protected void add(Object component){
  if (component == null) {
    return;
  }
  components.add(component);
}

protected void add ( Object component ) { if ( component == null ) { return ; } components . add ( component ) ; }
add a single component to the identifier . the given component is added to the end of the identifier . duplicate instances are not added - - only one instance of a component will exist in the identifier .
