2.4 Software construction  (Page 5/6)

Unlike C++, which has become standardized, The Smalltalk language differs somewhat from one implementation to another. The most popular commercial "dialects" of Smalltalk are:

• VisualWorks from ParcPlace-Digitalk, Inc.
• Smalltalk/V and Visual Smalltalk from ParcPlace-Digitalk Inc.
• VisualAge from IBM

1. VisualWorks

VisualWorks is arguably the most powerful of Smalltalks. VisualWorks was developed by ParcPlace, which grew out of the original Xerox PARC project that invented the Smalltalk language. VisualWorks is platform-independent, so that an application written under one operating system, say, Microsoft Windows, can work without any modification on any of a wide range of platform supported by ParcPlace, from Sun Solaris to Macintosh. VisualWorks also features a GUI (Graphic User Interface) builder that is well-integrated into the product.

2. Smalltalk/V and Visual Smalltalk

Digitalk's versions of Smalltalk are somewhat smaller and simpler, and are specifically tailored to IBM compatible PCs. A Macintosh version was available, but support has since been abandoned. This does not bode well for Digitalk cross-platform efforts. Digitalk has a separate GUI builder, called PARTS Workbench (bundled with Visual Smalltalk), which allows quick construct of an application.

ParcPlace and Digitalk were merged into a single company, ParcPlace-Digitalk, Inc. The future of the Digitalk product line is uncertain, and it may just be spun off back into a separate company.

3. VisualAge

IBM's version of Smalltalk, VisualAge, is comparable to Smalltalk/V with PARTS. Both of these Smalltalks allow programmers to readily exploit machine-specific features, at the expense of some portability. IBM has adapted existing industry standards for such things as file management and screen graphics. When IBM talks, people listen, and IBM has made a substantial commitment to Smalltalk.

Java

Java is the latest, flashiest object-oriented language. It has taken the software world by storm due to its close ties with the Internet and Web browsers. It is designed as a portable language that can run on any web-enabled computer via that computer's Web browser. As such, it offers great promise as the standard Internet and Intranet programming language.

Java is a curious mixture of C++ and Smalltalk. It has the syntax of C++, making it easy (or difficult) to learn, depending on your experience. But it has improved on C++ in some important areas. For one thing, it has no pointers, low-level programming constructs that make for error-prone programs. Like Smalltalk, it has garbage collection, a feature that frees the programmer from explicitly allocating and de-allocating memory. And it runs on a Smalltalk-style virtual machine, software built into your web browser which executes the same standard compiled Java bytecodes no matter what type of computer you have.

Java development tools are being rapidly deployed, and are available from such major software companies as IBM, Microsoft, and Symantec.

Coding

The following considerations apply to the software construction coding activity: