在java中生成10位唯一随机数

Question

我正在尝试使用以下代码生成10位唯一随机数.根据我的要求,我必须创建大约5000个唯一数字(ID).这没有按预期工作.它还会生成-ve数字.此外,有时生成的数字中缺少一个或两个数字,导致8或9个数字不是10.

public static synchronized  List generateRandomPin(){

    int START =1000000000;
    //int END = Integer.parseInt("9999999999");
    //long END = Integer.parseInt("9999999999");
    long END = 9999999999L;

    Random random = new Random();

    for (int idx = 1; idx <= 3000; ++idx){
        createRandomInteger(START, END, random);
    }

    return null;
}


private static void createRandomInteger(int aStart, long aEnd, Random aRandom){
    if ( aStart > aEnd ) {
      throw new IllegalArgumentException("Start cannot exceed End.");
    }
    //get the range, casting to long to avoid overflow problems
    long range = (long)aEnd - (long)aStart + 1;
    logger.info("range>>>>>>>>>>>"+range);
    // compute a fraction of the range, 0 <= frac < range
    long fraction = (long)(range * aRandom.nextDouble());
    logger.info("fraction>>>>>>>>>>>>>>>>>>>>"+fraction);
    int randomNumber =  (int)(fraction + aStart);    
    logger.info("Generated : " + randomNumber);

  }

Answer 1

所以你想要一个10位数的固定长度随机数？这可以更容易:

long number = (long) Math.floor(Math.random() * 9_000_000_000L) + 1_000_000_000L;

请注意,10位数字Integer.MAX_VALUE不适合a int,因此long.

Answer 2

我认为你得到8/9位数值和负数的原因是你要添加fraction一个long(带符号的64位值),它可能大于正值int范围(32位值)aStart.

该值溢出,使得randomNumber它处于负32位范围内或者几乎缠绕到aStart(因为int是有符号的32位值,fraction只需要稍微小于(2 ^ 32 - aStart)就可以看到8或者9位数值).

您需要使用long所有值.

   private static void createRandomInteger(int aStart, long aEnd, Random aRandom){
    if ( aStart > aEnd ) {
      throw new IllegalArgumentException("Start cannot exceed End.");
    }
    //get the range, casting to long to avoid overflow problems
    long range = aEnd - (long)aStart + 1;
    logger.info("range>>>>>>>>>>>"+range);
    // compute a fraction of the range, 0 <= frac < range
    long fraction = (long)(range * aRandom.nextDouble());
    logger.info("fraction>>>>>>>>>>>>>>>>>>>>"+fraction);
    long randomNumber =  fraction + (long)aStart;    
    logger.info("Generated : " + randomNumber);

  }