Delphi in a Nutshell

Chapter 2. The Delphi Object Model

Delphi’s support for object-oriented programming is rich and powerful. In addition to traditional classes and objects, Delphi also has interfaces (similar to those found in COM and Java), exception handling, and multithreaded programming. This chapter covers Delphi’s object model in depth. You should already be familiar with standard Pascal and general principles of object-oriented programming.

Classes and Objects

Think of a class as a record on steroids. Like a record, a class describes a type that comprises any number of parts, called fields. Unlike a record, a class can also contain functions and procedures (called methods), and properties. A class can inherit from another class, in which case it inherits all the fields, methods, and properties of the ancestor class.

An object is a dynamic instance of a class. An object is always allocated dynamically, on the heap, so an object reference is like a pointer (but without the usual Pascal caret operator). When you assign an object reference to a variable, Delphi copies only the pointer, not the entire object. When your program finishes using an object, it must explicitly free the object. Delphi does not have any automatic garbage collection (but see the section Interfaces,” later in this chapter).

For the sake of brevity, the term object reference is often shortened to object, but in precise terms, the object is the chunk of memory where Delphi stores the values for all the object’s fields. An object ...