Java Networking and Communications FAQ

Frequently Asked Questions for the book Java Networking and Communications by Todd Courtois.

Q: What do I need to do to run the code in the exercises?
The examples are not, in general, executable straight off the CDROM. We recommend compiling all of the JNC classes you intend to use, to make certain that the .class files match the .java files. In order to do this, what you might do is move the entire JNC hierarchy to your hard disk, and remove all the .class files that are already compiled in that hierarchy. Because the JNC code files are compact, it will not take long to recompile these classes.
Many of the examples rely on a package hierarchy which does not exist on the CDROM. You will need to construct this package hierarchy inside your CLASSPATH. One way to do this is to simply create a JNC directory inside your CLASSPATH. For instance, the path for the HttpdSimple example might look like this:
```
jdk1.1.4
-classes
--JNC
---HttpdSimple.java
---HttpdSimpleTest.java
```
This assumes that the jdk1.1.4/classes directory is in your CLASSPATH.
Almost all of the examples given in the book are inside the package JNC. This means that the .java file and the .class file MUST end up inside the directory JNC under your CLASSPATH if you intend to run the example using, say, the JDK.
After you have recompiled these classes you can simply run them using the JDK "java" command, the Java Runtime Environment, or your favorite IDE's java execution facility.
Q: How can I create subpackages under the JNC package?
Simply create a directory underneath the JNC directory. Then, move all the example code you wish to appear in that subpackage into the new directory. Let's say you wanted to create a JNC subpackage which contained only the WebDroneGroup example code. You could create a directory called "WDG" underneath the JNC directory on your classpath. Then, you could move the files "WebDroneGroup.java" and "WebDroneGroupTest.java" into the WDG directory.
Once you've moved the files, you need to make a slight modification to the package and import statements in the "WebDroneGroup.java" file. Change the package statement to "package JNC.WDG;" and add an import line: "import JNC.*;". This indicates to the JDK that all classes compiled from this code should be placed in the path /JNC/WDG and that the WebDroneGroup class should be able to access all of the classes stored in the toplevel JNC package.
Q: How do I use "javac" from the JDK to compile .java files?
If you simply type "javac" and return at your command line (Win32 and Solaris), javac should dump a list of options that it understands. Typically you use javac like "javac MyClass.java".
There are a few important things to note about javac:
- It is case-sensitive, even if your platform's OS is not. "javac myclass.java" is NOT the same as "javac MyClass.java". You will get weird errors such as "Class MyClass must be defined in a file called MyClass.java" if you do not provide the correct filename case.
- It doesn't like whitespace in filenames.
- You must have set up your CLASSPATH correctly for it to work. Specifically, javac needs to be able to find the core JDK classes which the JDK typically provides under jdk/classes/classes.zip. It also needs to be able to find the class you wish to compile.
- It outputs compiled classes to your CLASSPATH. So if you compile a class under JNC.mySubPackage, the compiled .class file will appear under CLASSPATH/JNC/mySubPackage.
If you have any questions about the operation of javac, look at the documentation that came with the JDK or is available from the JavaSoft websites.
How do I use "java" from the JDK to run examples?
First off, note that you MUST follow the directions provided elsewhere in this FAQ on how to compile the examples. Once you have compiled them under your CLASSPATH, then you can run them using the JDK's "java" command. You can ONLY run classes which have a "public static void main" method. Many of the examples provide a "FooTest" class which is a class associated with class "Foo" that contains a main method. You can then run the FooTest class, and thereby test the Foo class, by doing "java FooTest". If this does not make sense, then read the JDK tools documentation that came with the JDK or is available from the JavaSoft websites.
Q: Where is the "DeathStarPackage" package?
Q: Why do I sometimes I get a ClassNotFoundException for a class in the "DeathStarPackage" package?
There are specific classes on the CDROM we absolutely know must be recompiled in order to work correctly. These .class files contain references to an early development package which no longer exists: the "DeathStarPackage" package. In the source code files, this package has been replaced by the "JNC" package.
```
\src\ceCTBMac\ceCTBMac.class
\src\CESerialWin32\CESerialWin32.class
\src\cesersol\cesersol.class
\src\DNS\DNSTest.class
\src\FingerClient\FingerClientTest.class
\src\FunkyTerm\FunkyTerm.class
\src\icb\ICBMain.class
\src\NMEAStreamParser\NMEAStreamTest.class
\src\ScheduledEvent\ScheduledEvent.class
\src\SevenBitFilterInputStream\SevenBitFilterInputStream.class
\src\SimpleSocketClient\SimpleSocketClientTest.class
\src\StdioShell\StdioShell_Test.class
\src\WebDrone\WebDroneTest.class
```
If you delete these class files and then recompile, the examples should work smoothly.
Q: What is this "DeathStarPackage" file I see in some subdirectories?
A zero kB file named "DeathStarPackage" appears in certain subdirectories. This are leftovers from alias files used on the MacOS during earlier development. You can safely ignore these or delete them.
Q: What are these "Ws_ftp.log" files that appear on the CDROM?
The "Ws_ftp.log" files are leftovers from when files for the CDROM were transferred via FTP-- you can ignore these or delete them.
Q: Who do I sometimes have trouble opening the native IDE project files with my IDE (Borland C++, CodeWarrior, Cafe, etc.)?
Unfortunately, there are many versions of these platform-specific IDEs floating around, and project files created with one may not be openable by another. We sometimes have problems opening IDE project files with the same version of the IDE as created the file in the first place.
If you can't get your IDE to open a particular project file, what you can do is essentially recreate the project file in your IDE. From the list of native files in the particular project's subdirectory, it should be fairly easy to determine which files should go into the project. Also, the "Linking with the Natives" chapter gives a great deal of detail about special native project settings necessary for compiling and linking.
Q: Why do I have problems using the ScheduledEvent class with the ScheduledEventTest and SimpleWebDrone classes?
In ScheduledEvent, there are some methods with the word "Occurrence" in them. These methods are spelled correctly. However, in the ScheduledEventTest, SimpleWebDrone, and perhaps other classes, the spelling is incorrect ("occurence"). When you compile the examples, the compiler should complain that it can't find a method with the word "occurence" in it. To fix this problem, simply fix the spelling of the method name in the class you're trying to compile and it should work. We'll be placing some examples with the correct spelling up on the JNC website shortly. (Thanks to Alen Peacock for reporting this error.)
Q:On page 10 a method mark(index) is listed-- where can I find this?
This is an error. The correct method signature is mark(int readLimit) and a full explanation of mark/reset used with input streams is given on page 32. (Thanks to Laurence Vanhelsuwe for reporting this error.)
Q:On page 92 it says IP includes the concept of a port-- is this true?
This is an error. The IP protocol itself does not include the concept of a host port. However, the two main IP-based protocols used in Java, UDP and TCP, do use this concept. (Thanks to Laurence Vanhelsuwe for reporting this error.)

Q: What do I need to do to run the code in the exercises?

Q: How can I create subpackages under the JNC package?

Q: How do I use "javac" from the JDK to compile .java files?

How do I use "java" from the JDK to run examples?

Q: Where is the "DeathStarPackage" package?

Q: Why do I sometimes I get a ClassNotFoundException for a class in the "DeathStarPackage" package?

Q: What is this "DeathStarPackage" file I see in some subdirectories?

Q: What are these "Ws_ftp.log" files that appear on the CDROM?

Q: Who do I sometimes have trouble opening the native IDE project files with my IDE (Borland C++, CodeWarrior, Cafe, etc.)?

Q: Why do I have problems using the ScheduledEvent class with the ScheduledEventTest and SimpleWebDrone classes?

Q:On page 10 a method mark(index) is listed-- where can I find this?

Q:On page 92 it says IP includes the concept of a port-- is this true?