How to implement Observer Pattern?

Hello guys,
I have some problems with implementing the observer pattern. So i m making an sound application and i need to put a meter changing with the volume.
I have already the meter designed and the volume is calculated.
So i have a class called Application (is the main class) and this class have the graphic designer from the application, makes the audio capture and calculate the volume.
And i have the MeterMic class and in this class i have the graphic Meter where i send this graphic meter to the application via JPanel.
In MeterMic i have the variable "value" and this variable will make the changes in the bars of the meter and i want to equal the value to the volume from the application. I try referencing by the Application object but doesnt pass the value from the volume.
So i would like to implement the Observer pattern.
I need to observ the variable volume and than the volume have changes i want to send that change to variable value in MeterMic.
My problem is: who is the observer and observ? And what i need to do to implement the pattern.
My best,
David

Kayaman wrote:
DavidHenriques wrote:
So i just need to implement the observers interfaces and than implement the method update and notify in the classes.You should probably forget the Observer/Observable classes, they're Java 1.0 stuffDo you think they are usless just because they are old?
so you don't have to or need to use them, even though the names sound appealing.I still like them because the Observable saves me from repetitively implementing (hopefully thread save) method for notifying the observers...
It's basically the same thing, you just see a lot more talk about Events/Listeners than Observers/Observables these days.The good thing on Events/Listeners is that they are type save which is an importand feature.
But I like to build them on top of Observer/Observable on the event source side.
bye
TPD

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An Interface
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endasil wrote:
georgemc wrote:
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Observer Pattern
Observer pattern is a well known pattern especially with Java, here i continue my work in patterns.
This is my humble understanding of a way how we can apply observer pattern
The main components of this pattern is:
Observer pattern:
Subject
Observer
Context
Why do we need?
Cant i do without this pattern, well of course you can do although you will be having a tightly coupled application
The main reason is we don't want to couple the objects
The main goal is the " Least knowledge in objects across each other"
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interface lif_subject.
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ENDINTERFACE.
Here is the subject:
class lcl_subject definition .
public section.
INTERFACES lif_subject.
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     importing
       !IV_MATNR type MATNR
       !IV_SPRAS type SPRAS
    methods GET_MATNR
     returning
       value(RV_MATNR) type MATNR .
   methods GET_SPRAS
     returning
       value(RV_SPRAS) type SPRAS .
    methods SET_MATNR
     importing
       !IV_MATNR type MATNR .
   methods SET_SPRAS
     importing
       !IV_SPRAS type SPRAS .
protected section.
private section.
   data MV_MATNR type MATNR .
   data MV_SPRAS type SPRAS .
ENDCLASS.
CLASS lcl_subject IMPLEMENTATION.
METHOD constructor.
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   mv_spras = iv_spras.
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METHOD get_matnr.
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ENDMETHOD.
METHOD get_spras.
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ENDMETHOD.
METHOD set_matnr.
   mv_matnr = iv_matnr.
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ENDMETHOD.
METHOD set_spras.
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   RAISE EVENT lif_subject~SUBJECT_IS_CHANGED.
ENDMETHOD.
ENDCLASS.
Observer:
Observer is the one thats interested in the change of the subject
That could be any observer
Here is the code sample
****Observer
INTERFACE lif_observer.
METHODS: update.
ENDINTERFACE.
class lcl_observer1 DEFINITION.
PUBLIC SECTION.
INTERFACES lif_observer.
ENDCLASS.
class lcl_observer1 IMPLEMENTATION.
method lif_observer~update.
WRITE:/ ' Observer 1 is updated '.
ENDMETHOD.
ENDCLASS.
class lcl_observer2 DEFINITION.
PUBLIC SECTION.
INTERFACES lif_observer.
ENDCLASS.
class lcl_observer2 IMPLEMENTATION.
method lif_observer~update.
WRITE:/ ' Observer 2 is updated '.
ENDMETHOD.
ENDCLASS.
Context: Its the manager of the all communication like a channel
It separates the observer from the observable.
class   lcl_channel definition.
PUBLIC SECTION.
methods: add_observer IMPORTING io_observer type REF TO lif_observer.
methods: remove_observer IMPORTING io_observer type REF TO lif_observer.
methods: constructor.
methods: notify_observers FOR EVENT lif_subject~SUBJECT_IS_CHANGED of lcl_subject IMPORTING sender.
PRIVATE SECTION.
DATA: lo_list type REF TO CL_OBJECT_MAP.
class-DATA: lv_key type i.
ENDCLASS.
Notice that the event listener for the subject is the channel itself
and notify_observers method is responsible for that.
****Manager!!
class   lcl_channel definition.
PUBLIC SECTION.
methods: add_observer IMPORTING io_observer type REF TO lif_observer.
methods: remove_observer IMPORTING io_observer type REF TO lif_observer.
methods: constructor.
methods: notify_observers FOR EVENT lif_subject~SUBJECT_IS_CHANGED of lcl_subject IMPORTING sender.
PRIVATE SECTION.
DATA: lo_list type REF TO CL_OBJECT_MAP.
class-DATA: lv_key type i.
ENDCLASS.
class lcl_channel IMPLEMENTATION.
method constructor.
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ENDMETHOD.
method add_observer.
lo_list->PUT(
   EXPORTING
     KEY      = lv_key
     VALUE    = io_observer
lv_key = lv_key + 1.
ENDMETHOD.
method remove_observer.
ENDMETHOD.
METHOD notify_observers.
DATA: lo_map_iterator TYPE REF TO CL_OBJECT_COLLECTION_ITERATOR.
DATA: lo_observer type REF TO lif_observer.
break developer.
lo_map_iterator ?= lo_list->GET_VALUES_ITERATOR( ).
while lo_map_iterator->HAS_NEXT( ) = abap_true.
lo_observer ?= lo_map_iterator->GET_NEXT( ).
lo_observer->UPDATE( ).
ENDWHILE.
ENDMETHOD.
Notice the use of the Collections as well cl_object_collections object in SAP Standard
I hope you find this useful
The sample code is attached as a text file
ENDCLASS.

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If you want to check for patterns in the ABAP source itself, you can check for patterns in ABAP source using SCII Code inspector.
Enter SCII and select the object or set of objects to check.
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Search of ABAP Tokens
Search ABAP Statement Patterns
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