Write A Java Program To Check If A String Is Valid

Write a Java program that checks whether a string is a valid password

Suppose the password rules are as follows: A password must have exactly eight characters. A password consists of only letters and digits. No punctuations or special symbol is allowed. A password must contain at least two digits. The first and last character must be a digit. No two digits or characters can be the same. You are to write a Java application (no regular expression is allowed) to allow users to register their password. Loop must be used to validate each character (marks will be deducted if no loop is not used).

Paper For Above instruction

The task of devising a Java program to validate a password based on specific rules involves careful consideration of input validation, string processing, and control flow structures. The password validation rules include constraints on length, character composition, digit inclusion, positional requirements, and uniqueness of characters. This comprehensive implementation ensures that passwords conform strictly to security and formatting standards, thereby enhancing application robustness.

The core of the validation process begins with prompting the user to input a password string, which will be evaluated against each criterion. Given the restriction of not using regular expressions, the validation relies on iterative loops and explicit character checks, providing a clear and controlled method to analyze each input character. The primary steps involve verifying length, character types, digit counts, positional digit placement, and duplicate characters. These checks collectively maintain the integrity of the password, making it suitable for secure registration.

The implementation employs a while loop to verify character content, ensuring that every character in the password is either a letter or a digit. This looping mechanism facilitates character-by-character validation, respecting the rule that no special symbols or punctuations are allowed. During the iteration, counters track the number of digits, and a comparison against previous characters ensures that duplicates are not present. The process repeats until the user inputs a valid password, with explicit prompts guiding corrections based on where the failure occurred.

Furthermore, the program incorporates checks for positional digit placement—the first and last characters must be digits—which are verified immediately after length and character type validation. The digit counting process confirms that at least two digits are present in total. To prevent duplication, the program maintains an array of characters encountered so far and compares each new character to this array during validation.

By combining these sequential validation steps within loops, the program ensures comprehensive assessment of the password input. It enhances user interaction by providing specific feedback on validation failures, prompting for re-entry until all conditions are satisfied. This iterative approach aligns with best practices in input validation, security protocols, and user interface design for registration systems.

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