Kangry.com: java compile/run

Topics:
DVR
nvrec
Mplayer
Links
Misc
Commands
Humor

New user

uploaded files

submited by Russell Mon 23 May 05
Edited Thu 12 Jan 06

so I'm trying to learn java. I already had jre (java runtime) and I installed jdk (java development kit)

Now I know that I have jre installed cause Azureus works, but for some reason I do not understand, after installing the java rpms I found broken symlinks for both /usr/bin/java and /usr/bin/javac

I was able to fix this problem by ( as root) deleting those two symlinks and installing two new ones that work

ln -s /usr/java/jre1.5.0_02/bin/java /usr/bin/java
ln -s /usr/java/jdk1.5.0_03/bin/javac /usr/bin/javac

I found the correct location of the files by doing an rpm -q -l jre-1.5.0_02-fcs|more and paging though until I saw what I was looking for

I am using Head first Java to learn. It's a fun book, in a very different style than a traditional tech book.
I found it lacking in the most basic stuf, how to actually run a program

Here is what I found out that was not in the book (besides the stuff about the broken symlinks.

Each public class must be declared in a file with the same name as the class. (case counts)
```
public class MyFirstApp {
   public static void main (String[] args){
   System.out.print("I Rule");
  }
}
```
Must be in a file named MyFirstApp.java
To compile a file you type javac MyFirstApp.java
This creates MyFirstApp.class
To RUN the file you type java MyFirstApp (NOTE THE ABSENCE OF THE .class)

It just would have been nice if somebody told me that. Instead I waisted time like this

$ java MyFirstApp.class
Exception in thread "main" java.lang.NoClassDefFoundError: MyFirstApp/class

What the hell kind of error message is that ?
I mean with C it's gcc hello.c, which creates a.out (which is another issue for another time ;-) ) and to run the file it's ./a.out nobody assumes the extention for you. It just would have been nice if somebody told me this.

Replys: