Is there functionality to generate a random character in Java?

2022-12-26 20:25 问答作者：

Does Java have any functionality to generate random characters or strings? Or must one simply pick a r开发者_JAVA百科andom integer and convert that integer's ascii code to a character?

To generate a random char in a-z:

Random r = new Random();
char c = (char)(r.nextInt(26) + 'a');

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 < 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).

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);

private static char rndChar () {
    int rnd = (int) (Math.random() * 52); // or use Random or whatever
    char base = (rnd < 26) ? 'A' : 'a';
    return (char) (base + rnd % 26);

}

Generates values in the ranges a-z, A-Z.

String abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

char letter = abc.charAt(rd.nextInt(abc.length()));

This one works as well.

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.

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
  }
}

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);

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.