Hope some smart guys can help me with this Java! Thank you! Consider a system th

Question

Hope some smart guys can help me with this Java! Thank you!

Consider a system that requires unique user names. A method called checkUserName (below) takes in a user name and a list of existing names. If the user name already exists, this is considered an erroneous situation.

There are three parts to this question:

Part A: Write the class to represent the erroneous situation.

Part B: Write code to use this class to indicate the error has occurred.

Part C: Does your Part B code require any changes to the method header?

// Part A: Write your own class to represent the erroneous situation.

public void checkUserName(String userName, ArrayList<String> existingNames) { // Part C: Any changes required to the method header based on your code in Part B?

if(existingNames.contains(userName) {

// Part B: What code goes here?

} else {

existingNames.add(userName);

}

}

Explanation / Answer

/**The java program that throws an error message if the duplicate value is passed to the checkUserName
* method using DuplicateNameError class.

Create a Class called DuplicateNameError that handles the exceptio for part B

*/

//PartA program
//ArrayListProgram.java
import java.util.ArrayList;
public class ArrayListProgram {
   public static void main(String[] args) throws DuplicateNameError {      
       //Create an ArrayList of type string
       ArrayList<String>names=new ArrayList<String>();
       names.add("Johnson");
       names.add("Micheal");
       names.add("Gupta");
       names.add("Singh");
      
       //calling checkUserName
       checkUserName("Gupta", names);

   }

   /**The method checkUserName that takes string user name and
   * an ArrayList as input arguments and calls the method contains
   * to check if the username is exists then thorws an exception
   * DuplicateNameError */
   public static void checkUserName(String userName, ArrayList<String> existingNames) throws DuplicateNameError
   {
       if(existingNames.contains(userName)) {
           throw new DuplicateNameError(userName+" is already exists.");
       } else {
           //otherwise call add method to username to the existingNames array
           existingNames.add(userName);
       }
   }
}

--------------------------------------------------------------------------------------------------------------------------------------------

//DuplicateNameError.java
//The class DuplicateNameError that extends the Exception class
public class DuplicateNameError extends Exception{

   //constructor that takes string name and
   //calls the super class with name
   public DuplicateNameError(String name) {
       super(name);
   }  
}

--------------------------------------------------------------------------------------------------------------------------------------------

Sample output:

Exception in thread "main" DuplicateNameError: Gupta is already exists.

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