Записаться на курсы Java

Question

Я работаю над кодом, который регистрирует студентов на курсы.Мне дали копию учителя, и мне нужно было написать код для метода validateChoice.Я закончил, но я все еще получаю две ошибки.Программа распознает 0 как дубликат вместо неверного номера курса и позволяет пользователю дублировать дважды, прежде чем выбросить недопустимое сообщение.Не должно быть никаких дубликатов.Любые идеи о том, почему это произойдет?Я уже включил это, потому что он работает правильно с кодами курса, которые мне дали для назначения, я просто хочу знать для личной справки.Спасибо!

/*
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 */
package u6a1_consoleregisterforcourse;

import java.util.Scanner;

/**
*
 * @author omora
 */
public class U6A1_ConsoleRegisterForCourse {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    // TODO code application logic here


    System.out.println("Kim's Copy");

    Scanner input = new Scanner(System.in);

    //choice is the current menu selection
    //firstChoice is the first menu selection mande by the user
    //secondChoice is the second menu selection mande by the user
    //thirdChoice is the third menu selection mande by the user
    // a choice of 0 means the choice has not been made yet
    int choice;
    int firstChoice = 0, secondChoice = 0, thirdChoice = 0;
    int totalCredit = 0;
    String yesOrNo = "";



    do {

        choice = getChoice(input);

        switch (ValidateChoice(choice, firstChoice, secondChoice, thirdChoice, totalCredit)) {
            case -1:
                System.out.println("**Invalid** - Your selection of " + choice + " is not a recognized course.");
                break;
            case -2:
                System.out.println("**Invalid** - You have already registerd for this " +  ChoiceToCourse(choice) + " course.");
                break;
            case -3:
                System.out.println("**Invalid** - You can not register for more than 9 credit hours.");
                break;
            case 0:
                System.out.println("Registration Confirmed for course " + ChoiceToCourse(choice) );
                totalCredit += 3;
                if (firstChoice == 0)
                    firstChoice = choice;
                else if (secondChoice == 0)
                    secondChoice = choice;
                else if (thirdChoice == 0)
                    thirdChoice = choice;
                break;
        }

        WriteCurrentRegistration(firstChoice, secondChoice, thirdChoice);

        System.out.print("\nDo you want to try again? (Y|N)? : ");

        yesOrNo = input.next().toUpperCase();

    } while (yesOrNo.equals("Y"));

    System.out.println("Thank you for registering with us");

}


public static int getChoice(Scanner input) {
    System.out.println("Please type the number inside the [] to register for a course");
    System.out.println("[1]IT4782\n[2]IT4784\n[3]IT4786\n[4]IT4789\n[5]IT2230\n[6]IT3345\n[7]IT3349");
    System.out.print("Enter your choice : ");
    return (input.nextInt());

}

//This method validates the user menu selection
//against the given registration business rules
//it returns the following code based on the validation result
// -1 = invalid, unrecognized menu selection
// -2 = invalid, alredy registered for the course
// -3 = invalid, No more than 9 credit hours allowed
// 0 = menu selection is valid
   public static int ValidateChoice(int choice, int firstChoice, int secondChoice, int thirdChoice, int totalCredit) {

    // TO DO - Add Code to:
    // Validate user menu selection (the int choice method arguement)
    // against the given registration business rules
    int result = 0;  


    if (choice <=0 ||choice >7){  
    result = -1; 
    }

    if(choice==firstChoice||choice == secondChoice||choice == thirdChoice) {
    result = -2;  
   }
   if(totalCredit == 3) {            
    result = 0;
   }    

   if (totalCredit > 9) {        
     result = -3;  
      } 

    return result;
}

public static void WriteCurrentRegistration(int firstChoice, int secondChoice, int thirdChoice) {

    if (firstChoice == 0)
        System.out.println("Current course registration:  { none } " );     
    else if (secondChoice == 0)
        System.out.println("Current course registration: { " + ChoiceToCourse(firstChoice) + " }" );
    else if (thirdChoice == 0)
        System.out.println("Current course registration: { " + ChoiceToCourse(firstChoice) + 
                ", " + ChoiceToCourse(secondChoice) + " }");
    else
        System.out.println("Current course registration: { " + ChoiceToCourse(firstChoice) + 
                ", " + ChoiceToCourse(secondChoice) + ", " + ChoiceToCourse(thirdChoice) + " }");

}

public static String ChoiceToCourse(int choice) {
        String course = "";
        switch (choice)
        {
            case 1:
                course = "IT4782";
                break;
            case 2:
                course = "IT4784";
                break;
            case 3:
                course = "IT4786";
                break;
            case 4:
                course = "IT4789";
                break;
            case 5:
                course = "IT2230";
                break;
            case 6:
                course = "IT3345";
                break;
            case 7:
                course = "IT3349";
                break;
            default:
                break;
        }
        return course;
}


}