Abap oo constructor prob

Question

data: g_dock type ref to cl_gui_docking_container,
        g_split type ref to cl_gui_easy_splitting_container,
        g_cont type ref to cl_gui_container.
create object g_dock       " this is a constructor
  exporting
     *side = cl_gui_docking_container=>dock_at_top*      ..... "pls explain this syntax in general
extension = 200.
'dock_at_top'  is a constant in the attributes component of the class  'cl_gui_docking_container'.
1.) we are already creating an instance of this class as  'g_dock'.
so instead of writing  'g_dock -> dock_at_top',  why are we using  ' clgui_docking_container=>dock_at_top_ '. pls explain this.
2.) pls clarify 1 thing ....the syntax ...  
"create object g_dock
exporting
it is a constructor method, so why are we writing   'cl_gui_docking_container=>dock_at_top'  instead of writing  only 'dock_at_top'
pls help.
detailed answers will be appreciated, thnks in adv

Answer 1

Hi Akash,
The replies to your question are good, in case you are not clear, let me try my bit
1.) we are already creating an instance of this class as 'g_dock'.
so instead of writing 'g_dock -> dock_at_top', why are we using ' clgui_docking_container=>dock_at_top_ '. pls explain this.
You mean to say something like this,
data: g_dock type ref to cl_gui_docking_container,
        g_split type ref to cl_gui_easy_splitting_container,
        g_cont type ref to cl_gui_container.
create object g_dock       " this is a constructor
  exporting
     *side = g_dock=>dock_at_top*      ..... "pls explain this syntax in general
extension = 200.
Well, as Marcin said object G_DOCK is not yet created at this point, so it is not possible to get a reference to any of it's attributes(constant/static/instance), when you try to compile the above code it will throw a compile error that g_dock=>dock_at_top is not known. Now if your question is how "cl_gui_docking_container=>dock_at_top" is valid syntax, the compiler checks if the global class "cl_gui_docking_container" exists and if yes, then checks for a constant attribute "DOCK_AT_TOP" within it.
2.) pls clarify 1 thing ....the syntax ...
"create object g_dock
exporting
it is a constructor method, so why are we writing 'cl_gui_docking_container=>dock_at_top' instead of writing only 'dock_at_top'
Again, "DOCK_AT_TOP" doesn't have any existence on its own, an attribute irrespective of whether it is constant/static/instance...will always be accessed via it's class reference, and again you cannot use g_dock until it's instance has been created already, not while creating it's instance.
Not sure if i understood your doubt in the above post, the parameter SIDE of the constructor let's you choose where do you want the container to show up top, left, bottom etc...by default it will be left, so if you do not pass anything to the parameter side, it will be created on the left. Now if you want it to be in any other place other than left then you have to specify the same by passing the corresponding value.
@TREASURE - My understanding is that the below is incorrect, and would hold good only within the class and not outside of it.
You could just have
DOCK_AT_TOP
Regards,
Chen
Edited by: Chen K V on Jun 6, 2011 4:54 PM
Edited by: Chen K V on Jun 6, 2011 4:56 PM