Java中的Runnable、Callable、Future、FutureTask的区别与示例
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;
-
}
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
-
}
-
public static <T> Callable<T> callable(Runnable task, T result) {
-
if (task == null)
-
throw new NullPointerException();
-
return new RunnableAdapter<T>(task, result);
-
}
-
/**
-
* 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() {
-
-
-
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() {
-
-
-
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>() {
-
-
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>() {
-
-
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
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;
-
}
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
-
}
-
public static <T> Callable<T> callable(Runnable task, T result) {
-
if (task == null)
-
throw new NullPointerException();
-
return new RunnableAdapter<T>(task, result);
-
}
-
/**
-
* 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() {
-
-
-
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() {
-
-
-
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>() {
-
-
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>() {
-
-
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);
-
}
-
-
}