Click on our Sponsors to help Support SunWorld

Welcome to Java Developer

There is much interest in the Java programming language. Our new regular column offers you access to Java experts.

By Rinaldo DiGiorgio

November  1995
[Next story]
[Table of Contents]
Subscribe to SunWorld, it's free!

Java offers many features that make it an applicable language for applications of all kinds. Java's designers built a practical language for distributed computation, while avoiding the complexity found in other languages. This article outlines Java's strengths and features, and offers references to additional information. (See the sidebar to witness a whimsical discussion on Java between four computer legends.) (5,200 words, including sidebar)

Mail this
article to
a friend

Java is the new language developed by Sun Microsystems that significantly raises the level of technology on the Web. Java allows individuals, Web designers, and organizations large and small to build highly interactive and safe applications. The technology is based on

Running some Java applets will demonstrate the above features. For those of you with a mathematical or financial background run the derivative calculator applet at For those of you with a consumer preference, there is the multimedia application at (If you do not have HotJava and you click on the link, your browser should just ignore the applet.) For those of you using HotJava you have just downloaded a program that can be run on your system. This same program runs on Solaris for SPARC, Solaris for Intel, Windows 95, and NT without modification.

HotJava Alpha 3 is the current release of the browser. Until now, releases contained a browser and interpreter, with its corresponding API. The JDK (Java Development Kit) is the next iteration of the API. The JDK does not contain a browser but does contain an appletviewer, which allows you to view applets for debugging and development, and deployments that use no HTML other than a tag to call an applet. More information on obtaining the JDK is available.

Alpha 3 applets do not work with the JDK or Netscape. Small modifications are required. The procedure for converting an Alpha 3 applet is described in Converting Alpha 3 applets. The HTML interface language was changed slightly, requiring some minor edits to applets. To get an Alpha 3 applet working with the JDK and Netscape you need to convert the applet and modify the HTML file that calls the applet.

At the time of this writing a new Netscape version of a browser that supports Java Applets was not released. To avoid confusion, we will discuss Netscape's Java abilities in the next issue and focus on HotJava this month.


Let the games begin
The HotJava browser reads standard HTML just like any other Web browser. It also has the ability to download Java applets. To accomplish this, a small addition was made to HTML. An additional tag was added (<APPLET>) that allows the specification of a Java applet class to be loaded. When a user clicks on an application that requires an applet, the HotJava browser calls a thread that loads the applet from the network or local filesystem. The code that is loaded is the architecture-neutral bytecodes produced by the Java compiler. These bytecodes are verified and then decoded into machine instructions. It is hoped future versions will compile these bytecodes to native machine instructions for improved performance.

Many languages share some of the features of Java. The Java designers built a practical language for distributed computation without the complexity associated with such languages. Why another language? It can be argued that there are systems with enough ubiquity (consider the proliferation of DOS/Windows 3.x) that there is no need for Java's benefits. Many years ago, Japan launched a project called TRON. The purpose of this project was to provide one OS and one hardware platform for the entire country of Japan. This project ultimately failed. Java, unlike TRON, is based on standards, proven network infrastructure, and is architecture independent at runtime.

The salient features of the Java Language are:

Security -- downloading code over the Internet can be safe
There are several layers to the Java security model. These layers build on each other to provide built-in security that can be extended and or modified.

Late-breaking news
While this article was being written the beta API was released. This API is referred to as the JDK -- Java development Kit. The JDK offers many new improvements and new functionality. Two of our favorite additions are the Java Debugger and the Java Applet Viewer. The imaging model has also been changed significantly and offers an excellent graphics foundation that understands various color models as well as the performance issues with loading images over slow lines. We'll discuss these and other parts of the JDK in future columns. In the mean time, additional information on several topics is available below:

Uses for Java
Java will play a key role in defining the infrastructure of the emerging electronic world. We can actually think of several hundred uses for Java. Here are some of the more common:

Future columns
In future columns we will discuss:

Next month, we discuss Netscape 2.0, including example applets demonstrating the use of various methods.

Click on our Sponsors to help Support SunWorld


What did you think of this article?
-Very worth reading
-Worth reading
-Not worth reading
-Too long
-Just right
-Too short
-Too technical
-Just right
-Not technical enough

[Table of Contents]
Subscribe to SunWorld, it's free!
[Next story]
Sun's Site

[(c) Copyright  Web Publishing Inc., and IDG Communication company]

If you have technical problems with this magazine, contact

Last modified:

SidebarBack to story

A dialogue on HotJava/Java

The scene: The neighborhood cyber-style coffee house. Four friends are sitting at a table, having an animated discussion about the new developments in computing. A PC running a popular Web browser is within arm's reach on the next table.

The four friends differ quite a bit in age. They are (from oldest to youngest): Leonardo Fibonacci, Blaise Pascal, Galileo Galilei, and Ada Augusta. They are all reviewing a recent manuscript written by Galileo.

Galileo: Thank you for your comments. My brain swells with delight. I've interspersed my annotations among yours. (He passes out some papers). What time is it? Can I get an espresso?

Ada:: It's early yet. Senta! Four espressos!

Pascal: But Galileo, I still don't understand. Why should I learn yet another computer programming language?

Galileo: You know, the previous languages have not been as productive as we have hoped. (The waiter comes by and serves the espressos. He accidentally spills one on Fibonacci.)

Fibonacci: I will have to find some statistics on this! (All stare and frown at the waiter who rushes off.)

Galileo: I mean to say that Java is a natural evolution of an object-oriented language. I think its a molto-usable version. You should learn it because you will be more productive. (He slowly takes a sip.)

Pascal: Bien sure -- I've heard that before. What new language? I bet you would even say that if you know C++, then learning Java will be quite easy.

Galileo: If you already know C then you need only learn the simple concepts of object oriented design. Writing in Java is fun, and it is easy. There are so many things that can bite you programming in C, especially around pointers, that just aren't an issue in Java. No more memory leaks or memory smashes, no more indexing off the end of an array that you declare with eight elements and use nine. So many things that you don't have to worry about. It lets you concentrate on what you are writing, not so much on how you write it.

Ada:: That pleases me. So Java eliminates a common source of programming bugs?

Galileo: Exactly. But our friend Fibonacci would probably want to enumerate all the other bugs that Java helps avoid. Could you do that?

Fibonacci: Give me a few weeks and a Javatized browser and I'll show you some real good examples. You know, I can clearly show you the C and C++ nature of Java. I think it should be real easy for C and C++ programmers to make the leap into the Java paradise.

Pascal: That's fine for you. I personally never understood C++, and you all know what I think of C. I like structure. Modularity. Do I have to know C? I actually like HTML. Isn't that a language?

Ada:: Oh, don't be so lazy. I even learned C and C++.

Galileo: Actually, last week I met someone who said Java reminded them of Lisp. You remember, there was a cool Lisp dialect in the old days called Flavors. It had methods and objects and mixins. I think it was named after an ice cream. And you know, yesterday I met someone who said that Java reminded them of Ada? (Ada turns red.)

Ada:: But he should learn C.

Pascal: Don't tell me what I should learn! What do you know!

Ada:: I have a famous programming language named after me.

Pascal: So do I. Big deal.

Fibonacci: Well, I guess we should show the advantages of Java for people like Pascal. What do you say, Galileo? Do we need C++?

Galileo: We need more espresso. I like these interactive sessions. It reminds me of the good old days in Pisa.

Fibonacci: Ah, Pisa. Those were the good old days. What a tower!

Galileo: But Leonardo, you were in Pisa 400 years before me!

Fibonacci: Oh. Yeah. Uh.

Ada:: I was in Pisa once. It must have been 200 years after you, Galileo.

Galileo: How time flies.

Pascal: I was never in Pisa. Who needs it. Do they make you learn C in Pisa? Is that why you all love Pisa? And why is interactivity a good thing? what could you do with it?

Galileo: Interactivity has a single selling point in my opinion. People are different so their needs are different. Providing a static form of interaction will be useful or desirable to some segment of the population, but allowing the user's needs and desires to affect the interaction allows you to target a much larger segment of the population. Consider this trivial example:

Lets say I've got a Web page dedicated to the Grateful Dead. OK, its got a group of people interested in it and they will visit my pages and interact with me.

Fibonacci: Cool.

Galileo: Now let's say I've got a Web page dedicated to rock and roll, the band that is "featured" on my page is selected by the user. Now my Web page is attractive to a much larger audience because the individuals in that audience can select the band that they are interested in. Now extend it to "contemporary music" where the user can select style as well as artists. Now my page appeals to country and western aficionados as well as rock and roll fans and reggae fans as well.

This is because the more interactive my pages are, the more they can adapt to being just what you want to see. And the more "you's" come and visit them. Ergo, I am more successful.

Pascal: Agreed. But the functionality you discuss above can be implemented with a tree of HTML links to various sub-pages tailored to particular musical tastes. Java might make accessing those pages a bit more animated, but it doesn't seem to truly demonstrate the raw power of a Javatized Web site's interactivity.

Galileo: Good point, Pascal. Let's think about it some more. I agree that HTML can point you to the links, but you still have to manage all those helper applications. In Java, it is more manageable.

Ada:: Tell him about the instant distribution of applications.

Pascal: Oh, shut up. Why is the instant distribution of applications so special?

Galileo: Actually, this is a key benefit of Java technology. Do you know, Pascal, that corporate America spends billions on software installation and setup?

Fibonacci: It's up there, I am not sure its in the billions.

Galileo: Get the figures next month. Anyway, the average home consumer does not have the desire to keep reinstalling software. (He takes another slow sip on the coffee.)

Distributing new code is very cheap. If the present distribution paradigm is buy install and leave on disk, then the new Java paradigm is to use and discard.

Pascal: Maybe yes, maybe no. I think that it is possible because Java is architecture-neutral. And that is a very very good thing. I remember many times in Paris when this neutrality was crucial for the success of an application. In my time, neutrality makes it possible for the MIS department to concentrate on its mission, that is, giving efficient access to enterprise networking infrastructure without bogging down in the intricacies of all the platforms that happen to use it. Computers become opaque, you have six units of compute power on your desk, and it doesn't matter if the compute power comes in the Apple, Sun, or Windows flavor, as your CIO or MIS person I can deliver an application to your desktop that runs with six units of compute power and gives you access to the manufacturing inventory projections.

Monsieur Galileo, perhaps it may be nice to mention OSF's and other architecture neutral distribution methods and discuss why it failed where Java succeeded?

Galileo: Yes. I think both the immediate distribution and the architecture neutrality of it are worthy of discussion. The examples mentioned above handsomely illustrate these points. appreciating the benefit of immediate distribution is obtained quickly, but fully appreciating what architecture neutrality offers may require some elucidation.

Pascal: But why should I trust those Java applications, those HTML add-ins, those -- as you call them-- Java applets?

Ada:: I told you he should learn C++!

Galileo: Oh, Basta! No. You don't need to know anything about C++ to understand Java applets. You know Pascal, Java Applets are inherently safer as a distribution system than the current infrastructure in most corporations when the Web architecture is used as an internal architecture. This is due to the fact that the applets are bytecode verified. Future enhancements like MD5 will provide support for digitally signed applications.

Fibonacci: I looked at it already. I trust it.

Pascal: Why should anyone trust any executable you just loaded over the network?

Galileo: One of the most common techniques of system compromise today is to gain access to a network server and install a subverted binary on the system. This gives the bad guys access to every client that loads that binary. Java applets on the other hand are designed to be safe, specifically they can't do anything "bad," only the classes that are already installed on your local disk can do that. Think of applets as an expression of what should be done, not the capability to do it. If an applet is compromised, about the worst that can happen is that it can try to lure you into doing something bad, it in itself is unable to.

Fibonacci: As Galileo said, when the ability to digitally sign classes is part of the system, even this avenue will be unavailable to the undesirables.

Pascal: All well and good, but I would like to see some discussion of why the bytecode verification process can be trusted. What exactly is it and why (and how) does it ensure runtime-safe applets?

Fibonacci: Pascal, I could go into specific details about the safety features of the language and the environment if you would like but that would fill a manuscript in itself.

Ada:: I think it would be cool to provide instructive applets demonstrating or refuting aspects of each of these points. For instance, the security of Java applets can be demonstrated, I guess, by attempting to do harm and having the attempt thwarted. The applet in this case might attempt to remove /kernel/UNIX or something.

Fibonacci: I have an example of writing to the disk and trying to remove files and also an example of zapping the bytecodes. It's cool.

Galileo: These are pretty easy to come by. Of course the question becomes how subtle do you want the attack examples to be? For example we can construct a class that accesses a "private" member of another class and tries to export it and see it fail if you'd like.

Pascal: Subtle examples would be grand! I love the class accessing a private member of another class. But can you tell me just what it means?

Galileo: Sure, but not now. It's getting late. I have an important council meeting tomorrow morning. But let's get together next month and we'll go over some of these examples in more detail!

Pascal: Without C++?

Galileo: For you -- no C++. Buona Notte!

(They all get up to leave.)

SidebarBack to story

About the author
Rinaldo S. DiGiorgio works for Sun Microsystems as a Systems Engineer in the New York City office and provides frequent demonstrations of Java Technology. DiGiorgio is currently working on the integration of many technologies into HotJava/Java. Some of these technologies are database connectivity, portfolio management, low-cost video, and analytical applications in the financial and emerging genetics market. DiGiorgio has been using Unix-based operating systems since 1979, when he was deploying Unix solutions in paper mills. He sees HotjJava/Java as the technology to minimize two great cost factors in the computer industry: distribution and code development.