Fork/Join实例

(1)含返回值

           问题:1+2+...+100

          1.思路

             分解为1+2,3+4,,...99+100,然后对这50个结果进行求和

          2.任务实现

import java.util.concurrent.ExecutionException;
import java.util.concurrent.RecursiveTask;

public class CalculateTask extends RecursiveTask<Integer>{//因为需要返回值,所以使用RecursiveTask
	private static final long serialVersionUID = -8486729149866588744L;

	private static final int THRESHOLD = 2;// 阈值
	
	private int start;
	
	private int end;
	
	public CalculateTask(int start, int end) {
        this.start = start;
        this.end = end;
    }
	
	@Override
	protected Integer compute() {
		int sum = 0;
		if (end-start<THRESHOLD) {//分解为2个数的和然后计算
			for(;start<=end;start++){
				sum += start;
			}
		}else {
			int mid = (start + end) >>> 1;
		    RecursiveTask<Integer> task1 = new CalculateTask(start, mid);
		    RecursiveTask<Integer> task2 = new CalculateTask(mid+1, end);
		    invokeAll(task1,task2);
		    
		    try {
				sum = task1.get()+task2.get();
			} catch (InterruptedException e) {
				e.printStackTrace();
			} catch (ExecutionException e) {
				e.printStackTrace();
			}
		}
		
		return sum;
	}
}

          3.测试
package com.test;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;

import org.junit.Test;

public class QuickSortTest {

	@Test
	public void test(){
		ForkJoinPool forkJoinPool = new ForkJoinPool();
		
		// 生成一个计算任务,负责计算1+2+3+4
		CalculateTask task = new CalculateTask(1, 4);
		// 执行一个任务
		Future<Integer> result = forkJoinPool.submit(task);
		forkJoinPool.shutdown();
		try {
			System.out.println(result.get());
		} catch (InterruptedException e) {
			e.printStackTrace();
		} catch (ExecutionException e) {
			e.printStackTrace();
		}
	}
}

(2)无返回值

           问题:快排

          1.思路

             根据中间值分解为2个区间,然后区间内再执行

          2.任务实现

import java.util.concurrent.RecursiveAction;

public class CalculateTask extends RecursiveAction{//这里不需要返回值,所以使用RecursiveAction
	private static final long serialVersionUID = 2476846494375574971L;

	private int[] number = {};
	
	private int begin;
	
	private int end;
	
	private static final int THRESHOLD = 1;// 阈值
	
	public QuickSortTask(int[] number,int begin, int end){
		this.number = number;
		this.begin = begin;
		this.end = end;
	}
	
	@Override
	protected void compute() {
		if (end-begin<THRESHOLD) {//只有一个数,那么不用排序了
			return;
		}else{
			int mid = adjust(number,begin,end);
			
			QuickSortTask task1 = new QuickSortTask(number,begin, mid - 1);
			QuickSortTask task2 = new QuickSortTask(number,mid + 1, end);
			
			invokeAll(task1, task2);
		}
	}

	private int adjust(int[] a, int begin, int end) {
		int flag = a[begin];
		
		while (begin<end) {
			while (a[end]>=flag && begin<end) 
				end--;
			if (begin<end) 
				a[begin] = a[end];
			
			while (a[begin]<=flag && begin<end) 
				begin++;
			if (begin<end)
				a[end] = a[begin];
		}
		a[begin] = flag;
		
		return begin;
	}
}
          3.测试
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

import org.junit.Test;

public class QuickSortTest {

	@Test
	public void test() {
		ForkJoinPool forkJoinPool = new ForkJoinPool();

		int[] a = {54,12,36,16,96,62};

		QuickSortTask task = new QuickSortTask(a,0, 5);
		// 执行一个任务
		forkJoinPool.submit(task);
		while(!task.isDone()){
	        }

		for (int i : a) {
			System.out.print(i+" ");
		}
		forkJoinPool.shutdown();
	}
}


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