Chapter 3
Vacationing in Java
"Java is a huge opportunity for all of us."
--Marc Andreesen of Netscape at the JavaOne Conference, May 31, 1996
Before you venture further into Java programming, it's worthwhile to learn more
about the language and see what Java programmers are doing today. One of the reasons
that Java has become popular quickly is that it can be used to offer programs on
the World Wide Web. Because of this capability, the best examples of how to use Java
are also on the Web. During this hour, we'll take a look at some sites that feature
Java programs and talk about the history and development of the language.
To go on this vacation, you need a Web browser that can handle Java programs.
Most current versions of Netscape Navigator and Microsoft Internet Explorer can run
Java programs that are found on Web pages.
If you're using a current version of Netscape Navigator or Microsoft Internet
Explorer and it isn't working with Java programs, check your setup configuration
from one of the program's pull-down menus (select View | Options
in Internet Explorer or Options | Network Preferences | Languages
in Navigator). Make sure your browser software is configured to run Java programs.
Load your browser software of choice, put on your best Hawaiian shirt, and get
ready to vacate. Because you won't be leaving your house, you won't get a chance
to experience the simpler pleasures of tourism: odd driving rituals, exotic food,
exotic members of the opposite sex, exotic members of the opposite sex with food,
and so on. But look on the bright side: no antibacterial shots, traveler's checks,
or passports are required either.
The following topics will be covered during this hour:
- A definition of the Java language
- The benefits of using Java
- Some examples of Java at work
- An explanation of object-oriented programming
- Sites of note for Java programmers
The Web site-seeing examples that you visit during this hour's vacation are just
a small sampling of the Java programs in use on the Web. A search of the AltaVista
Web search database finds more than 4,900 pages that have included a Java program
as of this writing.
First Stop: JavaSoft
The Java vacation begins at a place you'll be visiting regularly now that you're
a Java programmer: the Web site of JavaSoft, the group that developed the Java language.
To get there, go to the following address:
http://java.sun.com
JavaSoft is the division of Sun Microsystems that is responsible for the advancement
of the Java language and the development of related software. To see a simple example
of Java in action, choose the hyperlink on the JavaSoft main page that offers a "Java
version" of the site. If you can't find one, you can reach the Java front page
by visiting the following Web address:
http://java.sun.com:81/index.aspl?
A Java program is used on this page to add pull-down menus on top of the page.
Drag your mouse across the different section titles on the page to see the pull-down
menus that appear. Figure 3.1 shows a pull-down menu that appears when the mouse
is over the Where Can I Read About...? text.
Figure
3.1. The JavaSoft Web site uses
a Java program to add pull-down menus on top of a Web page.
This Web site is the place to find the latest released versions of the Java Developer's
Kit, as well as other programmer's resources. This site also has press releases about
Java-related products, full documentation for Java, and sample Java programs that
run on the Web. Sun Microsystems made Java available for free via this Web site in
late 1995.
A Brief History of
Java
Company cofounder Bill Joy called Java the end result of 15 years of work to produce
a better, more reliable way to write computer programs. Java's creation was a little
more complicated than that.
Java was invented five years ago by Sun engineer James Gosling as a language to
use as the brains for smart appliances (interactive TVs, omniscient ovens, and the
like). Gosling was unhappy with the results he was getting by writing programs with
C++, another programming language, so he holed up in his office and wrote a new language
to better suit his needs.
Most people who are holed up in their office aren't producing new programming
languages or other achievements. They're playing Quake. How many lasting contributions
to mankind have been lost because of Id Software?
At the time, Gosling named his language Oak after a tree he could see from his
office window. The language was part of Sun's strategy to make millions when interactive
TV became a multimillion-dollar industry. That still hasn't happened today (five
years down the road), but something completely different took place. Just as Sun
was ready to scrap Oak development and scatter its workers to other parts of the
company, the World Wide Web became popular.
In a fortuitous circumstance, many of the qualities that made Gosling's language
good on its appliance project made it suitable for adaptation to the World Wide Web.
Sun developers devised a way for programs to be run safely from Web pages and chose
a catchy new name to accompany the language's new focus: Java.
You might have heard that Java is an acronym that stands for Just Another Vague
Acronym. You also might have heard that it was named for the developers' love of
coffee, especially the percolating product of a shop near Sun's offices. Actually,
the story behind Java's naming contains no secret messages or declarations of liquid
love. Instead, Java was chosen for the same reason that comedian Jerry Seinfeld likes
to say the word salsa. It sounds cool.
Although Java can be used for many other things, the Web provided the showcase
that it needed to capture international attention. A programmer who puts a Java program
on a Web page makes it instantly accessible to the entire Web-surfing planet. Because
Java was the first tool that could offer this capability, it became the first computer
language to receive as much press as Dennis Rodman, Madonna's baby, and the alien
autopsy. In 1996, you had to be in solitary confinement or a long-term orbital mission
to avoid hearing about Java.
Going to School with
Java
As a medium that offers a potential audience of millions, the World Wide Web includes
numerous resources for educators and schoolchildren. Because Java programs can offer
a more interactive experience than standard Web pages, some programmers have used
the language to write learning programs for the Internet.
For one of the strongest examples of this use of Java, visit the following address:
http://www.npac.syr.edu/projects/vishuman/VisibleHuman.asp
This Web site uses data from the National Library of Medicine's Visible Human
Project. The project is a database of thousands of cross-sectional images of human
anatomy. A Java program is being used to enable users to search the collection and
view images. Instead of making requests by text commands, users make the requests
to see different parts of the body graphically, and the results are shown immediately
in graphic detail. The Java program is shown in Figure 3.2.
Figure
3.2. Images from the National Library
of Medicine's Visible Human Project can be viewed interactively on the Web using
a Java program.
Numerous educational programs are available for many different computer systems,
but what makes this program remarkable is its versatility. The Visible Human Project
tool is similar in function and performance to CD-ROM software that users might run
on their computer systems. However, it is run directly from a Web page. No special
installation is needed, and unlike most CD-ROM software, it isn't limited to PC-compatible
and Macintosh systems. Just like Web pages, Java programs can be run on any computer
system that can handle them.
In order to handle Java programs, a Web browser must have a Java interpreter.
The interpreter included with a browser serves a similar function as the interpreter
that you used to run the BigDebt program during Chapter 2, "Writing Your
First Program." The difference is that a browser's interpreter can only run
Java programs that are set up to run on Web pages and cannot handle programs set
up to run from the command line. Currently, Java-enabled browsers are available for
most common systems, including PCs running a version of Microsoft Windows, Apple
Macintosh systems, SPARC workstations, and computers running the Linux operating
system.
A Java program such as the Visible Human Project database does not have to be
written for a specific computer system. This advantage is called platform independence.
Java was created to work on multiple systems. Originally, Java's developers believed
it needed to be multiplatform because it would be used on a variety of appliances
and other electronic devices.
The programs that you write using Java can be run on a variety of computer systems
without requiring any extra work from you. This advantage is one of the primary reasons
that so many people are learning to write Java programs and are using them on software
projects. Many professional software companies are using Java for the same reason.
Under the right circumstances, Java can remove the need to create specific versions
of a program for different computer systems. The potential audience for software
grows with a multiplatform solution such as Java.
Lunch in JavaWorld
If you didn't lose your appetite after searching through the innards of a visible
human, take a lunch break with JavaWorld, an online magazine for Java programmers
and other Internet developers. The JavaWorld Web site is available at the following
address:
http://www.javaworld.com
JavaWorld offers how-to articles, news stories related to Java development, and
other features in each monthly edition. One of the advantages of the publication's
Web format is that it can display functional Java programs in conjunction with articles.
Figure 3.3 shows a working example from a tutorial on Java animation programming.
Figure
3.3. A JavaWorld how-to article on Java
animation programming includes a working example of a program.
In addition to offering information of benefit to Java programmers, JavaWorld
publishes articles and commentary about the language and its development. One issue
that has been hotly debated since Java's release is whether the language is secure.
Security is important because of the way Java programs work when they are placed
on a Web page. The Java programs that you have tried during this hour were downloaded
to your computer first. When the program was finished downloading, it ran on your
computer. It was as though someone sat down at your computer, popped in a disk, and
ran his own program.
Unless you know a whole lot of people, most of the Web pages you visit will be
published by strangers. In terms of security, running their programs isn't a lot
different than letting the general public use your computer on weekends. If the Java
language did not have safeguards to prevent abuse, its programs could introduce viruses
onto your system, delete files, and do other malicious things. Java includes several
different types of security to make sure that its programs are safe when run from
Web pages.
The main security is provided by the following restrictions on Java programs running
over the Web:
- No program can open, read, write, or delete files on the user's system.
- No program can run other programs on the user's system.
- All windows created by the program will be identified clearly as Java windows.
This identification prevents someone from creating a fake window asking for the user's
name and password.
- Programs cannot make connections to Web sites other than the one they came from.
- All programs will be verified to make sure that nothing was modified after they
were compiled.
At this time, the general consensus among Java developers is that the language
has enough safeguards in place to be usable over the Web. Several security holes
have been found, often by programming security experts, and these holes have been
dealt with quickly by Sun or the Web browser programmers. Because JavaWorld covers
the latest news of note in the Java development community, it is a good way to keep
track of any security issues that arise.
Caution: None of the safeguards in place
are a complete block against malicious programs. Just as loopholes were found in
the past year, more will undoubtedly be found in the future. If you are concerned
about running Java programs through your Web browser, you might want to run programs
only from a source such as Gamelan because it tests the programs before including
them in the directory. You also should back up anything you can't afford to lose
on your computer, which is good practice for anyone who runs programs received from
the Internet.
Taking in a Ball
Game at Instant Ballpark
The first afternoon stop on the Java tour will be a trip to the old ball game.
Instant Sports, a Texas company that provides sports reporting information, is using
Java to present baseball games as they happen in a visual, pitch-by-pitch fashion.
To see how baseball is played in cyberspace, visit the following address:
http://www.instantsports.com/
The Java program called Instant Ballpark presents each pitch in a major league
game. The ball travels from the pitcher's icon to the batter and goes out to the
fielders when it's hit. Sound effects, such as the umpire's strike call and the ball
hitting the bat, also are presented.
The program is a unique way to follow live games and past games that are available
from the Instant Ballpark archive. Figure 3.4 shows the last play in a game between
the Chicago White Sox and the Seattle Mariners from the 1996 season.
Figure
3.4. Mariners shortstop Alex Rodriguez
drives home the winning run in Instant Ballpark, a presentation of a live baseball
game using a Java program.
One of the things that you might notice about Instant Ballpark is that it updates
the day's scores in other games as you are using the program to follow a game. This
update is relatively easy to do because the Java language is multithreaded. Multithreading
is a way for the computer to do more than one thing at the same time. One part of
a program takes care of one task, another part takes care of a different task, and
the two parts can pay no attention to each other. Each part of a program in this
example is called a thread.
In a program such as Instant Ballpark, the league scoreboard along one side of
the window could run in its own thread. The rest of the program could be another
thread. If you use an operating system such as Microsoft Windows 95, you're using
a type of this behavior when you run more than one program at the same time. If you're
at work and you surf the Web for European aerobics videos in one window while running
a company sales report in another window, congratulate yourself--you're multithreading!
Getting Down to
Business
At this point in your travels, you might be getting the impression that Java is
primarily of use to baseball fans and those who have body parts to show the world.
Although those two subject areas are enough to keep most of us entertained for hours,
the next stop on our trip shows an example of Java getting down to business.
Direct your Web browser to the following address:
http://www.engine.com/java/engbrowse/Employee.asp
This example is an employee payroll database managed as a pair of Java programs.
Employee information is viewed in one program, and the other program is used to edit
items from the payroll record of a specific employee. Figure 3.5 shows Bart Simpson's
record as it is being edited.
Unlike other payroll tracking systems that require the installation of software
on the computers of each employee who needs access, the use of Java enables Software
Engine to make the program available to any employee with a Web browser. With some
kind of password security system in place, the program could even be used by employees
who are away from the office on business trips. All the employees would have to do
is access the company's Web site.
Figure
3.5. A Java program from Software Engine
that is used to maintain employee payroll records.
A database program such as Software Engine's can be thought of in several different
ways. One way is to think of a program as an object--something that exists in the
world, takes up space, and has certain things it can do. Java, like the C++ language,
uses object-oriented programming, as you will see during Chapter 10, "Creating
Your First Object." Object-oriented programming (OOP) is a way of thinking about
computer programs. A program is thought of as a group of objects. Each object handles
a specific task and knows how to speak to other objects. For example, a word-processing
program could be set up as the following group of objects:
- A document object, which is the area where you type in text
- A spell-checking object, which can look over the document object to find any
possible spelling errors
- A printer object, which handles the printing of the document
- A menu object, a mouse object, and many others
Each of these objects is an independent computer program that doesn't need the
others to do its job. The word-processing software is a collection of all the objects
necessary to get work done.
OOP is a powerful way to create programs and it makes the programs you write more
useful. Consider the word-processing software. If the programmer wants to use the
spell-checking capabilities of that program with some other software, the spell-checking
object is ready for use with the new program. No changes need to be made.
Stopping by Gamelan
to Ask Directions
This world tour of Java programs is being led by a professional who is well-versed
in the hazards and highlights of Web-based travel. You'll be venturing out on your
own trips soon, so it's worthwhile to stop at the best tour guide currently available
for the Java-hungry tourist, the Gamelan Web site:
http://www.gamelan.com
Gamelan is the most comprehensive directory of Java programs, programming resources,
and other information related to the language. Most of the programs visited during
this hour were originally found on a trek through the searchable database maintained
by Gamelan. Updates are made on a daily basis, so this is another place that you'll
be visiting often as you develop your Java programming skills.
One of the best uses of Gamelan for programmers is to see what programs are available
that offer source code. In case you're unfamiliar with the term, source code is another
name for the text files that are used to write computer programs. The BigDebt.java
file that you created during Chapter 2, "Writing Your First Program," is an
example of source code.
Gamelan's directory listings indicate when a compiled Java program is accompanied
by the source code used to create it. After you have finished your first 24 Chapters
as a Java programmer, you ought to take a look at some of these programs. Figure
3.6 shows a Java program being used on Gamelan to provide instant access to the different
areas that comprise the site.
Figure
3.6. The Gamelan directory offers more
than 4,000 Java resources and links to programs. It uses this Java program as a navigational
aid.
The large number of programs listed in Gamelan show that the language has been
adopted quickly by thousands of programmers around the world. Part of the reason
is that Java's popularity inspires people to learn it, which is the same principle
that caused parachute pants and breakdancing to be briefly popular in the mid-'80s.
Another reason for the swiftly growing population of Java programmers is the simplicity
of the language.
One of the goals of Java's design was to make it easier to learn than C++, the
language James Gosling was having fits with on Sun's smart-appliance project. Much
of Java is based on C++, so programmers who have learned to use that language will
find it easier to learn Java. However, some of the elements of C++ that are the hardest
to learn--and the hardest to use correctly--have been removed from Java.
For people who are learning programming for the first time, Java is easier to
learn than C++ would be. Also, Java will not work if its variables and other elements
of a program are used incorrectly. This adherence to rules can be painful for experienced
programmers, but it forces everyone to develop good habits as they create programs.
Some languages are created to make it easier for experienced programmers to harness
the capabilities of the computer in their programs by including shortcuts and other
features that programming veterans easily understand. Java does not use these features,
preferring to make the language as simple as an object-oriented programming language
can be. Java was created to be easy to learn, easy to debug, and easy to use.
A Big Finish with
Castanets
The second-to-last stop on your Java vacation has a certain Caribbean flair to
it--castanets, marimbas, and bongos are involved. If you packed a ruffly Cuban bandleader
shirt just like the one Carmine Ragusa used to wear on episodes of Laverne and Shirley,
now's the best chance you'll ever have to wear it. Visit the following Web address:
http://www.marimba.com
Unlike the other sightseeing locations you have visited, this site can't be viewed
with a Web browser alone. Marimba, a startup company formed by several former Java
developers at Sun, has used Java to create Castanet, a new way to receive and run
software over the Internet.
Castanet is a way to send out computer programs that automatically update themselves
on the computers of people who request them. It's a service not unlike television,
where you turn to a channel and immediately start receiving the broadcast signal
of that channel. In fact, the Java programs sent by this method are called channels.
Figure 3.7 shows a Castanet channel offered by Excite that presents the lineup of
other channels that are currently available. Like TV listings, Excite's guide offers
previews of each channel and a way to immediately request them. If Excite updates
its guide channel program, Castanet sends that update automatically over the Internet.
No effort is required on the user's end to keep up with new versions of the software.
Figure 3.7. The Excite guide to Castanet channels, which itself is
a channel.
Java is not able to send out its programs in this manner, so Castanet requires
the use of special software called the Tuner. The Castanet Tuner is a sophisticated
Java program that runs from the command line. Although Netscape has announced plans
to include the Tuner's functionality in a future version of its software, this feature
has not become available at the time of this writing. To find out more about downloading
the Tuner for your system, visit the following Web page:
http://www.marimba.com/products/castanet-tuner.asp
The Tuner is several megabytes in size, so you might not want to install it on
your system immediately. Visit the Marimba Web site to find out more about channels
and what services they offer.
Castanet illustrates a point about Java that sometimes get lost: Although Java
is most popular as a way to write Web page programs, it is not limited to use on
the Internet. You can use it to write any kind of software.
Workshop: Putting
Java on Your Desktop
The last stop on your whirlwind tour of Java is ESPNET SportsZone, the electronic
edition of the cable sports channel. So far, your guides have asked nothing of you
other than an occasional wardrobe change, but that's going to change. Redirect your
Web browser to the following address:
http://espnet.sportszone.com
If you're using a browser such as Netscape Navigator or Microsoft Internet Explorer,
your first assignment is to find the Java programs on this page. This assignment
ought to be a lot easier than finding Waldo in those Where's Waldo? children's guides,
but if you need a hint, here it is: They're the parts with changing text and graphics.
ESPN uses Java programs to provide constant updates to scores and headlines in
the same way it uses a sports ticker during some events. In the scoreboard program,
scores are frequently updated in the program's window, along with graphical advertisements.
The scoreboard Java program is offered as part of a Web page, but it has a special
feature that adds to its usefulness. It can be detached from the page and placed
on your system's desktop as a stand-alone window. Click the Display on Desktop button
and then minimize your Web browser. This might be more sports than you're able to
handle in a short period of time, but it shows how Java can present information in
a way much different from standard Web pages. Figure 3.8 shows the scoreboard program
on a Windows 95 desktop.
Figure 3.8. Scores are presented in a desktop window with the
ESPNet SportsZone Scorepost program.
Once you're completely caught up on the sports events that have taken place during
your world-in-an-hour jaunt, it's time to put away your luggage and get ready for
a return to programming. More Web sites and other items of note for Java programmers
are described in Appendix A, "Where to Go from Here: Java Resources."
Q&A
- Q Can I use the sample Java programs from the JavaSoft Web site on my own
home page?
A JavaSoft encourages the use of its sample programs on Web sites. Take a look
at the directories that were created when you installed the Java Developer's Kit
on your system. You will find more than a dozen sample programs along with the .java
files that were used to compile them. These programs can be a valuable resource when
you're working on your own Java programs later on.
Q What other ways have been devised to offer programs on Web pages?
A Several programming strategies are aimed at making Web pages smarter. The main
competitor to Java is ActiveX, an extension of Microsoft technology called the Component
Object Model. ActiveX programs are similar in function to Java programs--they are
placed on Web pages and are run when browsers are equipped to handle them. The primary
differences are that ActiveX uses a way to verify the identity of ActiveX programmers,
and ActiveX programs are not downloaded each time they are encountered. Unlike Java
programs, an ActiveX program stays on a user's system. In addition to ActiveX, JavaScript
and VBScript offer some programming capabilities on Web pages. These programs must
be more simple than Java and ActiveX programs, however.
Q I ran a useful Java program on a Web page. Can I run it on my system without
the browser?
A Under most circumstances, no. Java programs typically are developed either
to run on a Web page or to run from the command line. A program can be written so
that it works in both ways, but most of the programs you will find in a directory
such as Gamelan do not include this functionality. You'll learn much more about the
different types of Java programs during Chapter 4, "Understanding How Java Programs
Work."
Q If Java programs are platform-independent, why are some Java programs such as
SunSoft Java WorkShop only available for specific systems?
A Java programs might be limited to specific systems such as PC compatibles because
the programs include the use of non-Java programming for some features. For example,
a Java program might use a program written in C++ to communicate with a modem because
Java does not support this capability in its current version. Java is still relatively
young in its development, and some of its goals concerning complete platform independence
have not been achieved yet. Web programs are the area where Java's multiplatform
promise is most fully realized. Anyone with a Java-capable Web browser can use one
of Java's Web programs on a page.
Q Is there a print edition of JavaWorld?
A At present, JavaWorld is distributed strictly through the World Wide Web. However,
several newsstand magazines are available that cover the language, including Java
Report, Dr. Dobb's Journal, and others.
Q Can a Java program I run on a Web page give my computer a virus?
A Because of security restrictions that prevent Web programs from reading, writing,
or modifying files, there's no way for a virus to be transmitted from a Java program
on a Web page to your system. Java programs that you download and run from the command
line have the same risk of viruses as any program you download. If you're using programs
received over the Internet, you need to acquire a good antivirus program and use
it regularly.
Quiz
If your mind hasn't taken a vacation by this point in the hour, test your knowledge
of this chapter with the following questions.
Questions
- 1. How did object-oriented programming get its name?
(a) Programs are considered to be a group of objects working together.
(b) People often object because it's hard to master.
(c) Its parents named it.
2. Which of the following isn't a part of Java's security?
(a) Web programs cannot run programs on the user's computer.
(b) The identity of a program's author is verified.
(c) Java windows are labeled as Java windows.
3. What is a program's capability to handle more than one task called?
(a) Schizophrenia
(b) Multiculturalism
(c) Multithreading
Answers
- 1. a. It's also abbreviated as OOP.
2. b. ActiveX programs verify the author of the program, but this security method
is not implemented with Java.
3. c. This also is called multitasking, but the term multithreading is used in
conjunction with Java because an independently running part of a program is called
a thread.
Activities
Before unpacking your luggage, you can explore the topics of this hour more fully
with the following activities:
