其中Runnable應該是我們最熟悉的接口，它只有一個run()函數(shù)，用于將耗時操作寫在其中，該函數(shù)沒有返回值。然后使用某個線程去執(zhí)行該runnable即可實現(xiàn)多線程，Thread類在調用start()函數(shù)后就是執(zhí)行的是Runnable的run()函數(shù)。Runnable的聲明如下 :
[java] view plain copy
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與Runnable的功能大致相似，Callable中有一個call()函數(shù)，但是call()函數(shù)有返回值，而Runnable的run()函數(shù)不能將結果返回給客戶程序。Callable的聲明如下 :
[java] view plain copypublic 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; } Executor就是Runnable和Callable的調度容器，Future就是對于具體的Runnable或者Callable任務的執(zhí)行結果進行
取消、查詢是否完成、獲取結果、設置結果操作。get方法會阻塞，直到任務返回結果(Future簡介)。Future聲明如下 :
[java] view plain copy/** * @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則是一個RunnableFuture<V>，而RunnableFuture實現(xiàn)了Runnbale又實現(xiàn)了Futrue<V>這兩個接口，
[java] view plain copypublic class FutureTask<V> implements RunnableFuture<V> public interface RunnableFuture<V> extends Runnable, Future<V> { /** * Sets this Future to the result of its computation * unless it has been cancelled. */ void run(); } 另外它還可以包裝Runnable和Callable<V>， 由構造函數(shù)注入依賴。
[java] view plain copypublic 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實現(xiàn)了Runnable，因此它既可以通過Thread包裝來直接執(zhí)行，也可以提交給ExecuteService來執(zhí)行。
并且還可以直接通過get()函數(shù)獲取執(zhí)行結果，該函數(shù)會阻塞，直到結果返回。因此FutureTask既是Future、
Runnable，又是包裝了Callable( 如果是Runnable最終也會被轉換為Callable )， 它是這兩者的合體。
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, 無返回值 */ static void runnableDemo() { new Thread(new Runnable() { @Override public void run() { System.out.
Thread、Runnable、Callable，其中Runnable實現(xiàn)的是void run()方法，Callable實現(xiàn)的是 V call()方法，并且可以返回執(zhí)行結果，其中Runnable可以提交給Thread來包裝下，直接啟動一個線程來執(zhí)行，而Callable則一般都是提交給ExecuteService來執(zhí)行。新聞熱點
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