Programming Reference: OpenDoc Classes and Methods

# Programming Reference

# OpenDoc Classes and Methods

This chapter provides technical details, organized alphabetically by object class, for OpenDoc object classes and their methods. These sections contain technical reference information. See the OpenDoc Programming Guide for information on how to use OpenDoc object classes and methods. For information on the System Object Model (SOM), see the SOMObject Developer Toolkit Users Guide.

The following list describes terms used in this book:

class | A way of categorizing objects based on their behavior and shape. A class is a definition of a generic object. In SOM, a class is a special kind of object that can manufacture other objects that all have a common shape and exhibit similar behavior. More precisely, all of the SOM class objects manufactured by a class have the same memory layout and share a common set of methods. New OpenDoc classes can be defined in terms of existing classes through a technique known as inheritance.
class method | A class method of class <X> is a method provided by the metaclass of class <X>. Class methods are executed without requiring any instances of class <X> to exist and are frequently used to create instances.
inheritance | The technique of specifying the shape and behavior of one class (called a subclass) as incremental differences from another class (called the parent class or superclass). The subclass inherits the parent's state representation and methods and can provide additional data elements and methods. The subclass also can provide new functions with the same method names used by the parent class. Such a subclass method overrides the parent class method and will be selected by method resolution on subclass instances. An overriding method can elect to call upon the parent class' method as part of its own implementation
instance | (Or object instance). A specific object, as distinguished from the abstract definition of an object referred to as its class.
instance method | A method that is valid for a particular object.
metaclass | A class whose instances are all classes. In SOM, any class descended from SOMClass is a metaclass. The methods of a metaclass are sometimes called "class" methods.
method | One of the units that make up the behavior of an object. A method is a combination of a function and a name, such that many different functions can have the same name. Which function the name refers to, at any point, depends on the object that is to execute the method and is the subject of method resolution.

object

The elements of data and function that programs create, manipulate, pass as arguments, and so forth. An object is a way of associating specific data values with a specific set of named functions (called methods) for a period of time (referred to as the lifetime of the object). The data values of an object are referred to as its state. In SOM, objects are created by other objects called classes. The specification of what comprises the set of functions and data elements that make up an object is referred to as the definition of a class.

SOM objects offer a high degree of encapsulation. This property permits many aspects of the implementation of an object to change without affecting client programs that depend on the object's behavior.

object class | See class.
object instance | See instance.
parent class | A class from which another class inherits. See inheritance.
subclass | A class that inherits from another class. See inheritance.
superclass | See parent class.

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