java抽奖算法

publicclass LotteryTool {

private double factor;
private double probability;
private Random rand;

private LotteryTool(double probability, long expireTime, int reduce){
this.factor = (double) System.currentTimeMillis() / expireTime;
this.probability = probability * Math.pow(factor, reduce);
this.rand = new Random(System.currentTimeMillis());
}

public static LotteryTool getInstance(double probability, longexpireTime,
int reduce) {
return new LotteryTool(probability, expireTime, reduce);
}

public boolean isLucky(long expected) {
long token = generateLong();
expected = expected % (int) (1 / probability);
if (expected == token) {
return true;
}
return false;
}