Java Password Checker

Question

My problem is to create a password that contains between 6 and 10 characters and contains at least one letter and one digit, and then to have the user re-enter the password and confirm that they match.

The only issue I have is checking to see if the password has a letter or digit. I have browsed and found the same problem on the website, but I was confused about some of the methods and other things they referenced in their code since I seemed to build mine differently. I thought about using the indexOf() method to see if it returned a -1 value, but I'm not really sure where to begin.

I'm really new at java and I'm sure there is a much more efficient way to construct this, and I would love any tips.

import java.util.Scanner;
public class Password
{
   public static void main(String[] args)
   {
      //Input from user
      String password;
      Scanner input = new Scanner(System.in);
      System.out.print("Please create your password: ");
      password = input.nextLine();

      //Checking password length
      while( (password.length() < 6) || (password.length() > 10) )
      {
         System.out.print("This password must be between 6 and 10 characters. Try again: ");
         password = input.nextLine();
      }

      //Checking to see if passwords contain digit/letter
      /*Need to add code here */

      //Confirming if passwords match   
      String password2;   
      System.out.print("\nPlease type your password again to confirm: ");
      password2 = input.nextLine();

      while( !password2.equals(password) )
      {
         System.out.print("Those passwords do not match. Try again: ");
         password2 = input.nextLine();
      }

   }
} 

Answer 1

With Regex

You should use a regular expression, to check for theese crits.

First, the code:

pwd.matches("^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).{6,10}$")

Here's a full example:

public class HelloWorld{    
     public static void main(String []args){
        String password = "aA2";
        String regexp = "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).{6,10}$";
        System.out.println(password.matches(regexp));
        password = "12345678";
        System.out.println(password.matches(regexp));
        password = "aA345678";
        System.out.println(password.matches(regexp));
     }
}

gives the following output:

false
false
true

The regexp matches any string, that conatins at least upper case, one lower case letter and one digit, and 6 - 10 character long.

You can find more examples of theese here. And some info about the regexps on the Wikipedia. A very good tutorial about regexps and Java can be found on Vogella. (It's a very good site, with very good tutorials, I think!) And, a handy tool to display what a regexp matches: http://www.regexper.com/

In case of the previous example, it gives you a very visually output.

Without Regexs

So, if you cannot use Regulax Expressions, I would create a function, which returns true, if the password is OK, false in any other case. Here's a small example for this function:

public static boolean passwordOk(String password){
    if (password == null) return false;
    if (password.length() < 6 || password.length() > 10) return false;
    boolean containsUpperCase = false;
    boolean containsLowerCase = false;
    boolean containsDigit = false;
    for(char ch: password.toCharArray()){
        if(Character.isUpperCase(ch)) containsUpperCase = true;
        if(Character.isLowerCase(ch)) containsLowerCase = true;
        if(Character.isDigit(ch)) containsDigit = true;
    }
    return containsUpperCase && containsLowerCase && containsDigit;
}

The main idea thing in this solution, is a for-each loop. I create a character array from the String, and loop over the elements of it. If the current character is a digit, or uppercase, or lowercase, I set a flag, to sign, that one of the statements are true. At the beginning, all of the statements are false, and at the end I'll return the result of their sum.

In the first two lines I check, if the argument isn't null, and if it has the right length.

I hope, that after this you'll be able to solve your homework! You can call this function even with null pointers, so I would create a while loop, to run while this function do not returns true.

If it's hopeless, to solve this problem, here's the full code.
Believe me, it'll be more useful, if you try to solve this by your own, first!

Answer 2

You can use something like this...

if( password.matches(".*[a-zA-Z]+.*")){
     System.out.println( "Has characters ");
} else {
     System.out.println("Ok");   
}

This is to check if the password contains a letter

Similarly you can use the regular expression ".*[0-9]+.*" to check if the password contains a digit.