Can't get dupe checking working

Question

I'm currently making an inventory management system in java for college. The user enters a two letter combination (specified in a 2d array, the other side holds the full name for display purposes later). Now I also need to check whether or not the item number has already been entered. This is where I have a problem, it compiles fine but it just doesn't work at all. Here is the item number function, I know its something really small that I'm not seeing. Thanks for any help.
     public static void setItemNo()
          int index = 0;
          String item;
          error = true;
          do
               //get item number
               System.out.print("\n\t\tEnter an item number: ");
               item = TextIO.getlnString();
               item = item.toUpperCase();
               //checking for duplicate entries
               for (int dupeCheck = 0; dupeCheck == publicItemNumber.length; dupeCheck++)
                    if (item == publicItemNumber[dupeCheck])
                         System.out.print("\n\t\titem already entered");
                         dispmenu();
               //item length not equal to 5
               if (item.length() != 5)
                    //item length must be five, it isn't
                    System.out.print("\n\t\tPlease enter a vailid item number\n");
                    error = true;
               //passed error check, item number is 5 chars!
               else
                    error = false;
          }while(error == true);
          //now we check if the first two chars are actually letters
          found = false;
          String firstTwoCharacters = item.substring(0,2);
          while ((found == false) && (index < depts.length))
               if (depts[index][0].equals(firstTwoCharacters))
                    found = true;
                    publicItemNumber[counter] = item;
                    return;
               else if ((found == false) && (index < depts.length))
                    found = false;
                    index = index + 1;
          if (found == false)
               System.out.print("\n\t\tPlease enter a valid number!\n\n");
               return;
     }

Answer 1

In this line:
if (item == publicItemNumber[dupeCheck])Use ".equals" to compare the values. They are Strings. You do it correctly in the 'while' loop near the bottom.