How to store updated value of an integer in java?

Question

Here's my code for vending machine-

import java.util.Scanner;

public class VendingMachine
{
    public static final Scanner sc = new Scanner(System.in);
    public static double totalAmt;
    public static double change;
    public static String food = null;
    public static int stockPC = 2;
    public static int stockCo = 2;
    public static int stockCa = 2;
    
    public static void MainMenu(){
        
         System.out.println("Main menu - "); 
         System.out.println("a - Potato Chips -$1.25");
         System.out.println("b - Cookies - $0.85 ");
         System.out.println("c - Candies - $0.95");
         
         
         
         String input = sc.next().toLowerCase(); 
         change = 0;
         if(input.equals("a")){
            stockPC = stockPC -1;
            change = totalAmt - 1.25;
            food ="Potato chips";
                if(stockPC == 0){
                 System.out.println("Sorry we're out of Potato Chips:(");
                }else{
                    System.out.println("Please take your "+ food + "\n");       
                     System.out.println("Here is your change $" + change);
                }

         }else if ( input.equals("b")){
            stockCo = stockCo -1;
            change = totalAmt - 0.85;
            food ="Cookies";
                 if(stockCo == 0){
                 System.out.println("Sorry we're out of Cookies:(");
                }else{
                    System.out.println("Please take your "+ food + "\n");       
                     System.out.println("Here is your change $" + change);
                }
         }else if ( input.equals("c")){
            stockCa = stockCa -1;
            change = totalAmt - 0.95;
            food ="Candies";
                 if(stockCa == 0){
                 System.out.println("Sorry we're out of Candies:(");
                }else{
                    System.out.println("Please take your "+ food + "\n");       
                     System.out.println("Here is your change $" + change);
                }
         }else{
               System.out.println("Our system only accepts a,b or c");
         }
         
        }
    
    
    public static void main(String[] args){
         System.out.println("Hi! Welcome to Vending Machine!");
         
        
         System.out.println("How many quarters do you have?");
         double noOfQt = sc.nextDouble();
         totalAmt = noOfQt * 0.25;
         
         System.out.println("How many dimes do you have?");
         double noOfDm = sc.nextDouble();
         totalAmt = totalAmt + (noOfDm * 0.1);
         
         System.out.println("How many nickels do you have?");
         double noOfNk = sc.nextDouble();
         totalAmt = totalAmt + (noOfNk * 0.05);
         
         System.out.println("You have = $" + totalAmt);
         
         MainMenu();
            
         }
    }

I having trouble in my MainMenu method. After selecting one of the inputs in my MainMenu method, I want to update the value of 'integers' like change, stockPC, stockCo and stockCo at the end of the method. I don't want to print these value. I just want to use these updated value in my main method.

How can I do it?

Answer 1

where do you instantiate your scanner? It needs to be a part of the main method, and then pass the value from the user to the MainMenu(-put value here-) method. That way -> Scanner would work.

MainMenu(double amount);

Do your calculations in the receiving method and just pass a "generic" double input from the user

Also, it's not a good practice in your case to declare the items in your stock as public static. Remember that it's always a good practice to declare variables as private, and use setters/getters for those.

The data members shouldn't be initialized like you did, but instead:

private int stockPC;
private int stockCo;
private int stockCa;

Use a constructor to define the value of those upon initialisation:

 public VendingMachine(int stockPC, int stockCo, int stock){
 this.stockPC = stockPC;
 this.stockCo = stockCo;
 this.stockCa = stockCa;
}

And finally getters/setters:

public int getStockPC(){
return stockPC;}

public int getstockCo(){
return stockCo;}

public int stockCa(){
return stockCa;}

public void setstockPC(int stockPC){
this.stockPC = stockPC;}

public void stockCo(int stockCo){
this.stockCo = stockCo;}

public void stockCa(int stockCa){
this.stockCa = stockCa;}

I hope that's helpful