Welcome to Java Developer
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
- true executable content embedded in an extensible language;
- automatic download of applications ("applets") in a safe manner;
- portability by standardizing on a "neutral" architecture;
- client/server functionality on the Internet or "intranet;"
- built-in security that is extensible.
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 http://zeitgeist.com. For those of you with a consumer preference,
there is the multimedia application at http://www.vectorman.com. (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 (http://java.sun.com/JDK-prebeta1/converting/). 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
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