Password Verifier

The problem

Imagine you are developing a software package for Amazon.com that requires users to enter their own passwords. Your software requires that users' passwords meet the following criteria:

The password should be at least six characters long.
The password should contain at least one uppercase and at least one lowercase letter.
The password should have at least one digit.

Write a class that verifies that a password meets the stated criteria. Demonstrate the class in a program that allows the user to enter a password and then displays a message indicating whether it is valid or not.

Breaking it down

Password class

This exercise will use java 8 predicates extensively. A predicate is often used in mathematics that something that takes a value for an argument and then returns true or false. Each logic check is a java.util.function.Predicate and the isValid method will chain each predicate together validating the requirements in the problem. The Character:isDigit, Character:isLowerCase and Character:isUpperCase return a predicate so we could of removed the wrapping predicate but if the logic were to change it would require us rewrap.

static class Password {

    private String password;

    public Password(String password) {
        this.password = password;
    }

    public boolean isValid() {
        return hasUpperCase.and(hasLowerCase).and(hasLengthOfSix)
                .and(hasAtLeastOneDigit).test(this.password);
    }

    Predicate<String> hasAtLeastOneDigit = new Predicate<String>() {
        @Override
        public boolean test(String t) {
            return t.chars().anyMatch(Character::isDigit);
        }
    };

    Predicate<String> hasLengthOfSix = new Predicate<String>() {
        @Override
        public boolean test(String t) {
            return t.length() >=6 ? true : false;
        }
    };

    Predicate<String> hasLowerCase = new Predicate<String>() {
        @Override
        public boolean test(String t) {
            return t.chars().anyMatch(Character::isLowerCase);
        }
    };

    Predicate<String> hasUpperCase = new Predicate<String>() {
        @Override
        public boolean test(String t) {
            return t.chars().anyMatch(Character::isUpperCase);
        }
    };
}

Main

public static void main(String[] args) {

    // Create a Scanner object for keyboard input.
    Scanner keyboard = new Scanner(System.in);

    // get password to verify logic
    System.out.print("Enter a string to represent password: ");
    String input = keyboard.nextLine();

    // close keyboard
    keyboard.close();

    // validate
    Password password = new Password(input);

    boolean validPassword = password.isValid();

    System.out.println("The password of " + input + "is "
            + (validPassword ? " valid password " : " an invalid password"));

}

Output

Enter a string to represent password: jwef2323
The password of jwef2323 is an invalid password