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Object-oriented Programming
Object-oriented Programming and ABL : Overview of class-based ABL : Creating and destroying a class instance
 

Creating and destroying a class instance

The first requirement to program with classes is to instantiate a class (create a class-based object). In ABL, you must use the NEW function (classes) to create an instance of a class. You can also assign the object reference for that instance to an appropriate object reference data element using the NEW statement, which calls the NEW function. This function invokes the specified class constructor to complete class instantiation. To help support OERA-compliant applications, you can also use the DYNAMIC-NEW statement, which allows you to instantiate a class from an object type determined at run time. You can also instantiate a class from criteria identified at run time using the New( ) method of the Progress.Lang.Class class.
The first class in an ABL application must be instantiated in a procedure file (not a class definition file). Thus, you must use an initial procedure file to startup a class-based application.
Objects (class instances) are automatically deleted (garbage collected) by the AVM some time after no reference to the object exists in the ABL session. However, you can force any class instance to be deleted immediately using the DELETE OBJECT statement. As with garbage collection, this statement invokes any destructor specified for the class instance. If you or the AVM create a class instance that is never assigned to an ABL data element (for example, when NEW appears in an expression without assignment), you do not need to delete the object; the AVM cleans it up automatically. Note that, once initialized, static members of a class cannot be re-created or destroyed.
For more information on managing the creation and destruction of class instances, see Managing the object life-cycle. For more information on how the class hierarchy of an object is created and destroyed, see Designing Objects: Inheritance, Polymorphism, and Delegation. For more information on using the NEW function and DYNAMIC-NEW statement to instantiate a class, see Creating a class instance. For more information on initializing static class members, see Initializing and deleting static members.
* Comparison with procedure-based programming