如何生成的android一个唯一的哈希code字符串输入...？ [英] How to generate a unique hash code for string input in android...?

问题描述

我想生成一个唯一的哈希code的字符串中投放机器人。 有pdefined库中的任何$ P $是存在的，或者我们需要手动生成。请任何机构如果知道请present链接或code的东西。

I wanted to generate a unique hash code for a string in put in android. Is there any predefined library is there or we have to generate manually. Please any body if knows please present a link or a code stuff.

推荐答案

这要看你是什么意思：

• 正如 String.hash code（）为您提供了一个32位散列code。

• As mentioned String.hashCode() gives you a 32 bit hash code.

如果你想（比如说）C你是64位的散列$ C $可以很容易地实现它自己。

If you want (say) a 64-bit hashcode you can easily implement it yourself.

如果你想有一个字符串的加密哈希，Java的加密库包括MD5的实现，SHA-1等。你通常需要将字符串转换为字节数组，然后喂了哈希生成器/消化发电机。例如，看到@Bryan坎普的答案。

If you want a cryptographic hash of a String, the Java crypto libraries include implementations of MD5, SHA-1 and so on. You'll typically need to turn the String into a byte array, and then feed that to the hash generator / digest generator. For example, see @Bryan Kemp's answer.

如果你想有一个保证唯一散code，你的运气了。哈希和散列codeS是唯一的。

If you want a guaranteed unique hash code, you are out of luck. Hashes and hash codes are non-unique.

长Java字符串N具有 65536 ^ N 可能的状态，并需要使用整数16 * N 位重新present所有可能的值。如果你写产生整数与一个较小的范围的哈希函数（如小于 16 * N 位），你最终会发现情况下，多个字符串散列相同整数;即，散列codeS不能是唯一的。这就是所谓的鸽巢原理的，并且有一个直向前数学证明。 （你可以不打数学和赢！）

A Java String of length N has 65536 ^ N possible states, and requires an integer with 16 * N bits to represent all possible values. If you write a hash function that produces integer with a smaller range (e.g. less than 16 * N bits), you will eventually find cases where more than one String hashes to the same integer; i.e. the hash codes cannot be unique. This is called the Pigeonhole Principle, and there is a straight forward mathematical proof. (You can't fight math and win!)

但是，如果可能唯一的一个非常小的几率非唯一性是可以接受的，那么加密哈希是一个很好的答案。数学会告诉你有多大（即有多少位），哈希已是实现一个给定的（足够低）的非唯一性的概率。

But if "probably unique" with a very small chance of non-uniqueness is acceptable, then crypto hashes are a good answer. The math will tell you how big (i.e. how many bits) the hash has to be to achieve a given (low enough) probability of non-uniqueness.

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