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I'm trying to figure out how organize source and class files working with packages. I found a very useful tutorial. But I still have some questions.

As far as I understood it is a good practice to have an isomorphism between name of packages and name of the directories where elements of a package are stored. For example if I have a package named aaa.bbb.ccc which contains class ddd it is a good practice to have a class file called "ddd.class" and located in "$CLASSPATH/aaa/bbb/ccc/". Did I get it right?

If it is the case, will Java compiler put *.class files into the correct directory automatically?

I was not able to get this behavior. I set the $CLASSPATH variable to "/home/myname/java/classes". I executed javac KeyEventDemo.java which contains package events;. I expected that javac will create a subdirectory events under /home/myname/java/classes and put the KeyEventDemo.class in this subdirectory.

It did not happen. I tried to help to javac and created "events" subdirectory by myself. I used javac again but it does not want to put class files under "/home/myname/java/classes/events". What am I doing wrong?

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3 Answers 3

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You need to use the -d option to specify where you want the .class files to end up. Just specify the base directory; javac will create any directories necessary to correspond to the right package.

Example (based on your question):

javac -d ~/java/classes KeyEventDemo.java
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And to clarify $CLASSPATH: it will tell the JVM where to look for classes during runtime, not to tell javac where to create classes this answer and your experience show.
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For example if I have a package named "aaa.bbb.ccc" which contains class "ddd" it is a good practice to have a class file called "ddd.class" and located in "$CLASSPATH/aaa/bbb/ccc/". Did I get it right?

That's not "good practice" - this is how the Sun JDK expects things to be. Otherwise, it will not work. Theoretically, other Java implementations could work differently, but I don't know any that do.

If it is the case, will Java compiler put *.class file into a correct directory automatically?

Yes

What am I doing wrong?

The source code must also already follow this structure, i.e. KeyEventDemo.java must reside in a subdirectory named "events". Then you do "javac events/KeyEventDemo.java", and it should work.

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If you use the -d option (highly recommended, so binaries live in a different place from the source), then in theory, your source does not have to follow that hierarchy.
On the java.sun.com I found out that it can be convenient to keep *java and *class files in different directories. And I would like to use this approach.
As Chris wrote, you can use the -d option for this. But it's still a very good idea to keep the source files in the same directory hierarchy, or it will be very confusing.
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It is not only good practice but a must in most cases.

consider a Java class named:

com.example.Hello

If you store it on the filesystem, it has to got to

/path/to/my/classes/com/example/Hello.java

The compiler (or at least the vast majority) will create the class file at

/path/to/my/classes/com/example/Hello.class

Personally I would not use the CLASSPATH variable to set the path but the -cp option on java. A call to the above "application" could be done with:

java -cp /path/to/my/classes com.example.Hello
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