How to break my code into subroutines? - Java

Question

I have written a code for data management and parallel arrays but it has to be broken into methods/subroutines. Whenever I try to do so, some aspect of my code stops working. Would it be possible for anyone to roughly outline how and what I can break into subroutines without it causing problems in my code?

 Scanner keyedInput = new Scanner(System.in); // input
 
 // variables
 String userInput;
 int numberOfBooks = 0; // setting to 0
 int userChoice = 0; // setting to 0
 final double taxAmount = 1.13;
 boolean valid = false;
 double total = 0; // setting to 0
 double taxedTotal;
 
 // while loop for number of books
 while (valid == false)
 {
 // user enters info
 System.out.print("Please enter the number of books you have purchased: ");
 userInput = keyedInput.nextLine();
 System.out.println();
 
 // try catch statements for invalid input/exceptions
 try
 {
 numberOfBooks = Integer.parseInt(userInput); // converting to int
 valid = true; // setting to true so loop won't repeat
 } // end of try
 
 // outputting invalid input message
 catch (NumberFormatException e)
 {
 System.out.println("Your input is not valid");
 System.out.println();
 } // end of catch
 } // end of valid == false while loop
 
 
 // arrays to hold info user will input
 String bookName [ ] = new String [numberOfBooks];
 double price [ ] = new double [numberOfBooks];
 
 // user enters all data required
 System.out.println("* * * * DATA ENTRY * * * *");
 // for loop that prompts for and stores name of books purchases
 for (int i = 0; i < numberOfBooks; i = i + 1)
 {
 System.out.println();
 System.out.print("Please enter the name of book " + (i + 1) + ": ");
 bookName[i] = keyedInput.nextLine(); // stores the name of each book in the array
 
 // set valid to false again for loop below
 valid = false;
 
 // while loop for price of books
 while (valid == false)
 {
 System.out.println();
 System.out.print("Please enter the price of '" + (bookName[i] + "': "));
 userInput = keyedInput.nextLine();
 
 
 // try catch statements for invalid input/exceptions
 try 
 {
 price[i] = Double.parseDouble(userInput); // converting to double
 valid = true; // setting to true so loop won't repeat
 } // end of try
 
 // outputting invalid input message
 catch (NumberFormatException e) 
 {
 System.out.println("Your input is not valid");
 } // end of catch
 } // end of valid == false while loop
 } // end of for loop
 
 
 // while loop to output data
 while (userChoice != 3)
 {
 // set valid to false for loop below
 valid = false; 
 
 while (valid == false)
 {
 // outputting choices menu
 System.out.println();
 System.out.println("* * * *\n" + "1. Output original data \n" + "2. Output calculated data \n" + "3. Exit \n" + "* * * *\n");
 
 // user enters their choice
 System.out.print("Please enter the number in front of your choice: ");
 userInput = keyedInput.nextLine();
 System.out.println();
 
 // try catch statements for invalid input/exceptions
 try 
 {
 userChoice = Integer.parseInt(userInput); // converting to int
 valid = true; // setting to true so loop won't repeat
 } // end of try
 
 // outputting invalid input message
 catch (NumberFormatException e) 
 {
 System.out.println("Your input is not valid");
 System.out.println();
 } // end of catch
 } // end of valid == false while loop
 
 
 // switch statements for each option
 switch (userChoice)
 {
 // option 1
 case 1:
 {
 // for loop to output existing data
 for (int i = 0; i < numberOfBooks; i = i + 1)
 {
 System.out.println("'" + bookName[i] + "'" + " cost: " + price[i]);
 } // end of for loop
 break;
 } // end of case 1
 
 // option 2
 case 2: 
 {
 // calculations for total + taxed total
 for (double value : price) 
 {
 total = total + value;
 total = Math.round(total * 100.0) / 100.0; // rounding
 //totalAmount = totalAmount + total;
 } // end of for loop 
 
 taxedTotal = (total * taxAmount); // calculating total with taxes
 taxedTotal = Math.round(taxedTotal * 100.0) / 100.0; // rounding
 
 System.out.println("Total: $" + total);
 System.out.println("Taxed total: $" + taxedTotal);
 break;
 } // end of case 2
 
 // option 3
 case 3:
 {
 System.out.println("Goodbye!");
 } // end of case 3
 } // end of switch statements
 } // end of userChoice while loop

• BCdotWEB: The current question title of your question is too generic to be helpful. Please edit to the site standard, which is for the title to simply state the task accomplished by the code. Please see How do I ask a good question?.

Answer 1

How to broke your code into sub rutines

Well, there I see some util things you could do in order to separate the code:

• First, you could create some functions which job is to request the data to the user and until that data is correctly entered, the function continues requesting data, Example:

 //let this be a static field so you can call it in any other new static function
 private static Scanner scanner = new Scanner(System.in);
 private static readInt(String requirement) {
 System.out.print(requirement + " : ");
 int input;
 boolean correctInput = false;
 do {
 try {
 input = scanner.nextInt();
 } catch (Exception ignored) {
 System.out.println("An error has occurred, introduce the number again");
 }
 } while(!correctInput);
 //equivalent to correctInput != true or correctInput == false
 return input;
 }

(I suppose you're working with only a main class which has the public static void main)

I would recommend you to create two more functions readString and readDouble so that you are simplifying the data gathering process and not repeat code.

• Now, you use the readString function to request the user the book name and the readDouble for the book price. and so you are saving more code.

• Finally, each case in a switch can be turned into a function.

Referent to your code style

• Do not use comparisons of type if ([booleanVariable] == true) or if ([booleanVariable] == false), until I have knowledge it is also a comparison that your machine has to do in runtime, if you are coding a very large system part the effect will be more notorious. Instead use if ([booleanVariable]) or if (![booleanVariable]) the ! symbol means not.

It doesn't apply only to Java, it works for many other languages (Python, C++, C, C#, GO, JS, PHP, ...), syntax may variate but still applies.

• Do not over-comment, it is good to have documentation about your code, but writting a lot of comments where it is intuitive what the code does, is bad, it consumes your time and the code gets messy.

• Last, it perhaps is not the big deal, but most Java programmers uses

[expression] { //this brace opening
}
[expression]
{//rather than this.
 //I may say, it is more likely to be done for someone who comes from C#, C++ or C
}

it doesn't matter at the end, but you know, some people care about it and well, it is better to work under the same language, using a common terminology.

Note: certainly it is better to use read instead of get according to Roland Illig's comment.

Hope it helped you, cheers.

• Roland Illig: The method getInt is missing the return type. Instead of get, these method names should rather start with read since they have side effects.