学步园

辅助类提供了3个方法：

(1)addWeightNumber(int weight,int num):为某个num赋予weight权重，此权重代表此数字在随机获取时的获得概率；权重大， 则获得的概率就大，权重小，则获得的概率就小。

(2)addWeightNumRange(int weight,int numfrom,int numto,int ... numExcludes);同时为连续多个数字赋予权重，最后这个参数可以排除例外数字，比如addWeightNumRange(5,1,10,5); 表示为1~10（除去5）的数字赋予权重5；

(3)getNextInt();在你赋予权重之后，此方法会随即在你赋予权重的这些数字之中取出一个；

优点：此方法和new Random().nextInt()的优势在于，可以为每个数字赋予权重，并且可以随机取出用户指定的数字集合；

package org.xiazdong.util;

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

public class IntegerWeightRandom {
	private List<Integer> weights = new ArrayList<Integer>();
	private List<List<Integer>> numbers = new ArrayList<List<Integer>>();
	private Integer totalWeight;
	private Random random = new Random();
	public IntegerWeightRandom() {
		
	}
	
	private Integer getTotalWeight(){
		if(totalWeight == null){
			totalWeight = 0;
			for(Integer weight:weights){
				totalWeight += weight;
			}
		}
		return totalWeight;
	}
	/*
	 * 为某个number赋予一个weight，可能一个weight对应多个numbers，因此List<Integer>weight中一个元素对应List<List<Integer>>numbers中的一个List<Integer>
	 * */
	//此函数表示一个weight对应一个number
	public void addWeightNumber(int weight,int num){	
		weights.add(weight);
		List<Integer> list = new ArrayList<Integer>();
		list.add(num);
		numbers.add(list);
	}
	//此函数表示一个weight对应多个number
	public void addWeightNumRange(int weight,int numFrom,int numTo,int...numExcludes){
		weights.add(weight);
		List<Integer> list = new ArrayList<Integer>();
		for(int i = numFrom;i <= numTo;i++){
			boolean exclude = false;
			for(int numExclude:numExcludes){
				if(i == numExclude){
					exclude = true;
				}
			}
			if(!exclude){
				list.add(i);
			}
		}
		numbers.add(list);
	}
	/*
	 * 举例：
	 * 如果数字8的weight为1，数字9的weight为2，则totalWeight=3，8的范围为(0,1],9的范围为[2,3]如果随机数为2，则在9的范围内
	 * */
	//此函数为随机取一个整数（按照权重概率取）
	public Integer getNextInt(){
		int weightRandom = random.nextInt(getTotalWeight());
		int weightCount = 0;
		for(int i = 0;i < weights.size();i++){
			int weight = weights.get(i);
			if(weightRandom >= weightCount && weightRandom < weightCount + weight){
				List<Integer> numList = numbers.get(i);
				if(numList.size() == 1){
					return numList.get(0);
				}
				int numRandom = random.nextInt(numList.size());
				return numList.get(numRandom);
			}
			weightCount += weight;
		}
		
		return null;
	}

}

测试类：

package test.org.xiazdong.util;

import org.junit.Test;

import org.xiazdong.util.IntegerWeightRandom;

public class IntegerWeightRandomTest {
	@Test
	public void testGetNextInt(){
		IntegerWeightRandom random = new IntegerWeightRandom();
		random.addWeightNumber(1, 0);
		random.addWeightNumber(5, 1);
		random.addWeightNumber(9, 2);
		random.addWeightNumber(15, 3);
		random.addWeightNumber(20, 4);
		random.addWeightNumber(30, 5);
		random.addWeightNumber(40, 7);
		random.addWeightNumber(50, 6);
		random.addWeightNumber(60, 8);
		random.addWeightNumber(70, 9);
		for(int i=0;i<10;i++){
			System.out.println(random.getNextInt());
		}
		
	}
}