JAVA面向对象学习——java多线程———线程的创建和启动——使用Callable和Future创建线程...

迷南。 2023-09-30 12:20 15阅读 0赞

**Callable接口**

Callable接口，该接口怎么看都像是Runnable接口的增强版，Callable接口也提供了一个call()方法可以作为线程执行体，但call方法比run()方法功能更强大：

——call()方法可以有返回值。

——call()可以声明抛出异常。

**Future接口**

JDK1.5提供了Future接口来代表Callable接口里call()方法的返回值，并为Future接口提供了一个FutureTask实现类，该实现类实现了Future接口，并实现了Runnable接口——可以作为Thread类的target。

**实现Callable创建多线程**

(1)定义Callable接口的实现类，并重写该接口的call方法，该call方法的方法体同样是该线程的线程执行体。

(2)创建Callable实现类的实例，并将该实例包装成FutureTask，FutureTask实现了Runnable接口。

(3)将FutureTask实例作为Thread的target来创建Thread对象，该Thread对象才是真正的线程对象。

(4)调用线程对象的start方法来启动该线程。

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import java.util.concurrent.*;
    
    
    public class ThirdThread
    {
    	public static void main(String[] args)
    	{
    		// 创建Callable对象
    		var rt = new ThirdThread();
    		// 先使用Lambda表达式创建Callable<Integer>对象
    		// 使用FutureTask来包装Callable对象
    		FutureTask<Integer> task = new FutureTask<>((Callable<Integer>)() -> {
    			var i = 0;
    			for ( ; i < 100; i++)
    			{
    				System.out.println(Thread.currentThread().getName()
    					+ " 的循环变量i的值：" + i);
    			}
    			// call()方法可以有返回值
    			return i;
    		});
    		for (var i = 0; i < 100; i++)
    		{
    			System.out.println(Thread.currentThread().getName()
    				+ " 的循环变量i的值：" + i);
    			if (i == 20)
    			{
    				// 实质还是以Callable对象来创建、并启动线程
    				new Thread(task, "有返回值的线程").start();
    			}
    		}
    		try
    		{
    			// 获取线程返回值
    			System.out.println("子线程的返回值：" + task.get());
    		}
    		catch (Exception ex)
    		{
    			ex.printStackTrace();
    		}
    	}
    }

===================================================

import java.util.concurrent.*;
    
    public class ThirdThread
    {
        public static void main(String[] args)
        {
            ThirdThread rt = new ThirdThread();
    
            FutureTask<Integer> task = new FutureTask<>((Callable<Integer>)() -> {
                int i = 0;
                for ( ; i < 100; i++)
                {
                    System.out.println(Thread.currentThread().getName() + "-------------" + i);
                }
                return i;
            });
    
            for (int i = 0; i < 100; i++)
            {
                System.out.println(Thread.currentThread().getName() + "+++++++++++++++" + i);
                if (i == 20)
                {
                    new Thread(task, "return  ").start();
                }
            }
            try
            {
                System.out.println("子线程的返回值：" + task.get());
            }
            catch (Exception ex)
            {
                ex.printStackTrace();
            }
        }
    }

下午 03:01:45: Executing task 'ThirdThread.main()'...

> Task :compileJava  
> Task :processResources NO-SOURCE  
> Task :classes

> Task :ThirdThread.main()

main+++++++++++++++0  
main+++++++++++++++1  
main+++++++++++++++2  
main+++++++++++++++3  
main+++++++++++++++4  
main+++++++++++++++5  
main+++++++++++++++6  
main+++++++++++++++7  
main+++++++++++++++8  
main+++++++++++++++9  
main+++++++++++++++10  
main+++++++++++++++11  
main+++++++++++++++12  
main+++++++++++++++13  
main+++++++++++++++14  
main+++++++++++++++15  
main+++++++++++++++16  
main+++++++++++++++17  
main+++++++++++++++18  
main+++++++++++++++19  
main+++++++++++++++20  
main+++++++++++++++21  
main+++++++++++++++22  
main+++++++++++++++23  
main+++++++++++++++24  
main+++++++++++++++25  
main+++++++++++++++26  
main+++++++++++++++27  
main+++++++++++++++28  
main+++++++++++++++29  
main+++++++++++++++30  
main+++++++++++++++31  
main+++++++++++++++32  
main+++++++++++++++33  
main+++++++++++++++34  
main+++++++++++++++35  
main+++++++++++++++36  
main+++++++++++++++37  
main+++++++++++++++38  
main+++++++++++++++39  
return -------------0  
main+++++++++++++++40  
return -------------1  
return -------------2  
return -------------3  
return -------------4  
return -------------5  
return -------------6  
main+++++++++++++++41  
return -------------7  
return -------------8  
return -------------9  
return -------------10  
return -------------11  
return -------------12  
main+++++++++++++++42  
main+++++++++++++++43  
main+++++++++++++++44  
main+++++++++++++++45  
main+++++++++++++++46  
main+++++++++++++++47  
main+++++++++++++++48  
main+++++++++++++++49  
main+++++++++++++++50  
main+++++++++++++++51  
main+++++++++++++++52  
main+++++++++++++++53  
main+++++++++++++++54  
main+++++++++++++++55  
main+++++++++++++++56  
main+++++++++++++++57  
main+++++++++++++++58  
main+++++++++++++++59  
main+++++++++++++++60  
main+++++++++++++++61  
main+++++++++++++++62  
main+++++++++++++++63  
main+++++++++++++++64  
main+++++++++++++++65  
main+++++++++++++++66  
main+++++++++++++++67  
return -------------13  
return -------------14  
return -------------15  
main+++++++++++++++68  
return -------------16  
main+++++++++++++++69  
main+++++++++++++++70  
main+++++++++++++++71  
main+++++++++++++++72  
main+++++++++++++++73  
main+++++++++++++++74  
main+++++++++++++++75  
main+++++++++++++++76  
main+++++++++++++++77  
main+++++++++++++++78  
return -------------17  
main+++++++++++++++79  
main+++++++++++++++80  
main+++++++++++++++81  
main+++++++++++++++82  
main+++++++++++++++83  
main+++++++++++++++84  
main+++++++++++++++85  
main+++++++++++++++86  
main+++++++++++++++87  
main+++++++++++++++88  
main+++++++++++++++89  
return -------------18  
main+++++++++++++++90  
main+++++++++++++++91  
main+++++++++++++++92  
main+++++++++++++++93  
main+++++++++++++++94  
main+++++++++++++++95  
main+++++++++++++++96  
main+++++++++++++++97  
main+++++++++++++++98  
main+++++++++++++++99  
return -------------19  
return -------------20  
return -------------21  
return -------------22  
return -------------23  
return -------------24  
return -------------25  
return -------------26  
return -------------27  
return -------------28  
return -------------29  
return -------------30  
return -------------31  
return -------------32  
return -------------33  
return -------------34  
return -------------35  
return -------------36  
return -------------37  
return -------------38  
return -------------39  
return -------------40  
return -------------41  
return -------------42  
return -------------43  
return -------------44  
return -------------45  
return -------------46  
return -------------47  
return -------------48  
return -------------49  
return -------------50  
return -------------51  
return -------------52  
return -------------53  
return -------------54  
return -------------55  
return -------------56  
return -------------57  
return -------------58  
return -------------59  
return -------------60  
return -------------61  
return -------------62  
return -------------63  
return -------------64  
return -------------65  
return -------------66  
return -------------67  
return -------------68  
return -------------69  
return -------------70  
return -------------71  
return -------------72  
return -------------73  
return -------------74  
return -------------75  
return -------------76  
return -------------77  
return -------------78  
return -------------79  
return -------------80  
return -------------81  
return -------------82  
return -------------83  
return -------------84  
return -------------85  
return -------------86  
return -------------87  
return -------------88  
return -------------89  
return -------------90  
return -------------91  
return -------------92  
return -------------93  
return -------------94  
return -------------95  
return -------------96  
return -------------97  
return -------------98  
return -------------99  
子线程的返回值：100

BUILD SUCCESSFUL in 2s  
2 actionable tasks: 2 executed  
下午 03:01:48: Task execution finished 'ThirdThread.main()'.

===========================================================

两种线程方式的对比

采用实现Runnable接口方式的多线程：

——线程类只是实现了Runnable接口，还可以可以继承其他类。

——在这种方式下，可以多个线程共享同一个target对象，所以非常适合多个相同线程来处理同一份资源的情况，从而可以将CPU，代码和数据分开，

形成清晰的模型，较好地体现了面向对象的思想。

——劣势是：编程稍稍复杂，如果需要访问当前线程，必须使用Thread.currentThread()方法。

采用继承Thread类方式的多线程：

劣势是：因为线程类已经继承了Thread类，所以不能再继承其他父类。

优势是：编写简单，如果需要访问当前线程，无需使用Thread.currentThread()方法，直接使用this即可获得当前线程。

[3f319450b9a2e7cd36e6952028be52aa.png]: https://img-blog.csdnimg.cn/img_convert/3f319450b9a2e7cd36e6952028be52aa.png
[e920a6f01d63fdf0fdd409288a8e3d54.png]: https://img-blog.csdnimg.cn/img_convert/e920a6f01d63fdf0fdd409288a8e3d54.png
[c0890205482f26d7e4599174e15328e5.png]: https://img-blog.csdnimg.cn/img_convert/c0890205482f26d7e4599174e15328e5.png
[a2cca1008f17c23dd068b0d486141287.png]: https://img-blog.csdnimg.cn/img_convert/a2cca1008f17c23dd068b0d486141287.png
[44a2edaaac7e1612c84fa270015f796b.png]: https://img-blog.csdnimg.cn/img_convert/44a2edaaac7e1612c84fa270015f796b.png