Java5新增了Callable接口获得线程的返回值，用法如下
package com.ronniewang;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;public class GetReturnValueFromCallable { private static final int SLEEP_MILLS = 3000; private static final int SECOND_MILLS = 1000; private static int sleepSeconds = SLEEP_MILLS / SECOND_MILLS; ExecutorService executorService = Executors.newCachedThreadPool(); /** * 在创建多线程程序的时候，我们常实现Runnable接口，Runnable没有返回值，要想获得返回值，Java5提供了一个新的接口Callable */ public static void main(String[] args) { new GetReturnValueFromCallable().testCallable(); } private void testCallable() { /** * Callable需要实现的是call()方法，而不是run()方法，返回值的类型有Callable的类型参数指定， * Callable只能由ExecutorService.submit() 执行，正常结束后将返回一个future对象 */ Future<String> future = executorService.submit(new Callable<String>() { public String call() throws Exception { Thread.sleep(SLEEP_MILLS); return "I from callable"; } }); while (true) { /** * 获得future对象之前可以使用isDone()方法检测future是否完成，完成后可以调用get()方法获得future的值，， * 如果直接调用get()方法，get()方法将阻塞值线程结束 */ if (future.isDone()) { try { System.out.println(future.get()); break; } catch (InterruptedException e) { // ignored } catch (ExecutionException e) { // ignored } } else { try { System.out.println("after " + sleepSeconds– + " seconds, we will get future"); Thread.sleep(SECOND_MILLS); } catch (InterruptedException e) { // ignored } } } }}输出结果：
after 3 seconds, we will get futureafter 2 seconds, we will get futureafter 1 seconds, we will get futureI from callable
每个人在他的人生发轫之初，总有一段时光，
