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 { /* * @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 :
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是一个RunnableFuture<V>
public class FutureTask<V> implements RunnableFuture<V>
RunnableFuture实现了Runnbale又实现了Futrue<V>这两个接口
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FutureTaslk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 }
上面代码块可以看出: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; } }
FutureTask实现Runnable,所以能通过Thread包装执行,
FutureTask实现Runnable,所以能通过提交给ExcecuteService来执行
注:ExecuteService:创建线程池实例对象,其中有submit(Runnable)、submit(Callable)方法
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是Future也是Runnable,又是包装了的Callable( 如果是Runnable最终也会被转换为Callable )。
Callable 和 Future接口的区别
1.Callable规定的方法是call(),而Runnable规定的方法是run().
2.Callable的任务执行后可返回值,而Runnable的任务是不能返回值的。
3.call()方法可抛出异常,而run()方法是不能抛出异常的。
4.运行Callable任务可拿到一个Future对象, Future表示异步计算的结果。
5.它提供了检查计算是否完成的方法,以等待计算的完成,并检索计算的结果。
6.通过Future对象可了解任务执行情况,可取消任务的执行,还可获取任务执行的结果。
7.Callable是类似于Runnable的接口,实现Callable接口的类和实现Runnable的类都是可被其它线程执行的任务。
示例:
package com.xzf.callable; import java.util.concurrent.Callable; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.FutureTask; public class RunnableFutureTask { static ExecutorService executorService = Executors.newSingleThreadExecutor(); //创建一个单线程执行器 public static void main(String[] args) { runnableDemo(); futureDemo(); } /** * new Thread(Runnable arg0).start(); 用Thread()方法开启一个新线程 * runnable, 无返回值 */ static void runnableDemo() { new Thread(new Runnable() { public void run() { System.out.println("runnable demo:" + fibc(20)); //有值 } }).start(); } /** * 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 * Runnable可以提交给Thread,在包装下直接启动一个线程来执行 * Callable一般都是提交给ExecuteService来执行 */ static void futureDemo() { try { Future<?> result1 = executorService.submit(new Runnable() { public void run() { fibc(20); } }); System.out.println("future result from runnable:"+result1.get()); //run()无返回值所以为空,result1.get()方法会阻塞 Future<Integer> result2 = executorService.submit(new Callable<Integer>() { public Integer call() throws Exception { return fibc(20); } }); System.out.println("future result from callable:"+result2.get()); //call()有返回值,result2.get()方法会阻塞 FutureTask<Integer> result3 = new FutureTask<Integer>(new Callable<Integer>() { public Integer call() throws Exception { return fibc(20); } }); executorService.submit(result3); System.out.println("future result from FutureTask:" + result3.get()); //call()有返回值,result3.get()方法会阻塞 /*因为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*/ FutureTask<Integer> result4 = new FutureTask<Integer>(new Runnable() { public void run() { fibc(20); } },fibc(20)); executorService.submit(result4); System.out.println("future result from executeService FutureTask :" + result4.get()); //call()有返回值,result3.get()方法会阻塞 //这里解释一下什么FutureTask实现了Runnable结果不为null,这就用到FutureTask对Runnable的包装,所以Runnable注入会被Executors.callable()函数转换成Callable类型 FutureTask<Integer> result5 = new FutureTask<Integer>(new Runnable() { public void run() { fibc(20); } },fibc(20)); new Thread(result5).start(); System.out.println("future result from Thread FutureTask :" + result5.get()); //call()有返回值,result5.get()方法会阻塞 } catch (Exception e) { e.printStackTrace(); }finally { executorService.shutdown(); } } static int fibc(int num) { if (num==0) { return 0; } if (num==1) { return 1; } return fibc(num-1) + fibc(num-2); } }