Java 中的 Java . util . concurrent . recursivetask 类，带示例

原文:https://www . geesforgeks . org/Java-util-concurrent-recursivetask-class-in-Java-with-examples/

RecursiveTask 是一个抽象类封装了一个返回结果的任务。它是叉车的一个子类。RecursiveTask 类被扩展以创建具有特定返回类型的任务。代表任务计算部分的代码保存在 RecursiveTask 的 compute() 方法中。

RecursiveTask 类多用于并行编程的上下文中。可以划分为独立子任务的任务，任务的最终结果可以从子任务的结果中获得，可以使用 RecursiveTask 更有效地实现。例如，在大数组中搜索元素。

阶级等级

java.lang.Object
↳ java.util.concurrent.ForkJoinTask
  ↳ java.util.concurrent.RecursiveTask<V>

施工方

  1. RecursiveTask()–使用默认设置创建 RecursiveTask 对象。

    ```java public RecursiveTask()

    ```

方法

  1. Calculation () – The method of defining the task.

    ```java protected abstract void compute()

    ```

  2. 【 exec () –This method realizes the basic rules necessary for executing tasks.

    ```java protected final boolean exec()

    ```

  3. Getrawesult () –The function returns the value obtained after the task is completed, even if the task is abnormally completed. If the task has not been completed, it will return null.

    ```java public final Void getRawResult()

    ```

  4. setrawesult () –The function sets the return value of the task to the value passed in the parameter.

    ```java protected final void setRawResult(Void mustBeNull)

    ```

示例演示 RecursiveTask

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

public class RecursiveTaskDemo {
    public static void main(String[] args)
    {
        ForkJoinPool fjp = new ForkJoinPool();

        double[] nums = new double[5000];
        for (int i = 0; i < nums.length; i++) {
            nums[i] = (double)(((i % 2) == 0) ? i : -1);
        }
        Sum task = new Sum(nums, 0, nums.length);
        double summation = fjp.invoke(task);
        System.out.println("Summation " + summation);
    }
}

class Sum extends RecursiveTask<Double> {
    final int seqThreshold = 500;
    double[] data;
    int start, end;

    Sum(double[] data, int start, int end)
    {
        this.data = data;
        this.start = start;
        this.end = end;
    }

    @Override
    protected Double compute()
    {
        double sum = 0;
        if ((end - start) < seqThreshold) {
            for (int i = start; i < end; i++)
                sum += data[i];
        }
        else {
            int middle = (start + end) / 2;

            Sum subtaskA = new Sum(data, start, middle);
            Sum subtaskB = new Sum(data, middle, end);

            subtaskA.fork();
            subtaskB.fork();

            sum += subtaskA.join() + subtaskB.join();
        }
        return sum;
    }
}

输出:

Summation 6245000.0

参考:https://docs . Oracle . com/javase/8/docs/API/Java/util/concurrent/recursivetask . html

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