problem in accessing java package

lemon09 · 02-16-2011, 10:39 AM

i am a complete newbie in java. while dealing with packages i faced the following problem.
I created a file named "CreatePackage"

Code:

package lobkush;

public class CreatePackage {
	  public CreatePackage() {
			 System.out.println("you are presently under package named \"lobkush\" ");
	  }
}

after this i created a folder named "lobkush".

I also compiled the source file and placed the .class file in the corresponding directory.

Now to test it i created another java file. This is where the problem arises.
while importing the class file if I write:

Code:

import lobkush.*;

the compiler shows an error
but if I write

Code:

import lobkush.CreatePackage;

no error is shown and the .class file generated.

Can anyone please explain to me this unnatural behaviour????

paulsm4 · 02-17-2011, 06:47 PM

Hi -

I think the problem is that when you use a "package", Java will expect you to have a SUBDIRECTORY for that package. For example:

Code:

cd /tmp
vi CreatePackage.java =>

package lobkush;

public class CreatePackage {
  public CreatePackage() {
    System.out.println("you are presently under package named \"lobkush\" ");
  }

  public static void main (String[] args)
  {
    CreatePackage p = new CreatePackage ();
  }
}
ls -l Create* =>
-rw-r--r--  1 paulsm users 253 2011-02-17 16:37 CreatePackage.java

Code:

javac CreatePackage.java => OK

ls -l Create* =>
-rw-r--r--  1 paulsm users 497 2011-02-17 16:39 CreatePackage.class
-rw-r--r--  1 paulsm users 253 2011-02-17 16:37 CreatePackage.java

java CreatePackage =>
Exception in thread "main" java.lang.NoClassDefFoundError: CreatePackage (wrong
name: lobkush/CreatePackage)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader
        ...

Code:

javac -d . CreatePackage.java => OK

ls -l lobkush =>
-rw-r--r--  1 paulsm users 497 2011-02-17 16:44 CreatePackage.class

java lobkush/CreatePackage =>
you are presently under package named "lobkush"
  <= This worked OK

Google for "packages" - that might make things a bit clearer.

IDE's like Eclipse and Netbeans automagically create your package subdirectories and set classpath's for you, so you don't have to worry about it so much.

And "package subdirectories" are a standard feature of .jar files.

In other words: packages are definitely "good". But some of the consequences of using packages might be a bit "surprising" at first

'Hope that helps .. PSM

lemon09 · 02-17-2011, 08:57 PM

Well, i didn't actually mean that. You see, I know what you have just shown. Now I have a problem in accessing that package from another class in other packages.

If I use " import.lobkush.*; " keyword to include all the classes of that package, it produces an error. However when the same code is compiled against the statement " import lobkush.CreatePackage; " no error is generated.

I wish I am clear to you about my problem. Now can you please help me out???

pgroover · 02-18-2011, 08:06 AM

Quote:

Originally Posted by lemon09

If I use " import.lobkush.*; "

I think your problem, at least from your last post, is pretty obvious. "import.lobkush.*"...

paulsm4 · 02-18-2011, 11:53 AM

Hi -

I think "import.lobkush.*" is a typo - you actually meant "import lobkush.*". Correct?

If "import lobkush.CreatePackage" works, and "CreatePackage is a public class (as you've shown)...
... and if the directories of your client classes reside *OUTSIDE* of directory "lobkush" (as I tried to show)...
... then it should work.

If it doesn't, please post:
1. Code for your current version of "create package".
2. Code for the client class that's failing.
3. Cut/paste exact compile command and exact error.
4. Specify file names and directory locations.