如何生成带小数点的随机数

Question

I would like to generate random numbers between 1 & 10, with a decimal place of 1 
(e.g. 1.5, 9.4, 6.3, 2.9)

I would like to generate random numbers between 1 & 10, with 2 decimal places
(e.g. 1.51, 9.46, 6.32, 2.93)

I would like to generate random numbers between 1 & 10, with 3 decimal places

    (e.g. 1.512, 9.346, 6.329, 2.935)

一种解决方案是使用一个仅用于小数点的随机生成器，然后与数字连接。有没有更简单的方法来实现这一点？

Answer 1

一个明显的建议是生成一个整数，并将其适当地除以。因此，对于3DPs，您可以生成一个介于1000和9999之间的数字（或10000，取决于您想要的确切界限），然后将其除以10000。

我建议你在实际除法中使用BigDecimal，以精确地保留小数。

Answer 2

1）
（int）（（Math.random（）*90) 10) / 10.0
2）
（int）（（Math.random（）*900) 100) / 100.03）
（int）（（Math.random（）*9000) 1000) / 1000.0

Answer 3

虽然BigDecimal的解决方案更灵活，但这里有一个使用int和双精度的更简单的解决方案。这个方法接受一个Random对象，一个上限和下限以及一些小数位数，并返回一个相应格式化的字符串：

/**
 * Generate a decimal string representation of a random number within the
 * supplied bounds.
 * 
 * @param random
 *            the random object (if null, a new one will be created)
 * @param lowerBound
 *            the lower bound, inclusive
 * @param upperBound
 *            the upper bound, inclusive
 * @param decimalPlaces
 *            the decimal places of the result
 * @return the formatted string
 */
public static String getRandomValue(final Random random,
    final int lowerBound,
    final int upperBound,
    final int decimalPlaces){

    if(lowerBound < 0 || upperBound <= lowerBound || decimalPlaces < 0){
        throw new IllegalArgumentException("Put error message here");
    }

    final double dbl =
        ((random == null ? new Random() : random).nextDouble() //
            * (upperBound - lowerBound))
            + lowerBound;
    return String.format("%." + decimalPlaces + "f", dbl);

}

测试代码：

final Random rnd = new Random();

for(int decpl = 0; decpl < 3; decpl++){
    for(int low = 0; low < 2; low++){
        for(int high = low + 1; high < low + 3; high++){
            System.out.println("Random Value between " + low + " and "
                + high + " with " + decpl + " decimal places:");
            System.out.println(getRandomValue(rnd, low, high, decpl));
        }
    }
}

输出：

Random Value between 0 and 1 with 0 decimal places:
0
Random Value between 0 and 2 with 0 decimal places:
1
Random Value between 1 and 2 with 0 decimal places:
1
Random Value between 1 and 3 with 0 decimal places:
3
Random Value between 0 and 1 with 1 decimal places:
0.6
Random Value between 0 and 2 with 1 decimal places:
1.5
Random Value between 1 and 2 with 1 decimal places:
1.1
Random Value between 1 and 3 with 1 decimal places:
1.9
Random Value between 0 and 1 with 2 decimal places:
0.52
Random Value between 0 and 2 with 2 decimal places:
0.82
Random Value between 1 and 2 with 2 decimal places:
1.75
Random Value between 1 and 3 with 2 decimal places:
1.10