Why is this Java program working?

[pmdkh]

You read it right. I don't understand why something is working.

I recently installed Xubuntu 7.10 on a flash drive, and I've been messing around with setting up Java. I got everything working correctly, and because of a stupid mistake of my own*, I started messing around with the CLASSPATH variable.

I ended up removing the CLASSPATH variable, and I am able to compile and run Java programs. I don't even have the current directory (./) set for the CLASSPATH, and I am able to run programs that call on different Java classes. I also don't use the -cp option for the java and javac commands.

So my question is, how does Java know where to look for other classes if I don't have CLASSPATH set?

Thanks for the help.

*The stupid mistake was trying to use a method from the Math class (java.lang.Math) in a program named Math.java. For quite a while I couldn't understand why it couldn't find the function, until it finally hit me.

[LaRoza]

Maybe it has a default.

[ghostdog74]

what does
echo $CLASSPATH
say?

[pmdkh]

It says nothing because I removed everything from it when I was trying to figure out the solution to the problem I was having.

[nitro_n2o]

Which Java you have? the default one, or the one from Sun?

[pmdkh]

I am using the Sun version. The packages I have installed are sun-java6-jdk, sun-java6-jre, and sun-java6-bin.


ubuntu@ubuntu:~$ java -version
java version "1.6.0_03"
Java(TM) SE Runtime Environment (build 1.6.0_03-b05)
Java HotSpot(TM) Client VM (build 1.6.0_03-b05, mixed mode, sharing)

[jespdj]

Since Java 5, the current directory is in the classpath by default, if you don't have the CLASSPATH environment variable set.

In fact, it is advisable to not set a CLASSPATH variable at all. If you need to run a program that needs certain directories or JAR files in the classpath, then use the "-cp" or "-classpath" switch on the command line to start it, for example:

java -cp /some/dir/with/classes:somejarfile.jar com.mypackage.MyProgram

You do not have to put the standard Java API classes in the classpath. (That's never necessary, also not on older versions of Java).

[pmdkh]

Since Java 5, the current directory is in the classpath by default, if you don't have the CLASSPATH environment variable set.

In fact, it is advisable to not set a CLASSPATH variable at all. If you need to run a program that needs certain directories or JAR files in the classpath, then use the "-cp" or "-classpath" switch on the command line to start it, for example:

java -cp /some/dir/with/classes:somejarfile.jar com.mypackage.MyProgram

You do not have to put the standard Java API classes in the classpath. (That's never necessary, also not on older versions of Java).

That's interesting. Based off of your post, and what I've read about the CLASSPATH variable, I'm going to be using the -cp option from now on. Thanks for the info.