>>>
>>> Just like EJBs, you should be careful about how much interaction you do
>>> beyond your object's scope within the constructor. Your component doesn't
>>> have a hierarchy, getPage() cannot be accessed, none of your subclass
>>> constructors have been invoked and therefore your instance is not properly
>>> initialized and ready for use.
>> not really sure what you mean by subclass constructors or how they
>> come into play when constructing an instance...
> If I understand correctly, here is an example of what he means :
Exactly. If B extends A and I do something in A's constructor that goes beyond
the scope of setting up A's instance variables, then I risk a side-effect that
relies on the instance to be constructed at B's level as well. There's nothing
in the JVM that prevents this and these bugs are very hard to see and debug.
They should be avoided by good coding practices.
On 08 Mar 2011, at 22:07, Igor Vaynberg wrote:
>
> i think code like this should be possible:
>
> NameEditor e=new NameEditor("name", firstNameModel, lastNameModel);
> e.getFirstNameEditor().setRequired(true);
> e.getLastNameEditor().setEnabled(false);
> taking the previous example of a name editor, with constructor we have:
>
> class nameeditor extends panel {
> public nameeditor(...) {
> add(new textfield("first",..);
> add(new textifled("last", ...);
> }
> public textfield getfirst() { return get("first"); }
> public textfield getlast() { return get("last"); }
> }
Firstly, it's my opinion that you really shouldn't be doing anything to
components directly, especially not from outside your class. As for why, see
Encapsulation and Law of Demeter.
But if you really wanted to use this pattern, it really wouldn't have to be as
cumbersome as you make it out to be. Also, I really don't like condoning
get(String), it's nasty and very type-unfriendly. It also breaks as soon as
you do any refactoring in your component hierarchy.
class NameEditor extends Panel {
TextField<String> firstField;
TextField<String> lastField;
@Override protected void onInitialize() { super.onInitialize();
add(getFirst(), getLast()); }
public textfield getFirst() { if (firstField == null) firstField = new
TextField<String>(); return firstField; }
public textfield getLast() { if (lastField == null) lastField = new
TextField<String>(); return lastField; }
}
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