b.santos/abap-cheat-sheets
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Update

Browse Source
This commit is contained in:
danrega
2024-02-05 13:05:39 +01:00
parent ccc950a81c
commit 1b2238f2b6
7 changed files with 176 additions and 44 deletions
Download Patch File Download Diff File Expand all files Collapse all files

134
04_ABAP_Object_Orientation.md
View File

@@ -14,13 +14,20 @@
- [Creating the Visibility Sections](#creating-the-visibility-sections)
- [Defining Components](#defining-components)
- [Working with Objects and Components](#working-with-objects-and-components)
- [Declaring Reference Variables](#declaring-reference-variables)
- [Creating Objects](#creating-objects)
- [Assigning Reference Variables](#assigning-reference-variables)
- [Accessing Attributes](#accessing-attributes)
- [Calling Methods](#calling-methods)
- [Method Chaining](#method-chaining)
- [Self-Reference me](#self-reference-me)
- [Notes on Inheritance](#notes-on-inheritance)
- [Notes on Polymorphism and Casting](#notes-on-polymorphism-and-casting)
- [Notes on Interfaces](#notes-on-interfaces)
- [Additional Notes](#additional-notes)
- [Excursions](#excursions)
- [Friendship](#friendship)
- [Events](#events)
- [Excursion: Factory Methods and Singletons as Design Patterns](#excursion-factory-methods-and-singletons-as-design-patterns)
- [Factory Methods and Singletons as Design Patterns](#factory-methods-and-singletons-as-design-patterns)
- [More Information](#more-information)
- [Executable Example](#executable-example)
@@ -293,7 +300,7 @@ ENDCLASS.
(also known as
[signature](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abensignature_glosry.htm "Glossary Entry"))
with which methods can get values to work with when being called and pass values
back to the caller.
back to the caller (see the notes on formal and actual parameters below).
- [Static
methods](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenstatic_method_glosry.htm "Glossary Entry")
can only access static attributes of a class and trigger static
@@ -329,7 +336,10 @@ In the simplest form, methods can have no parameter at all. Apart from that, met
[generic](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abengeneric_data_type_glosry.htm "Glossary Entry")
or
[complete](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abencomplete_data_type_glosry.htm "Glossary Entry")
type.
type. Examples:
> - `fp` is the formal parameter that has a complete type: `... meth IMPORTING fp TYPE string ...`
> - `gen` is the formal parameter that has a generic type: `... meth IMPORTING gen TYPE any ...`
> - Find more information about generic types also in the [Data Types and Data Objects](16_Data_Types_and_Objects.md#generic-types) cheat sheet.
> - This formal parameter includes the specification of how the
value passing should happen. Parameters can be [passed by
reference](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenpass_by_reference_glosry.htm "Glossary Entry")
@@ -420,11 +430,18 @@ CLASS local_class DEFINITION.
stat_meth3 IMPORTING VALUE(m) TYPE i, "pass by value
stat_meth4 IMPORTING REFERENCE(n) TYPE i, "pass by reference
stat_meth5 IMPORTING o TYPE i, "same as n; the specification of REFERENCE(...) is optional
stat_meth6 RETURNING VALUE(p) TYPE, "pass by value once more (note: it's the only option for returning parameters)
stat_meth6 RETURNING VALUE(p) TYPE i, "pass by value once more (note: it's the only option for returning parameters)
"OPTIONAL/DEFAULT additions
stat_meth7 IMPORTING q TYPE i DEFAULT 123
r TYPE i OPTIONAL.
r TYPE i OPTIONAL,
"The examples above use a complete type for
"the parameter specification. Generic types
"are possible.
stat_meth8 IMPORTING s TYPE any "Any data type
t TYPE any table "Any internal table type
u TYPE clike. "Character-like types (c, n, string, d, t and character-like flat structures)
ENDCLASS.
@@ -441,7 +458,7 @@ ENDCLASS.
## Working with Objects and Components
**Declaring reference variables**:
### Declaring Reference Variables
- To create an object, a [reference variable](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenreference_variable_glosry.htm "Glossary Entry")
must be declared.
- Such an [object reference
@@ -455,7 +472,9 @@ DATA: ref1 TYPE REF TO local_class,
ref3 LIKE ref1.
```
**Creating objects**:
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Creating Objects
- Using the instance operator
[`NEW`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenconstructor_expression_new.htm),
@@ -494,7 +513,10 @@ DATA(ref2) = NEW some_class( ). "Reference variable declared inline, explic
"CREATE OBJECT ref4 TYPE some_class. "Corresponds to the result of the expression above
```
**Assigning reference variables**: To assign or copy
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Assigning Reference Variables
To assign or copy
reference variables, use the [assignment
operator](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenassignment_operator_glosry.htm "Glossary Entry")
`=`. In the example below, both object reference variables have the same
@@ -510,6 +532,8 @@ ref1 = NEW #( ).
ref2 = ref1.
```
More examples for dealing with object reference variables:
**Overwriting reference variables**: An [object
reference](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenobject_reference_glosry.htm "Glossary Entry")
is overwritten when a new object is created with a reference variable
@@ -545,7 +569,9 @@ CLEAR ref.
> Objects use up space in the memory and should therefore be
cleared if they are no longer needed. However, the [garbage collector](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abengarbage_collector_glosry.htm "Glossary Entry") is called periodically and automatically by the [ABAP runtime framework](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenabap_runtime_frmwk_glosry.htm "Glossary Entry") and clears all objects without any reference.
**Accessing attributes**:
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Accessing Attributes
- Instance attributes: Accessed using
the [object component selector](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenobject_component_select_glosry.htm "Glossary Entry")
`->` via a reference variable.
@@ -572,7 +598,9 @@ DATA dobj1 TYPE some_class=>some_type.
DATA dobj2 LIKE some_class=>some_static_attribute.
```
**Calling methods**:
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Calling Methods
- Similar to accessing attributes, instance
methods are called using `->` via a reference variable.
- Static
@@ -580,11 +608,8 @@ methods are called using `=>` via the class name. When used
within the class in which it is declared, the static method can also be
called without `class_name=>...`.
- When methods are called, the (non-optional) parameters must be specified within parentheses.
- You might also stumble on method
calls with [`CALL METHOD`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abapcall_method_static.htm)
statements in older programs. It should no longer be used, however, `CALL METHOD` statements are the
only option in the context of dynamic programming.
- You might also stumble on method calls with [`CALL METHOD`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abapcall_method_static.htm)
statements. These statements should no longer be used. Note that `CALL METHOD` statements are the only option in the context of [dynamic programming](06_Dynamic_Programming.md). Therefore, `CALL METHOD` statements should be reserved for dynamic method calls.
Examples for instance method calls and static method calls:
@@ -642,13 +667,13 @@ class_name=>meth( CHANGING g = h ).
"Calling (static) methods having a returning parameter.
"Basically, they do the same as methods with exporting parameters
"but they are way more versatile and you save lines of code.
"but they are way more versatile, and you can save lines of code.
"They do not need temporary variables.
"In the example, the return value is stored in a variable declared inline.
"i and k are importing parameters
DATA(result) = class_name=>meth( i = j k = l )
DATA(result) = class_name=>meth( i = j k = l ).
"They can be used with other statements, e. g. logical expressions.
"In the example below, the assumption is that the returning parameter is of type i.
@@ -659,17 +684,78 @@ ENDIF.
"They enable method chaining.
"The example shows a method to create random integer values.
"The methods have a returning parameter.
DATA(random_no) = cl_abap_random_int=>create( )->get_next( ).
"Receiving parameter: Available in methods defined with a returning parameter;
"RECEIVING parameter: Available in methods defined with a returning parameter;
"used in standalone method calls only.
"In the snippet, m is the returning parameter; n stores the result.
class_name=>meth( EXPORTING i = j k = l RECEIVING m = DATA(n) ).
```
**Self-Reference me**
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Method Chaining
As shown in the previous example, method chaining is possible for functional method calls (i.e. methods that have exactly one return value declared with `RETURNING`) at appropriate read positions. In this case, the method's return value is used as an ABAP operand.
A chained method call can consist of multipled functional methods that are linked using component selectors `->`. The return values of each method are references to the next method.
```abap
"The following example demonstrates method chaining
"The following class creates random integers. Find more information in the
"class documentation.
"Both methods have returning parameters specified.
DATA(some_int1) = cl_abap_random_int=>create( seed = cl_abap_random=>seed( )
min = 1
max = 10 )->get_next( ).
"Getting to the result as above - not using method chaining and inline declarations.
DATA some_int2 TYPE i.
DATA dref TYPE REF TO cl_abap_random_int.
dref = cl_abap_random_int=>create( seed = cl_abap_random=>seed( )
min = 1
max = 10 ).
some_int2 = dref->get_next( ).
"Using the RECEIVING parameter in a standalone method call
DATA some_int3 TYPE i.
dref->get_next( RECEIVING value = some_int3 ).
"IF statement that uses the return value in a read position
IF cl_abap_random_int=>create( seed = cl_abap_random=>seed( )
min = 1
max = 10 )->get_next( ) < 5.
... "The random number is lower than 5.
ELSE.
... "The random number is greater than 5.
ENDIF.
"Examples using classes of the XCO library (see more information in the
"ABAP for Cloud Development and Misc ABAP Classes cheat sheets), in which
"multiple chained method calls can be specified. Each of the methods
"has a returning parameter specified.
"In the following example, 1 hour is added to the current time.
DATA(add1hour) = xco_cp=>sy->time( xco_cp_time=>time_zone->user )->add( iv_hour = 1 )->as( xco_cp_time=>format->iso_8601_extended )->value.
"In the following example, a string is converted to xstring using a codepage
DATA(xstr) = xco_cp=>string( `Some string` )->as_xstring( xco_cp_character=>code_page->utf_8 )->value.
"In the following example, JSON data is created. First, a JSON data builder
"is created. Then, using different methods, JSON data is added. Finally,
"the JSON data is turned to a string.
DATA(json) = xco_cp_json=>data->builder( )->begin_object(
)->add_member( 'CarrierId' )->add_string( 'DL'
)->add_member( 'ConnectionId' )->add_string( '1984'
)->add_member( 'CityFrom' )->add_string( 'San Francisco'
)->add_member( 'CityTo' )->add_string( 'New York'
)->end_object( )->get_data( )->to_string( ).
```
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Self-Reference me
When implementing instance methods, you can optionally make use of the implicitly available object reference variable [`me`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenme.htm) which is always available at runtime and points to the respective object itself. You can use it to refer to components of the instance of a particular class:
``` abap
@@ -1066,7 +1152,7 @@ i_ref = NEW class( ).
<p align="right"><a href="#top">⬆️ back to top</a></p>
## Additional Notes
## Excursions
### Friendship
@@ -1154,7 +1240,7 @@ SET HANDLER handler3.
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Excursion: Factory Methods and Singletons as Design Patterns
### Factory Methods and Singletons as Design Patterns
In object-oriented programming, there a plenty of design patterns. Covering these ones here to get a rough idea: factory methods and singletons. Both are relevant if you want to restrict or control the instantiation of a class by external users of this class.