RandomUtil.java

package com.snowcattle.game.common.util;

import java.util.List;
import java.util.Random;

/**
 * 随机数工具
 *
 */
public class RandomUtil {

	private static Random random = new Random();

	/**
	 * 获取一个范围内的随机值
	 *
	 * @param randomMin
	 *            区间起始值
	 * @param randomMax
	 *            区间结束值
	 * @return 返回左开右闭区间的一个随机值
	 */
	public static int nextInt(int randomMin, int randomMax) {
		int randomBase = randomMax - randomMin;
		if (randomBase < 0) {
			throw new IllegalArgumentException(
					"randomMax must be bigger than randomMin");
		} else if (randomBase == 0) {
			return randomMin;
		} else {
			return (random.nextInt(randomBase) + randomMin);
		}
	}

	/**
	 * 获取一个范围内的随机值结果为闭区间
	 *
	 * @param randomMin
	 *            区间起始值
	 * @param randomMax
	 *            区间结束值
	 * @return 返回全闭区间的一个随机值
	 */
	public static int nextEntireInt(int randomMin, int randomMax) {
		int randomBase = randomMax - randomMin +1;
		if (randomBase < 0) {
			throw new IllegalArgumentException(
					"randomMax must be bigger than randomMin");
		} else if (randomBase == 0) {
			return randomMin;
		} else {
			return (random.nextInt(randomBase) + randomMin);
		}
	}
	
	
	/**
	 * 按权重随机抽取一个
	 * @param listRate
	 * @param rateMaxNum
	 */
	public static int getRadomIndex(List<Integer> listRate,int rateMaxNum) {
		int left = 0;
		int right = 0;
		int index = -1;
		int random = nextInt(0, rateMaxNum);
		for(int i=0; i < listRate.size(); i++){
			right = left + listRate.get(i);
			if(random >= left && random < right){
				index = i;
				break;
			}
			left = right;
		}
		return index;
	}

}