Download chapter 6: 'Advanced Concepts in ABAP Objects'
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Chapter Excerpt:
6.3.2 Creating Interfaces
With regard to their declaration, interfaces in ABAP Objects play the
same role as classes. Just like classes, interfaces are object types that
reside in the namespace of all types. While a class describes all
aspects of a class, an interface only describes a partial aspect. As mentioned
above, standalone interfaces can be regarded as special
abstract classes without implementation that can be used in multiple
classes.
Accordingly, the declaration of a standalone interface hardly varies
from the declaration of a class. As with classes, we distinguish global
and local interfaces in the same way that we do global and local
classes. Therefore, the same rules apply regarding their usability.
Global interfaces can be used in any program if the package assignment
of the program permits it. Local interfaces can only be used in
the same program.
The syntax for declaring a local interface is:
INTERFACE intf.
DATA ...
CLASS-DATA ...
METHODS ...
CLASS-METHODS ...
...
ENDINTERFACE.
Basically, the declaration of an interface corresponds to the declaration
part of a class, where instead of CLASS—ENDCLASS, you simply use
INTERFACE—ENDINTERFACE. Interfaces can contain exactly the same
components as classes. Unlike classes, however, interfaces don't
need to be divided into different visibility sections because interface
components are always integrated in the public visibility section of
classes.
To create a global interface, use the Class Builder just as you would
for global classes. In the Object Navigator, select Create · Class
Library · Interface. In Transaction SE24, after selecting Create, select
the Interface object type instead of Class.
Figure 6.7 shows the Class Builder for a global interface ZIF_DRIVE_ Class Builder
OBJECT. You see the familiar user interface that you know from
working with classes. When creating components, you need to specify
the same input as you do for classes, except for the assignment to
a visibility section. In the shown example, we created the same
methods ACCELERATE and SHOW_SPEED as in ZCL_VEHICLE presented
in Figure 4.7 in Chapter 4. The shown interface can therefore
serve as an interface to objects that can be driven.
The Class Builder generates the corresponding ABAP statements in a
program of the interface pool type, the source code of which can also
be edited directly via Goto · Interface Section (see Figure 6.8). As in
class pools, the addition PUBLIC identifies the interface as a global
interface that can be used in all programs. Apart from the declaration
of the global interface, an interface pool cannot contain any local
type declarations except for the publication of type groups.
The essential difference between interfaces and classes is that there is
no implementation part for an interface. Therefore, it is not necessary
to add DEFINITION to INTERFACE. The methods of an interface are
all abstract. They are fully declared, including their parameter interface,
but not implemented in the interface. Like the subclasses that
implement the abstract methods of their abstract superclasses, all
classes that want to use an interface must implement its methods.
Chapter 6: 'Advanced Concepts in ABAP Objects'
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