CODEWITHSUNDEEP
javastringrandom
San
San

Reputation: 135

How to generate a random alphanumeric string of a custom length in java?

What is the most simple way? Minimizing any imports.

This one is good:

String str = Long.toHexString(Double.doubleToLongBits(Math.random()));

But it's not perfect, for example it complicates with custom length.

Also an option: How to make this String unique?

Upvotes: 4

Views: 9128

Answers (2)

Connor Anderson
Connor Anderson

Reputation: 106

Create a String of the characters which can be included in the string:

String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

Generate an integer using the Random class and use it to get a random character from the String.

Random random = new Random();
alphabet.charAt(random.nextInt(alphabet.length()));

Do this n times, where n is your custom length, and append the character to a String.

StringBuilder builder = new StringBuilder(n);
for (int i = 0; i < n; i++) {
    builder.append(/* The generated character */);
}

Together, this could look like:

private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

public String generateString(int length) {
    Random random = new Random();
    StringBuilder builder = new StringBuilder(length);

    for (int i = 0; i < length; i++) {
        builder.append(ALPHABET.charAt(random.nextInt(ALPHABET.length())));
    }

    return builder.toString();
}

Upvotes: 7

David Soroko
David Soroko

Reputation: 9086

RandomStringUtils from commons-lang. If you don't wish to import, check out its source.

Upvotes: 3

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