(task, result);
RunnableAdapter适配器
/**
* A callable that runs given task and returns given result
*/
static final class RunnableAdapter<T> implements Callable<T>
final Runnable task;
final T result;
RunnableAdapter(Runnable task, T result)
this.task = task;
this.result = result;
public T call()
task.run();
return result;
由于FutureTask实现了Runnable,因此它既可以通过Thread包装来直接执行,也可以提交给ExecuteService来执行。
并且还可以直接通过get()函数获取执行结果,该函数会阻塞,直到结果返回。因此FutureTask既是Future、
Runnable,又是包装了Callable( 如果是Runnable最终也会被转换为Callable ), 它是这两者的合体。
简单示例
package com.effective.java.concurrent.task;
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;
import java.util.concurrent.FutureTask;
/**
*
* @author mrsimple
*
*/
public class RunnableFutureTask
/**
* ExecutorService
*/
static ExecutorService mExecutor = Executors.newSingleThreadExecutor();
/**
*
* @param args
*/
public static void main(String[] args)
runnableDemo();
futureDemo();
/**
* runnable, 无返回值
*/
static void runnableDemo()
new Thread(new Runnable()
@Override
public void run()
System.out.println("runnable demo : " + fibc(20));
).start();
/**
* 其中Runnable实现的是void run()方法,无返回值;Callable实现的是 V
* call()方法,并且可以返回执行结果。其中Runnable可以提交给Thread来包装下
* ,直接启动一个线程来执行,而Callable则一般都是提交给ExecuteService来执行。
*/
static void futureDemo()
try
/**
* 提交runnable则没有返回值, future没有数据
*/
Future<?> result = mExecutor.submit(new Runnable()
@Override
public void run()
fibc(20);
);
System.out.println("future result from runnable : " + result.get());
/**
* 提交Callable, 有返回值, future中能够获取返回值
*/
Future<Integer> result2 = mExecutor.submit(new Callable<Integer>()
@Override
public Integer call() throws Exception
return fibc(20);
);
System.out
.println("future result from callable : " + result2.get());
/**
* FutureTask则是一个RunnableFuture<V>,即实现了Runnbale又实现了Futrue<V>这两个接口,
* 另外它还可以包装Runnable(实际上会转换为Callable)和Callable
* <V>,所以一般来讲是一个符合体了,它可以通过Thread包装来直接执行,也可以提交给ExecuteService来执行
* ,并且还可以通过v get()返回执行结果,在线程体没有执行完成的时候,主线程一直阻塞等待,执行完则直接返回结果。
*/
FutureTask<Integer> futureTask = new FutureTask<Integer>(
new Callable<Integer>()
@Override
public Integer call() throws Exception
return fibc(20);
);
// 提交futureTask
mExecutor.submit(futureTask) ;
System.out.println("future result from futureTask : "
+ futureTask.get());
catch (InterruptedException e)
e.printStackTrace();
catch (ExecutionException e)
e.printStackTrace();
/**
* 效率底下的斐波那契数列, 耗时的操作
*
* @param num
* @return
*/
static int fibc(int num)
if (num == 0)
return 0;
if (num == 1)
return 1;
return fibc(num - 1) + fibc(num - 2);
输出结果
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