How to generate a unique hash code for string input in android

Question

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

User · Answer

String input    some input string   int hashCode   input hashCode    System out println  input hash code       hashCode

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Let s take a look at the stock hashCode   method   public int hashCode         int h   hash      if  h    0  amp  amp  count  gt  0            for  int i   0  i  lt  count  i                  h   31   h   charAt i                     hash   h            return h      The block of code above comes from the java lang String class  As you can see it is a 32 bit hash code which fair enough if you are using it on a small scale of data  If you are looking for hash code with more than 32 bit  you might wanna checkout this link   http   www javamex com tutorials collections strong hash code implementation shtml

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You can use this code for generating has code for a given string   int hash   7  for  int i   0  i  lt  strlen  i          hash   hash 31   charAt i

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A few line of java code   public static void main String args    throws Exception         String str  test string          MessageDigest messageDigest MessageDigest getInstance  MD5           messageDigest update str getBytes   0 str length            System out println  MD5    new BigInteger 1 messageDigest digest    toString 16

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This is a class I use to create Message Digest hashes   import java security MessageDigest  import java security NoSuchAlgorithmException   public class Sha1Hex        public String makeSHA1Hash String input              throws NoSuchAlgorithmException  UnsupportedEncodingException                       MessageDigest md   MessageDigest getInstance  SHA1                md reset                byte   buffer   input getBytes  UTF-8                md update buffer               byte   digest   md digest                 String hexStr                   for  int i   0  i  lt  digest length  i                      hexStr     Integer toString    digest i   amp  0xff     0x100  16  substring  1                              return hexStr

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For me it worked      public static long getUniqueLongFromString  String value          return  UUID nameUUIDFromBytes value getBytes    getMostSignificantBits

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I use this i tested it as key from my EhCacheManager Memory map       Its cleaner i suppose                Return Hash256 of String value                param text         return              public static String getHash256 String text            try               return org apache commons codec digest DigestUtils sha256Hex text             catch  Exception ex                Logger getLogger HashUtil class getName    log Level SEVERE  null  ex               return                       am using maven but this is the jar commons-codec-1 9 jar

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It depends on what you mean    As mentioned String hashCode   gives you a 32 bit hash code  If you want  say  a 64-bit hashcode you can easily implement it yourself  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  If you want a guaranteed unique hash code  you are out of luck   Hashes and hash codes are non-unique      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    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

[java] How to generate a unique hash code for string input in android...?

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