Copy Link
Add to Bookmark
Report
Java Coffee Break Newsletter Volume 3 Issue 03
Java Coffee Break Newsletter Volume 3, Issue 3
http://www.javacoffeebreak.com/
ISSN 1442-3790
=================================================================
In this issue
* Featured Java Websites
* Book Review - Java Network Programming 2 Ed.
* Book Review - Thinking in Java
* Article : "Why is my applet gray?"
or What causes applets to fail
* Q&A : Who created Java?
* Q&A : How do I get the current time?
* Q&A : My classpath statement is too big, and causes an
"Out of environment space" error. How do I fix it?
=================================================================
/*
* Need a Java course to bring your team up to speed?
* Artima Software offers in-house and public seminars on
* Java programming and OO design with Java, taught by
* Bill Venners, a recognized expert on the Java platform.
* --> http://www.artima.com/javaseminars
*/
=================================================================
Featured Java Websites
Here are a selection of websites that may be of interest to
readers. This is a new section, profiling useful resources
for developers.
SERIOUS GAMING WITH JAVA
Looking to save a few bucks, and play some games online,
rather than buying shrinkwraped software? JavaGame.net has one
of the largest collections of Java games on the Net, grouped
together by category. Whether your interest is strategy or
arcade, board game or adventure games, kids fun or card games,
there's a huge range of Java applets just waiting for you, and
all for free. Who said Java wasn't designed for fun!
http://www.javagame.net/
IBM RELEASES C++ STYLE PRE-PROCESSOR FOR JAVA
Pre-processors allow developers to write conditional
statements, such as including debug code for an internal
test release, and stripping debug code out for a release
edition. Now, big blue has released a pre-processor class for
Java, which makes it possible to add conditional statements to
your Java applications. Very cool, and available from IBM,
with a good tutorial article on the topic.
http://www-4.ibm.com/software/developer/library/cprep/index.html
=================================================================
/*
* Looking for anti-virus software from leading vendors like
* Symantec or McAffee? If you want instant protection, purchase
* your anti-virus products from Beyond, the Internet's leading
* software superstore. McAffee Anti-Virus and Symantec's
* Anti-Virus 2000 is also electronically downloadable, for fast
* protection Best of all, you make the savings!
*
* --> http://www.beyond.com/AF10445/support/antivirus.htm
*/
=================================================================
Book Review - Java Network Programming 2 Ed.
Author : Merlin Hughes, Michael Shoffner, Derek Hamner
Publisher : Manning
ISBN : 188477749X
Experience: Beginner - Intermediate
Java Network Programming, Second Edition aims is the sequel to the
highly popular Java Network Programming title, and picks up where
the original left off. It offers considerably expanded coverage of
the Java networking API, for the Java 2 platform. The authors
build on chapters from the previous book, adding Java 2 specific
methods and classes, and covering newer topics such as servlets,
and CORBA (support for which was introduced in the Java 2
platform).
Readers unfamiliar with network programming, and the intricacies
of sockets, are guided fairly gently through the process, with a
thorough coverage of I/O streams (including files), UDP and TCP
sockets, from both client and server perspective. This gives a
good grounding for later development, with plenty of example
clients and servers. There's also coverage of Java HTTP support,
which is quite simple to work through.
That said, readers familiar with the original title may be in for
some disappointment. The strong cryptography coverage of the first
book has vanished, mentioned only in the preface as the subject of
a future book. Not being very cryptographically minded myself, I
really enjoyed reading about this topic in the first title.
Nonetheless, with the number of pages in this thick reference,
something probably had to go, to save room for other topics.
Newer topics covered in the second edition (or greatly enhanced
from coverage in the first edition) include servlets, CORBA, and
remote method invocation (RMI). There's even more examples than
in the first edition, but there are a few gaps where coverage
could have been improved (for example, the new RMI activation
features are barely mentioned, and the reader is referred
instead to the RMI documentation of Sun). Servlet coverage
could really be improved as well - there's some great books out
on the market though that can be used in companion with this book
Perhaps these, and other topics will be covered in a future
addition.
As networking books go, Java Network Programming 2Ed is close to
the top, but has room for improvement. Currently, however, you
won't find a book that can beat it, but for advanced topics
you'll probably need a second title for topics like servlets or
distributed computing.
For more information about this title, or to order it, visit
http://www.davidreilly.com/goto.cgi?isbn=188477749X
=================================================================
Book Review - Thinking in Java
Author : Bruce Eckel
Publisher : Thinking in Java
ISBN : 0136597238
Experience: Beginner-Intermediate
Thinking in Java is a comprehensive guide to the Java programming
language, written by the Bruce Eckel (author of the hugely
successful Thinking in C++ series). This is an amazing book, not
only for its content but also its distribution. Bruce Eckel gives
the entire text of his book in Adobe PDF format away from his
website, without charging. The 'electronic' edition of this book
is a companion to the print edition, which retails for a modest
price considering the size of the book and the value of the content
within.
There's a real sense, throughout the book, of the author's
personality and programming prowess. Some introductory Java books
will show you how to program applets, a little GUI design, a little
networking, and if you're lucky something about Swing. The focus
is on the base Java APIs, and little more. Thinking in Java goes
much further, tackling advanced issues like design patterns, I/O
and networking, and class design. It teaches you how to program
in Java, and to think like a Java programmer. The wealth of
experience of the author is contained within these pages, and is
an invaluable learning tool.
Many readers will be tempted to download the book, rather than
purchasing it. I'd highly recommend doing so - but if you're like
me you'll quickly find reading such a long book on a screen
tiresome. However, to whet your appetite, visit Bruce Eckel's
website at http://www.bruceeckel.com/ and try it for yourself.
This comprehensive guide to the Java programming language is
excellent value, and a long lasting reference when working with
Java.
For more information about this title, or to order it, visit
http://www.davidreilly.com/goto.cgi?isbn=0136597238
=================================================================
Article : "Why is my applet gray?"
or What causes applets to fail
Applets are both a revolutionary way to produce dynamic web-based
content and a major pain in the neck for developers. In an ideal
world pitched by Sun, applets are written once, and run on any
computer, any browser, any operating system. This vision has
been coined Write Once, Run Anywhere (WORA). What a wonderful
dream!
In the real world, experienced by thousands of developers, and
hundreds of thousands of users, Java applets are a frustrating
headache. When they work, they work great. But when they don't,
the problem is hard to diagnose, and even harder to repair.
Inconsistencies between browser versions and vendors, operating
systems, and user configurations make for plenty of problems.
Sure there is the occasional glitch in the GUI, or the slow
performance on certain machine/browser configurations. But the
problem goes further, to what Java developers and web users
dread the most. The Ugly Gray Box of Java.
What doesn't kill us makes us stronger
Provided that your browser installation is stable, it is unlikely
that your browser will crash or freeze (if it does repeatedly,
reinstalling the browser often solves this problem). More
likely is that you'll see the Ugly Gray Box of Java (almost
as frustrating as the Blue Screen of Death in Win 9x).
Here's an example of an applet that is guaranteed to give a
UGBoJ. Depending on your browser, you may also see a cryptic
message in the browser status bar.
import java.awt.*;
import java.applet.*;
public class NaughtyApplet extends Applet
{
private String message = null;
public void init()
{
// Check the length of message
// It will always be null
System.out.println (message.length());
}
}
What causes Ugly Gray Boxes?
They occur when an error in the loading or execution of an
applet has occurred, causing an applet crash. In Java, the
technical term for these errors is an Exception. Good Java
applets will "catch" these exceptions, or at least attempt to
catch the most likely of errors. Many though are unforeseen, and
some not even the fault of the applet. Let's look at some of the
most obvious causes.
Causes for Applet Exceptions
The causes for applet exceptions are numerous, but some of the
most common are: -
* failure to locate or load a Java class
* failure to access a network resource
* null-pointers
Failure to locate or load a Java class
Some applets are composed of a single class, while others are
made up of a large number of classes. Each class must be fetched
individually, and if a network fault occurs during the loading
of any of these classes, an exception will be thrown. These
exceptions occur before the applet even fully loads, and so
are hard to guard against.
The easiest way though to avoid these errors is to package your
applet into a .ZIP, .JAR, or .CAB archive. Netscape supports
.ZIP and .JAR archives, while .CAB is specific to Internet
Explorer.
Failure to access a network resource
Networking problems are very frustrating. Sometimes a networking
host is down, and so applets can't establish network connections
to it. Other times, the user is behind a firewall, and so Socket
or DatagramSocket requests will not work. Please, if you write
networking applets, consider using HTTP for communication rather
than TCP/UDP, as the number of people behind firewalls is growing.
Another cause of problems are networking applets that violate
browser security restrictions. They run fine in Appletviewer,
and then fail in Netscape / Internet Explorer. An applet can only connect to the host from which it is loaded.
Many applets also have problems when looking up IP addresses,
so specify the CODEBASE of the applet and the host it will
connect to as an IP address, rather than a hostname.
Null pointer exceptions
Null pointer exceptions are another of the most common types of
exceptions that crash applets. Unfortunately, this one is
usually a bug in the applet code. When assigning an object
reference to a variable, be sure to check that it is not null.
For example, consider the following code: -
// Get an applet parameter
String count = getParameter ("count");
if (count == null)
count = "1";
Notice the guard statement, which assigns a default value of no
parameter was specified. There are plenty of other places where
null pointers can creep in - be careful to check for them.
Summary
It can be frustrating for users to see the Ugly Gray Box of Java
- they think that they're somehow at fault. The UGBoJ is
equally annoying for developers. With a little care though, you
can guard against the more common causes, and help reduce the
number of gray applets on the web!
=================================================================
Q&A : Who created Java?
Java is still a relatively new language, so it is quite amusing
to some to think that Java has a "history" behind it. One of the
most frequent questions I've been getting lately though is about
the origins of Java.
Java was created by engineers working at Sun Microsystems. The
figure that stands out most of all is James Gosling, widely
regarded as the "father" of Java. James and his team were
working on a language whose original name was Oak. Oak was
designed for embedded devices, such as mobile phones. The first
publicly available version of Java, however, was as Java
applets, in the original HotJava browser. From there, Java
grew to what it is today.
=================================================================
Q&A: How do I get the current time?
The easiest way is to declare a new instance of java.util.Date.
When the default constructor is called, the date stores the
current time.
// Get the current time/date
Date d = new Date();
System.out.println (d);
If you're interested into a greater degree of precision, you can
also get the current time in milliseconds. The System class (part
of the java.lang package) provides a static method,
currentTimeMillis(). This returns the number of milliseconds
since midnight January 1, 1970.
// Get the current time in milliseconds
long milliseconds = System.currentTimeMillis();
=================================================================
Q&A: My classpath statement is too big, and causes an
"Out of environment space" error. How do I fix it?
This occurs only on Windows systems, and is a throwback to the
good old days of MS-DOS. You need to expand your environment
space, by adding the following line to your config.sys file: -
shell=c:\command.com /p /e:32000
This specifies almost 32kb for environmental variables, which
should be more than enough. If not, just increase the amount.
=================================================================
The Java Coffee Break Newsletter is only sent out to email
subscribers who have requested it, and to readers of the
comp.lang.java.programmer and comp.lang.java.help
newsgroups.
If you'd like to receive our newsletter, and get the latest
Java news, tips and articles from our site, then get your FREE
subscription & back issues from
http://www.javacoffeebreak.com/newsletter/
If you are an email subscriber and no longer wish to receive
the JCB Newsletter, please unsubscribe by emailing
javacoffeebreak-unsubscribe@listbot.com
