What Is Java?
Java is an object-oriented programming language developed by Sun Microsystems, a companybest known for its high-end Unix workstations. Modeled after C++, the Java language was
designed to be small, simple, and portable across platforms and operating systems, both at the
source and at the binary level .
Java is often mentioned in the same breath as HotJava, a World Wide Web browser from Sun
like Netscape or Mosaic. What makes HotJava different from most other browsers is that, in addition to all its basic Web features, it can also download and play applets on the reader’s system. Applets appear in a Web page much in the same way as images do, but unlike images, applets are dynamic and interactive. Applets can be used to create animations, figures, or areas that can respond to input from the reader, games, or other interactive effects on the same Web pages among the text and graphics.
Although HotJava was the first World Wide Web browser to be able to play Java applets, Java
support is rapidly becoming available in other browsers. Netscape 2.0 provides support for Java
applets, and other browser developers have also announced support for Java in forthcoming
products.
Java’s Past, Present, and Future
The Java language was developed at Sun Microsystems in 1991 as part of a research project to
develop software for consumer electronics devices—television sets, VCRs, toasters, and the
other sorts of machines you can buy at any department store. Java’s goals at that time were to
be small, fast, efficient, and easily portable to a wide range of hardware devices. It is those same
goals that made Java an ideal language for distributing executable programs via the World Wide
Web, and also a general-purpose programming language for developing programs that are easily
usable and portable across different platforms.
The Java language was used in several projects within Sun, but did not get very much commercial
attention until it was paired with HotJava. HotJava was written in 1994 in a matter of months,
both as a vehicle for downloading and running applets and also as an example of the sort of
complex application that can be written in Java.
At the time this book is being written, Sun has released the beta version of the Java Developer’s
Kit (JDK), which includes tools for developing Java applets and applications on Sun systems
running Solaris 2.3 or higher for Windows NT and for Windows 95. By the time you read this,
support for Java development may have appeared on other platforms, either from Sun or from
third-party companies.
Note that because the JDK is currently in beta, it is still subject to change between now and when
it is officially released. Applets and applications you write using the JDK and using the examples
in this book may require some changes to work with future versions of the JDK. However,
because the Java language has been around for several years and has been used for several projects,
the language itself is quite stable and robust and most likely will not change excessively. Keep
this beta status in mind as you read through this book and as you develop your own Java
programs.
Support for playing Java programs is a little more confusing at the moment. Sun’s HotJava is
not currently included with the Beta JDK; the only available version of HotJava is an older alpha
version, and, tragically, applets written for the alpha version of Java do not work with the beta
JDK, and vice versa. By the time you read this, Sun may have released a newer version of HotJava
which will enable you to view applets.
The JDK does include an application called appletviewer that allows you to test your Java applets
as you write them. If an applet works in the appletviewer, it should work with any Java-capable
browser. You’ll learn more about applet viewer later today.
What’s in store for the future? In addition to the final Java release from Sun, other companies
have announced support for Java in their own World Wide Web browsers. Netscape Communications
Corporation has already incorporated Java capabilities into the 2.0 version of their very
popular Netscape Navigator Web browser—pages with embedded Java applets can be viewed
and played with Netscape. With support for Java available in as popular a browser as Netscape,
tools to help develop Java applications (debuggers, development environments, and so on) most
likely will be rapidly available as well.
