DEV6: Advanced ObjectOriented Programming in the ABL

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DEV-6 Advanced Object-Oriented Programming in
the ABL
Evan Bleicher bleicher_at_progress.com
Shelley Chase schase_at_progress.com
Senior Development Manager
Architect
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Under Development

• This talk includes information about potential
  future products and/or product enhancements.
• What we are going to say reflects our current
  thinking, but the information contained herein is
  preliminary and subject to change. Any future
  products we ultimately deliver may be materially
  different from what is described here.

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Agenda

• Order Entry System Object Model
• Abstract Programming with Classes
• Working with Datasets / Temp-tables in Classes
• Miscellaneous Topics
• Debugging with Classes
• Using SUPER in Classes
• Accessing Classes on the AppServer
• Error Handling policy for Classes
• Proper Encapsulation in Classes
• Compiler Tips and Tricks
• Coding Standards

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Order Entry System Object Model
Use OpenEdge Reference Architecture
Business Entity Interface between DA layer and
Presentation / Integration
Data Access Object Interface to Data Store
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Order Entry Object Model - Handout
Inherits
Inherits
Implements
Inherits
Implements
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Order Entry Object Model Data Access Layer
Super Order Class
PROTECTED TEMP-TABLE ttOline PROTECTED TEMP-TABLE
ttOrder PROTECTED DATASET dsOrder
CLASS Acme.DAOrderSuper
Inherits
Specific Order Class
CLASS Acme.DAOrder
Data Access Interface
Implements
INTERFACE Acme.IDataAccess
METHOD LONGCHAR selectRecords ()
METHOD LONGCHAR selectRecords ()
Implements
Specific Item Class
Navigation Interface
CLASS Acme.DAItem
INTERFACE Acme.IList
Implements
METHOD LONGCHAR selectRecords ()
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Order Entry Object Model Business Servicing
Layer
Business Entity Class
DEF VAR rDataObject AS CLASS Acme.IDataAccess ME
THOD VOID fetchWhere ( ) METHOD VOID saveChanges
( )
CLASS Acme.BusinessEntity
Inherits
Order Class
CLASS Acme.BEOrder
METHOD VOID processOrder( )
Specific Internal Order Class
Specific External Order Class
Inherits
Inherits
CLASS Acme.BEInternalOrder
CLASS Acme.BEExternalOrder
METHOD OVERRIDE VOID processOrder ( )
METHOD OVERRIDE VOID processOrder ( )
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Physical Architecture of A Class Hierarchy
COMPILE Acme/BEExternalOrder.cls SAVE.
ltpropathgt / Acme / BusinessEntity.cls
Inherits
ltpropathgt / Acme / BEOrder.cls
Inherits
ltpropathgt / Acme / BEExternalOrder.cls
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Physical Architecture of A Class Hierarchy
COMPILE Acme/BEExternalOrder.cls SAVE.
ltpropathgt / Acme / BusinessEntity.cls
Inherits
ltpropathgt / Acme / BEOrder.cls
Inherits
ltpropathgt / Acme / BEExternalOrder.cls
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Physical Architecture of A Class Hierarchy
COMPILE Acme/BEExternalOrder.cls SAVE.
ltpropathgt / Acme / BusinessEntity.cls
Inherits
ltpropathgt / Acme / BEOrder.cls
Inherits
ltpropathgt / Acme / BEExternalOrder.cls
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Agenda

• Order Entry System Object Model
• Abstract Programming with Classes
• Working with Datasets / Temp-tables in Classes
• Miscellaneous Topics
• Debugging with Classes
• Using SUPER in Classes
• Accessing Classes on the AppServer
• Error Handling policy for Classes
• Proper Encapsulation in Classes
• Compiler Tips and Tricks
• Coding Standards

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Abstract (Generic) Programming

• Define super class / interface for abstraction
• Define abstract methods
• Use abstract object
• Define object reference for super class /
  interface
• Set object ref to NEW subclass object
• Polymorphism causes method calls on object ref to
  run method in subclass
• Abstract code should be put in top most class
• Supports abstraction and reuse

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Choosing between Super Classes and Interfaces

• Both
• Define API (contract) for abstract programming
• Support polymorphism
• Super class
• Contain common code for sharing / augmenting
• Contain protected data members
• Interfaces
• Use when no common behavior exists
• Use to emulate multiple inheritance

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Abstract Programming Using Interfaces

• Define an interface
• Common methods put in interface
• Implementer must provide code for methods

INTERFACE Acme.IDataAccess
METHOD LONGCHAR selectRecords ()
Interface
Implements
CLASS Acme.DAOrder
CLASS Acme.DAItem
Implementer
Implementer
METHOD LONGCHAR selectRecords ()
METHOD LONGCHAR selectRecords ()
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Abstract Programming Using Super Classes

• Define a super class
• Common methods including code put in super class
• Optionally, subclass can override common code

CLASS Acme.BEOrder
METHOD VOID processOrder ( )
Super Class
CLASS Acme.BEInternalOrder
CLASS Acme.BEExternalOrder
Subclass
Subclass
METHOD OVERRIDE VOID processOrder ( )
METHOD OVERRIDE VOID processOrder ( )
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Abstract Programming Sample

• CLASS Acme.BusinessEntity
• / Define variable for interface type
  /
• DEFINE PROTECTED VARIABLE rDataObject
• AS CLASS Acme.IDataAccess NO-UNDO.
• / Generic method works on any class that
• implements Acme.IDataAccess /
• METHOD PUBLIC LONGCHAR fetchWhere ()
• lcVar1 rDataObjectselectRecords ().

CLASS Acme.BEOrder CONSTRUCTOR BEOrder ( )
/ Create Order data object assign to super
class reference/ rDataObject NEW
Acme.DAOrder ( ). lcVar2 rDataObjectfetchWh
ere ().
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Demo of Abstract Programming
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Multiple Inheritance Using Interfaces

• Some older OO languages support multiple
  inheritance
• Newer OO languages support multiple APIs using
  interfaces class inheritance is single

INTERFACE Acme.IDataAccess
METHOD LONGCHAR selectRecords ()
CLASS Acme.DAOrder
Implements
METHOD LONGCHAR selectRecords () METHOD
NextRecord ( ) METHOD PrevRecord ( )
INTERFACE Acme.IList
METHOD NextRecord ( ) METHOD PrevRecord ( )
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Agenda

• Order Entry System Object Model
• Abstract Programming with Classes
• Working with Datasets / Temp-tables in Classes
• Miscellaneous Topics
• Debugging with Classes
• Using SUPER in Classes
• Accessing Classes on the AppServer
• Error Handling policy for Classes
• Proper Encapsulation in Classes
• Compiler Tips and Tricks
• Coding Standards

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Datasets and Temp-Tables in Classes

• Defined in a class as either PROTECTED or PRIVATE
  class data member
• Passed as parameters to methods (like procs)
• Cannot be returned from a method (like UDFs)
• Temp-table columns can contain Progress.Lang.Objec
  t
• Automatically upcast when put into column
• CAST column value to subclass before use

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Using a Class from a Temp-Table Column

• Use TYPE-OF function with CAST

DEFINE VAR rOrder AS Acme.BEOrder. FOR EACH
myTT / See if column is an external order
/ IF TYPE-OF (myTT.rObj, Acme.BEExternalOrder)
THEN rOrder CAST (myTT.rObj,
Acme.BEExternalOrder). / See if column is
an internal order / ELSE IF TYPE-OF
(myTT.rObj, Acme.BEInternalOrder) THEN
rOrder CAST (myTT.rObj, Acme.BEInternalOrder).
END.
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Protected DataSets / Temp-Tables

• PROTECTED access in subclass automatic use
  normal syntax
• Better than passing BY-REFERENCE or BIND,
  defining as SHARED
• No need to include definition in subclass

PROTECTED TEMP-TABLE ttOline PROTECTED TEMP-TABLE
ttOrder PROTECTED DATASET dsOrder
CLASS Acme.DAOrderSuper
Inherits
CLASS Acme.DAOrder
FOR EACH ttOrder DISPLAY ttOrder.CustomerName
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ProDataSet Event Handlers
CLASS Acme. DAOrderSuper

• Callbacks can be methods as well as internal
  procedures
• Protected datasets can have handlers in subclass

Inherits
CLASS Acme.DAOrder
/ Set callback in subclass for dataset in super
class / hDSOrder dsOrderHANDLE. hDSOrderSET-C
ALLBACK (AFTER-FILL, postDSFill). METHOD
VOID postDSFill (DATASET dsOrder).
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Demo of Datasets and Temp-Tables
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Agenda

• Order Entry System Object Model
• Abstract Programming with Classes
• Working with Datasets / Temp-tables in Classes
• Miscellaneous Topics
• Debugging with Classes
• Using SUPER in Classes
• Accessing Classes on the AppServer
• Error Handling policy for Classes
• Proper Encapsulation in Classes
• Compiler Tips and Tricks
• Coding Standards

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Debugging Classes

• Debugger works with Classes
• Demos have been running classes in the debugger
• Steps into each constructor / destructor in
  hierarchy
• Shows polymorphism in action subclass method is
  stepped into
• Remember
• Open class file in debugger to see data members

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Using SUPER in Classes

• Use SUPER ( ) to call super class constructor
• Only valid in constructor
• Must be first line if present
• Use SUPERmethod-name ( ) to call a method higher
  in the class hierarchy
• Valid in constructor, destructor, methods
• Must specify method-name (unlike procedures)

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Running with Classes on an AppServer
Remote classes cannot be accessed from client

• Option 1 Classes on both client and server
• Provide serialize and deserialize methods
• Remote class access support coming
• Option 2 Dispatch procedure on AppServer
• Client interacts with dispatcher
• Data passed in temp-table or dataset

Client
AppServer
Data
Data
Data
Data
Data
Data
AppServer
Client
Dispatch.p
RUN dispatch.p SET h. RUN getData (myTT) in h.
Dataset / Temp-table
Data
Data
Data
Dataset / Temp-table
Dataset / Temp-table
Data
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Error Handling

• RETURN ERROR not allowed in classes
• Options
• Use output parameter or return type
• Use STOP mechanism
• Improved error handling coming!

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Options for Handling Errors in Constructor

• Constructor handles error
• Run DELETE THIS-OBJECT in constructor
• Automatically runs destructors for any successful
  constructors in hierarchy
• Caller checks object reference for unknown

• Compile/Deployment errors found during NEW
• Mismatched parameters, super class not found
• Automatically aborts new and cleans up
• Caller checks object reference for unknown or
  ERROR-STATUSERROR

• Use an output parameter to indicate error to
  caller
• Caller must check for error and delete object

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Demo of Error Handling in Classes
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Encapsulation

• Good practice to keep data members protected or
  private
• Provide getter and setter routines to access
  data members
• Safe access
• Support read-only or write-only
• PROPERTY class members coming!

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Compiling Tips and Techniques

• Strong-typing only works if you compile running
  compile-on-the-fly catches all errors at
  runtime
• Be safe always rebuild/compile your code
• Recompiling only super classes can result in
  runtime errors always recompile subclasses that
  depend on super classes to be safe
• Exceptions to this rule

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Compiling Tips and Techniques

• No recompile of subclasses required when
• Methods / data is added to super class
• Only implementation changes, not signature
• When subclass accesses new methods and data, must
  recompile

A
B
E
I
F
J
C
K
G
D
H
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Compiling Tips and Techniques
Build procedures (make.p)
A

• COMPILER MULTI-COMPILE TRUE
• Uses cache to store classes already compiled in
  session
• Cache cleared when set to FALSE
• OE Architect uses this option
• Otherwise COMPILE builds full class hierarchy
  no timestamp check

B
D
C
E
F
H
G
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Recommended Coding Standards

• Always use packages in your type name
  Acme.DAOrder
• First node is your company name
• Class and Interface names use CamelCase starting
  with uppercase letter
• Interface names start with leading I
  Acme.IList
• Methods and data member use camelCase with
  lowercase first letter
• Follow rules for encapsulation, abstraction, and
  delegation

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In Summary

• Object-oriented ABL supports standard OO design
  patterns abstraction, encapsulation,
  inheritance, polymorphism
• OO functionality still coming
• Overloading
• Properties
• Error handling

• Remote Objects
• CLASS-GLOBAL (Static)
• Strongly-typed events

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Related Sessions

• DEV1 Introduction to ObjectOriented Language
  Concepts and Programming in OpenEdge ABL
• MOVE11 Using Classes and Procedures in OpenEdge
  10

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Questions?
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Thank you foryour time
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