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?

Answer 1

You could also use the RandomStringUtils from the Apache Commons project:

Dependency:

<dependency> 
  <groupId>org.apache.commons</groupId> 
  <artifactId>commons-lang3</artifactId> 
  <version>3.8.1</version> 
</dependency>

Usages:

RandomStringUtils.randomAlphabetic(stringLength);
RandomStringUtils.randomAlphanumeric(stringLength);

Answer 2

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 <code>nValues</code> hex chars
 */
public static char[] createRandomHexValues(int nValues) {
    char[] ret = new char[nValues];
    for (int i = 0; i < nValues; i++) {
        ret[i] = HEX_VALUES[RANDOM.nextInt(HEX_VALUES.length)];
    }
    return ret;
}

Answer 3

I use this:

char uppercaseChar = (char) ((int)(Math.random()*100)%26+65);

char lowercaseChar = (char) ((int)(Math.random()*1000)%26+97);

Answer 4

using dollar:

Iterable<Character> chars = $('a', 'z'); // 'a', 'b', c, d .. z

given chars you can build a "shuffled" range of characters:

Iterable<Character> 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 > 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);

Answer 5

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.

Answer 6

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<Integer> any : someLists(integers())) {
    //A test executed with integer lists
  }
}