1 The Basics of Object-Oriented Programming.- Data Types.- Encapsulation.- Abstract Data Types.- Classes.- Defining a Class in Visual Basic.- Defining a Property in Visual Basic.- Defining a Method in Visual Basic.- Exposing Properties Through the Property Let/ Set/ Get Procedures.- Objects.- Explicit Object Creation.- Instance Variables and Member Variables.- The As Object Syntax.- Implicit Object Creation.- Referencing Public Variables and Procedures.- The Object/Message Model.- The Me Keyword.- Object Properties and Object Hierarchies.- Creating and Destroying Objects.- Creating Objects.- Destroying Objects.- Reference Counts.- Circular References.- The Notorious End Statement.- How to Control a Circular Reference-A Linked List Example.- Form Modules.- Properties and Methods in a Form Module.- Collection Classes.- Constructing a Collection Class.- Polymorphism and Overloading.- Overloading.- Polymorphism.- Inheritance.- 2 Handling Object Errors.- Error Detection and Error Handling.- Types of Errors.- The Error Object.- Dealing with Run-Time Errors.- Where to Handle a Run-Time Error.- Dealing with Logical Errors.- Detecting Logical Errors.- Where to Handle a Logical Error.- Handling the Error in the Calling Procedure.- Errors Occurring in Events.- An Error-Handling Example.- 3 Turing Machines - A Simple Object-Oriented Application.- What Is an Algorithm?.- What Is a Turing Machine?.- Informal Definition of a Turing Machine.- Describing a Turing Machine.- Coding a Turing Machine.- Error Handling.- The Symbol Class.- The Symbols Collection Class.- The State Class.- The States Collection Class.- The Transition Class.- The Transitions Collection Class.- The Machine Class.- The User Interface.- The Standard Module.- A Final Comment.- 4 OLE Automation Objects.- What IsOLE Automation?.- Public Really Means Public.- The Plan for This Chapter.- Communication Between OLE Automation Clients and Servers.- The Communication Problem.- Supplying Information to the Client.- What Is an Interface?.- The Vtable Interface.- Type Libraries.- OLE Interfaces.- The IUnknown Interface.- The IDispatch Interface.- Binding.- Putting It All Together.- In-Process and Out-of Process Servers.- Creating a Simple OLE Automation Server.- Creating a Simple Server.- A Small Client and the Three Forms of Binding.- Referencing the Server's Type Library.- Registering and Unregistering a Server.- How Servers Are Started and Ended.- Reference Counts for Servers.- Servers with a Visual Interface.- Servers with Dialog Boxes.- OLE Servers That Also Function as Stand-Alone Applications.- Handling Errors.- Be Nice.- Errors from Your Server's Servers.- Externally Creatable and Dependent Objects - The Object Hierarchy.- In-Process Issues.- Version Compatibility.- How Compatibility Can Be Affected.- How Visual Basic Handles Compatibility.- The Reference Server and Interim Builds.

This book is about object-oriented programming and how it is implemented in Microsoft Visual Basic. Accordingly, the book has two separate, but inter­ twined, goals. The first is to describe the general concepts of object orientation and the second is to describe how to do object-oriented programming in Visual Basic. I intend this to be a short, no-nonsense book that can be read through once and then easily referred to at later times. (Long stories about a mythical company and its programming problems are seldom interesting the first time through, let alone the second, third or fourth times!) To read this book, you need only a minimal acquaintance with Visual Basic. In particular, I assume you can construct a simple Visual Basic program and have some rudimentary knowledge of fundamental programming tech­ niques. This book does not teach Visual Basic - it teaches you how to pro­ gram Visual Basic in an object-oriented way. The issue here is not how much Visual Basic you already know - it is that you want to learn about object­ oriented programming techniques. With regard to the first goal of the book, it is my feeling that a discussion of the underlying concepts of object orientation Oust what is an object, a class, encapsulation, abstraction, and so on) is essential in order to take full advan­ tage of any object-oriented language. Simply put, it will help you understand what you are doing if you know why you are doing it.