Widgets declared as method local (final) VS class members

[Apikoulas]

Could someone highlight the pros and cons of declaring widget variables:

a) locally on the method (as final to allow reference in anonymous class listerner)
eg

Code: Select all

public void onModuleLoad() {            
      final  Button button = new Button();
                .....
}


b) declaring as class member variables (which to me looks more clear)

Code: Select all

public class ImageViewer implements EntryPoint {
   private Button button = new Button();
}

I have also come across some extremes, such as declaring vars in a method inside a block eg. { Button b = new Button()...} - Is there any point in that ?

I feel that b) has these pros :
- More clear code, seperation of declarations & code
- Vars can be referenced by other methods

[Eric Clayberg]

This is very simple. If you need to reference a widget programatically outside of the method that created it, you should create it as a field. If you don't need to access it, you can have it created as a simple local variable. Most static text labels, for example, can be created as local variables while most text widgets, tables, etc. should be created as fields. Fortunately, GWT Designer gives you full control over how each individual widget is declared. You can make all widgets fields by default or only widgets of specified types. You can also convert a widget from being a field to a local variable and vice versa at any time with a single click.

[Apikoulas]

Thank you Eric,

I understand we can do both.

The question is what are the benefits of local 'final' declaration inside the method, instead of always declaring everything as fields/class members, which is more 'clean' and OO.

I cant see any out-of-the-box benefit with local declaration (such as optimization for memory management , lazy initialization etc). Instead I consider it as cluttered spaghetti code.

Actually I think its better having widgets declared AND initialized on the class as fields, ie

Code: Select all

Class Foo extends ... {
     Button b = new Button("Click me");
}


which BTW initialasation breaks the Designer's ability to convert from 'field' to 'local' (not crucial anyway).

[Eric Clayberg]

I think the question you should be asking is what is the benefit of assigning a widget to a field that is never referenced. If you never need to reference a widget, there is no reason to declare it as a field.

Doing so does not make it more 'clean' or more OO. Cluttering your class with a bunch of extra, unneeded fields is more a symptom of bad OO design than good.

That said, if you prefer a GUI style that has every widget declasred as a field, GWT Designer will happily accomodate you.

[peterblazejewicz]

Could someone highlight the pros and cons of declaring widget variables:

a) locally on the method (as final to allow reference in anonymous class listerner)
eg

Code: Select all

public void onModuleLoad() {            
      final  Button button = new Button();
                .....
}


b) declaring as class member variables (which to me looks more clear)

Code: Select all

public class ImageViewer implements EntryPoint {
   private Button button = new Button();
}

I have also come across some extremes, such as declaring vars in a method inside a block eg. { Button b = new Button()...} - Is there any point in that ?

I feel that b) has these pros :
- More clear code, seperation of declarations & code
- Vars can be referenced by other methods

Hello,

this could be answered in many ways, especially if you also want to take JVM/Javac optimization into scope. There are sometimes rules within organization that put some design/implementation details rules to follow, sometimes one is free about implementation details and can follow own habits, etc.,
Here is a nice book you could read on that subject:
http://safari.informit.com/9780321413093
it covers most of answers you would probably receive from coders

In GWT (toolkit) terms: you're free of choice on implementation details, Even "final" has no real importance in GWT. That's because GWT (toolkit - i'm not writing about GWT Desinger plugin+Eclipse) does not use Javac - at least on code that is to run on client side. Everything is compiled by GWT compiler (transcoded from java to javascript, optimized, etc),

regards,
Peter

[Eric Clayberg]

Thanks for the info.

Our position with GWT Designer is to try and support most reasonable code generation styles as opposed to dictating the one, true, correct choice.

[Olivercomputing]

Eric - you'd said earlier, re: local vs. field variable definitions:

"Fortunately, GWT Designer gives you full control over how each individual widget is declared."

I can see under Eclipse Preferences how to change the general default, but how is this default changed on a per-widget basis?

[Eric Clayberg]

You can set defaults for each type...

http://download.instantiations.com/D2WB ... ables.html



...or set the local/field status of each widget...

http://download.instantiations.com/D2WB ... _menu.html