简体繁体 English

Java Math.random（）随机性如何？

[英]Java Math.random() How random is it?

原文 2013-11-24 07:49:59 7 1 java/ random

I am working on a project that needs to generate two random numbers from a given range (both of them at the same time, one after another) and check if they are equal to each other - if they are, proceed executing other code; 我正在做一个项目，该项目需要在给定范围内生成两个随机数（它们同时，一个又一个），并检查它们是否相等-如果相等，则继续执行其他代码。 if they aren't - generate the numbers again. 如果不是，请重新生成数字。 Now my question is, if we have a range [0;10], and the first randomly generated number turned out to be 5, is the probability of the second number also being 5 as good as any other number? 现在我的问题是，如果我们有一个范围[0; 10]，并且第一个随机生成的数字竟然是5，那么第二个数字也和其他任何一个数字一样好5的可能性是吗？ Specifically, does Math.random() have any "defense" against generating same number if it is called twice consecutively? 具体来说，如果Math.random（）被连续调用两次，是否对生成相同的数字有任何“防御”？ or it "tries" to not generate the same number? 还是“尝试”不生成相同的数字？

1 个解决方案

Generating the same number in the range [0,10] twice in succession is a perfectly valid occurrence for any random number generator. 对于任何随机数生成器而言，连续两次生成[0,10]范围内的同一数字是完全有效的情况。 If it took any steps to prevent that it wouldn't be random. 如果采取了任何措施来防止这种情况发生，那将不是随机的。

On any invocation, the chances of any individual number being chosen should be 1:11, and each choice should be independent of previous choices, so the chances that in a pair the second number matches the first is 1 in 11. 在任何调用中，选择任何单个数字的机会应为1:11，并且每个选择均应独立于先前的选择，因此，一对第二个数字与第一个匹配的几率是11分之一。

As to how random Math.random() is, it's pseudo-random , meaning it uses an algorithm to generate a series of evenly distributed numbers starting with a "seed" value. 至于Math.random()随机性，它是伪随机的 ，这意味着它使用一种算法来生成一系列以“ seed”值开头的均匀分布的数字。 It's not suitable for cryptography but quite good for simulations and other non-cryptographic uses. 它不适用于密码学，但是非常适合模拟和其他非密码学用途。