I have a problem i have all my .java files in a uploadEquity folder.
All files have a
package uploadEquity;
When I compile a javac *.java Everything compiles. But when I do one
file on its own it says cannot resolve symbole ClassName. Everything
has the same package name in teh same directory. ALso when my web app
runs it is using an older version of the class file taht wont compile
even afer I did a rm *.class and replaced them with the javac *.java.
I am baffled by this problem, spending the last day or two trying all
sorts of things, moving folders, changing packages.
Please any help would be greatly appreciated.
Thank-you
Suppose you have two classes; Main and Util. Main uses some method or
variable in Util. Both sourcefiles are saved in same directory called
"mypackage", and both have package specification
package mypackage;
in the top of the source.
Now you have something like:
~/javaprojects/test/src/mypackage/Main.java
~/javaprojects/test/src/mypackage/Util.java
First you tried something like
cd ~/javaprojects/test/src/mypackage/
javac *.java
This worked nicely
Then
javac Main.java
didn't work.
Now try
cd ..
javac mypackage/Main.java
Worked nicely too ...
I'm not going to attempt to explain this fully, because I can't really,
but it goes something like this:
javac needs a defined sourcepath to work. If none is provided, it'll
assume that it is the current directory, ie ./
So when you are compiling and the current directory is "mypackage" you
are really confusing javac. Compiling *.java just happens to work,
supposedly because it somehow explicitly means that javac will consider
all java files in the current directory and then it is able to figure
everything out because of the package statements in the actual source
files or something.
But when you compile just Main.java this is what happens.
1. javac supposes that classpath is ./, ie.
~/javaprojects/test/src/mypackage
2. javac can find Main.java and opens the file.
3. javac finds that Main.java somehow needs the class Util. Since
Main.java resides in the package mypackage, javac assumes Util also
does, because no explicit import statement for Util was found in Main.
4. javac starts to look for Util in package mypackage along classpath
and sourcepath. As per sourcepath javac would expect to find Util.java
in ~/javaprojects/test/src/mypackage/mypackage actually, because the
sourcepath is ~/javaprojects/test/src/mypackage/, or ./ if you will
(current directory), and because javac already has deduced that Util
must live in the same package as Main, ie. mypackage, it will look for
that file in a subdirectory called mypackage residing under the current
sourcepath, which already is .../mypackage, and it won't find it.
5. As for classpath I assume just the same happens (4).
Now, for the final exercice:
As you already have successfully compiled both classes, you also have a
Util.class file along with Util.java (and Main.java).
cd back to ~/javaprojects/test/src/mypackage
Now, we're going to tell javac exactly where to start to look for class
files (specify classpath), ie compiled sources.
javac -cp ../ Main.java
voila, this time javac will find Main.java, just like before, and deduce
the need for the class Util. It'll like before try to find Util.class in
a package called mypackage, but now it'll start looking in
~/javaprojects/test/src/
it'll append mypackage directory to~/javaprojects/test/src/ because it
assumes Util to live in the package mypackage as per the same deducement
as prevously, and hence find
~/javaprojects/test/src/mypackage/Util.class.
Now try
javac -sourcepath ../ Main.java
This also works. I'm not sure what the difference really is. What I
really am confused about is that if I delete Util.class, so that only
sourcefile Util.java is available, it still works to compile like this
cd ~/javaprojects/test/src/mypackage
javac -cp ../ Main.java
Without the -cp it'd naturally fail, that we have seen. So javac seems
to find a sourcefile along classpath and compiles it, ie. classpath
seems to work somewhat like a sourcepath?
Oh, well, I've programmed java for years now and I really don't worry
about this, I just use some Ide and pretend inconsistencies doesn't
exist rather than spending braincycles trying to figure out why it's not
inconsistent after all
