Is there functionality to generate a random character in Java

Question

Does Java have any functionality to generate random characters or strings   Or must one simply pick a random integer and convert that integer s ascii code to a character

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In fact mentioned methods don t generate real random char  To generate real random char you should give it a random seed  in example time in millisecond  this code generate 10 random char and then Convert it to String   import java util Random  public class MyClass       public static void main           String randomKey       char   tempArray  0 0 0 0 0 0 0 0 0 0      ten characters      long seed System currentTimeMillis        Random random new Random seed       for  int aux 0  aux lt 10 aux              tempArray aux   char  random nextInt 255           System out println tempArray aux               randomKey String copyValueOf tempArray             System out println randomKey

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Here is the code to generate random alphanumeric code  First you have to declare a string of allowed characters what you want to include in random number and also define max length of string   SecureRandom secureRandom   new SecureRandom     String CHARACTERS    ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789       StringBuilder generatedString  new StringBuilder        for  int i   0  i  lt  MAXIMUM LENGTH  i              int randonSequence   secureRandom  nextInt CHARACTERS length             generatedString append CHARACTERS charAt randonSequence            Use toString   method to get String from StringBuilder

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java util Random is the more effective one I have tried out so far  having a precision of 98 65  uniqueness  I have provided bellow some tests which generate 10000 batches of a hundred 2 alphanumeric chars strings and calculates the average  Other random tools were RandomStringUtils from commons lang3 and java util Math  public static void main String   args        int unitPrintMarksTotal   0      for  int i   0  i  lt  10000  i              unitPrintMarksTotal    generateBatchOfUniquePrintMarks i              System out println  quot The precision across 10000 runs with 100 item batches is   quot     float  unitPrintMarksTotal   10000      private static int generateBatchOfUniquePrintMarks int batch        Set lt String gt  printMarks   new HashSet lt  gt         for  int i   0  i  lt  100  i              printMarks add generatePrintMarkWithJavaUtil                System out println  quot Batch  quot    batch    quot  Unique number of elements is  quot    printMarks size          return printMarks size          the best so far   gt  98 65    with 3 chars   gt  99 98    with 4 chars   gt  99 9997 private static String generatePrintMarkWithJavaUtil         int leftLimit   48     numeral  0      int rightLimit   122     letter  z      int targetStringLength   2      String printMark      do           printMark   new Random   ints leftLimit  rightLimit   1                   filter i - gt   i  lt   57    i  gt   65   amp  amp   i  lt   90    i  gt   97                    limit targetStringLength                   collect StringBuilder  new  StringBuilder  appendCodePoint  StringBuilder  append                   toString          while   isValid printMark         return printMark        95 46 private static String generatePrintMarkWithCommonsLang3         String printMark      do           printMark   RandomStringUtils randomAlphanumeric 2  toUpperCase          while   isValid printMark         return printMark        95 92 private static String generatePrintMarkWithMathRandom         final String ALPHA NUMERIC STRING    quot ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 quot       StringBuilder printMark      do           printMark   new StringBuilder            int i    int   Math random     ALPHA NUMERIC STRING length             printMark append ALPHA NUMERIC STRING charAt i            int j    int   Math random     ALPHA NUMERIC STRING length             printMark append ALPHA NUMERIC STRING charAt j          while   isValid printMark toString           return printMark toString       private static boolean isValid final String printMark        return true

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polygenelubricants  answer is also a good solution if you only want to generate Hex values       A list of all valid hexadecimal characters     private static char   HEX VALUES      0    1    2    3    4    5    6    7    8    9    0    A    B    C    D    E    F          Random number generator to be used to create random chars     private static Random RANDOM   new SecureRandom            Creates a number of random hexadecimal characters          param nValues the amount of characters to generate         return an array containing  lt code gt nValues lt  code gt  hex chars     public static char   createRandomHexValues int nValues        char   ret   new char nValues       for  int i   0  i  lt  nValues  i              ret i    HEX VALUES RANDOM nextInt HEX VALUES length              return ret

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To generate a random char in a-z   Random r   new Random    char c    char  r nextInt 26     a

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You could also use the RandomStringUtils from the Apache Commons project   Dependency    lt dependency gt      lt groupId gt org apache commons lt  groupId gt      lt artifactId gt commons-lang3 lt  artifactId gt      lt version gt 3 8 1 lt  version gt    lt  dependency gt    Usages   RandomStringUtils randomAlphabetic stringLength   RandomStringUtils randomAlphanumeric stringLength

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In following 97 ascii value of small  a       public static char randomSeriesForThreeCharacter     Random r   new Random    char random 3 Char    char   97   r nextInt 3    return random 3 Char      in above 3 number for a   b   c or d and if u want all character like a to z then you replace 3 number to 25

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I use this   char uppercaseChar    char    int  Math random   100  26 65    char lowercaseChar    char    int  Math random   1000  26 97

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My propose for generating random string with mixed case like   DthJwMvsTyu   This algorithm based on ASCII codes of letters when its codes a-z  97 to 122  and A-Z  65 to 90  differs in 5th bit  2 5 or 1  lt  lt  5 or 32    random nextInt 2   result is 0 or 1   random nextInt 2   lt  lt  5  result is 0 or 32   Upper A is 65 and lower a is 97  Difference is only on 5th bit  32  so for generating random char we do binary OR     random charCaseBit  0 or 32  and random code from A to Z  65 to 90    public String fastestRandomStringWithMixedCase int length        Random random   new Random        final int alphabetLength    Z  -  A    1      StringBuilder result   new StringBuilder length       while  result length    lt  length            final char charCaseBit    char   random nextInt 2   lt  lt  5           result append  char   charCaseBit     A    random nextInt alphabetLength                return result toString

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public static void  main String   args           System out println  Enter a number to changeit at char          Random random   new Random         int x   random nextInt 26  65       0  to 25     System out println  char x

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Take a look at Java Randomizer class  I think you can randomize a character using the randomize char   array  method

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private static char rndChar          int rnd    int   Math random     52      or use Random or whatever     char base    rnd  lt  26     A     a       return  char   base   rnd   26        Generates values in the ranges a-z  A-Z

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Random randomGenerator   new Random        int i   randomGenerator nextInt 256      System out println  char i     Should take care of what you want  assuming you consider  0  1   2    as characters

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If you don t mind adding a new library in your code you can generate characters with MockNeat  disclaimer  I am one of the authors    MockNeat mock   MockNeat threadLocal     Character chr   mock chars   val    Character lowerLetter   mock chars   lowerLetters   val    Character upperLetter   mock chars   upperLetters   val    Character digit   mock chars   digits   val    Character hex   mock chars   hex   val

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This is a simple but useful discovery  It defines a class named RandomCharacter with 5 overloaded methods to get a certain type of character randomly  You can use these methods in your future projects       public class RandomCharacter           Generate a random character between ch1 and ch2        public static char getRandomCharacter char ch1  char ch2            return  char   ch1   Math random      ch2 - ch1   1                   Generate a random lowercase letter        public static char getRandomLowerCaseLetter             return getRandomCharacter  a    z                   Generate a random uppercase letter        public static char getRandomUpperCaseLetter             return getRandomCharacter  A    Z                   Generate a random digit character        public static char getRandomDigitCharacter             return getRandomCharacter  0    9                   Generate a random character        public static char getRandomCharacter             return getRandomCharacter   u0000     uFFFF              To demonstrate how it works let s have a look at the following test program displaying 175 random lowercase letters   public class TestRandomCharacter           Main method        public static void main String   args            final int NUMBER OF CHARS   175          final int CHARS PER LINE   25             Print random characters between  a  and  z   25 chars per line         for  int i   0  i  lt  NUMBER OF CHARS  i                  char ch   RandomCharacter getRandomLowerCaseLetter                if   i   1    CHARS PER LINE    0                  System out println ch               else                 System out print ch                       and the output is     if you run one more time again     I am giving credit to Y Daniel Liang for his book Introduction to Java Programming  Comprehensive Version  10th Edition  where I cited this knowledge from and use in my projects    Note  If you are unfamiliar with overloaded methhods  in a nutshell Method Overloading is a feature that allows a class to have more than one method having the same name  if their argument lists are different

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There are many ways to do this  but yes  it involves generating a random int  using e g  java util Random nextInt  and then using that to map to a char  If you have a specific alphabet  then something like this is nifty       import java util Random                  Random r   new Random         String alphabet    123xyz       for  int i   0  i  lt  50  i              System out println alphabet charAt r nextInt alphabet length                prints 50 random characters from alphabet     Do note that java util Random is actually a pseudo-random number generator based on the rather weak linear congruence formula  You mentioned the need for cryptography  you may want to investigate the use of a much stronger cryptographically secure pseudorandom number generator in that case  e g  java security SecureRandom

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You could use generators from the Quickcheck specification-based test framework   To create a random string use anyString method   String x   anyString      You could create strings from a more restricted set of characters or with min max size restrictions   Normally you would run tests with multiple values    Test public void myTest       for  List lt Integer gt  any   someLists integers             A test executed with integer lists

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String abc    ABCDEFGHIJKLMNOPQRSTUVWXYZ    char letter   abc charAt rd nextInt abc length        This one works as well

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using dollar   Iterable lt Character gt  chars      a    z        a    b   c  d    z   given chars you can build a  shuffled  range of characters   Iterable lt Character gt  shuffledChars      a    z   shuffle      then taking the first n chars  you get a random string of length n  The final code is simply   public String randomString int n        return    a    z   shuffle   slice n  toString        NB  the condition n  gt  0 is cheched by slice  EDIT   as Steve correctly pointed out  randomString uses at most once each letter  As workaround you can repeat the alphabet m times before call shuffle   public String randomStringWithRepetitions int n        return    a    z   repeat 10  shuffle   slice n  toString        or just provide your alphabet as String   public String randomStringFromAlphabet String alphabet  int n        return   alphabet  shuffle   slice n  toString       String s   randomStringFromAlphabet  00001111   4

[java] Is there functionality to generate a random character in Java?

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