public class GetIndex {
	private int weightAdder ; //權(quán)值加法器基數(shù)
	private int index ; //權(quán)值加法器填充時下標(biāo)
	private int dex; //中獎值下標(biāo)
	private int max; //最大權(quán)值
	private int random;
	private Random ran;
	private ArrayList<String> record = new ArrayList<String>();
	private int[] weights; //權(quán)值加法器數(shù)組
	public static DecimalFormat df = new DecimalFormat("0.00"); //格式化數(shù)值
	public static int[] map = new int[] {10,8450,1000,500,40}; //中獎權(quán)值 
	public static int looptime = 100;//抽獎次數(shù)
	public static void main(String[] args) {
	 GetIndex getindex = new GetIndex();
	 
	 for (int j = 0;j<looptime;j++) {
		getindex.index = 0;
		getindex.weightAdder = 0;
		getindex.ran = new Random();
		getindex.weights = new int[map.length];
		//生成權(quán)限加法器數(shù)組，保證新生成數(shù)據(jù)值有序遞增
		for(int w : map ) {
			getindex.weights[getindex.index++] = (getindex.weightAdder = getindex.weightAdder + w);
			
		}
		/*
		 * for(int w : weights) { System.out.println("數(shù)組："+w); }
		 */
		getindex.max = getindex.weights[getindex.weights.length-1]; //獲取權(quán)限加法器數(shù)組最大值
		getindex.random = getindex.ran.nextInt(getindex.max)+1; //生成隨機(jī)數(shù)
		getindex.dex = Arrays.binarySearch(getindex.weights, getindex.random);//重要：獲取該數(shù)組的一個下標(biāo)即為中獎值
		System.out.println("隨機(jī)數(shù)："+getindex.random);
		System.out.println("Dex: "+getindex.dex);
		//計算dex時數(shù)組被加1，所以在此減一
		if(getindex.dex < 0) {
			getindex.dex = -1 - getindex.dex;
		}
		System.out.println("Result: "+getindex.dex+" 加法器數(shù)組數(shù)據(jù)："+getindex.weights[getindex.dex]+" 選中號："+map[getindex.dex]);
		if(getindex.dex == 4 || getindex.dex == 0 || getindex.dex == 3) { //假設(shè)第一位與第五位中獎
			getindex.record.add("中獎號："+map[getindex.dex]);
		}
	 }
	  for(String rec: getindex.record) {
		  System.out.println(rec );
	  }
	  String odds = df.format((float)getindex.record.size()/map.length);
	  System.out.println("中獎率: "+ odds );
	 
	}
}
以上是抽獎過程中的主要邏輯，其核心就是利用binarySearch函數(shù)在隨機(jī)搜索值中找到一個搜索數(shù)組的一個下標(biāo)，根據(jù)該下標(biāo)定位到具體的獎品信息。