ARTICLE
Nesting Interfaces
Interfaces can be nested. An interface can include
one or more interfaces as components, which can contain interfaces
themselves. An interface that includes another interface is called a
compound interface . An interface
nested within an interface is called a component interface. An interface
that does not contain any compound interfaces is called an elementary
interface.
All interface components of a compound interface have the same level. If
a compound interface i3 contains another compound interface
i2 , its interface component i1 becomes interface component of
i3 . A compound interface includes each interface component
exactly once. A component interface exists only once even if it is used
again as a component of another component interface.
The statement INTERFACES is used for nesting interfaces within an
interface definition:
INTERFACE i3.
INTERFACES: i1, i2 ...
ENDINTERFACE.
Here the interface i3 consists of its components and the
interfaces i1 and i2 . In the compound interface the
components of the component interfaces are visible using the interface
component selector (~). Within the above definition of i3 ,
expressions such as i1~comp or i2~comp are possible.
However, independent names can be defined using the
ALIASES statement.
Using Alias Names
Within interface definitions, the statement ALIASES
can be used to assign alias names to the components of component
interfaces, and therefore make those nested to a depth greater than one
level visible within the interface definition.
INTERFACE i2.
INTERFACES i1.
ALIASES alias21 FOR i1~comp1.
ENDINTERFACE.
INTERFACE i3.
INTERFACES i2.
ALIASES alias31 FOR i2~alias21.
ALIASES alias32 FOR i2~comp2.
ENDINTERFACE.
Accessing Interface Reference Variables
Reference variables typed with reference to a compound interface can be
assigned reference variables typed with reference to one of the
component interfaces ( up cast ). The latter
can be used to address the components of the component interfaces. The
opposite case cannot be checked statically and must take place with the
casting operator (?= or CAST
) ( down cast ).
INTERFACE i1.
DATA comp1.
ENDINTERFACE.
INTERFACE i2.
DATA comp2.
INTERFACES i1.
ENDINTERFACE.
INTERFACE i3.
INTERFACES i2.
ENDINTERFACE.
DATA: iref1 TYPE REF TO i1,
iref2 TYPE REF TO i2,
iref3 TYPE REF TO i3.
iref2 = iref3 .
iref1 = iref2 .
* recommended access:
... iref1- comp1 ...
... iref2- comp2 ...
* this access is not recommended:
... iref2- i1~comp1 ...
... iref3- i2~comp2 ...
Implementing Nested Interfaces in Classes
When a nested interface is implemented in a class, all associated
interfaces are implemented in the class at the same level irrespective
of their nesting hierarchy and the class must implement all methods only
once.
INTERFACE i1.
DATA comp1.
METHODS meth1.
ENDINTERFACE.
INTERFACE i2.
DATA comp2.
INTERFACES i1.
ENDINTERFACE.
INTERFACE i3.
DATA comp3.
INTERFACES i2.
ENDINTERFACE.
CLASS class DEFINITION.
PUBLIC SECTION.
INTERFACES i3.
ENDCLASS.
CLASS class IMPLEMENTATION.
METHOD i1~meth.
...
ENDMETHOD.
ENDCLASS.
DATA cref TYPE REF TO class.
DATA iref1 TYPE REF TO i1.
DATA iref2 TYPE REF TO i2.
DATA iref3 TYPE REF TO i3.
iref1 = iref2 = iref3 = cref.
* recommended access:
... iref1- comp1 ...
... iref2- comp2 ...
... iref3- comp3 ...
* this access is not recommended:
... cref- i1~comp1 ...
... cref- i2~comp2 ...
... cref- i3~comp3 ...
... iref3- i1~comp1 ...
... iref3- i2~comp2 ...
... iref2- i1~comp1 ...
Assignments using up casts are always possible. Class reference
variables for classes that implement a compound interface can be ass
igned to all interface references that are typed with reference to an
associated interface component. In the class, the interface reference
variables know only the components of their respective interfaces. The
same applies for assignments between interface reference variables. It
is possible to access components using the interface component selector,
but this is not recommended. Compound expressions such as
cref- i3~i2~comp2 or cref- i3~i2~i3~comp3 are not possible.
Documentation extract taken from SAP system, � Copyright SAP AG. All rights reserved