@Override
   public boolean equals(Object obj) {
      if (obj == null) {
         return false;
      }
      if (getClass() != obj.getClass()) {
         return false;
      }
      final Ball other = (Ball) obj;
      if (this.color != other.color) {
         return false;
      }
      if (this.coords != other.coords && (this.coords == null || !this.coords.equals(other.coords))) {
         return false;
      }
      return true;
   }