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Java Unleashed

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Chapter 1

Java Makes Executable Content Possible

By the mid 1990s, the World Wide Web had transformed the online world. Through a system of hypertext, users of the Web were able to select and view information from all over the world. However, while this system of hypertext gave users a high degree of selectivity over the information they chose to view, their level of interactivity with that information was low. Hypermedia had opened up many options for new kinds of sensory input a user might receive, including access to graphics, text, or even videos. However, the Web lacked true interactivity—real-time, dynamic, and visual interaction between the user and application.

Java brings this missing interactivity to the Web. With a Java-enabled Web browser, you can encounter animations and interactive applications. Java programmers can make customized media formats and information protocols that can be displayed in any Java-enabled browser. Java’s features enrich the communication, information, and interaction on the Web by enabling users to distribute executable content—rather than just HTML pages and multimedia files—to users. This ability to distribute executable content is the power of Java.

With origins in Sun Microsystem’s work to create a programming language to create software that can run on many different kinds of devices, Java evolved into a language for distributing executable content through the Web. Today, Java brings new interest to Web pages through applications that can all give the user immediate feedback and accept user input continuously through mouse or keyboard entries.

In this chapter, I first present a description and definition of Java and explore what Java brings to Web communication. Then I present a brief “armchair” tour of some examples of what Java can do. If you want to go directly to programming in Java, see the other parts of this book. Otherwise, read this chapter and the others in this part for a survey of the potential of Java and the basics of its technical organization. These chapters should prepare you for the more detailed look at existing Java programming in the rest of this book.

What Can Java Do?

Java animates pages on the Web and makes interactive and specialized applications possible. Figure 1.1 illustrates how the software used with the Web can support a variety of communication. With hypertext, the basis for information organization on the Web, you can select what information to view. Programmers can create some interactivity through gateway programs that use files of hypertext on the Web as interfaces. When you use a Web page with such a gateway program, you can access databases or receive a customized response based on a query.

Java adds to these communication possibilities by making it possible to distribute executable content. This gives Web information providers the opportunity to create a hypertext page that engages users in continuous, real-time, and complex interaction. This executable content is literally downloaded to the user’s computer. Once downloaded, the executable content might run an animation, perform computation, or guide a user through more information at remote network sites.

Figure FIGURE 1.1.

The Web’s software supports selectivity, display, computation, and interactivity.

One metaphor for hypertext is that it offers a visually static page of information (which can include text, graphics, sound, and video). The hypertext page can also have “depth” where it contains hyperlinks connecting to other documents or resources.

Java transforms this static page metaphor into a more dynamic one. The information on a Java page on the Web does not have to be visually static or limited to a pre-defined set of ways to interact with users. Users encountering Java programs can take part in a wider variety of interactive behavior, limited only by the imagination and skill of the Java programmer. Java thus transforms a hypertext page into a stage, complete with the chance for actors and players to appear and things to happen. And, instead of the user being in the audience, a user of a Java-enabled Web browser is actively a part of the activity on this stage, changing what transpires and reacting to it, and shaping the information content delivered on the Web.

Java thus brings Web pages alive through animation and a higher degree of interaction than what is possible through gateway programming alone.

Sun Microsystems, the developers of Java, provide a one-stop collection of information about Java on the Web at This site includes a full range of the latest information on Java and Java-enabled browsers. Links from this site take you to detailed announcements, release information, documentation, and links to Java demonstrations.

What Is Java?

The name Java is a trademark of Sun Microsystems and refers to the programming language developed by Sun and released in public alpha and beta versions in 1995. Java is used to create executable content that can be distributed through networks. Used generically, the name Java refers to a set of software tools for creating and implementing executable content using the Java programming language.

In order for users to use Java content, they must have a key piece of Java software—the Java interpreter. To view Java content on the Web, a user’s Web browser must be Java-enabled. In the alpha release of Java, available during the spring and summer of 1995, only the special browser called HotJava could interpret programs created by the Java language. HotJava was developed by Sun to showcase the capabilities of the Java programming language. Other brands of Web browsers have since been upgraded to be able to interpret Java programs, most notably, the Netscape Navigator Web browser.

A Java-enabled Web browser has the same capabilities as a non-Java Web browser, but additionally has the capability to interpret and display Java’s executable content. A Web browser that is not Java-enabled does not recognize Java and thus can’t display the Java executable content. Thus, Java-enabled browsers “see” the Web plus more—applications written using Java.

As described in the section on Java’s origins (Java Origins and Direction), Java capability is expected to be integrated into future versions of other Web browsers and network tools.

You can download the Java Developer’s Kit (JDK), which contains Java language development tools, from Sun Microsystems. Chapter 2 describes this software as well as Java’s technical design in more detail.

What Is Executable Content?

Executable content is a general term that characterizes the important difference between the content that a Java-enabled Web browser downloads and the content a non–Java-enabled browser can download. Simply put: In a non-Java Web browser, the downloaded content is defined in terms of Multipurpose Internet Mail Extensions (MIME) specifications, whichinclude a variety of multimedia document formats. This content, once downloaded by the user’s browser, is displayed in the browser. The browser may employ a helper application (such as in displaying images, sound, and video). The overall pattern for the use of this content is user choice, browser download, and browser display.

A Java-enabled browser also follows this pattern, but adds another crucial step. First, the Java-enabled browser, following requests by the user, downloads content defined by MIME specifications and displays it. However, a Java-enabled browser recognizes a special hypertext tag called APPLET. When downloading a Web page containing an APPLET tag, the Java-enabled browser knows that a special kind of Java program called an applet is associated with that Web page. The browser then downloads another file of information, as named in an attribute of the APPLET tag, that describes the execution of that applet. This file of information is written in what are called bytecodes. The Java-enabled browser interprets these bytecodes and runs them as an executable program on the user’s host. The resulting execution on the user’s host then drives the animation, interaction, or further communication. This execution of content on the user’s host is what sets Java content apart from the hypertext and other multimedia content of the Web.

The process of using executable content in a Java-enabled browser, for the user, is seamless. The downloading and start of the execution of content happens automatically. The user does not specifically have to request this content or start its execution. And, as will be explored more in the next chapter, this executable content is platform-independent: Java programmers need not create separate versions of the applets for different computer platforms, as long as the user has a Java interpreter (or Java-enabled browser) installed on his or her computer.

Thus, when surfing the Web with a Java-enabled browser, you might find not only all the hypertext content that the pre-Java age Web offered, but also animated, executable, and distributed content. Moreover, this executable content can include instructions for handling new forms of media and new information protocols.

How Java Changes the Web

Java profoundly changes the Web because it brings a richness of interactivity and information delivery not possible using previous Web software systems. Java makes it possible for programmers to create software that can be distributed across networks and run on many different kinds of computers. The resulting executable content shifts the site of activity from the Web server to the Web client (the Java-enabled browser).

Figure 1.2 illustrates the technical difference between Java’s interactivity and hypertext selectivity and gateway programming. The figure illustrates how gateway programming allows for computation and response but not in realtime. Java’s interactivity is much richer and is centered on the client rather than the server.

Figure FIGURE 1.2.

Java interactivity is based on executable content downloaded to the user’s computer.

Java Origins and Direction

According to Michael O’Connell’s feature article on the origins of Java in the July 7, 1995 issue of SunWorld Online (, the development of Java began at Sun Microsystems in California by a team which included Java creator James Gosling even as the World Wide Web was being developed in Switzerland in 1991. The goal of this early development team was to develop consumer electronic products that could be simple and bug-free. What was needed was a way to createplatform-independent code and thus allow the software to run on any Central Processing Unit (CPU).

As a starting point for a computer language to implement this platform-independence, the development team focused first on C++. However, the team could not get C++ to do everything they wanted in order to create a system to support a distributed network of communicating heterogeneous devices. The team abandoned C++ and developed a language called Oak (later renamed Java). By the fall of 1992, the team had created a project named Star 7 (*7), which was a personal hand-held remote control.

The development team was incorporated as FirstPerson, Inc., but then lost a bid to develop a television set-top box for Time-Warner. By the middle of 1994, the growth in the Web’s popularity drew the team’s attention. They decided they could build an excellent browser using Java technology. With a goal of bringing their CPU-independent, real-time programming system to the Web, they built a Web browser.

The browser, called WebRunner, was written using Java and completed early in the fall of 1994. Executives at Sun Microsystems were impressed and saw the technology and commercial possibilities that could result from a new browser: tools, servers, and development environments.

On May 23, 1995, Sun Microsystems, Inc. formally announced Java and HotJava at SunWorld ’95 in San Francisco. Throughout the summer of 1995, interest in Java grew rapidly. The first wave of developers downloaded and used the alpha release of Java and the HotJava browser and experimented with this new software. The alpha release of Java was the basis for the entries in the first Java contest, with prizes awarded in September 1995. In late September, the pre-beta release of Java was announced. The pre-beta release was Sun’s move toward stabilizingthe language so that programmers could begin investing their efforts into more significantapplications.

By the end of 1995, Java had gained the attention of the major players in the online world. Sun licensed Java to Netscape Communications, Inc. for use in its very popular Netscape Navigator browser. In addition, other major computer software and network players announced products involving Java, including Borland, Mitsubishi Electronics, Dimension X, Adobe, Lotus, IBM, Macromedia, Natural Intelligence, Oracle, and Spyglass. Most dramatic was Microsoft’s announcement on December 7, 1995 of their intent to license Java. Microsoft’s announcement was particularly dramatic, because, during the summer and fall of 1995, Bill Gates, chairman and CEO of Microsoft, had downplayed Java’s role, calling Java “just another language.” However, Microsoft’s year-end licensing announcement clearly showed that Microsoft considers Java part of an overall Internet strategy.

Java’s Current Status and Timeline

You can connect to a bibliography of online articles and key press releases tracing the history and current status of Java at

Java was essentially not a player in the online world in the spring of 1995. However, by the end of that year, it had rocketed to a (perhaps over-hyped) prominence. Along the way, it passed through its alpha and beta stages and grabbed the attention of Web information providers.

At SunWorld in May 1995, Sun unveiled Java and HotJava to the world and Netscape announced that it would license Sun’s Java programming language for its Netscape Navigator browser. By summer, Java and HotJava were in alpha stages of development. The Alphas were released for Sun Solaris 2.3, 2.4 and 2.5 SPARC-based and Microsoft Windows NT. Ports were underway for Microsoft Windows 95, and MacOS 7.5 and, in third-party projects, for other platforms and operating systems, including Windows 3.1, Amiga, NeXT, Silicon Graphics, and Linux.

By the end of 1995, in the wake of the splashy launch of Microsoft Windows 95, there was much debate about the possibility of a “Java terminal” or an “Internet PC” (IPC), a device which would provide an inexpensive view into the Internet. An IPC would have minimal hardware and software in it and be specifically dedicated to supporting a Java-enabled Web browser, which could be continuously upgraded. Potentially, such an IPC could be a cheap, efficient way to encounter Web information. Widespread use of such IPCs could overthrow years of “API lock” on personal computing communications based on the Microsoft Windows/Intel (“Wintel”) standards.

For the most current information on Java’s software releases for different platforms, see Sun Microsystem’s Java site: or other Java information sources at

Java Future Possibilities

Java technology is not necessarily limited only to the Web. Java technology can be deployed in embedded systems, such as handheld devices, telephones, and VCRs. Mitsubishi Electronics has been working to use Java technology in these devices.

The association of Netscape and Sun Microsystems that brought Java technology into Netscape browsers by late 1995 will be sure to have significance for Net software. With Netscape Navigator’s widespread installed base, the use of Java in applications could rapidly increase. Therefore, other Web browser manufacturers might be compelled to also license Java in order to keep pace with the information environment on the Web.

The market for third-party object and tool libraries for Java is also a potential bonanza. Software layers on top of “raw” Java will enable developers to use more sophisticated tools to create applications and users to more easily build and incorporate Java applets in their Web pages. Chapter 2 describes how Java’s nature as an object-oriented programming language makes it particularly amenable for creating reusable, extensible software components.

By integrating Java with Virtual Reality Modeling Language (VRML) (, developers can create virtual worlds that are not only three-dimensional but also animated and interactive. Dimension X ( has developed a Java-VRML mix called Iced Java which has the potential to take Web communication and interaction to an even richer level.

Illustrations of Java’s Potential

Java is a new programming language, and programmers outside of Sun Microsystems have just begun to explore its potential. Since the public release of Java in its alpha and beta versions, however, many good examples of Java have already been developed. The rest of this chapter shows you examples of the kinds of functionality that Java can support, with an emphasis on the unique way Java enables the distribution of animated, executable content. Information on developing applications which can achieve this potential of Java is in later parts of this book.

The initial, or alpha, release of Java is incompatible with later releases: the alpha bytecodes won’t run in beta or later Java-enabled browsers; also, the alpha Java language used an HTML APP tag rather than the APPLET tag of the beta and later versions of Java. The development sections of this book focus on the beta version of Java which is upward compatible with later versions of Java.


Java’s applications put animated figures on Web pages. Figure 1.3 shows a still image of Duke, the mascot of Java, who tumbles across a Web page displayed in the browser. Duke tumbles across the page, cycling through a set of graphic images that loop while the user has this page loaded.

Figure FIGURE 1.3.

Tumbling Duke, mascot of Java. (Courtesy of Arthur van Hoff, Sun Microsystems)

Animation isn’t limited to cartoon figures, however. Pages can have animated logos or text that moves or shimmers across the screen. Java animations also need not just be a decorative pre-generated figure, but can be a graphic that is generated based on computation. Figure 1.4 shows a bar chart applet.

Figure FIGURE 1.4.

A bar chart applet. (Courtesy of Sun Microsystems)


While the animations shown can be static images that are drawn or generated, or animated images that can behave according to a preset algorithm (such as the tumbling Duke in Figure 1.3), animation can also be made interactive, where the user has some input on its appearance. Figure 1.5 shows a three-dimensional rendering of chemical models. Using the mouse, you can spin these models and view them from many angles. Unlike the source code for the graph applet shown in Figure 1.4, of course, the source code for the chemical modeling is more complicated. To the user, however, the chemical models seem three-dimensional, giving an insight into the nature of the atomic structure of these elements as no book could.

Figure FIGURE 1.5.

Three-dimensional chemical models. (Courtesy of Sun Microsystems)

The chemical models in Figure 1.5 respond to user clicks of the mouse. Another variation on this animation involves providing the user with a way to interact with an interface to get feedback. The “impressionist” drawing canvas in Figure 1.6 is an excellent example of this. Paul Haeberli at Silicon graphics developed an “impressionist” Java applet at He originally developed this technique for creating this kind of graphic in 1988 for a Silicon Graphics IRIS workstation. Later patented, this technique drives his Java applet. The result is that you can draw using various size brushes on a canvas and reveal one of several pictures.

Figure FIGURE 1.6.

Interactive impressionist drawing. (Courtesy of Paul Haeberli at Silicon Graphics)

Another variation on interactivity is real-time interactivity. Figure 1.7 shows an interactive application that involves moving graphics that the user manipulates. This is the game of Tetris, in which you can try to line up the falling tile shapes to completely fill the rectangle. Using designated keys for playing, you interact with the interface to steer the falling shapes. This Tetris implementation demonstrates the possibilities for arcade-like games using Java technology.

Figure FIGURE 1.7.

Tetris game. (Courtesy of Nathan Williams)

Interactivity and Computation

The Tetris game described in the previous section, for example, demonstrates how interactivity and animation can work together. Both applets customized their animated output based on user input, so both applets were actually performing computation. However, an example that shows this computational capability in more concrete terms is in Figure 1.8, a simple spreadsheet.

This spreadsheet works in much the same manner as the other applets, but emphasizes that the computational possibilities can enable users to have an environment in which to work instead of just a puzzle to solve. The spreadsheet shown enables you to change the contents of any of the 24 cells (A1 through D6) by replacing its label, value, or formula. (Not all cells are shown in the figure.) This is just like a real spreadsheet, which is more of an environment in which the user can work than a fixed game such as the crossword puzzle. This subtle difference is a profound one: using Java, a user can obtain an entire environment for open-ended interaction rather than a fixed set of options for interaction—opening up the Web page into a Web stage.

Figure FIGURE 1.8.

A simple spreadsheet. (Courtesy of Sami Shaio, Sun Microsystems)

This ballistic simulator shown in Figure 1.9 ( enables you to explore how a canon operates. You can adjust the muzzle angle and velocity, gravitational field strength, wind speed, and the density of the projectile. The purpose of this applet is to helpstudents understand the relation between muzzle velocity and gravitational potential and drag.

Figure FIGURE 1.9.

A virtual canon. (Coding by Sean Russell, Software Manager, University of Oregon; Graphic images by Amy Hulse)

Just as the user can download a canon, so too can a user download a “kit” for doing almost anything. Patrick A. Worfolk of the Geometry Center, University of Minnesota) has created a simulation that users can use to discover the properties of Lorenz equations ( The user can see the results of the numerical integration (the equations in the bottom of Figure 1.10) as well as graphical representations of their numerical solution.

Figure FIGURE 1.10.

Numerical Simulation of the Lorenz Equations. (Courtesy of The Geometry Center, University of Minnesota)


The preceding examples demonstrate many informational, animation, and computational applications of Java. Another application area is communication among people.

Paul Burchard has created a system for users to share “chats” over the Web using a Java applet (

Not only do users see each other’s text, but they can follow each other on tours of the Web. Figure 1.11 shows this “chat touring” applet in action.

Figure FIGURE 1.11

Of course, communication takes place all the time on nearly all Web pages through text or other media. But a Java-enabled browser can also display multimedia. Figure 1.12 illustrates a player piano applet—you see the keyboard play and hear the music at the same time.

Figure FIGURE 1.12

Java can also be used to support mass communication in new ways. The Nando Times is a Web-based news service that has been very innovative in news delivery on the Web. Using Java, this news agency now provides a tickertape of headlines across its front page. The text under the Nando banner in Figure 1.13 scrolls continuously to show the world, national, sports, and political top stories at the moment. The four pictures under the labels for these categories also change, giving a “slide show” that is very effective in displaying new information without requiring the user to select it for viewing. This transforms the Web into something people can watch to get new information.

Figure FIGURE 1.13

Similarly, Figure 1.14 shows how current information feeds can act as surveillance for specific activities. The figure shows an applet from The Sports Network ( This provides you with a life sportswire pop-up window. You can follow NFL and NHL action live, as it happens. As the scores change, this display changes, so that the sports-minded can keep up with the current games and scores. Like the Nando Times news feed, this sports feed changes the Web into something to watch in addition to something to interact with.

Applications and Handlers

In addition to applets like the ones shown here, Java programmers can also create applications, or standalone programs, that don’t require the Java-enabled browser to run. (The HotJava browser itself is such an application, written using Java.) Applications could thus conceivably be new browsers or interfaces that interact with other network or local resources.

Figure FIGURE 1.14

Another kind of software program available with Java is a handler. A protocol handler enables a Java programmer to specify how a Java browser should interpret a particular type of protocol. The HotJava browser knows how to interpret the Internet protocols such as HTTP, FTP, Gopher, and others because of the browser distribution code. But if new protocols are invented, a Java programmer can specify how they should be handled by creating a protocol handler.

Another type of handler is a content handler. This handler translates a particular specification for a file type based on Multipurpose Internet Mail Extensions (MIME). This content handler will specify how the HotJava browser should handle a particular type of file type. By creating a specification in a content handler, all Java-enabled browsers will be able to view this special format.

The handlers and applications that Java makes possible have the potential to dramatically extend what can be browsed on the Web. No longer will information developers have to be concerned about making sure their users have the proper software to view a particular type of file or handle a new kind of protocol. The protocol and content handlers, like the executable content Java makes possible as applets, can be distributed as needed to requesting Java-enabled browsers.

What Java Might Make Possible

The previous examples illustrate only some of the potential of Java. A few of these examples are “toy” demonstrations meant to show the possibilities of Java. What kind of communication might Java foster? The Nando Times example shows an innovative application for providing information in a way that lets you to sit back and observe rather than selecting hypertext links.

Java opens up a new degree of interactivity and customizability of interaction for the Web. Earlier Web development techniques of creating pages and linking them together will still be necessary in a Java-flavored Web. However, Java creates possibilities for richer kinds of content to be developed. The user can interact with and change the appearance of a Web page along with the state of a database using a Java-enabled browser. Thus, Java profoundly changes the texture of the Web in the following ways:

The true potential of Java to transform the Web is still in its initial stages. New potential applications for commerce, information delivery, and user interaction still await the imagination and skill of future Java developers.


Java is a programming language designed to deliver executable content over networks. A user or programmer should know what kinds of interaction Java can make possible and what its true potential can be: enlivening the Web, enriching the display of information in the form of animation and interactive applications.

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