Password Program

Here is a program for generating random passwords:

import java.util.*;

public class PasswordGenerator
{
  public static void main ( String[] args )
  {
    Scanner scan = new Scanner( System.in );
    Random rand = new Random();    
    int digits = 0;
    
    // Ensure that the password is 5 or more characters
    while ( digits < 5 )
    {
      System.out.println("Your password must have at least 5 characters.");
      System.out.print("How many characters do you want in your password? ");
      digits = scan.nextInt();
    }
    
    // Create a long string of characters to randomly pick from
    String choices = "abcdefghijklmnopqrstuvwxyz" ;
    choices = choices + choices.toUpperCase() ;
    choices = choices + "1234567890" ;

    String password = "";
    int j = 0;
    
    // Randomly pick characters from the string
    while ( j<digits )
    {
      password = password + choices.charAt( rand.nextInt( choices.length() ) );
      j = j + 1;
    }
    
    System.out.println("Here is your password: " + password );
  }
}

Here are a few runs of the program:

K:\>java PasswordGenerator
Your password must have at least 5 characters.
How many characters do you want in your password? 4
Your password must have at least 5 characters.
How many characters do you want in your password? 3
Your password must have at least 5 characters.
How many characters do you want in your password? 8
Here is your password: BaXpmUsA

K:\>java PasswordGenerator
Your password must have at leas 5 characters.
How many characters do you want in your password? 12
Here is your password: ly3YFAhM8HDH

The details of this program are explained in the next few pages.

while ( digits < 5 )
{
  System.out.println("Your password must have at least 5 characters.");
  System.out.print("How many characters do you want in your password? ");
  digits = scan.nextInt();
}