创建线程的两种方式

一种是实现Runnable接口&＃xff0c;实现其run方式&＃xff1b;另外一种是继承Thread类&＃xff0c;重写其run方法。

这一点可以从Thread类中的注释看到&＃xff1a;

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Runnable

Thread类也实现了Runnable接口&＃xff0c;Runnable接口的源码如下&＃xff1a;

public static CompletableFuture supplyAsync(Supplier supplier) public static CompletableFuture supplyAsync(Supplier supplier,Executor executor); public static CompletableFuture runAsync(Runnable runnable); public static CompletableFuture runAsync(Runnable runnable,Executor executor);

因此&＃xff0c;可以看得出&＃xff0c;不管我们是实现Runnable接口&＃xff0c;还是继承Thread类&＃xff0c;run方式的返回类型都是void&＃xff0c;我们都无法拿到线程运行的返回结果。

如果非要拿到线程运行的结果怎么办&＃xff1f;Callable便应运而生了。

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Callable

&＃64;FunctionalInterfacepublic interface Callable { /** * Computes a result, or throws an exception if unable to do so. * * &＃64;return computed result * &＃64;throws Exception if unable to compute a result */ V call() throws Exception;}

Callable还是一个函数式接口&＃xff0c;其泛型参数类型与返回值类型一致。

为了更清晰的说明他们之间的关系&＃xff0c;这里先放上类图结构

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类图关系

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Future

Callable接口&＃xff0c;只是用于单纯地去获得返回值&＃xff0c;但是什么时候去获取&＃xff0c;或者查看线程运行的状态&＃xff0c;就需要借助Future

Future的源码如下&＃xff1a;

public CompletableFuture whenComplete(BiConsumer super T, ? super Throwable> action); public CompletableFuture whenCompleteAsync(BiConsumer super T, ? super Throwable> action); public CompletableFuture whenCompleteAsync(BiConsumer super T, ? super Throwable> action, Executor executor); public CompletableFuture exceptionally(Function fn);

可以看得出来&＃xff0c;Future提供了取消任务、获取任务执行的状态与获取结果的能力。

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RunnableFuture

public interface RunnableFuture extends Runnable, Future { /** * Sets this Future to the result of its computation * unless it has been cancelled. */ void run();}

RunnableFuture继承了Runnable与Future接口&＃xff0c;没什么好说的。

以上说的&＃xff0c;Runnable、Callable、Future以及RunnableFuture都是接口&＃xff0c;真正干活还得靠FutureTask

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FutureTask

FutureTask实现了RunnableFuture接口&＃xff0c;而RunnableFuture继承了Runnable与Future接口&＃xff0c;因此FutureTask既可以作为一个Runnable被Thread执行&＃xff0c;也可以获取到Future异步计算的结果。

从上面的类图可以看到&＃xff0c;传入一个Callable类型的参数可以构造FutureTask对象。

下面这个例子&＃xff0c;使用构造出来的FutureTask对象&＃xff0c;传入Thread的构造函数中&＃xff0c;调用start方法以启动线程。

package com.qcy.testFutureTask;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.FutureTask;/** * &＃64;author qcy * &＃64;create 2020/09/07 09:27:06 */public class Main { static class Task implements Callable { &＃64;Override public Integer call() throws Exception { //模拟任务耗时 Thread.sleep(2000); return 1; } } public static void main(String[] args) throws ExecutionException, InterruptedException { //FutureTask接收一个Callable实现类 FutureTask futureTask &＃61; new FutureTask<>(new Task()); //FutureTask实现了RunnableFuture,间接实现了Runnable接口,因此可作为参数传给Thread的构造方法中 new Thread(futureTask).start(); //get()方法会阻塞2秒,输出1 int result &＃61; futureTask.get(); System.out.println(result); }}

当然也可以将构造出来FutureTask对象&＃xff0c;提交进线程池中。对线程池不了解的同学&＃xff0c;可以移步这一篇文章说说线程池

package com.qcy.testFutureTask;import java.util.concurrent.*;/** * &＃64;author qcy * &＃64;create 2020/09/07 09:27:06 */public class Main { static class Task implements Callable { &＃64;Override public Integer call() throws Exception { //模拟任务耗时 Thread.sleep(2000); return 1; } } public static void main(String[] args) throws ExecutionException, InterruptedException { ExecutorService pool &＃61; Executors.newFixedThreadPool(1); //FutureTask接收一个Callable实现类 FutureTask futureTask &＃61; new FutureTask<>(new Task()); //这里使用一个Runnable的实现类&＃xff0c;因此可以使用FutureTask pool.submit(futureTask); //get()方法会阻塞2秒,输出1 int result &＃61; futureTask.get(); System.out.println(result); pool.shutdown(); }}

当然&＃xff0c;ExecutorService内的submit方法&＃xff0c;可以直接传入Callable的实现类。

package com.qcy.testFutureTask;import java.util.concurrent.*;/** * &＃64;author qcy * &＃64;create 2020/09/07 09:27:06 */public class Main { static class Task implements Callable { &＃64;Override public Integer call() throws Exception { //模拟任务耗时 Thread.sleep(2000); return 1; } } public static void main(String[] args) throws ExecutionException, InterruptedException { ExecutorService pool &＃61; Executors.newFixedThreadPool(1); //这里使用一个Callable的实现类&＃xff0c;因此可以使用FutureTask Future future &＃61; pool.submit(new Task()); //get()方法会阻塞2秒,输出1 int result &＃61; future.get(); System.out.println(result); pool.shutdown(); }}