Java:在负双精度和正双精度范围之间生成随机双精度 [英] Java: Generating a random double between the range of a negative double and a positive double

问题描述

我不太熟悉如何更改 Math.random 或新的 Random() 的范围以生成这样的双精度值.我需要能够在 -10 到 25 美分之间生成双倍(我的程序正在处理金钱；因此我说美分).一个单独的实例正在生成 90 到 -75 美分之间的随机双倍.我在寻找答案时看到了这个:

I am not very familiar with how to alter the range of both Math.random or a new Random() to generate a double like this. I need to be able to generate a double between -10 and 25 cents (my program is dealing with money; hence why I said cents). And a separate instance is generating a random double between 90 and -75 cents. I saw this when I was searching for my answer:

double result = Math.random() * (upper -lower) +lower;

double result = Math.random() * (upper - lower) + lower;

但是当我将这个想法实现到我的代码中时，使用正数和负数之间的范围时，该范围似乎不起作用......我用 0.25 的上限和 -0.10 的下限对其进行了测试，但注意到它在我所做的一个测试实例中打印了 0.3567587946356543.所以由此我得出结论，我显然没有正确调整范围..

But when I implemented the idea into my code, the range didn't seem to work when using a range between a positive and a negative number... I tested it with the upper limit of 0.25 and lower of -0.10, but noticed it printed 0.3567587946356543 at one instance of the test I did. So by this I concluded that I obviously didn't adjust the range correctly..

请帮忙:(

这是我第一次使用 stackoverflow，所以请放轻松，如果我说的任何内容没有意义，我会详细说明..

This is my first time using stackoverflow so please go easy on me, I will elaborate if anything I said didn't make sense..

这是我使用此代码的现有方法:

This is my existing method using this code:

public double variation(double price){
    //formula: (Math.random() * range) + min; where range = max - min
    //80% of the time returns amount between -10 & 25 cents
    if(Math.random() > 0.19){ 
        return (Math.random() * 0.35) - 0.10;
    }
    //20% of the time returns amount between -75 & 90 cents
    return (Math.random() * 1.65) - 0.75;
}

我知道该方法需要支付它不使用的双倍价格；接受双倍价格而忽视其价值是老师要求的一部分.所以请忽略这一点.

I know the method takes in a double price that it doesn't use; it's part of the teacher's requirements to take in a double price but to disregard its value. So ignore that please.

推荐答案

现在你已经在问题中包含了你的所有代码，所以我的答案改为:

当它打印 0.3567587946356543 时，当第一个 Math.random() 调用 if 时，它来自 20% 的部分，范围为 -.75 到 0.90(Math.random() > 0.19){ 变为 false.

When it printed 0.3567587946356543 then it comes from the 20% part with range -.75 to 0.90 when the first Math.random() call in if(Math.random() > 0.19){ becomes false.

旧答案:

我想您忘记了较低值处的减号:

I think you forgot the minus at the lower value:

double upper = 0.25;
double lower = -0.10;
double result = Math.random() * (upper - lower) + lower;

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