Question

Debug and fix the Java console application that uses 2 dimensional arrays but the application does not compile nor execute. Student enters only integers to select courses for registration from a menu. No data type validation of the user menu selection is checked or required. The program terminates only when the student closes it. No registration of other courses not displayed by the program . No registration more than once for the same course. No registration for more than 9 credit hours (e.g. no more than 3 courses). This program has 4 errors/bugs. Use these to test the outcome IT1006 IT4079 IT2230 Successful completion of this assignment will display a valid message or an invalid message, with reason, for the selected course code. In addition, the application should display and update current list of registered courses. Here is the code I have so far: package registerforcourse; import java.util.Scanner; public class RegisterForCourse { public static void main(String[] args) { // TODO code application logic here System.out.println("Register for classes"); Scanner input = new Scanner(System.in); // courses 2d array hold course code and their credit hours String[][] courses = { {"IT1006", "IT4782", "IT4789", "IT4079", "IT2230", "IT3345", "IT2249"}, {"6", "3", "3", "6", "3", "3", "6"} }; // validChoices 2d array holds valid number choices (as strings) selected by user // and their corresponding courses //e.g String[][] choices = { {"5", "IT2230"}, {"1", "IT1006"}, {"6", "IT3345"} }; String[][] validChoices = { {"", ""}, {"", ""}, {"", ""} }; int choice; int totalCredit = 0; String yesOrNo = ""; do { choice = getChoice(courses, input); switch (ValidateChoice(choice, validChoices, totalCredit, courses)) { 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 " + courses[0][choice-1] + " 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 " + courses[0][choice-1] ); totalCredit += Integer.parseInt(courses[1][choice-1]); if (validChoices[0][0].equals("")) { validChoices[0][0] = Integer.toString(choice); validChoices[0] = courses[0][choice-1]; } else if (validChoices[1][0].equals("")) { validChoices[1][0] = Integer.toString(choice); validChoices[1][1] = courses[0][choice-1]; } else if (validChoices[2][0].equals("")) { validChoices[2][0] = Integer.toString(choice); validChoices[2][1] = courses[0][choice-1]; } break; } WriteCurrentRegistration(validChoices, totalCredit); 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"); } //This method prints out the selection menu to the user in the form of //[selection number]Course Code (Course Credit Hours) //from the courses array one per line //and then prompts the use to make a number selection public static int getChoice(String[] courses, Scanner input) { System.out.println("Please type the number inside the [] to register for a course"); System.out.println("The number inside the () is the credit hours for the course"); for(int i = 0; i < courses[0].length; i++ ) System.out.println("[" + (i+1) + "]" + courses[0][i] + "(" + courses[1][i] + ")"); 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, String[][] validChoices, int totalCredit, String[][] courses) { String choiceAsString = Integer.toString(choice); if (choice < 1 || choice > 7) return -1; else if (choiceAsString.equals(validChoices[0][0]) || choiceAsString.equals(validChoices[]) || choiceAsString.equals(validChoices[2][0])) return -2; else if ( totalCredit + Integer.parseInt(courses[1][choice-1]) > 9) return -3; return 0; } //This method prints the current list of registered courses thus far //from the courses array separated by , and enclosed inside { } //It also prints the total credit registered for thus far public static void WriteCurrentRegistration(String[][] validChoices, int totalCredit) { if (validChoices[0][0].equals("")) System.out.println("Current course registration: { none } " ); else if (validChoices[1][0].equals("")) System.out.println("Current course registration: { " + validChoices[0][i] + " }" ); else if (validChoices[2][0].equals("")) System.out.println("Current course registration: { " + validChoices[0][1] + ", " + validChoices[1][1] + " }"); else System.out.println("Current course registration: { " + validChoices[0][1] + ", " + validChoices[1][1] + ", " + validChoices[2][1] + " }"); System.out.println("Current registration total credit = " + totalCredit); } } Expert Answer

Answer 1

I've gone through the source code and first tried to reformat it.

Then I started to find the bugs to resole them.

It's somewhat hard to tell the line numbers as it gets changed considering new lines and may change while posting in browser so I am writing the line of code that has the error.

1. choice = getChoice(courses, input)

It is in main() method.

2.   for (int i = 0; i < courses[0].length; i++) {
3. System.out.println("[" + (i + 1) + "]" + courses[0][i] + "(" + courses[1][i] + ")")

These two lines are in getChoice() method.

The cause for all the 3 is first bug.

The header of method getChoice() is defined as   public static int getChoice(String[ ] courses, Scanner input) where courses is written a single dimension array but actually in main() it is 2-D array. And as it is 2D array, one can write statement like this courses[0].length which is valid otherwise courses[0] would be an array element which does not have a length property. The next line is the code referring to 2-D array and as it was defined 1-D in getChoice(), these lines are giving errors

So, when I changed the method header and wrote courses as a 2-dimension array, all the 3 lines were not having any error now.

Second bug/error is in main() in the line: validChoices[0] = courses[0][choice - 1];

'validChoices' is a 2-D array but its only first dimension is mentioned second is not.

If you see the code written along with this line, you can say that if validChoices[0][0] is empty, then the course name should be addedd to validChoices[0][1]. So, adding [1] will solve this error.

Next error is in the following line in the method ValidateChoice() :

else if (choiceAsString.equals(validChoices[0][0]) || choiceAsString.equals(validChoices[ ]) || choiceAsString.equals(validChoices[2][0])) {

Here, if you see, the second condition written is choiceAsString.equals(validChoices[ ])

In other two conditions in the same else if, choiceAsString is compared with validChoices[0][0] and validChoices[2][0] but in the second part. there's no index specified for validChoices [ ] [ ].

Here it should be validChoices[1][0] as other two course names stored at index [0] [0] and [2] [0] are compared in the same line, validChoices[1] [0] is remaining.

The last error is in the following line in the method WriteCurrentRegistration()..

System.out.println("Current course registration: { " + validChoices[0][i] + " }")

Here, validChoices[0][i] is written but variable 'i' is not defined inside WriteCurrentRegistration() method.

If you see the other statements in the same method, in the first value printed inside all other println() is validChoices[0][1].

So, here also it should be the validChoices[0][1] instead of validChoices[ 0 ][ i ].

So when we fix the 4 errors we'll get the modified source code as follows.. In the code, I've make the text BOLD where the changes are done.

Modified Source Code:

package registerforcourse;

import java.util.Scanner;

public class ResgisterForCourse {

public static void main(String[ ] args) {
System.out.println("Register for classes");
Scanner input = new Scanner(System.in);
String[ ][ ] courses = {{"IT1006", "IT4782", "IT4789", "IT4079", "IT2230", "IT3345", "IT2249"}, {"6", "3", "3", "6", "3", "3", "6"}};
String[ ][ ] validChoices = {{"", ""}, {"", ""}, {"", ""}};
int choice;
int totalCredit = 0;
String yesOrNo = "";
do {
choice = getChoice(courses, input);
switch (ValidateChoice(choice, validChoices, totalCredit, courses)) {
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 " + courses[0][choice - 1] + " 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 " + courses[0][choice - 1]);
totalCredit += Integer.parseInt(courses[1][choice - 1]);
if (validChoices[0][0].equals("")) {
validChoices[0][0] = Integer.toString(choice);
validChoices[0][1] = courses[0][choice - 1]; // to solve bug 2
} else if (validChoices[1][0].equals("")) {
validChoices[1][0] = Integer.toString(choice);
validChoices[1][1] = courses[0][choice - 1];
} else if (validChoices[2][0].equals("")) {
validChoices[2][0] = Integer.toString(choice);
validChoices[2][1] = courses[0][choice - 1];
}
break;
}
WriteCurrentRegistration(validChoices, totalCredit);
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(String[ ][ ] courses, Scanner input) { // to solve first bug
System.out.println("Please type the number inside the [ ] to register for a course");
System.out.println("The number inside the () is the credit hours for the course");
for (int i = 0; i < courses[0].length; i++) {
System.out.println("[" + (i + 1) + "]" + courses[0][i] + "(" + courses[1][i] + ")");
}
System.out.print("Enter your choice : ");
return (input.nextInt());
}

public static int ValidateChoice(int choice, String[ ][ ] validChoices, int totalCredit, String[ ][ ] courses) {
String choiceAsString = Integer.toString(choice);
if (choice < 1 || choice > 7) {
return -1;
} else if (choiceAsString.equals(validChoices[0][0]) || choiceAsString.equals(validChoices[1][0]) || choiceAsString.equals(validChoices[2][0])) { // to solve bug 3
return -2;
} else if (totalCredit + Integer.parseInt(courses[1][choice - 1]) > 9) {
return -3;
}
return 0;
}

public static void WriteCurrentRegistration(String[ ][ ] validChoices, int totalCredit) {
if (validChoices[0][0].equals("")) {
System.out.println("Current course registration: { none } ");
} else if (validChoices[1][0].equals("")) {
System.out.println("Current course registration: { " + validChoices[0][1] + " }"); // to solve bug 4
} else if (validChoices[2][0].equals("")) {
System.out.println("Current course registration: { " + validChoices[0][1] + ", " + validChoices[1][1] + " }");
} else {
System.out.println("Current course registration: { " + validChoices[0][1] + ", " + validChoices[1][1] + ", " + validChoices[2][1] + " }");
}

System.out.println("Current registration total credit = " + totalCredit);
}
}

Output:

run: Register for classes Please type the number inside the [1 to register for a course The number inside the ) is the credit hours for the course [1IT1006(6) [2] IT4782 (3) [31IT4789(3) [4]IT4079(6) [5]IT2230(3) [61IT3345(3) [71IT2249(6) Enter your choice 1 Registration Confirmed for course IT1006 Current course registration: IT1006 Current registration total credit 6 鴞 Do you want to try again? (YIN)? : y Please type the number inside the [] to register for a course The number inside the () is the credit hours for the course [11IT1006(6) [2]IT4782(3) [31IT4789(3) [4]IT4079 (6) [5]IT2230(3) [61IT3345(3) [71IT2249(6) Enter your choice : 4 **Invalid** - You can not register for more than 9 credit hours. Current course registration: IT1006 Current registration total credit 6

Do you want to try again? (YIN)? y Please type the number inside the [] to register for a course The number inside the () is the credit hours for the course [11IT1006(6) [21IT4782(3) [31IT4789(3) [4]IT4079(6) [5]IT2230(3) [6]IT3345(3) [71IT2249(6) Enter your choice : 5 Registration Confirmed for course IT2230 Current course registration: IT1006, IT2230 Current registration total credit 9 1 6 Do you want to try again? (YIN)? n Thank you for registering with us BUILD SUCCESSFUL (total time: 29 seconds) 0 2 1

So when I executed this modified code, it had no error and it executed successfully as per the output above.

See it is allowing to register for a course and maximum allowed hrs = 9 so it refuses to add 6 to current 6 while entering a course second time, but in third time it allows as total hours become 6 + 3 = 9 which is acceptable.

So, this is how to solve the bugs in the code. The concepts and the code is already designed and these were the things which were preventing the code to be executed. Now they are solved.

Go through the process of identifying the lines where the errors were and why they were an error and how they were solved.

Do comment if there's any query. I will address it for sure.

Thank you. :)