I have an ABAP include containing only constants. (Not my code)
I want to use these constants in an ABAP OO method. (My code)
How can I use these constants in an object oriented ABAP environment without copying them?
The idea is to define these constants once and only once. And they are already defined in this include.
Additional question: is it possible to create a class that contains the constants of the above include in a public section, so that I do the include only once and use these constants in an object oriented way from other classes?
Assuming that the include really only contains constant definitions: From the Class Builder, select Goto --> Class-relevant Local Definitions and place an INCLUDE statement there. This should make the constants available throughout your implementation.
Will you need these constants just for this class? Create private atributes in the class.
Will you use it in other classes (and programs as well)? Create and class with static components and use it everywhere...
Related
I know that ABAP Objects are kinda old but as far as my knowledge goes you still have to use at least two "sections" to create a complete class.
ABAP:
CLASS CL_MYCLASS DEFINITION.
PUBLIC SECTION.
...
PROTECTED SECTION.
...
PRIVATE SECTION.
...
ENDCLASS.
CLASS CL_MYCLASS IMPLEMENTATION.
...
ENDCLASS.
Java:
public class MyClass {
<visibility> <definition> {
<implementation>
}
}
Wouldn't it make development easier/faster by having a combination of both like most modern languages have?
What are the reasons for this separation?
Easier/faster for the human (maybe), but costly for the compiler: It has to sift through the entire code to determine the structure of the class and its members, whereas in the current form, it only needs to compile the definition to determine whether a reference is valid. ABAP is not the only language that separates definition from implementation: Pascal did so for units, and Object Pascal for classes. One might argue that C++ allows for same construct without specifying an implementation section when you're not using inline member function declarations.
Maybe another reason:
Most (?) classes are not defined with manual written code, but via SE24. There you define the interface in one dynpro and write the code in another one.
Internally the interfaces are stored in one source, the code is stored in another source. So it is reasonable to separate the interface and the implementation.
Official docs on visibility modifiers in Kotlin say that package-level elements marked private are be visible only in the module in which they are declared.
So class A declared in Module1.kt isn't visible in Module2.kt. But if I try to add to Module2.kt it's own class A I get the Redeclaration: A error.
Since I can't access in Module2.kt to Module1's A class, why isn't the name A free to use?
"A module is a set of Kotlin files compiled together" (Visibility Modifiers - Kotlin Programming Language).
In your example, Module1.kt and Module2.kt are separate source files and despite their names they are not necessarily part of separate modules:
If they are compiled together then they are part of the same module.
If they are compiled separately from one another then they will be part of different modules and each can define their own private class A.
Keep in mind that visibility is different from identity. Even if a class is not visible elsewhere it doesn't mean that it does not exist. Loading multiple class declarations with the same fully-qualified name can (and likely will) cause issues at run-time.
I read somewhere that interfaces can have member variables.
Static final constants only, can use
them without qualification in classes
that implement the interface. On the
other paw, these unqualified names
pollute the namespace. You can use
them and it is not obvious where they
are coming from since the
qualification is optional.
I am not quite understood by what they meant? Any help?
What you read is incorrect. Interfaces cannot have member variables.
In VB.Net the only allowable definitions inside an interface are
Properties
Methods
Events
Type Definitions (not legal in C#)
I'm not entirely sure what the above paragraph is referring to. Based on the text though it sounds like it's refering to Java. They phrase static and final is most often associated with Java code and not .Net (static and readonly).
Can you give us some more context on it?
If you define a constant like this inside a class MyClass:
public static final int MY_CONSTANT = 1;
you can refer to it from other classes as MyClass.MY_CONSTANT, using the MyClass qualifier. This hints the location of the constant definition.
If you define such a constant in an interface MyInterface, you still can refer to it using MyInterface.MY_CONSTANT. However in the classes implementing MyInsterface you can simply use MY_CONSTANT without "MyInterface" prefix.
It may look convenient (less key strokes), but may lead to confusion because without qualifier (prefix) it is not clear where the constant was originally defined.
Adding member variables to interfaces would be bringing in MI through the back door.
Not available in .NET, sorry.
I wish it were there though.
What advantage is there, if any, to using Modules rather than classes in VB? How do they differ, and what advantages/disadvantages are there in using modules? In VB or VB.NET, I use both.
(A) Modules
and
(B) Classes with only Shared functions
solve the same problem: Both allow you to logically group a set of functions.
Advantages of using a module:
It allows you to define extension methods.
For someone reading your code, it is immediately obvious that this is not a class representing a group of stateful objects but just a "function container".
Advantages of using a class with shared functions:
It's easy to extend it with instance (= non-shared) variables, functions and properties later on.
So, if you are writing a set of helper functions and want to logically group them (where the concept of a state of this group just doesn't make sense), use a module -- this is exactly what they are here for. On the other hand, if you have a function that conceptually fits to an already existing class, add it as a shared function to that class.
A major difference is that methods in modules can be called globally whereas methods in classes can't. So instead of ModuleName.MyMethod() you can just call MyMethod(). Whether that is an advantage or disadvantage depends on the circumstances.
Module are come earlier and now VB.NET just let it for backward compatibility. Modules and Class are nearly same. You can call Module.Function() directly as it treat as Shared Function in a class. Class you can define Shared Function/Method and additionally can create an instance like Dim c as Class = New Class().
Avoid use of Module, instead use Class. it is good for you to write a better OOP programming.
I'm writing some unit tests in cocoa for a data driven application.
I've got a constants header file which defines a whole heap of variables including paths to the databases etc.
I was wondering if it's possible to get all the classes to use a different set of constants which would link to a testing version of the database etc.
I've tried redefining the constants, but it doesn't take effect globally.
You could instead have a structure that contained all of the constants used and pass it into your objects' constructors. Normally that structure will be whatever values are necessary to run but when you're testing, you would instead pass a structure with the fields initialized to test parameters
I'm know absolutely nothing about objective C though, so I'm not sure if this is possible for you.
You can put all your constants into a singleton object that has read only properties for the constants. Then you can mock the constants object and change the constants.