Packages (possible set-up problems)

Question

Hi,
I have recently set up sdk1.4.2_01 and I have set up both path and classpath variables as C:\j2sdk1.4.2_01\bin and .;C:\j2sdk1.4.2_01\lib\tools.jar respectively (the classpath variable was suggested as a solution to the upcoming problem)
I have been following learn Java in 21 days and all has been going fine until I had to create my own packages.
As I understand, a class contained within a package must have the initial line:
package com.prefect.ecommerce;
where in this case, com.prefect.ecommerce is the package. Also I understand that a directory structure must accompany the package such that the classes are placed in this directory (com\prefect\ecommerce).
I have two classes Item.java and Storefront.java that need to be placed in the above named package, so I performed the following steps:
1) Created the directory: C:\j2sdk1.4.2_01\com\prefect\ecommerce
2) Placed both Item.java and Storefront.java in this directory with the initial package com.prefect.ecommerce; line in place.
3) Compiled Item.java successfully
The problem lies when I try to compile Storefront.java. This class creates and uses an instance of the Item class, however I get the following error message:
Storefront.java:16: cannot resolve symbol
symbol : class Item
location: class com.prefect.ecommerce.Storefront
public Item getItem(int i){
^
Storefront.java:12: cannot resolve symbol
symbol : class Item
location: class com.prefect.ecommerce.Storefront
Item it = new Item(id, name, price,quant){
^
The Storefront class dosent recognize or cant find the Item class even though they are in the same folder? When I remove the line package com.prefect.ecommerce; Storefront compiles fine and uses the Item class?
Were am I going wrong? can someone help me?
many thanks in advance!

Answer 1

there seem to be two problems:
first: in your Item.java I think there is no package statement, otherwise you would not have been able to compile it using a similar statement as one of the following:
C:\j2sdk1.4.2_01\com\prefect\ecommerce> javac
Storefront.javathe easiest way of compiling is to ALWAYS compile from the root of the package hierarchy: in this case:
C:\j2sdk1.4.2_01> javac com\prefect\ecommerce\Storefront.javashould compile both Storefront and item, as long as they are both in package
com.prefect.ecommerce, i.e. there is a line in the sources saying:
package com.prefect.ecommerce;
>
Tonight I will try out 2 things, firstly I will change
the above command to:
C:\j2sdk1.4.2_01\com\prefect\ecommerce> javac
-classpath C:\j2sdk1.4.2_01 Storefront.javaas stated above, this should not work! try it from the package root directory as described above!
>
and see if this works! Next I will add to my classpath
variable such that it will look like:
.;C\j2sdk1.4.2_01\lib\tools.jar;C:\j2sdk1.4.2_01
(I want to see if my original javac command will work
using this!)
I would like to know whether the first part of the
classpath variable (.;C\j2sdk1.4.2_01\lib\tools.jar;)
is necessary or should I just have the classpath
variable set to C:\j2sdk1.4.2_01 ?neither, nor! for simplicity, you should have the "." in your classpath, which means "current directory" but not the tools.jar. C:\j2sdk1.4.2_01 is not necessary, although this seems to be your "home" :-)
however, for some older versions of the jdk it could be of use to add the path of the rt.jar (runtime) to the classpath, but i don't think you will need this.
and finally, even if i had not set the classpath
variable, when I typed my javac command in the
directory listed above
(C:\j2sdk1.4.2_01\com\prefect\ecommerce>) should it
not have looked in the ecommerce folder for Item.class
by default?well, in your case only if they were both in the same package (same package declaration in the source) and same source directory)
Regards, Sebastian