Within an object-oriented model, an object must descend from a parent object. One object in the model, the root, has no parent, and is called
. All objects within the model can trace their ancestry back to
TObject, which contains properties and methods necessary for basic participation in the model itself. An object, plus all its ancestor objects, specifies the class of an object.
By convention, object class names begin with the capital letter T, which stands for type, the reserved word used in PASCAL to declare an object in code. Properties and methods within objects are separated from the class name by a period, as in
. All identifiers used with Delphi objects are case insensitive. For example, "CLASSNAME" is the same as "ClassName."
When an object descends from a parent, it inherits all properties and methods not specifically excluded from inheritance. At run-time, it is possible to treat multiple objects of different types as the same class by accessing properties and methods common to the objects through inheritance. This is called polymorphism, and it is the key strength of an object-oriented model. It means that for abstract operations, the exact type of an object, and therefore, its underlying memory structure, is unimportant. Such abstract code is written only once, simplifying code maintenance.
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