lecture 13 abap objects

8/18/2019 Lecture 13 Abap Objects

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Lecture 13

ABAP Objects

BCO5647 Applications Programming Techniques (ABAP)


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Readings & Objectives

Readings

Keller & KellerChapter 5

Section 5.3

Objecties

!his lect"re #ill

Reie# the $roced"ral $rogra%%ing odel

'ntrod"ce the Object Oriented $rogra%%ing odel

()a%ine ho# *B*$ has applied OO +eat"res to its lang"age

()a%ine ho# classes are de+ined in *B*$ Objects

()a%ine ho# attrib"tes and %ethods o+ a class are de+ined in *B*$ Objects

()a%ine the objects are created in *B*$ Objects

()a%ine ho# re+erences are assigned in *B*$ Objects

()plain the %eaning o+ a constr"ctor and ho# it is "sed in *B*$ Objects

,isc"ss the concept o+ inheritances and ho# it is "sed in *B*$ Objects


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The Procedural Programming Model

• Separation of data and functions.• Non-encapsulated (i.e. direct) access to data.

• Possibility of encapsulating functions using modularization.

Data Data

Data Data

Data

Function

FunctionFunction Function

FunctionFunction FunctionFunction


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The Procedural Programming Model

• Type denitions.

• Data declarations

• ain program- !alling subroutines- !alling function modules

• Denition of subroutines.

report . . .*--------------------------------types: . . .

data: . . .. . .perform form1 . . .call function ‘FB1’.. . .call function ‘FB2’.. . .

*--------------------------------form f1 . . . . . .endform.


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The Object Oriented Programming Model

"ncapsulation of Data and #unctions

!ree

/o"se

Crane

Objects are an abstraction o+ the real #orld

Objects are "nits %ade "p o+ data and o+ the

+"nctions belonging to that data

Real #orld&odel

,ata&ethod

&ethod

&ethod

,ata&ethod

&ethod

&ethod

,ata&ethod &ethod

&ethod

Boat

,ata&ethod

&ethod

&ethod


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!lass

• $i%es a general descriptionof ob&ects ('blueprint)

• "stablises status types

(attributes) and bea%ior(metods)

*b&ect• +e,ection of real orld

• Specic instance of a class

lcl_class Attribute

Attribute

Attribute Method

Method


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• /P ob&ect statements can be used in procedural /Pprograms.

• *b&ects (classes) contain procedural statements.

report . . .

*--------------------------------

data: counter type i. wa type kna1.

. . .

class lcl_car definition.

. . .

endclass.

*------ main program ------

counter = counter 1.

create o!"ect . . .

mo#e wa to . . .


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Advantages of the Object-Oriented Programming Model

over the Procedural Programming Model

• 0mpro%ed softare structure andconsistency in te de%elopment process.

• +educed maintenance e1ort and less susceptibility to errors.

• /etter integration of te customer2user into te analysis3 design3 and

maintenance process.

• "asier and safer possibilities for e4tending te softare.


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Uniied Modeling Language !UML"

• 56 is a orldide standardized modelinglanguage.

• 0t is used for te specication3 construction3%isualization and documentation of models forsoftare systems.

• 56 contains a number of di1erent diagram typesin order to represent di1erent %ies of a system. Tese include 7

• !lass diagrams

• *b&ect diagrams

• 5se !ase diagrams

• State Diagrams

• Se8uence diagrams etc.


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UML Re#resentation o a $lass

• class is represented by a rectangle in 56 notation. #irst3te class9s name is gi%en3 ten its attributes3 and nally its

metods.• ttributes describe te data tat can be stored in teob&ects of a class. Tey also determine te status of anob&ect.

• etods describe te functions tat an ob&ect can perform. Tey terefore determine te ob&ect9s bea%ior.


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UML $lass %iagram

class diagram describes all static relationsips beteen teclasses. Tere are to basic forms of static relationsips7

Association0n tis e4ample7 customer boo:s a car at a rentalcar company.

Generalization / Specialization0n tis e4ample7 car3 a bus3 and a truc: are all %eicles.


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OO %einitions Objects

$riate access

• Encapsulation

• As a rule, attributes

$"blic access

• Interface

• As a rule,methods, events

*ttrib"tes

(ents

*ttrib"tes

&ethods

(ents

6a%e 8/ Berlin

8ength 7 %

-eight 39 :g

landed

&ethods

+l;land

()a%ple airplane

• Te ob&ect in te abo%e model as to layers7 an outer sell and aninner core. 5sers can only see te outer sell3 ile te inner coreremains idden.

• Public components (outer sell)7 te outer sell contains tecomponents of te ob&ect tat are %isible to users.

• Pri%ate components (inner core)7 te components of te inner core(attributes3 metods and e%ents) are only %isible itin te ob&ectitself.


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OO %einitions $lasses

$lane tic:et$lane

• 0n te real orld3 tere are ob&ects3 suc as %arious airplanes and planetic:ets. Some of tese ob&ects are %ery similar3 tat is3 tey can bedescribed using te same attributes or caracteristics and pro%ide tesame functions.

• Similar ob&ects are grouped togeter in classes. class is terefore adescription of a 8uantity of ob&ects caracterized by te same structureand te same bea%ior.


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$lass %einition '(nta)

$%&'' ()F+,+.

. . .

)+($%&''.

$%&'' /%))+,&,+.

. . .

)+($%&''.

• Denition Part Te class components (e.g. attributes and metods).

• 0mplementation Part Te metod implementations.

• Te !6SS statement cannot be nested.


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$lass %einition *)am#le

0)/0, )&/%)1 .

* $lass (efinitions.

$%&'' lcl_airplane ()F+,+. /3B%$ ')$,+.

(&,&: name type strin45

wei46t type i5

carrier type strin4.

),7(': add_airplane5

display_airplane5

)+($%&''.*

* $lass mplementations.*

$%&'' lcl_airplane /%))+,&,+.

),7( add_airplane.

. . .

)+(),7(.

),7( display_airplane.

. . .

)+(),7(.

)+($%&''.


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OO %einitions Attributes

• ttributes are te data ob&ects itin a class. Tey re,ect an

ob&ects state.• ll /P data types can be used for attributes. Te DT

statement is used to declare instance attributes.

• To declare a static attribute3 use te !6SS-DT statement.

$%&'' ()F+,+.

/08&,) ')$,+.

. . . types: . . .

constants: . . .

data: #aria!le1 type local-type5

#aria!le2 type global_type5

#aria!le9 like #aria!le15

#aria!le type . . . read-only.

#aria!le; type ref to class-name5

#aria!le< type ref to type-name.


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OO %einitions Methods

• Methods are internal procedures in classes tat determinete bea%ior of te ob&ects.

• etods a%e a signature (interface parameters ande4ceptions) tat enables tem to recei%e %alues en teyare called and pass %alues bac: to te calling program.

• etods can a%e any number of 0P*+T0N$3 ";P*+T0N$3and !


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$lass Methods '(nta)

$%&'' ()F+,+.

. . .

),7(':

/0,+ . . . )/0,+ . . .

$7&++ . . .

0),30++ . . . )$)/,+' . . .

)+($%&''.

$%&'' /%))+,&,+.

),7(

. . .

)+(),7(

)+($%&''.


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$lass Methods *)am#le

0)/0, )&/%)2.

$%&'' lcl_airplane ()F+,+.

/3B%$ ')$,+.

(&,&: name type strin45

wei46t type i5

carrier type strin4.

),7(': init_airplane

importin4 iname type strin4 iwei46t type i5

display_airplane.)+($%&''.

$%&'' lcl_airplane /%))+,&,+.

),7( init_airplane.

name = iname.

wei46t = iwei46t.

carrier = ‘%7’.

)+(),7(.

),7( display_airplane. write:> ‘name :?5 name.

)+(),7(.

)+($%&''.


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$reating Objects

•*b&ects are created using te statement !+"T" */="!T ref_name . . .

• Tey can only be created and addressed using reference%ariables.

• class contains te generic description of an ob&ect.

• During te program runtime3 te class is used to create discreteob&ects (instances) in te memory. (instantiation).

• 0f tis is te rst time te class is accessed3 te class is alsoloaded into te memory.

lcl


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$reating Objects *)am#le

0)/0, )&/%)9.


/3B%$ ')$,+.

(&,&: . . .

),7(': . . .

)+($%&''.

$%&'' lcl_airplane /%))+,&,+.

),7( init_airplane. . . .

)+(),7(.

),7( display_airplane. . . . )+(),7(.

)+($%&''.

',&0,-F-')%)$,+.

(&,& : airplane1 ,@/) 0)F to lcl_airplane5

airplane2 ,@/) 0)F to lcl_airplane.

$0)&,) BA)$, airplane1.$0)&,) BA)$, airplane2.

$&%% ),7( airplane1-init_airplane

eCportin4 iname = ‘($’

iwei46t = 9;.

$&%% ),7( airplane1-display_airplane.


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Assigning Reerences

0n te pre%ious e4ample3 te !+"T" */="!T statement createsan ob&ect in te main memory.

0f te folloing statement is added after te ob&ects a%e beencreated 7

airplane> ? airplane@

Te reference %ariables ill be assigned to eac oter. *nce itas been assigned3 airplane> points to te same ob&ect as

reference airplane@.


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$onstructors

CREATE

OBJECT

• constructor is a special metod for creating ob&ects it adened initial state.

• 0t only as importing parameters and e4ceptions.

• "4actly one constructor is dened per class.

• 0t is e4ecuted e4actly once per instance.

lcl_airplane

name

weight

count

constructor


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$onstructors *)am#le

0)/0, )&/%).


/3B%$ ')$,+. (&,&: name type strin45

wei46t type i5 carrier type strin4.

),7(': constructor importin4

icarrier type strin4.)+($%&''.

$%&'' lcl_airplane /%))+,&,+. ),7( constructor.

$arrier = icarrier. )+(),7(.

)+($%&''.

',&0,-F-')%)$,+.(&,& : airplane1 ,@/) 0)F to lcl_airplane5

airplane2 ,@/) 0)F to lcl_airplane.

$0)&,) BA)$, airplane1 eCportin4

icarrier = ‘%7’.$0)&,) BA)$, airplane2 eCportin4

icarrier = ‘D&’.


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+nheritance

• 0neritance is a relationsip in ic one class (te subclass)inerits all te main caracteristics of anoter class (tesuperclass).

• 0neritance is an implementation relationsip tat empasizessimilarities beteen classes.

• Te ineritance relationsip is often described as an 'is-arelationsip7 a passenger plane is an airplane.

lecture 13 abap objects

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