public void add(OffsettedItem item){
  throwIfPrepared();
  try {
    if (item.getAlignment() > getAlignment()) {
      throw new IllegalArgumentException("incompatible item alignment");
    }
  }
 catch (  NullPointerException ex) {
    throw new NullPointerException("item == null");
  }
  items.add(item);
}

public void add ( OffsettedItem item ) { throwIfPrepared ( ) ; try { if ( item . getAlignment ( ) > getAlignment ( ) ) { throw new IllegalArgumentException ( "incompatible item alignment" ) ; } } catch ( NullPointerException ex ) { throw new NullPointerException ( "item == null" ) ; } items . add ( item ) ; }
adds an item to this instance . this will in turn tell the given item that it has been added to this instance . it is invalid to add the same item to more than one instance , nor to add the same items multiple times to a single instance .
