public void addElement(AstNode element){
  assertNotNull(element);
  if (elements == null)   elements=new ArrayList<AstNode>();
  elements.add(element);
  element.setParent(this);
}

public void addElement ( AstNode element ) { assertNotNull ( element ) ; if ( elements == null ) elements = new ArrayList < AstNode > ( ) ; elements . add ( element ) ; element . setParent ( this ) ; }
adds an element to the list , and sets its parent to this node .
