说说Runnable与Callable
Callable接口:
public interface Callable<V> { V call() throws Exception; }
Runnable接口:
public interface Runnable { public abstract void run(); }
相同点:
- 两者都是接口;(废话)
- 两者都可用来编写多线程程序;
- 两者都需要调用Thread.start()启动线程;
不同点:
- 两者最大的不同点是:实现Callable接口的任务线程能返回执行结果;而实现Runnable接口的任务线程不能返回结果;
- Callable接口的call()方法允许抛出异常;而Runnable接口的run()方法的异常只能在内部消化,不能继续上抛;
注意点:
- Callable接口支持返回执行结果,此时需要调用FutureTask.get()方法实现,此方法会阻塞主线程直到获取‘将来’结果;当不调用此方法时,主线程不会阻塞!
Callable工作的Demo:
package com.callable.runnable; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.FutureTask; /** * Created on 2016/5/18. */ public class CallableImpl implements Callable<String> { public CallableImpl(String acceptStr) { this.acceptStr = acceptStr; } private String acceptStr; @Override public String call() throws Exception { // 任务阻塞 1 秒 Thread.sleep(1000); return this.acceptStr + " append some chars and return it!"; } public static void main(String[] args) throws ExecutionException, InterruptedException { Callable<String> callable = new CallableImpl("my callable test!"); FutureTask<String> task = new FutureTask<>(callable); long beginTime = System.currentTimeMillis(); // 创建线程 new Thread(task).start(); // 调用get()阻塞主线程,反之,线程不会阻塞 String result = task.get(); long endTime = System.currentTimeMillis(); System.out.println("hello : " + result); System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!"); } }
测试结果:
hello : my callable test! append some chars and return it! cast : 1 second! Process finished with exit code 0
Runnable工作的Demo:
package com.callable.runnable; /** * Created on 2016/5/18. */ public class RunnableImpl implements Runnable { public RunnableImpl(String acceptStr) { this.acceptStr = acceptStr; } private String acceptStr; @Override public void run() { try { // 线程阻塞 1 秒,此时有异常产生,只能在方法内部消化,无法上抛 Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } // 最终处理结果无法返回 System.out.println("hello : " + this.acceptStr); } public static void main(String[] args) { Runnable runnable = new RunnableImpl("my runable test!"); long beginTime = System.currentTimeMillis(); new Thread(runnable).start(); long endTime = System.currentTimeMillis(); System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!"); } }
测试结果:
cast : 0 second! hello : my runable test! Process finished with exit code 0
写此篇的原因是一次面试中问到Callable与Runnable的区别,当时用的多的是Runnable,而Callable使用很少!
比较了两者后(网上查了不少),发现Callable在很多特殊的场景下还是很有用的!最后留点抄的代码,加深对Callable的认识!
package com.inte.fork; /** * Created on 2016/4/20. */ import java.util.*; import java.util.concurrent.*; import static java.util.Arrays.asList; public class Sums { static class Sum implements Callable<Long> { private final long from; private final long to; Sum(long from, long to) { this.from = from; this.to = to; } @Override public Long call() { long acc = 0; for (long i = from; i <= to; i++) { acc = acc + i; } System.out.println(Thread.currentThread().getName() + " : " + acc); return acc; } } public static void main(String[] args) throws Exception { ExecutorService executor = Executors.newFixedThreadPool(3); List<Future<Long>> results = executor.invokeAll(asList( new Sum(0, 10), new Sum(0, 1_000), new Sum(0, 1_000_000) )); executor.shutdown(); for (Future<Long> result : results) { System.out.println(result.get()); } } }