ARTICLE
Objects
Objects are instances of classes. There can be any number of objects or
instances in a class. Each object has a unique identity and its own
attributes.
As standard, all objects have the same priority in the
data area of an
internal session . This means that
objects can only be accessed from within an internal session.
For transaction-independent objects,
shared objects are available, which can be accessed by all
programs of an application server at the same time.
Object Services are available
for handling persistent objects in the database. These link the
attributes of objects with the content of database tables and can
execute object-oriented transactions.
Creating Objects
Before an object can be created, an object reference
variable is required that can point to the required class:
Once a class reference variable obj is declared for a class
class , an object of that class can be created using the statement
CREATE OBJECT obj . This statement
creates an instance of the class class and the reference variable
obj contains a reference to this object.
Once a class reference variable obj is declared for a superclass
of the class class or an interface reference variable obj
for an interface implemented by the class class , the TYPE
class addition of the CREATE OBJECT obj
statement can be used to create an instance of the class class
.
The instance operator NEW
enables objects to be created in
general expression positions .
Access to Instance Components
A program can access the visible instance components of an object only
through references in reference variables . For
the syntax, see Accessing
Components of Classes .
Lifetime of Objects
An object is kept alive for as long as it is used in the internal
session ( Heap ). The system will continue
use the object provided that at least one
Heap reference points to the
object, an instance attribute or part of the instance attribute or
provided that at least one method of the object is registered as an
event handler . Field symbols to which
an instance attribute or part of an instance attribute is assigned still
work in the same way as data references.
As soon as an object has no more references and none of its methods is
registered as an event handler, it can be deleted by the
Garbage Collector ). This
releases the identity of the object to be taken by a new object.
Note
Alongside these regular references, weak
references represented by objects exist that do not keep an object
alive.
Documentation extract taken from SAP system, � Copyright SAP AG. All rights reserved