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 {/*** 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 {/*** 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 cancel is called,
* this task should never run. If the task has already started,
* then the mayInterruptIfRunning parameter determines
* whether the thread executing this task should be interrupted in
* an attempt to stop the task.*/boolean cancel(boolean mayInterruptIfRunning);/*** Returns true if this task was cancelled before it completed
* normally.*/boolean isCancelled();/*** Returns true 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
public class FutureTask
RunnableFuture实现了Runnbale又实现了Futrue
public interface RunnableFutureextends Runnable, Future {/*** 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， 由构造函数注入依赖。public FutureTask(Callable 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 Callable callable(Runnable task, T result) {if (task == null)throw new NullPointerException();return new RunnableAdapter(task, result);
}
RunnableAdapter适配器
/**
* A callable that runs given task and returns given result*/static final class RunnableAdapterimplements Callable {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Futureresult2 = executorService.submit(new Callable() {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FutureTaskresult3 = new FutureTask(new Callable() {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*/FutureTaskresult4 = new FutureTask(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FutureTaskresult5 = new FutureTask(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);
}
}
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