dev-12: object-oriented programming in openedge ® abl evan bleicher senior development manager,...

DEV-12: Object-oriented Programming in OpenEdge® ABL

Evan BleicherSenior Development Manager,

Progress OpenEdge

© 2007 Progress Software Corporation2 DEV-12, Object-oriented Programming in OpenEdge ABL

Terminology / Concept Review

Type - Strong-typing at compile time• Data member – state

• Methods – behavior

• Package – type name fully qualified

Class – Defines type; data and methods

Object – Runtime instance of a class

Interface – Set of method definitions; contract

Inheritance – Inherit / specialize from super class


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties

Class Compiler Enhancements

Roadmap 10.1C and Beyond


File name: Acme\Inv\Order.cls

CLASS Acme.Inv.Order:

END CLASS.

CLASSStatement

CLASS <class-type> [package.]classname Single inheritence Multiple interface

ProPath

\Acme

\Inv

\Order.cls

\Order.r


Class Statement - Optional Modifiers

FINAL• Class can not be inherited

USE-WIDGET-POOL• Creates an unnamed widget pool scoped to

the class

• Dynamically created handle based within the class placed in pool

• Automatically deleted when class is destroyed

• Can be specified anywhere in the hierarchy


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties




Type Name

Type defines• State• Behavior• Inheritance relationship with other types

Enable strong-typing• Early binding - types determined at compile

time• Type-consistency enforced at compile time

and runtime

Full type names used to reference all classes

A Type is a definition


Example:Type Names

DEF VAR myOrder AS CLASS Acme.Inv.Order.

DEF VAR myInternalOrder AS CLASS Acme.Inv.InternalOrder.

DEF VAR myExternalOrder AS CLASS Acme.Inv.ExternalOrder.

myOrder = NEW Acme.Inv.Order ( ).

myInternalOrder = NEW Acme.Inv.InternalOrder ( ).

myExternalOrder = NEW Acme.Inv.ExternalOrder ( ).


USING Statement (10.1B)

Identifies a package of classes or a single qualified class

Supported in both Procedures and Class files

Applied at compile time to unqualified class names

First executable statement in file

Supports use of unqualified class name references


Example:Type Names with USING

USING Acme.Inv.*.

DEF VAR myOrder AS CLASS Order.

DEF VAR myInternalOrder AS CLASS InternalOrder.

DEF VAR myExternalOrder AS CLASS ExternalOrder.

myOrder = NEW Order ( ).

myInternalOrder = NEW InternalOrder ( ).

myExternalOrder = NEW ExternalOrder ( ).


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties




Methods

Keywords defining methods• METHOD

• CONSTRUCTOR

• DESTRUCTOR

Supports access modifiers• PRIVATE, PROTECTED, PUBLIC

• Default is PUBLIC

Define data type it returns or VOID

Methods define the behavior of an object


Overriding

Method in subclass can specialize method in super class

Can replace or augment behavior in super class

Overridden method must have:• Same signature

• OVERRIDE keyword

To access super class’ methods use • SUPER:method-name ( )

Specialization of methods


METHOD PUBLIC DECIMAL getOrderTotal ( ):

/* Calculate total */

RETURN totalOrder.

END METHOD.

Example:Overriding Acme\Inv\Order.cls

METHOD PUBLIC OVERRIDE DECIMAL getOrderTotal ( ): DEFINE VAR dTotal AS DECIMAL. DEFINE VAR dDiscount AS DECIMAL INITIAL 0.85.

dTotal = SUPER:getOrderTotal ( ). RETURN dTotal * dDiscount.END METHOD.

Acme\Inv\InternalOrder.cls

OVERRIDE keyword

Pre / Post processing


Polymorphism

Execution of an overridden method in a subclass from a reference to a super class

Code written using super class• Tightly coupled to inheritance and overriding

• Super class used at compile time, subclass assigned at runtime

• Method call on super class dispatched to subclass’ method

Same method can perform different behavior in subclass


Polymorphism – Example

Acme.Inv.InternalOrder

Acme.Inv.OrderMETHOD PUBLIC DECIMAL getOrderTotal ( ):

Acme.Inv.ExternalOrder

METHOD PUBLIC OVERRIDE DECIMAL getOrderTotal ( ):

METHOD PUBLIC OVERRIDE DECIMAL getOrderTotal ( ):


Polymorphism - Example Continued

USING Acme.Inv.*.

DEFINE VARIABLE myOrder AS CLASS Order.DEFINE VARIABLE bInternalCust AS Logical.DEFINE VARIABLE dTotal AS Decimal.

IF (bInternalCust = TRUE)THENmyOrder = NEW InternalOrder( ).

ELSE myOrder = NEW ExternalOrder( ).

dTotal = myOrder:getOrderTotal( ).

Super Class Reference

Calls either Acme.Inv.InternalOrder or Acme.Inv.ExternalOrder getOrderTotal ( )


Benefits of Polymorphism

Supports generic programming using super class or interface• Type used at compile time is super class or

interface

Specialized behavior is called at runtime automatically• Built on inheritance and overriding


Overloading (10.1B)

Different behavior / same name – based on different signature

Routines with the same name• Constructors and Methods

Must have different signatures• Number, type and mode of parameters• Can not differ by only return type or access

mode

No keyword to identify overloaded method

Multiple methods with the same name


Example:Overloading

METHOD PUBLIC INTEGER getOrder ( ):

END METHOD.

METHOD PUBLIC INTEGER getOrder (

INPUT iCustNum AS INTEGER):

END METHOD.

METHOD PUBLIC INTEGER getOrder (

INPUT cSalesRep AS CHARACTER):

END METHOD.

No arguments

One argument

- integer

One argument - character


Widening (10.1B)

Object-oriented features are strongly-typed• Data type of parameter must match

DATE DATETIME DATETIME-TZ

INTEGER INT64 DECIMAL

Mode is significant – Input, Output, Input-Output

Widening allows passing ‘smaller’ data type for ‘larger’


Example:WideningMETHOD PUBLIC INTEGER updateSalesDate (

INPUT dtTransRecord AS DATETIME-TZ):

END METHOD.

DEFINE VARIABLE myDate as DATE.

updateSalesRecord (INPUT myDate).

DEFINE VARIABLE myDateTime as DATETIME.

updateSalesRecord (INPUT myDateTime).

DEFINE VARIABLE myDateTimeTZ as DATETIME-TZ.

updateSalesRecord (INPUT myDateTimeTZ).


Hey, how does widening affect overloading?

Follows Overloading rules:• Number of parameters must match exactly

• Mode of parameter must match exactly

Relaxes data type matching rules:• With widening the caller’s data type does not

have to match exactly the callee’s data type

Overloading looks for the best match

Application design concern:• May result in ambiguity error


Example:Widening with Overloading

METHOD PUBLIC INTEGER updateSalesRecord (

INPUT dtTransDate AS DATETIME-TZ,

INPUT szSalesRep AS CHARACTER):

METHOD PUBLIC INTEGER updateSalesRecord (

INPUT dtTransDate AS DATE,

INPUT szSalesRep AS CHARACTER):

updateSalesRecord (INPUT myDate, INPUT “ABC”).

updateSalesRecord (INPUT myDateTime, INPUT “ABC”).

updateSalesRecord (INPUT myDateTimeTZ, INPUT “ABC”).


Example:Widening with Overloading

METHOD PUBLIC INTEGER UpdateSalesRecord (

INPUT dtTransDate AS DATETIME-TZ,

INPUT iSalesAmount AS INTEGER):

METHOD PUBLIC INTEGER UpdateSalesRecord (

INPUT dShipDate AS DATE,

INPUT deUnitsSold AS DECIMAL):

UpdateSalesRecord (INPUT myDate, INPUT myInt64).

UpdateSalesRecord (INPUT myDateTime, INPUT myDecimal).

UpdateSalesRecord (INPUT myDate, INPUT myInteger).

Does not compile – no match

Does not compile –

Ambiguity error


Overloading:Other considerations

Interoperability remains for static / dynamic • Table / Table-Handle

• Dataset / Dataset-Handle

Overloading supported for class and interface types

May result in runtime ambiguity error• Buffer-field

• Dynamic-function


Raising Error (10.1B)

Methods can raise error

RETURN ERROR [<error string>]

Caller handles error condition • NO-ERROR

• ON ERROR phrase

Retrieve <error string> via RETURN-VALUE function


Error Raised in an Expression

All methods invoked left-to-right• Order of operands apply to results of methods

On error the result of expression is unchanged

myInt = objA:methA( ) – objB:methB( ) * objC:methC( ).


Example:Error in an Expression

myInt = objA:methA( ) – objB:methB( ) * objC:methC( ).

If methA raises error, methB and methC are not invoked• myInt’s value remains unchanged

If methB raises error, methC is not invoked• myInt’s value remains unchanged


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties




Object Instantiation

Constructor of specified class is invoked on NEW

Constructor used to initialize data members

Constructor must call super class’s constructor• Via SUPER ( )

OpenEdge provides a call to the ‘default’ constructor• One with no parameters

• Only if super class has no other constructor


Example:Object Instantiation

refD = NEW D (D’s params).

Invokes D’s constructor

Class A

Class D

Class C

CONSTRUCTOR PUBLIC D (D’s params ):

SUPER (C’s params).

/* D’s constructor body */

END.

CONSTRUCTOR PUBLIC C (C’s params ):

SUPER (B’s params).

/* C’s constructor body */

END.

Class B


Overloading of Constructor

Classes can have multiple constructors

Same rules as overloading for methods

Parameters specified in NEW determine which constructor is invoked


Example:OverloadingCONSTRUCTOR PUBLIC Order ( ):

/* Constructor code goes here */END CONSTRUCTOR.

CONSTRUCTOR PUBLIC Order (INPUT iCustNum AS INTEGER):


CONSTRUCTOR PUBLIC Order (INPUT cSalesRep AS CHARACTER):


No argumentsOne argument - Character

One argument - Integer


Raising Error (10.1B)

Constructors can raise error

RETURN ERROR [<error string>]

Caller handles error condition • NO-ERROR• ON ERROR phrase

Object reference unchanged

Destructor invoked for all classes in hierarchy whose constructor completed successfully


Example:Raising Error in a Constructor

DEFINE VARIABLE refD AS CLASS D.

refD = NEW D ( ) NO-ERROR.

IF ERROR-STATUS:ERROR THEN

MESSAGE “INSTANTIATION FAILED: “

RETURN-VALUE.

Class D

Class C

Class A

CONSTRUCTOR PUBLIC D (D’s params ):

SUPER (C’s params).

/* D’s constructor body */

RETURN ERROR “ret code 101”.

END.

Class B


Object Deletion

Destructor of specified class is invoked on DELETE OBJECT

Destructor can not be called directly

OpenEdge calls all destructors in the class hierarchy

Destructors invoked from subclass to super class


Example:Object Deletion

DELETE OBJECT refD.

Invokes D’s Destructor

Class A

Class D

Class C

DESTRUCTOR PUBLIC D ( ):

/* D’s destructor */

END.

DESTRUCTOR PUBLIC C ( ):

/* C’s destructor */

END.

Class B


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties




Properties (10.1B)

Combine data member and method

Provide getter and setter accessors• Promotes data encapsulation

Optional access mode on accessors

Caller uses Property as data member

Support data encapsulation


DEFINE PUBLIC PROPERTY Salary AS DECIMAL GET ( ): /* Verify current user’s status */

RETURN Salary. END GET. PROTECTED SET (INPUT iVal AS DECIMAL): /* Is it within range? */ IF ival LT 100000 THEN Salary = ival. ELSE RETURN ERROR. END SET.

Example:Defining Property


Example:Accessing a Property

Same syntax as setting / retrieving a data member

Can be used in expression

EmployeeObj:Salary = newValue.

DISPLAY EmployeeObj:Salary.

DeptObj:Record (INPUT EmployeeObj:Name,

INPUT EmployeeObj:Salary).


DEFINE PUBLIC PROPERTY pi AS DECIMAL INITIAL 3.14

GET ( ):

RETURN pi.

END GET.

Example 2:Defining Read-Only Property (Constant)

DEFINE PUBLIC PROPERTY pi AS DECIMAL INITIAL 3.14

GET.


Example 3:Defining Property – not using default memory

DEFINE PUBLIC PROPERTY numUnits AS INTEGER

GET ( ):

/* Retrieve from temp-table – current value */

RETURN someTT:currentInventory.

END GET.

IF numRequested LT orderObj:numUnits THEN

orderObj:processOrder(INPUT numRequested).

ELSE

...


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties




Compiling Tips and Techniques

Strong-typing only works if you compile – running “compile-on-the-fly” delays errors until 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…


Call new method

Recompile

Add new method

Compile


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

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BB EE

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CC

II



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

Total files compiled:

MULTI-COMPILE = FALSE: 25

MULTI-COMPILE = TRUE: 8

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BB

EE FF HHGG

DDCC

Build procedures (make.p)


Recommended Coding Standards

Always use packages in your type name: Acme.DAOrder• First node is your company name

Class and Interface names use Pascal Case• Interface names start with leading “I”: Acme.IList

Methods and data member use camelCase with lowercase first letter

Use object-oriented design patterns -encapsulation, abstraction, and delegation


Today’s Agenda

Class Statement

Type Names

Methods

Object Hierarchy

Properties

Interface




10.1A

Class

Interface

Inheritance

Overriding

Access mode for data members

Strong type checking

Compiler improvements


10.1B

USING

Overloading

Properties

Default access mode methods - PUBLIC

Raising error from Constructor / Methods

Compiler system handle changes


D I S C L A I M E R

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.

D I S C L A I M E R


Targeted for 10.1C

Structured Error Handling• Similar to Try, Catch, Throw

Statics• Constructors, Data Members, Methods

Character to Longchar widening

NEW function


Future Release

Remote objects• Instantiating a class on the AppServer

Strongly typed application events• Publish / Subscribe for methods

Arrays of object references

Properties in interfaces

Inheritance of interfaces

Reflection

Dynamic invocation


In Summary

Object-oriented ABL supports standard object-oriented design patterns – abstraction, encapsulation, inheritance, polymorphism

ABL supports standard object-oriented constructs – interfaces, overriding, overloading, properties, strong-typing

More object-oriented functionality coming


Additional Object-oriented Exchange Sessions

DEV-6: Getting Started with Object-oriented ABL Programming (Evan Bleicher)

ARCH-7: A Class-based Implementation of the OERA (John Sadd)

ARCH-9: Using Object-oriented ABL Features in N-Tier Environment (Mike Fechner)

ARCH-12: Leveraging Design Patterns in ABL Applications (Phil Magnay)

DEV-20: Using Classes and Procedures in OpenEdge 10.1B (Phil Magnay)


For More Information, go to…

PSDN

Progress eLearning Community• What's New OE 10.1 Object Oriented

Programming

Documentation• 10.1B Object-oriented Programming manual

• 10.1B New and Revised Features manual


Questions?


Thank you for your time!

dev-12: object-oriented programming in openedge ® abl evan bleicher senior development manager,...

Documents

progress software corporation

class externalorder

class filesapplied

end class

progress openedge

new acme

var myinternalorder

var myexternalorder