第六章JavanewFixedThreadPool示例|

在本教程中，我们将学习 Executor 的 newFixedThreadPool 工厂方法。 在上一篇教程中，我分享了ThreadPoolExecutor的介绍。如果您不了解 的概念ThreadPoolExecutor，您应该先了解一下。

Executor 的 newFixedThreadPool 工厂方法：

此方法返回ThreadPoolExecutor其最大大小（假设 n 个线程）是固定的。如果所有 n 个线程都忙于执行任务并且提交了其他任务，那么它们将必须在队列中，直到有线程可用。

句法：

ExecutorService executorService=Executors.newFixedThreadPool(noOfThreads);

Java newFixedThreadPool 示例：

让我们创建一个非常简单的示例。

第 1 步：创建一个名为“LoopTask.java”的可运行任务。

package org.arpit.java2blog;

public class LoopTask implements Runnable {

    private String loopTaskName;

    public LoopTask(String loopTaskName) {
        super();
        this.loopTaskName = loopTaskName;
    }

    @Override
    public void run() {
        System.out.println("Starting "+loopTaskName);
        for (int i = 1; i <= 10; i++) {
            System.out.println("Executing "+loopTaskName+" with "+Thread.currentThread().getName()+"===="+i);
        }
        System.out.println("Ending "+loopTaskName);
    }
}

第 2 步：创建一个名为FixedThreadPoolMain.java. 这将是我们的主要课程。

package org.arpit.java2blog;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class FixedThreadPoolMain {

    public static void main(String args[])
    {
        ExecutorService es=Executors.newFixedThreadPool(3);

        for (int i = 1; i <= 6; i++) {
            LoopTask loopTask=new LoopTask("LoopTask "+i);
            es.submit(loopTask);
        }
        es.shutdown();
    }
}

让我们运行上面的程序来检查输出：

Starting LoopTask 1
Starting LoopTask 3
Starting LoopTask 2
Executing LoopTask 3 with pool-1-thread-3====1
Executing LoopTask 1 with pool-1-thread-1====1
Executing LoopTask 3 with pool-1-thread-3====2
Executing LoopTask 2 with pool-1-thread-2====1
Executing LoopTask 3 with pool-1-thread-3====3
Executing LoopTask 1 with pool-1-thread-1====2
Executing LoopTask 3 with pool-1-thread-3====4
Executing LoopTask 2 with pool-1-thread-2====2
Executing LoopTask 3 with pool-1-thread-3====5
Executing LoopTask 3 with pool-1-thread-3====6
Executing LoopTask 1 with pool-1-thread-1====3
Executing LoopTask 3 with pool-1-thread-3====7
Executing LoopTask 2 with pool-1-thread-2====3
Executing LoopTask 3 with pool-1-thread-3====8
Executing LoopTask 1 with pool-1-thread-1====4
Executing LoopTask 3 with pool-1-thread-3====9
Executing LoopTask 2 with pool-1-thread-2====4
Executing LoopTask 3 with pool-1-thread-3====10
Executing LoopTask 1 with pool-1-thread-1====5
Executing LoopTask 1 with pool-1-thread-1====6
Ending LoopTask 3
Executing LoopTask 2 with pool-1-thread-2====5
Executing LoopTask 2 with pool-1-thread-2====6
Executing LoopTask 2 with pool-1-thread-2====7
Executing LoopTask 2 with pool-1-thread-2====8
Executing LoopTask 2 with pool-1-thread-2====9
Executing LoopTask 1 with pool-1-thread-1====7
Executing LoopTask 2 with pool-1-thread-2====10
Starting LoopTask 4
Ending LoopTask 2
Executing LoopTask 1 with pool-1-thread-1====8
Starting LoopTask 5
Executing LoopTask 4 with pool-1-thread-3====1
Executing LoopTask 5 with pool-1-thread-2====1
Executing LoopTask 1 with pool-1-thread-1====9
Executing LoopTask 1 with pool-1-thread-1====10
Ending LoopTask 1
Executing LoopTask 5 with pool-1-thread-2====2
Executing LoopTask 4 with pool-1-thread-3====2
Executing LoopTask 4 with pool-1-thread-3====3
Executing LoopTask 5 with pool-1-thread-2====3
Starting LoopTask 6
Executing LoopTask 5 with pool-1-thread-2====4
Executing LoopTask 4 with pool-1-thread-3====4
Executing LoopTask 5 with pool-1-thread-2====5
Executing LoopTask 5 with pool-1-thread-2====6
Executing LoopTask 6 with pool-1-thread-1====1
Executing LoopTask 6 with pool-1-thread-1====2
Executing LoopTask 6 with pool-1-thread-1====3
Executing LoopTask 6 with pool-1-thread-1====4
Executing LoopTask 5 with pool-1-thread-2====7
Executing LoopTask 4 with pool-1-thread-3====5
Executing LoopTask 4 with pool-1-thread-3====6
Executing LoopTask 4 with pool-1-thread-3====7
Executing LoopTask 4 with pool-1-thread-3====8
Executing LoopTask 5 with pool-1-thread-2====8
Executing LoopTask 6 with pool-1-thread-1====5
Executing LoopTask 5 with pool-1-thread-2====9
Executing LoopTask 4 with pool-1-thread-3====9
Executing LoopTask 4 with pool-1-thread-3====10
Executing LoopTask 5 with pool-1-thread-2====10
Ending LoopTask 5
Executing LoopTask 6 with pool-1-thread-1====6
Ending LoopTask 4
Executing LoopTask 6 with pool-1-thread-1====7
Executing LoopTask 6 with pool-1-thread-1====8
Executing LoopTask 6 with pool-1-thread-1====9
Executing LoopTask 6 with pool-1-thread-1====10
Ending LoopTask 6

我们使用了 new newFixedThreadPool，所以当我们提交时6 tasks，3 new threads将被创建并执行3 tasks。Other 3 tasks将在等待中queue。一旦线程完成任何任务，该线程将选择另一个任务并执行它。 这就是 Java newFixedThreadPool 示例的全部内容。