public class BurritoInventory {

  // Protect the constructor, so no other class can call it
  private BurritoInventory() { }

  // Create the only instance, save it to a private static variable
  private static BurritoInventory instance = new BurritoInventory();

  // Make the static instance publicly available
  public static BurritoInventory getInstance() { return instance; }

  // How many "servings" of each item do we have?
  private int cheese = 0;
  private int rice = 0;
  private int beans = 0;
  private int chicken = 0;

  // Add to the inventory
  public void addCheese(int added) { cheese += added; }
  public void addRice(int added) { rice += added; }
  public void addBeans(int added) { beans += added; }
  public void addChicken(int added) { chicken += added; }

  // Called when it's time to make a burrito.
  // Returns true if there are enough ingredients to make the burrito,
  // false if not.  Decrements the ingredient count when there are enough.
  synchronized public boolean makeBurrito() {
    // Burritos require one serving of each item
    if (cheese > 0 && rice > 0 && beans > 0 && chicken > 0) {
      cheese--; rice--; beans--; chicken--;
      return true;  // can make the burrito
    }
    else {
      // Could order more ingredients
      return false;  // cannot make the burrito
    }
  }
}