CS 4448 - Fall 1998
Object-Oriented Programming and Design
Talk 11.2
by
Wei Tao

Http://www.soft-design.com/softinfo/objects.html

* The Heart of the Matter – The "Black Box"

• An object is a "black box", which receives and sends messages.

1. Contains code and data, merge into a single indivisible thing – an object.
2. User doesn’t need open the box for look at the code.

* Classes

• An object is defined via its class, which determines everything about an object.

• Definition for what is "method", simply the action that a message carries out.

* Some Real Life Examples

• Add two numbers.

1. In C, there is expressed for how that each code means.
2. In Smalltalk, there is the other one expressed for how that each code means.

• Add two strings together.

1. In C, that does not work because it does not know what to do with a and b.
2. In Smalltalk, it works because the list class was created with a method which

* Using Non-Object-Oriented Language

• int plus(int arg1, int arg2)

* Inheritance

• The relation between the superclass and subclass. Subclass inherits all the existing messages from the superclass.
• A subclass is said to be a specialization of its superclass, and the conversely a superclass a generalization of its subclasses.

* Object-Oriented Languages

• Three leading commercial o-o languages are far fewer in number

1. C++

• Compatible with C.
• C++ uses compile-time binding.
• Program in C++ instead of C.

1. Smalltalk

• Its use run-time binding.
• Faster to develop than C++ programs.
• Not standardized, differs somewhat from on implementation to another.
• Most popular commercial of Smalltalk are:

1. VisualWorks from parcplace-Digitalk, Inc.

• Platform-independent.
• Also features a GUI (Graphic User Interface) builder that is well-integrated into the product.

1. Smalltalk/V and Visual Smalltalk from ParcPlace-Digitalk Inc.

• Tailored to IBM compatible PCs.

• Is comparable to Smalltalk/V with PARTS.

• Allow programmers to readily exploit machine-specific features.

• Standard Internet and Intranet programming language.
• Mixture of C++ and Smalltalk, No pointers like C++.

• OO programming offers a new and powerful model for writing computer software.
• Objects are "black boxes" which send and receive messages.
• C++ offers and easier transition via C.
• Smalltalk offers pure o-o environment.
• Java promises much for Web-enabling o-o programs.