随机数发生器没有在Java中的重复类 [英] Random number generator without repetition Class in Java

问题描述

首先，我是一个新手，Android应用程序开发者。在我的应用程序，我需要这在一个给定的范围内避免重复产生随机数的类。我搜索了很多这个问题，但我还没有发现我的情况下，任何具体的解决方案。好了，以为我找到了一个我稍微重新适应，但它无法正常工作。在code是下列之一：

First of all, I'm a newbie Android App developer. In my App I need a class which generates random numbers in a given range avoiding repetition. I've searched much for this issue, but I haven't found any concrete solution for my case. Well, thought I found one which I slightly readapt, but it's not working fine. The code is the following one:

public class NoRepeatRandom {

  private int[] number = null;
  private int N = -1;
  private int size = 0;
  public NoRepeatRandom(int minVal, int maxVal)
  {
    N = (maxVal - minVal) + 1;
    number = new int[N];
    int n = minVal;
    for(int i = 0; i < N; i++)
      number[i] = n++;
    size = N;
  }

  public void Reset() { size = N; }

   // Returns -1 if none left
  public int GetRandom()
  {
    if(size <= 0) return -1;
    int index = size * (int)Math.random();
    int randNum = number[index];

    // Swap current value with current last, so we don't actually
    // have to remove anything, and our list still contains everything
    // if we want to reset
    number[index] = number[size-1];
    number[--size] = randNum;

    return randNum;
  }
}

当我请GetRandom（）本人没有达到预期的结果，因为它总是返回给定的范围内的最小数目。例如：

When I call GetRandom() I don't achieve the expected result, because it always returns the minimum number of the range given. For example:

NoRepeatRandom nrr = new NoRepeatRandom(0, 10);
int yes = nrr.GetRandom();
//Here I create a Toast just to see the numbers that the method is returning.    
Toast toast = Toast.makeText(MainActivity.this, Integer.toString(yes), Toast.LENGTH_SHORT);
toast.show();

和结果是：0,0,0,0,0,0 ....
对于范围（5,10），结果是5,5,5,5 ....

And the result is: 0,0,0,0,0,0.... For range (5,10) the result is 5,5,5,5....

有谁知道什么是错的code？我真的AP preciate任何帮助！

Does anybody knows what is wrong with the code? I would really appreciate any help!

感谢您提前。

推荐答案

我想这条线是问题。

int index = size * (int) Math.random();

该计算结果为零始终。

编辑：

刚刚合并来自吉荣Vannevel和OP的意见。

Just consolidating comments from Jeroen Vannevel and OP.

的Math.random（ ）将返回在0.0和1.0之间的值，当其与 CAST（INT）将始终计算结果为零。您ca的如下使用。

Math.random() will return a value between 0.0 and 1.0, which when cast with (int) will always evaluates to ZERO. You ca use as below.

int index = (int) (size * Math.random());

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