public void add(T item){
  if (set.add(item)) {
    fireContentsChanged(this,0,getSize() - 1);
  }
}

public void add ( T item ) { if ( set . add ( item ) ) { fireContentsChanged ( this , 0 , getSize ( ) - 1 ) ; } }
adds the specified item to this list model . if the item already exists , the list model is unchanged .
