Release 10.1A: OpenEdge Getting Started:
Object-oriented Programming

> ## Defining behavior in a class file

> The behavior within a class file is defined using methods. A method must specify an access mode, which defines the scope of the method. The scope of a method determines the context within an application where the method is visible and available for execution. Thus, private methods are only accessible from within the class where they are defined; protected methods are only accessible from within the class where they are defined and in any subclass of the defining class; and public methods are accessible both within the class hierarchy and from outside the class hierarchy of the instantiated object where they are defined. Thus, only public methods of a given class-based object are accessible from another object or procedure that instantiates the class.

> A method must also specify a return type, but that return type can be `VOID`, which means that no value is returned by the method. Methods can have zero or more parameters. Classes support two special methods—a constructor and destructor. Both are optional in a class definition.

> A constructor is invoked during the instantiation of a class. An application can provide a constructor, with or without parameters, when the class needs to initialize data or state within an object. If a constructor is not provided, Progress provides a default constructor in order to instantiate the class. The default constructor has no parameters.

> A destructor is invoked during the destruction of an object. An application can provide a destructor when the class needs to free resources or do other cleanup work. If a destructor is not provided, Progress provides a default destructor in order to delete the object.

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