一个非常非常大的int类型数组，用多线程计算和。假设数组长度M线程数量N

MultipleThreadCalSum.java

import java.util.concurrent.CountDownLatch;

import org.apache.commons.lang.math.RandomUtils;

public class MultipleThreadCalSum {

	public static void main(String[] args) {

		final int M = 10000000; // 10万个元素
		final int N = 100; // 100个线程

		int[] ia = new int[M]; // 需要求和的数组

		init(ia);

		new CalculatorII(ia).start();

		// 数组分区partition，多少个线程就分多少partition

		// 不考虑空间因素

		int m = partition(ia, N);

		int l = M - 1;

		long[] rst = new long[N];

		int start = 0, end = 0;

		int s = 0; // 第几个计算工人

		CountDownLatch threadSignal = new CountDownLatch(N);// 初始化countDown

		while (l >= 0) {
			// 求出每段的start，end，每段开启一个线程
			// 刚好会开启N个线程
			if (l > m) {
				end = l;
				l = l - m;
				start = l + 1;
			} else {
				end = l;
				start = 0;
				l = Integer.MIN_VALUE; // 退出
			}
			new Calculator(ia, start, end, rst, s++, threadSignal).start();
		}

		// 等待所有线程执行完毕
		try {
			threadSignal.await();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}

		// 累加结果
		long sum = 0;

		for (int idx = 0; idx < N; idx++) {
			sum += rst[idx];
		}

		System.out.println("Calculator sum " + sum);
	}

	private static void init(int[] a) {
		int size = a.length;
		for (int i = 0; i < size; i++) {
			a[i] = RandomUtils.nextInt();
		}
	}

	private static int partition(int[] a, int number) {
		int l = a.length;
		int t = l / number; // 获得理想的每个分区元素个数
		if (number * t < l) {
			// 如果元素个数超过，则每个区增加一个元素
			t++;
		}
		return t;
	}
}

class Calculator extends Thread {
	int[] part;
	long[] t;
	int start, end, s;

	CountDownLatch latch;

	public Calculator(int[] a, int start, int end, long[] rst, int s,
			CountDownLatch singal) {
		this.part = a;
		this.t = rst;
		this.start = start;
		this.end = end;
		this.s = s;
		this.latch = singal;
	}

	@Override
	public void run() {
		for (int i = start; i <= end; i++) {
			t[s] += part[i];
		}
		this.latch.countDown();
	}
}

class CalculatorII extends Thread {
	int[] ia;

	public CalculatorII(int[] a) {
		this.ia = a;
	}

	@Override
	public void run() {
		long sum = 0;
		for (int i = 0; i < ia.length; i++) {
			sum += ia[i];
		}
		System.out.println("CalculatorII sum " + sum);
	}
}