public class FutureGet { public static void main(String[] args) throws ExecutionException, InterruptedException { ExecutorService executor=Executors.newFixedThreadPool(2); //建设一个Callable，三秒返回String范例 Callable callable = new Callable() { @Override public Object call() throws Exception { Thread.sleep(3000); System.out.println("callable要领执行！"); return "callable"; } }; System.out.println("提交任务之前："+getStringDate()); Future future = executor.submit(callable); System.out.println("提供任务之后，获取功效之前："+getStringDate()); System.out.println("获取返回值："+future.get()); System.out.println("获取到功效之后："+getStringDate()); } public static String getStringDate(){ Date date = new Date(); SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss"); String dataString = format.format(date); return dataString; } }
通过上面的输出可以看到，在更换submit提交任务之后，主线程原来是继承运行到future.get()的时候就阻塞了，一直比及任务执行完毕，拿到了返回的返回值，主线程才会继承运行；
阻塞性是因为挪用了get()要领时，任务没有执行完毕，所以会一直比及任务完成，形成了阻塞；
任务是在挪用submit要领时就开始执行了，假如在挪用get要领时，任务已经执行完毕，那么就不会造成阻塞；
下面挪用要领前先休眠四秒，这时能顿时获得返回值：
submit(Runnable task)
因为Runnable是没有返回值，所以假如submit一个Runnable的话，get获得的值必定为null；
public class SubmitRunnable { public static void main(String[] args) throws ExecutionException, InterruptedException { ExecutorService executor= Executors.newFixedThreadPool(2); Runnable runnable = new Runnable() { @Override public void run() { try { Thread.sleep(2000); System.out.println(Thread.currentThread().getName()); } catch (InterruptedException e) { e.printStackTrace(); } } }; Future future = executor.submit(runnable); System.out.println("得到返回值："+future.get()); } }
submit(Runnable task,T result)
固然传入Runnable不能直接返回内容，可是可以通过submit(Runnable task,T result)传入一个载体，通过这个载体获取返回值；
public class Data { String name; String sex; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } }
在Runnable的结构要领中传入：
public class MyThreadData implements Runnable { Data data; public MyThreadData(Data data) { this.data = data; } @Override public void run() { try { Thread.sleep(2000); System.out.println("线程执行："); data.setName("张三"); data.setSex("女"); } catch (InterruptedException e) { e.printStackTrace(); } } public static void main(String[] arg) throws ExecutionException, InterruptedException { ExecutorService executor= Executors.newFixedThreadPool(2); Data data = new Data(); Future<Data> submit = executor.submit(new MyThreadData(data), data); System.out.println("返回功效："+submit.get().getName()+",sex:"+submit.get().getSex()); } }
get(long var1,TimeUnit var3)