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The world of software programming is replete with alternative tools for writing code that can be used to provide the same solutions to the same problems. The range of programming aids available, and their disparate approaches, make ubiquity and platform neutrality a myth. Nowadays, someone who says that the Z80 assembly language is also a programming language will be shot down with a barrage of e-mail arrows fired by technical gurus. I think the only absolutely platform-independent, language-neutral, ubiquitous truth is that everything ultimately translates into a sequence of zeros and ones.

In the world of programming languages, the kingdom of "high-level programming" is shared by two types of languages: system programming languages and scripting languages. High-level languages such as C++, Java, Smalltalk and Pascal basically abstract programmers from the low-level, machine-specific programming details required in assembly programming. System programming languages and assembly languages have the same purpose: to develop applications directly using system resources. Scripting languages on the other hand supplement system programming languages by providing "glue-code" to integrate components written in other languages (usually system programming languages). Applications and components written in system programming languages can be glued together for quick prototyping, configuration and deployment using scripting languages.

The Cosmic Cup's purpose is to allow true believers to peer into the different facets and pieces of the Java Platform. The platform would be incomplete without scripting language support. As the Java programming language gained popularity, two kinds of evolutions took place in the world of scripting languages. The first involved the inception of new languages that facilitated the integration of Java into the Web - more specifically into HTML.

The other involved the enhancement of existing scripting languages that added Java support to their existing codebase. These scripting languages differ from the former in that they have a substantial presence outside the Internet. The languages in this category enhanced their features and provided hooks to integrate components from non-Java environments to components developed in Java.

This month we'll take a look at the Java support provided by five popular scripting languages:

  • Tcl
  • Python
  • JavaScript
  • JScript
  • VBScript

Of these, the first two provide enhancements to existing languages; the other three are primarily HTML-based scripting languages. Our discussion will focus primarily on the three languages in the first category.

The role of these languages in Java-based development is illustrated in Figure 1, and brief descriptions are provided in Table 1. The remainder of this column describes these scripting languages in more detail.

Figure 1
Figure 1:

Table 1

Tcl, built on the C environment, is an ideal scripting language for embedding into other applications. It focuses on small scripts, rapid application development and dynamic environments. Started in 1990 as a research project at the University of California, Berkeley, by John Ousterhout, it has been supported informally by Sun since 1994. It is available on popular computing hardware platforms (UNIX, Windows, Macintosh) and is used by about half a million programmers.

A salient aspect of Tcl is that it can be treated as a library and easily embedded in existing Java applications. Java developers can use this functionality as a means to wrap existing legacy components into their Java applications. It can also be used as the glue that ties together components developed in Java, adding flexibility, dynamism and rapid integration to the development process.

Tk is Tcl's toolkit of widgets, graphical objects similar to those of other GUI tool-kits such as Xlib, Xview and Motif. Tk can be used to create prototype GUIs with the Tcl scripting language.

The Tcl-Java integration effort involves development in the following areas that add functionality to different facets of the Java Platform:

  • TclBlend - A new package for Tcl that allows Tcl applications to load and interact with the Java Virtual Machine. This allows developers to use Java objects in their existing legacy code. The final 1.0 release is available for Solaris and NT and uses Tcl 8.0 with JDK 1.1.
  • Jacl - Tcl's 100% Java solution, the objective and result of Tcl's port to the JVM. The Jacl effort involves porting the entire Tcl and Tk code to the Java programming language, thus providing a Pure Java solution that includes a system programming language with tightly integrated scripting support. Currently, the core of the Tcl language is being ported. The Tk widgets are being wrapped into Java-Beans to reuse existing code. (Jacl doesn't yet have applet support, i.e., it doesn't run in browsers.)
  • Tcl Bean - A JavaBean built for Java Studio - Sun Microsystems' Java IDE - is used to create ports and generate messages via the studio package. Java Studio uses ports to graphically represent Java-Bean events.

Sun recently created a new business unit, Sunscript, which has evolved into a company called Scriptics, the official owner of Tcl/Tk. Detailed information on the Tcl-Java integration is available at www.scriptics.com/java.

Python is a portable, interpreted, object-oriented programming language that incorporates modules, exceptions, dynamic typing, high-level dynamic data types and classes. Created in 1990 by Guido van Rossum, it's currently distributed freely, and is maintained by an informal development organization called the Python Software Activity, or PSA, which houses a large developer community. Python's syntax is closer to traditional programming languages such as C. It may be used for rapid prototyping as well as for medium- to large-scale systems development.

JPython is a new implementation of Python integrated with the Java Platform. Recently certified as 100% Pure Java by KeyLabs, it consists of a compiler that translates Python source code into Java bytecodes that can run directly on a JVM, a set of support libraries used by the compiled Java bytecodes and extra support for using Java packages from within JPython.

JPython enhances the functionality of Java programs by providing programmers with a rapid application development environment for integrating Java components. Java programmers can add the JPython libraries to their system to allow end users to write simple or complicated scripts that add functionality to an application. JPython has an interactive interpreter that allows dynamic interaction with Java packages or Java applications.

As JPython is written in Java, interoperability between the two languages is more intuitive. JPython provides the following functionality to the Java programming language:

  • Dynamic compilation of "glue-code" written in JPython to Java bytecodes. This makes the executable code available to all platforms that support the JVM.
  • Inheritance capability that allows JPython code to extend Java classes. Thus implementation of abstract classes defined in a Java program may be provided by the scripting code.
  • Support for the JavaBeans component model. JPython uses JavaBean properties that make it easier to interact with most Java classes. These properties can be used as normal object attributes, and can also be specified to the class constructor as keyword arguments. JPython uses Java's Introspection mechanism to achieve this.
Detailed information on JPython is available at www.python.org/jpython.

Web Scripting Languages
The remainder of this article focuses on the three HTML-based scripting languages listed earlier. The sole purpose of these languages is to enhance the content of Web pages displayed by Web browsers. In the current Internet world "Web pages" inherently implies HTML authoring. The languages discussed below allow the programmer to add sophisticated Web content to Web pages, and to support object orientation and the capability of embedding programming language components into Web pages. In other words, the Web scripting languages provide "glue-code" for Internet (or intranet) Web pages. This aspect makes the scripting language dependent on the Web browser that displays the Web page. The browser should be able to recognize the tags for a particular language. If it doesn't, all code between the open and close tags (the code provided for the respective scripting language) will be ignored.

The scripting language code is embedded in the HTML page as follows:

<script LANGUAGE="[language]">
[Scripting Code]

The "[language]" string could be "JavaScript," "VBScript," "JScript," etc.

I'll provide very brief descriptions of these scripting languages as there are ample sources of information that discuss them in detail.

JavaScript provides object-based interpreted scripting that is embedded in HTML pages. Originally developed by Netscape as "LiveScript," Netscape and Sun Microsystems entered into an agreement to jointly enhance the language in December 1995. The name was changed to JavaScript as the addition of Java support was the main aspect of the enhancement.

JavaScript syntax is similar to that of the Java programming language. It also uses elements from the Awk and Perl scripting languages, and its object-based nature can be attributed to the object prototype system used in the Self language. JavaScript is supported by Netscape Navigator versions 2.0+ and Microsoft Internet Explorer.

JavaScript also has a server-side component, LiveWire, which contains server-side Java code and extensions to the client-side JavaScript. This code is compiled into Java bytecodes and can be used as an alternative to CGI. Since the 1.2 release of JavaScript, the client- and server-side versions have been consolidated into a single technology supported by Netscape Communicator 4.0 and Netscape's Enterprise Server.

Detailed information on JavaScript is available at http://developer.netscape.com/openstudio/tech/index_frame.html.

JScript, Microsoft's implementation of JavaScript, adds support specific to its Internet Explorer browser. Like JavaScript, JScript allows developers to link and automate objects in Web pages, including ActiveX controls and Java Applets. JScript is supported in both Netscape and Microsoft browsers. Some of its key features are dynamic redefinition of the executing program, object-based support, DHTML support, a rich support for regular expressions and the capability to immediately evaluate code at runtime.

More information on JScript is available at www.microsoft.com/workshop/languages/clinic/vbsvjs.asp.

A subset of Microsoft's Visual Basic programming language, VBScript offers a lightweight interpreter for use in World Wide Web browsers, and other applications such as ActiveX controls, Automation servers and Java Applets. The main features of VBScript are:

  • It adds Web development capabilities to the client and server.
  • It brings a useful scripting language to the Web.
  • It expands the scope of the Visual Basic programming languages to platforms not covered by either Visual Basic or Visual Basic for Applications.
More information on JavaScript is available at www.microsoft.com/workshop/languages/clinic/vbsvjs.asp.

Cosmic Reflections
System programming languages and scripting languages try to address application development in their own way. The scopes of programming covered by these languages usually overlap. Though they supplement each other, they also compete with each other. The main attraction of scripting languages is their ease of use and their extremely rapid development. Furthermore, they're free. Developers need to carefully consider the roles and division of responsibilities they want to assign to the chosen scripting language when they are architecting enterprise-level applications. Recent developments and the direction of the popular scripting languages seem to indicate that the Java Platform is not just Java.

About the Author
Ajit Sagar is a member of the technical staff at i2 Technologies in Dallas, Texas. He holds a BS in electrical engineering from BITS Pilani, India, and an MS in computer science from Mississippi State University. He is a Java certified programmer with eight years of programming experience, including two in Java. Ajit can be reached at [email protected].


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