Java SDK setup and installation...

[encompass]

I have learned java this last year in school and would like to begin programming on my own with it this summer to further improve my programming skills. I have experience in C and perl but can't seem to figure out the way that java likes to compiles its code.

I have got both the jdk and java runtime installed in my /opt/ directory. I can compile the .java files with javac however, can't run them because it give me this error...
jason@lappy:/opt/j2sdk1.4.2_11/bin$ ./java /home/jason/PROGRAMMING/java/myfirstjavaprog.class
Exception in thread "main" java.lang.NoClassDefFoundError: /home/jason/PROGRAMMING/java/myfirstjavaprog/class
jason@lappy:/opt/j2sdk1.4.2_11/bin$
as I don't want to lose what little java I know so far... can anyone help me get this setup right...
I am still so knew I use the keyboard class. But that is for another day.
I also am trying to avoid eclipse as I love good ol nano on my 200mb ram lappy.

[thumper]

You are running java from /opt/j2sdk1.4.2_11/bin
The default CLASSPATH does not know the location of /home/jason/PROGRAMMING/java/myfirstjavaprog.class

That is what the error is from.

Post back what the default CLASSPATH is.

I'm not entirely certain as I haven't touched java for some time.

[encompass]

I am sorry, but I don't know how to get that information. is it a variable somewhere?
Thanks for the help so far...
export CLASSPATH=(WHAT)
and could you explain if possible why it has to be set?

[thumper]

Unless you have set one it is likely to be empty (like mine is)
tim@spike:~/sandbox/prog$ echo $CLASSPATH

tim@spike:~/sandbox/prog$ env | grep CLASS
tim@spike:~/sandbox/prog$

There's two ways...

What package is your class in?

[encompass]

Class path... coudl you tell me what that is and what it is for? how do I set that up?
something to do with export CLASSPATH... but that do I set it at...
I set it to the dir where my class was but it still didn't work

[thumper]

The CLASSPATH is used by the JAVA runtime to find classes (surprise :) )

The CLASSPATH should contain either directories or jar files.

Lets say you have a class called Foo in package bar. The directory layout should look like

src-dir/
src-dir/bar
src-dir/bar/Foo.java
src-dir/bar/Foo.class # assuming that it is in the same location

Note: this is not the way to do it, but illustrates a point.
In this situation the src-dir should be in the CLASSPATH, or set on the command line for java
$ java --classpath /full/path/to/src-dir bar.Foo

Note: learn ant (http://ant.apache.org)

[encompass]

Hate to saw it... but java was too hard to set up for my simple programming mind...
I have started to learn python and am loving it... I love how powerful it is. Sorry to take all your time just to move to something else.

[jvictor]

Well Java is not a tuff language.. IMHO.. yes it suits a set of problems , whereas python suits a different set of problems. So comparing bwn Java/Python/C may not be a good Idea.

[gekkio]

If you haven't abandoned Java yet, here's the solution:

First of all, I recommend you to get the Sun Java JDK package:
sudo apt-get install sun-java5-jdk
(it's in multiverse, so you might need to edit your /etc/apt/sources.list to include multiverse repos)

After installing it, you'll have the necessary java tools in your PATH, which greatly simplifies working with Java.
Then you can do
cd /home/jason/PROGRAMMING/java/
java myfirstjavaprog
Note that the .class extension is not used when calling java. You are supposed to only give the name of your class.
(This is the actual problem you had. Don't worry, you're not the first one to make this mistake. :p )
You actually tried to call class called class in package myfirstjavaprog, which would look like this (doesn't really work, because AFAIK you can't use the keyword 'class' as a class name) :
package myfirstjavaprog;

public class class{
}
Oh, and if you want to call java from /opt (instead of using the sun-java5-jdk package), you should do
./java -cp /home/jason/PROGRAMMING/java myfirstjavaprog
instead. -cp specifies the classpath(s) you want to use (and myfirstjavaprog is without .class).