Java: Check whether a string is a valid password

Last update on May 14 2025 13:03:08 (UTC/GMT +8 hours)

Validate Password

Write a Java method to check whether a string is a valid password.

Password rules:
A password must have at least ten characters.
A password consists of only letters and digits.
A password must contain at least two digits.

Sample Solution:

Java Code:

import java.util.Scanner;

public class Exercise11 {
    
public static final int PASSWORD_LENGTH = 8;

public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        System.out.print(
                "1. A password must have at least eight characters.\n" +
                "2. A password consists of only letters and digits.\n" +
                "3. A password must contain at least two digits \n" +
                "Input a password (You are agreeing to the above Terms and Conditions.): ");
        String s = input.nextLine();

        if (is_Valid_Password(s)) {
            System.out.println("Password is valid: " + s);
        } else {
            System.out.println("Not a valid password: " + s);
        }

    }

    public static boolean is_Valid_Password(String password) {

        if (password.length() < PASSWORD_LENGTH) return false;

        int charCount = 0;
        int numCount = 0;
        for (int i = 0; i < password.length(); i++) {

            char ch = password.charAt(i);

            if (is_Numeric(ch)) numCount++;
            else if (is_Letter(ch)) charCount++;
            else return false;
        }


        return (charCount >= 2 && numCount >= 2);
    }

    public static boolean is_Letter(char ch) {
        ch = Character.toUpperCase(ch);
        return (ch >= 'A' && ch <= 'Z');
    }


    public static boolean is_Numeric(char ch) {

        return (ch >= '0' && ch <= '9');
    }

}

Sample Output:

1. A password must have at least eight characters.                                                            
2. A password consists of only letters and digits.                                                            
3. A password must contain at least two digits                                                                
Input a password (You are agreeing to the above Terms and Conditions.): abcd1234                              
Password is valid: abcd1234

Flowchart:

For more Practice: Solve these Related Problems:

Write a Java program to validate a password that must contain at least one special character in addition to letters and digits.
Write a Java program to assess password strength by checking for uppercase, lowercase, digits, and symbols.
Write a Java program to validate a password using regular expressions and provide specific error messages for each rule violation.
Write a Java program to check if a password is valid when it must start with a letter and contain no whitespace.

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