Java 中奖

在游戏里，有一种宝箱，打开这个宝箱获得传奇武器的概率是

20%,现在你打开5个这样的宝箱，获得传奇武器的概率是多少？

平均值即期望，有时我们会被平均，很多样本来实验大概是每人完5次就即中奖。

public class WinngPrize {
    private double chance;
    private int playTime;
    private int N;

    public  WinngPrize(double chance, int playTime, int  N)
    {
        if( chance < 0 || chance > 1.0)
            throw  new IllegalArgumentException("chance must be  0 < chance < 1");

        if( playTime <= 0 || N <= 0)
            throw  new IllegalArgumentException("playTime or N must be > 0 ");

        this.chance = chance;
        this.playTime = playTime;
        this.N = N;
    }

    public void run(){

        int wins = 0;

        for ( int i = 0; i < N; i ++)
        {
            if(play())
                wins ++;
        }
        System.out.println("winng rate:" + (double)wins/N);
    }

  private boolean play(){
        for(int i = 0; i < playTime; i ++)
            if(Math.random() < chance)
                return true;
        return false;
  }

    public static void main(String[] args) {

        double chance = 0.2;
        int playTime = 10;
        int N = 1000000;

       WinngPrize exp = new WinngPrize(chance, playTime, N);
       exp.run();
    }

}