Password Verification Program Java

Question

The below are the instructions and my code that I have tried so far. I am almost done but just having problems with part four. So the expected output should be:

Please enter a password: abc
Password much have at least 8 characters 
Please enter a password: abcd1234$
Password must only contain letter and digits
Please enter a password: ####
Password must have at least 8 characters
Password must only contain letters and digits
Please enter a password: abcd1234
Password accepted!

When I type abc this is what I get:

Please enter password and then hit enter:abc
Password must have at least 8 characters
Password Accepted

When I do this the program ends! Could someone help me with this?

Problem

1. Write a program that prompts the user to enter a password.
2. Create a boolean variable named valid and set it to true. If any of these tests below fail, set it to true.
3. Check the password to see if it has at least 8 characters. If it does not, display the message, "Password must have at least 8 characters"

4. Check the password to see if it consists of only letter and digits. To do this, you will need to loop through all of the characters in the string. A character c is a letter of digit if this expression is true:

   ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || ('0' <= c && c <= '9')

if this is even not true, break from your loop and display the message, "Password must contain only letter and digits" 5. If valid is still true at the end of the program, display the message, "Password accepted!"

My code

    import java.util.Scanner; 
    public class PasswordVerification {

        public static void main(String[] args) {
            //Creates a scanner
            Scanner sc = new Scanner(System.in);
            boolean valid = false; 
            String password;


            //Asks user to enter password
            System.out.print("Please enter password and then hit enter:");
            password = sc.nextLine(); 

            //Checks to see if password is at least 8 characters. 
            if (password.length()<8) 
                {
                    valid = false;
                    System.out.println("Password must have at least 8 characters");
                }

            //Checks each character to see if it is acceptable.
            for (int i = 0; i < password.length(); i++){
                        char c = password.charAt(i);

                        if (       ('a' <= c && c <= 'z') // Checks if it is a lower case letter
                                || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter
                                || ('0' <= c && c <= '9') //Checks to see if it is a digit
                        ) 
                        {

                            valid = true;
                        } 

                        else 
                        {
                            // tells the user that only letters & digits are allowed
                            System.out.println("Only letter & digits are acceptable.");
                            valid = false;
                            break;
                        }

            }

            // if the password is valid, tell the user it's accepted
            System.out.println("Password Accepted");
            }


    }

Answer 1

As @cralfaro stated you have to repeat the process if the password is invalid:

import java.util.Scanner; 
public class PasswordVerification {

    public static void main(String[] args) {
        //      Creates a scanner
        Scanner sc = new Scanner(System.in);
        boolean valid = false; 
        String password;

        do { // start a loop
            //      Asks user to enter password
            System.out.print("Please enter password and then hit enter:");
            password = sc.nextLine(); 

            //      Checks to see if password is at least 8 characters. 
            if (password.length()<8) 
            {
                valid = false;
                System.out.println("Password must have at least 8 characters");
                continue; // skip to next iteration
            }

            //      Checks each character to see if it is acceptable.
            for (int i = 0; i < password.length(); i++){
                char c = password.charAt(i);

                if (       ('a' <= c && c <= 'z') // Checks if it is a lower case letter
                        || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter
                        || ('0' <= c && c <= '9') //Checks to see if it is a digit
                ) 
                {

                    valid = true;
                }
                else 
                {
                    // tells the user that only letters & digits are allowed
                    System.out.println("Only letter & digits are acceptable.");
                    valid = false;
                    break;
                }

            }
        } while(!valid); // verify if the password is valid, if not repeat the process

        // if the password is valid, tell the user it's accepted
        System.out.println("Password Accepted");
    }


}

In this way the program will continue to ask the user input if the password is not valid.

EDIT: Thanks to GC_'s comment, the problem was that I missed a continue statement in the first check.

Answer 2

Your problem ist this part of code:

if (    ('a' <= c && c <= 'z') // Checks if it is a lower case letter
     || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter
     || ('0' <= c && c <= '9') //Checks to see if it is a digit
    ) { valid = true; }

Here you reset valid to true, even if the first check with the length being less than 8 already failed. So abc will fail 3. and print Password must have at least 8 characters which is fine. Then it will pass 4., reset valid to true and print Password Accepted.

So you want the replace the if (...) { valid = true; } else { ... } part by

if (!( // if the character is none of the options below, print error
       ('a' <= c && c <= 'z') // Checks if it is a lower case letter
    || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter
    || ('0' <= c && c <= '9') //Checks to see if it is a digit
    )) { 
        // tells the user that only letters & digits are allowed
        System.out.println("Only letter & digits are acceptable.");
        valid = false;
        break; 
    }

Edit: Also you should initially set boolean valid = true; instead of false, as you want to set it to false only if it fails a condition. Then at the end of your code, add a condition checking valid around the last output line, like

if(valid) {
    System.out.println("Password Accepted");
}

Answer 3

A little messy but try this:

public static void main(String[] args) {
//      Creates a scanner
Scanner sc = new Scanner(System.in);
boolean valid = false; 
String password;


//      Asks user to enter password
while(true){
System.out.print("Please enter password and then hit enter:");
password = sc.nextLine(); 

//      Checks to see if password is at least 8 characters. 
if (password.length()<8) 
    {
        valid = false;
        System.out.println("Password must have at least 8 characters");
    }
else {

//      Checks each character to see if it is acceptable.
for (int i = 0; i < password.length(); i++){
            char c = password.charAt(i);

            if (       ('a' <= c && c <= 'z') // Checks if it is a lower case letter
                    || ('A' <= c && c <= 'Z') //Checks if it is an upper case letter
                    || ('0' <= c && c <= '9') //Checks to see if it is a digit
            ) {
                valid = true;
            } else {
                System.out.println("Password denied");
                System.out.println("Only letter & digits are acceptable.");
                valid = false;
                break;
            }


}

if (valid == true) {
System.out.println("Password accepted");
    break;
        }            
}
}
}

Answer 4

Add a check to see if the password is still valid before printing that the password is accepted.

if(valid==true) {
    System.out.println("Password Accepted");
}

EDIT: You can also add this.

else {
    System.out.println("Password Denied");
}