public class Item {
  static int last = 0;
  public static boolean sell() {
    int current = 0;
    StackTraceElement[] lines = Thread.currentThread().getStackTrace();
    StackTraceElement ste = lines[2];
    current = ste.getLineNumber();
    if (last == current) return false;
    last = current;
    return true;
  }
}