import java.util.concurrent.*;
import java.util.*;

public class ExArray {
 private static int[] intArray;


 //返回一个整型数组,数组中的元素是并行地随机产生的
 public static int[] randomIntArray(int size) {
 if (size < 0) throw new IllegalArgumentException("Array size less than zero.");
 intArray = new int[size];
 ForkJoinPool pool = new ForkJoinPool();
 FillRandomArrayTask masterTask = new FillRandomArrayTask(0, size);
 pool.invoke(masterTask);
 return intArray;
 }

 //用于实现randomIntArray方法的内部类
 static class FillRandomArrayTask extends RecursiveAction {
 private final int left;
 private final int right; //Task负责填充的范围是[left,right-1]
 private static final int THRESHOLD = 100;

 public FillRandomArrayTask(int left, int right) {
 this.left = left;
 this.right = right;
 }

 public void compute() {
 //问题规模足够小,串行解决
 if (right - left + 1 <= THRESHOLD) {
 Random r = new Random();
 for (int i = left; i <= right - 1; i++) {
 intArray[i] = r.nextInt();
 }
 }
 else {
 int medium = (left + right) / 2;
 FillRandomArrayTask leftTask = new FillRandomArrayTask(left, medium);
 FillRandomArrayTask rightTask = new FillRandomArrayTask(medium, right);
 leftTask.invoke();
 rightTask.invoke();
 }
 }
 }
}