public RandomStringUtils() 
{
                                        
      super();
}

RandomStringUtils instances should NOT be constructed in standard programming. Instead, the class should be used as RandomStringUtils.random(5);.

This constructor is public to permit tools that require a JavaBean instance to operate.

 public static String random(int count) 
{
        return random(count, false, false);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of all characters.

 public static String random(int count,
    String chars) 
{
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, chars.toCharArray());
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of characters specified.

 public static String random(int count,
    char[] chars) 
{
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, 0, chars.length, false, false, chars, RANDOM);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of characters specified.

 public static String random(int count,
    boolean letters,
    boolean numbers) 
{
        return random(count, 0, 0, letters, numbers);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of alpha-numeric characters as indicated by the arguments.

 public static String random(int count,
    int start,
    int end,
    boolean letters,
    boolean numbers) 
{
        return random(count, start, end, letters, numbers, null, RANDOM);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of alpha-numeric characters as indicated by the arguments.

 public static String random(int count,
    int start,
    int end,
    boolean letters,
    boolean numbers,
    char[] chars) 
{
        return random(count, start, end, letters, numbers, chars, RANDOM);
}

Creates a random string based on a variety of options, using default source of randomness.

This method has exactly the same semantics as #random(int,int,int,boolean,boolean,char[],Random) , but instead of using an externally supplied source of randomness, it uses the internal static Random instance.

 public static String random(int count,
    int start,
    int end,
    boolean letters,
    boolean numbers,
    char[] chars,
    Random random) 
{
        if (count == 0) {
            return "";
        } else if (count <  0) {
            throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
        }
        if ((start == 0) && (end == 0)) {
            end = 'z" + 1;
            start = ' ";
            if (!letters && !numbers) {
                start = 0;
                end = Integer.MAX_VALUE;
            }
        }
        char[] buffer = new char[count];
        int gap = end - start;
        while (count-- != 0) {
            char ch;
            if (chars == null) {
                ch = (char) (random.nextInt(gap) + start);
            } else {
                ch = chars[random.nextInt(gap) + start];
            }
            if ((letters && Character.isLetter(ch))
                || (numbers && Character.isDigit(ch))
                || (!letters && !numbers)) 
            {
                if(ch  >= 56320 && ch < = 57343) {
                    if(count == 0) {
                        count++;
                    } else {
                        // low surrogate, insert high surrogate after putting it in
                        buffer[count] = ch;
                        count--;
                        buffer[count] = (char) (55296 + random.nextInt(128));
                    }
                } else if(ch  >= 55296 && ch < = 56191) {
                    if(count == 0) {
                        count++;
                    } else {
                        // high surrogate, insert low surrogate before putting it in
                        buffer[count] = (char) (56320 + random.nextInt(128));
                        count--;
                        buffer[count] = ch;
                    }
                } else if(ch  >= 56192 && ch < = 56319) {
                    // private high surrogate, no effing clue, so skip it
                    count++;
                } else {
                    buffer[count] = ch;
                }
            } else {
                count++;
            }
        }
        return new String(buffer);
}

Creates a random string based on a variety of options, using supplied source of randomness.

If start and end are both 0, start and end are set to ' ' and 'z', the ASCII printable characters, will be used, unless letters and numbers are both false, in which case, start and end are set to 0 and Integer.MAX_VALUE.

If set is not null, characters between start and end are chosen.

This method accepts a user-supplied Random instance to use as a source of randomness. By seeding a single Random instance with a fixed seed and using it for each call, the same random sequence of strings can be generated repeatedly and predictably.

 public static String randomAlphabetic(int count) 
{
        return random(count, true, false);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of alphabetic characters.

 public static String randomAlphanumeric(int count) 
{
        return random(count, true, true);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of alpha-numeric characters.

 public static String randomAscii(int count) 
{
        return random(count, 32, 127, false, false);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of characters whose ASCII value is between 32 and 126 (inclusive).

 public static String randomNumeric(int count) 
{
        return random(count, false, true);
}

Creates a random string whose length is the number of characters specified.

Characters will be chosen from the set of numeric characters.