Re: jar, package and import relationship?
- From: Mark Space <markspace@xxxxxxxxxxxxxx>
- Date: Wed, 09 Jan 2008 19:48:06 -0800
Dan Stromberg wrote:
sys.path.insert(0, '/my/directory')
This I don't really like. If you ever change the location of /my/directory, you have to edit each source file where this appears and alter the path. Maybe you've got a config file some place that you'd use in real production code, but still it feels a bit ugly.
1) /my/directory/interface.h has simply:
void hello_world();
In Java, the .class files themselves have this information.
2) implementation.c (in the current working directory) would look
This would be equivalent to Implementation.java.
like:
#include <stdio.h>
Note that import and #include do different things. However both require that you have a properly configured environment. #include requires a correct INCLUDE path. Java does too: the CLASSPATH must be correct. It's a bit different for anything that comes with the default with Java, because the JVM handles those a bit differently with out environment variables, but for any library (.jar) or .class file you download or create, you need to tell your tools (IDE, javac compiler, etc.) where to find them.
This is no different from C here. Totally the same idea.
void hello_world()
{
printf("hello world\n");
}
In file Hello_World.java:
public class Hello_World {
public static void hello_world() {
System.out.println("hello world");
}
}
3) ...and the main program (again in the CWD) would look like:
#include "interface.h"
int main()
{
hello_world();
return 0;
}
File Main.java:
public class Main {
public static void main(String ... args) {
Hello_World.hello_world();
}
}
4) And a basic Makefile (again in the CWD) for this would look
like:
Don't forget that C also requires your LIBPATH to be set correctly, for any libraries which load at runtime. For Java, this is the same with respect to any loose .class files that the runtime needs to find, or any ..jar files that you use. CLASSPATH is used for this as well.
(Remember that .jar files and .class files take the place of .h files in C., so really it makes sense to just configure one CLASSPATH variable rather than have one compile time include path and one separate LIBPATH at runtime.)
From the command line:
Brenden@Homer ~/Dev/misc/hwtest/src
$ ls
Hello_World.java Main.java
Brenden@Homer ~/Dev/misc/hwtest/src
$ javac Hello_World.java
Brenden@Homer ~/Dev/misc/hwtest/src
$ javac Main.java
Brenden@Homer ~/Dev/misc/hwtest/src
$ ls
Hello_World.class Hello_World.java Main.class Main.java
Brenden@Homer ~/Dev/misc/hwtest/src
$ java -cp . Main
hello world
Brenden@Homer ~/Dev/misc/hwtest/src
$ java Main
hello world
Brenden@Homer ~/Dev/misc/hwtest/src
$ echo $CLASSPATH
..;C:\Program Files\Java\jre1.6.0_03\lib\ext\QTJava.zip
Note that the last two runs are equivalent because I have "." in my classpath. Also, I haven't used packages, which is normally a bad idea. But it's enough for this very simple example.
.
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- From: Dan Stromberg
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