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Week 50 - 2001: Classpath - getting acquainted
Setting the classpath right is not always as easy as it should be. Every
OS has its own pitfalls which you should be aware of. This week you will
get familiar with your programming environment.
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First you need to figure out how you set the classpath in your OS.
As I said, this varies a lot so please refer to the Getting
started section if you are not sure.
Keep in mind that in Windows 95, 98 and ME you need to set the classpath
in the C:\AUTOEXEC.BAT file. (In Windows ME there might be other ways to
handle this. Please correct me if I am wrong.) Afterwards you need to restart
the computer.
While in Windows NT, 2000 and XP you find your way through Start
-> Settings -> Control Panel -> System -> Advanced -> Environment variables.
Here you only need to confirm the changes and restart any programs dependent
upon the classpath, like DOS-prompt, Ultra Edit or the likes.
When the variable is set, you may view it in the DOS-prompt by typing
echo
%classpath% (Or in Linux: echo $CLASSPATH). In Windows NT, 2000
and XP set classpath has the same function. |
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When you have put your package directories in the classpath, you will
now implement a small application which shows it on the screen, like the
echo command above. In fact, your application should have exactly the same
output as that command.
Hint: System.getProperty(String) and System.getProperties(). |
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For this exercise you need two or more paths in you classpath variable.
If you do not have several paths there, please add some for the sake of
this application.
You will now change the application above slightly so that each path
is displayed on a separate line. To achieve this, you need to separate
each path using the semicolon (;) in Windows or colon (:) in Linux. Your
application should work for both.
Hint: File.pathSeparator and StringTokenizer. |
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When you know the paths of your package directories, it would be interesting
to see which classes are included in these packages.
Implement an application which searches through the classpath and lists
all CLASS-files it finds. You may have to do some recursive searching here,
if your classes are located in sub directories.
Hint: remember the dir/ls exercises.
My solution requires a file filter called com.rememberjava.io.SimpleFileFilter.
Make the package directory and download the file SimpleFileFilter.java
by clicking the package icon to the left. |
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Finally, this week, if you still have some time to Remember Java, you
will extend the application above to check if the classes found can be
loaded. That this, for each CLASS-file you locate you need to figure out
the correct class name (including package name) for this file and try to
load it. Your application should list one class file on each line and whether
the loading succeeded or failed.
Hint: Class forName(String className)
My solution requires a file filter called com.rememberjava.io.SimpleFileFilter.
Make the package directory and download the file SimpleFileFilter.java
by clicking the package icon to the left. |
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