Random String of Characters in Java. Different Examples.

In this Java tutorial, I am going to share with you different ways how to generate a random string of characters. You will learn to generate the following types of random Strings of characters:

• alpha-numeric String of characters of any length or of a specific length,
• Letters only,
• Numbers only.

I hope you will find this tutorial useful.

Generate a Random String Using UUID

One of the easiest and quickest ways to generate a random alpha-numeric String of characters is probably to use the UUID, which stands for a Universal Unique Identifier and is a 128-bit number used to uniquely identify some object or entity on the Internet.

The String is generated using a cryptographically strong pseudo-random number generator. For this code to work, you do not need to add to your project any external third-party libraries.

Here is a complete example you can copy and run on your computer.

import java.util.UUID;
 
public class UUIDExample {
    public static void main(String[] args)
    {
        String uuid = UUID.randomUUID().toString();
        System.out.println(uuid);
    }
}

The output is 36 characters long: 5d87ab34-f9c1-4424-851c-58c9eddf21ff

You can also remove the dashes from the resulting String in the following way:

import java.util.UUID;
 
public class UUIDExample {
    public static void main(String[] args)
    {
        String uuid = UUID.randomUUID().toString();
        System.out.println(uuid + " of length " + uuid.length());
        
        // Remove dashes 
        String uuid2 = uuid.replaceAll("-", "");
        System.out.println(uuid2);
    }
}

The output is 32 characters long: 5d87ab34f9c14424851c58c9eddf21ff

Generate a Random String of Any Length

The below example generates a random alpha-numeric String of characters of a specific length. You can use it to generate a random string of characters of any length you need. For this code to work, you do not need to add to your project any external third-party libraries.

public class RandomStringExample {
    
    private final Random RANDOM = new SecureRandom();
    private final String ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";


    public static void main(String[] args) {

        RandomStringExample randomStringExample = new RandomStringExample();
        String randomString = randomStringExample.generateRandomString(30);
        
        System.out.println(randomString);
    }

    private String generateRandomString(int length) {
        StringBuilder returnValue = new StringBuilder(length);

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

        return new String(returnValue);
    }
}

The output is 30 characters long, but it could be 130 characters long: niq4ZtRZdN7rfSu81dyqy0oYhq7mmc

Random String of Any Length with Apache Commons

The below code examples uses Apache Commons Lang library to generate a random alpha-numeric string of characters. The advantage of this approach is that you can generate different types of random Strings:

• Generate a Random String of any length,
• Alpha-numeric String,
• A string of letters only,
• A string of numbers only.

Which is pretty cool.

package codeexamples;

import org.apache.commons.lang3.RandomStringUtils;

 
public class RandomStringWithApache {

    public static void main(String[] args) {
        int length = 30;
        boolean includeLetters = true;
        boolean includeNumbers = true;
       
        String randomString = RandomStringUtils.random(length, includeLetters, includeNumbers);

        System.out.println(randomString);
    }
}

If you are interested in learning more about Java and like learning by watching a series of step-by-step video tutorials, then have a look at the below list of online video courses that teach Java.

You will also find a lot of free video tutorials on this site. For example, check out this section with Spring Boot video tutorials for beginners.