Java: How can I compile an entire directory structure of code ?

The use case is simple. I got the source files that were created using Eclipse. So, there is a deep directory structure, where any Java class could be referring to another Java class in the same, child, sibling or parent folder.

How do I compile this whole thing from the terminal using javac ?

You have to know all the directories, or be able to use wildcard ..

javac dir1/*.java dir2/*.java dir3/dir4/*.java dir3/dir5/*.java dir6/*src/*.java

With Bash 4+, you can just enable globstar

shopt -s globstar

and then do

javac **/*.java

If all you want to do is run your main class (without compiling the .java files on which the main class doesn't depend), then you can do the following:

cd <root-package-directory>
javac <complete-path-to-main-class>

or

javac -cp <root-package-directory> <complete-path-to-main-class>

javac would automatically resolve all the dependencies and compile all the dependencies as well.

I would take Jon's suggestion and use Ant, since this is a pretty complex task.

However, if you are determined to get it all in one line in the Terminal, on Linux you could use the find command. But I don't recommend this at all, since there's no guarantee that, say, Foo.java will be compiled after Bar.java, even though Foo uses Bar. An example would be:

find . -type f -name "*.java" -exec javac {} \;

If all of your classes haven't been compiled yet, if there's one main harness or driver class (basically the one containing your main method), compiling that main class individually should compile most of project, even if they are in different folders, since Javac will try to the best of its abilities to resolve dependency issues.