Random Password Generator in Java — Rules, Examples and Program

Random Password Generator in Java

A random password generator is commonly used in real-world applications such as account creation, password reset systems, and security tools.

In this program, we generate a strong password by combining uppercase letters, lowercase letters, digits, and special characters.

Password Generation Rules

The generated password will:

• Contain uppercase letters (A–Z)
• Contain lowercase letters (a–z)
• Contain digits (0–9)
• Contain special characters
• Have a user-defined length

Example

Input: Password Length = 10

Output: A9@kP3#xT2

Logic Explanation

1. Create a string containing all allowed characters.
2. Use Java’s Random class to generate random indexes.
3. Select characters randomly from the allowed set.
4. Repeat until the desired password length is reached.

Java Program to Generate Random Password

import java.util.Random;
import java.util.Scanner;

public class RandomPasswordGenerator {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter password length: ");
        int length = sc.nextInt();

        String upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        String lower = "abcdefghijklmnopqrstuvwxyz";
        String digits = "0123456789";
        String special = "!@#$%^&*()_+-={}[]|:;<>,.?/";

        String allChars = upper + lower + digits + special;

        Random random = new Random();
        String password = "";

        for (int i = 0; i < length; i++) {
            int index = random.nextInt(allChars.length());
            password = password + allChars.charAt(index);
        }

        System.out.println("Generated Password: " + password);
    }
}

Sample Output

Enter password length: 12
Generated Password: A@9kL3#xP7!Q

Important Notes

• Password strength increases with length.
• Each run generates a different password.
• Characters may repeat.

Practice Challenges

1. Ensure at least one uppercase, lowercase, digit, and special character.
2. Generate password without repeating characters.
3. Allow user to choose which character sets to include.
4. Generate multiple passwords at once.

Random password generation is a practical application of strings, random numbers, and security concepts in Java.