import java.util.Random;

/**
*/
public class VendingMachine {

private static double totalSales = 0;

private VendingItem[][][] shelf;

private int luckyChance = 0;

private Random rand;

public VendingMachine(){
   shelf = new VendingItem[6][3][5];
   rand = new Random();
   restock();
}

public void restock(){
   VendingItem[] values = VendingItem.values();

   int n = values.length;

   for(int i=0; i<6; i++){
         //shelf[i] = new VendingItem[3][5];
         for(int j=0; j<3; j++){
            shelf[i][j] = new VendingItem[5];
            for(int k=0; k<5;k++){
               int index = rand.nextInt(n);
               VendingItem item = values[index];
               shelf[i][j][k] = item;
            }
         }
   }
}

public VendingItem vend(String code){

   if(code != null && !code.isEmpty() && code.length() == 2){

         char r = code.charAt(0);
         if(Character.isLetter(r)){
            if(Character.isLowerCase(r)){
               System.out.println("row character should be capital letter");
               return null;
            }else {
               r = Character.toUpperCase(r);
               int row = r - 65;
               if (row >= 0 && row <= 5) {
                     char c = code.charAt(1);
                     if (Character.isDigit(c)) {
                        int col = Integer.parseInt("" + c);
                        if (col >= 1 && col <= 3) {

                           if (shelf[row][col - 1][0] != null) {
                                 VendingItem item = shelf[row][col - 1][0];

                                 for (int k = 1; k < 5; k++) {
                                    shelf[row][col - 1][k - 1] = shelf[row][col - 1][k];
                                 }
                                 shelf[row][col - 1][4] = null;

                                 if (free()) {
                                    System.out.println("This item is free");
                                 } else {
                                    totalSales += item.getPrice();
                                 }

                                 return item;

                           } else {
                                 System.out.println("No Item found at this position");
                                 return null;
                           }

                        } else {
                           System.out.println("Invalid column");
                           return null;
                        }
                     } else {
                        System.out.println("Invalid column");
                        return null;
                     }
               } else {
                     System.out.println("Invalid row");
                     return null;
               }
            }

         }else {
            System.out.println("Invalid row");
            return null;
         }

   }else {
         System.out.println("Invalid row/column");
         return null;
   }
}

private boolean free(){

   if(rand.nextInt(100) < luckyChance){
         luckyChance = 0;
         return true;
   }else {
         luckyChance += 1;
         return false;
   }
}

public static double getTotalSales(){
   return totalSales;
}

public int getNumberOfItems(){
   int total = 0;
   VendingItem[] values = VendingItem.values();

   int n = values.length;

   for(int i=0; i<6; i++){
         for(int j=0; j<3; j++){
            for(int k=0; k<5;k++){
               if(shelf[i][j][k] != null){
                     total += 1;
               }
            }
         }
   }

   return total;
}

The class should have a double field named availableBalance that ho...