CODEWITHSUNDEEP
javavariablesubuntuenvironment
de3
de3

Reputation: 1990

An easy question about java and environment variables in ubuntu

I have Ubuntu 10.10 with java already installed. I am able to execute java command from any folder. I supposed that could be because I had java Classpath setted. But neither JAVA_HOME nor CLASSPATH are setted.

If I look at /etc/environment content I can see that PATH is setted to /usr/bin/ (among others). As 'which java' returns /usr/bin/java, is that the reason why I can execute java from anywhere? If not, why is it?

Upvotes: 0

Views: 401

Answers (2)

aalku
aalku

Reputation: 2878

Yes, if java binary (or a link to it) is on a folder that is listed on the path then you can execute java without specifying the path to it (for example /usr/local/java/latest/bin/java -jar x.jar) JAVA_HOME and CLASSPATH have nothing to do with system path. JAVA_HOME allow other software (or scripts) to know where to look for java installation. CLASSPATH tells java where to look for classes (.class files resulting of compiling .java files).

Upvotes: 1

Edwin Buck
Edwin Buck

Reputation: 70909

You can execute java because the command is on your path.

echo $PATH

will show you which directories are searched, in which order to find a particular program. Since /usr/bin is on your path, when you type java it will eventually look at /usr/bin/java. Note that in many systems this is a symbolic link (a file that points to another file) so /usr/bin/java often points to /etc/alternatives/java (which is also a symbolic link that points to the real executable).

Where the environmental variable JAVA_HOME comes into play is in tools and programs that check for JAVA_HOME and act on it instead of relying on the path. In most modern Linux systems, the work done by the alternatives subsystem replaces the earlier (more problematic) JAVA_HOME technique. That said, you might want to set JAVA_HOME anyway, should you encounter a tool that demands it.

One reason why JAVA_HOME is not as popular as it could be is that to access JAVA_HOME you need to run a shell, and not everyone wants to wrap every single Java item in a shell command.

Upvotes: 3

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