using a library (jcurses) that uses jni
I'm having trouble uses the JCurses library. Here's what's happening:
>ls -A
jcurses.jar .keepme libjcurses.so Test.java
>javac Test.java -classpath jcurses.jar
>ls -A
jcurses.jar .keepme libjcurses.so Test.class Test.java
>java Test -classpath jcurses.jar
Exception in thread"main" java.lang.NoClassDefFoundError: jcurses/system/Toolkit
at Test.main(Test.java:6)
>rm Test.class
>jar xvf jcurses.jar jcurses/
...(no jar error outputs)...
>ls -A
jcurses/ jcurses.jar .keepme libjcurses.so Test.java
>javac Test.java
>ls -A
jcurses/ jcurses.jar .keepme libjcurses.so Test.class Test.java
>java Test
Exception in thread"main" java.lang.ExceptionInInitializerError
at Test.main(Test.java:6)
Caused by: java.lang.NullPointerException
at jcurses.system.Toolkit.getLibraryPath(Toolkit.java:111)
at jcurses.system.Toolkit.<clinit>(Toolkit.java:37)
... 1 more
Why does running "java Test" the first time output something different than the second just because? Also, why isn't the second working?
[1231 byte] By [
rosenthaa] at [2007-11-26 12:59:06]
# 1
> Why does running "java Test" the first time output
> something different than the second just because?
Because you are running something different. The first has an explicit class path and the second doesn't.
> Also, why isn't the second working?
Probably because there is something wrong with the test code. Could be the library as well. Could be that you need something on your system that the library needs and which you don't have.
# 2
The reason >java Test
works the second time is because the current directory is apparently on the classpath (even though echo $CLASSPATH
for some reason prints CLASSPATH: Undefined variable.
). I was really asking why >java Test -classpath jcurses.jar
which prints Exception in thread "main" java.lang.NoClassDefFoundError: jcurses/system/Toolkit
at Test.main(Test.java:6)
does not work or even indicate that the jcurses library was found.
# 3
>java Test -classpath
> ... does not
> work or even indicate that the jcurses library was
> found.
Probably because the command syntax is wrong.
The syntax is
java [-options] class [args...]
Anything that follows the class is consider an command line option for the class, not java.
# 4
Ok I got it working now. I used
>java -cp .:jcurses.jar Test
The part that was really confusing me was:
>java -cp jcurses.jar Test
Exception in thread "main" java.lang.NoClassDefFoundError: Test
I forgot that the java command only includes the current directory in the classpath if none is specified. Thats why >java Test
worked: it used the default classpath which consists of the current directory, and the class I was executing and the library I was using were both in the current directory, so java located them, but the library failed because its classes assume that they will be executed from a jar. The reason >java -cp jcurses.jar Test
didn't work is because the current directory was no longer part of the classpath, so java couldn't find the Test class which was in the current directory.
Thanks.
