Question

I)

will create a rudimentary (and highly insecure) database for the storage of only the user generated identities. This

program will have the following behaviors:

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) - Prior to prompting for a new username, the existing list of usernames should be read and loaded

to an array.

1 ) Read the list from "users.txt", a prompt is not necessary. Do not change this data file name "users.txt".

2 ) The existing list of usernames should be displayed to the console (screen).

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username.

) - Upon prompting, the following checks must be made against an attempt to create a new

1 ) Duplicate usernames should be disallowed, and the usernames are case sensitive.

2 ) Usernames must be between 4 and 7 characters in length.

3 ) Username must have lower-case AND upper case.

4) a letter like [a-z A-Z]
5) have at least one number like [0-9]
6) have at least one of these special characters [!, #, ?]

C) (6 / 30 pts.

D) (8 / 30 pts.

-10 pts.

Usernames must start with

Usernames must Usernames must

7) If the rules from 1-6 are violated, an appropriate error message informing the user should be displayed.

i ) The error message should display *all* the reasons why the username is not correct.

ii ) Do not display merely the first problem the program identifies (unless, of course, the first problem is

the only problem).

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) - When a valid username is provided, this username should be written to an array and displayed

back to console.

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) - Finally, the "users.txt" database should be updated such that the new username appears should

the program be run again.

–

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E) (

) - Include appropriate program documentation and formatting including:

1) Your first and last name

2) Your contact information

3) Your student ID number

4) The date

5) A short description of the program’s function

6) Comments necessary to explain the operation of your program

7) Proper indentation

*Note that your student list may vary from the one below.

List of Usernames

Create a new user: bellevuecollege

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F) Save your file as “UserNames

.java” and upload to Canvas.(line break, 11 pt)

II ) A Sample log of execution is as follow (user inputs are in bold and underlined):

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Usernames must have at least one number

Usernames must have at least one number.
Usernames must have at least one special character. Usernames must have lower-case and upper-case.

a letter.

April4!

March3#

June!6

Create a new user: December!

Invalid Name.

Name too long.

  

Invalid Name.

Name too long.

Create a new user: April4!

Invalid Name. Name already in use.

Create a new user: 4!July

Invalid Name. Name must start with

Create a new user: July4!

User "July4!" added successfully!

List of Usernames

April4!

March3#

June!6

July4!

Answer 1

The java code is attached here

UserNames.java

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
import java.util.regex.Pattern;

public class UserNames {
  
   public static void main(String[] args) throws IOException {
      
       File f = new File("users.txt");
      
       //To determine if the string is invalid or valid
       boolean flag = false;
      
       Scanner s = new Scanner(new FileReader(f));
      
       //To store the list of users from text files
       String[] users = new String[100];
      
      
       String user = null;
      
       //Used for indexing through the array
       int i = 0;
       System.out.println("List of Usernames");
      
       while(s.hasNext())
       {
           user = s.nextLine();
           System.out.println(user);
           users[i] = user;
           i++;
       }
      
       Scanner s1 = new Scanner(System.in);

//To open the file in append mode
       BufferedWriter bw = new BufferedWriter(new FileWriter(f,true));
      
       System.out.println("Create a new user: ");
       String userName = s1.nextLine();
      
       for(String us:users)
       {
           if(us!= null && us.equals(userName))
           {
               System.out.println("Invalid Name. Name already in use.");
               flag = true;
           }
       }
      
       //To see that the userName is of valid length
       if(userName.length() < 4 || userName.length() > 7)
       {
           System.out.println("Invalid Name.Name too long");
           flag = true;
       }
      
       //To see if the username has one or more uppercase or lowercase letter
       if(!Pattern.matches(".*[a-zA-Z].*", userName))
       {
           System.out.println("Username doesn't have a lower case or upper case letter");
           flag = true;
       }
      
       //To see if username contains numbers
       if(!Pattern.matches(".*[0-9].*", userName))
       {
           System.out.println("Username doesn't have a number");
           flag = true;
       }
      
       //To see if the userName starts with alphabets
       if(!Pattern.matches(".*^[a-zA-Z].*", userName))
       {
           System.out.println("Invalid Name. Name must start with alphabets");
           flag = true;
       }
      
       //To see if the username has the following special characters
       if(!Pattern.matches(".*[!,#,?].*", userName))
       {
           System.out.println("Username doesn't have special characters");
           flag = true;
       }  
      
       //If the userNames passes all test,store it in the database
       if(!flag)
       {
           bw.append("\n" + userName);
           System.out.println("User " + userName + " added successfully!");
       }
      
       s.close();
       s1.close();
       bw.close();
   }
  
}

The screenshot of the code:-

The sampleoutput of the code :-