Help with packages in java - import does not work

Question

I m a C   developer - not a java developer  but have to get this code working     I have 2 public classes that will be used by another product   I used the package directive in each of the java files     package com company thing   class MyClass       When I try to compile a test app that uses that I add   import com company thing      The javac compiler fails with errors about com company does not exist    even if I compile it in the same directory as the class files I just made a package of   I am sure I am doing something bone-headed and silly   I ve read the http   java sun com docs books tutorial java package usepkgs html pages and tried to set up a directory structure like  com company thing  etc  but either I have totally screwed it all up or am missing something else   EDIT thanks for the suggestions - I had tried the classpath previously   It does not help   I tried compiling   javac -classpath  lt parent gt  client java    and the result is   package com company does not exist   I have the code I want to import  the two java files  in  com company product   I compile those fine    they contain MyClass  I even made a jar file for them   I copied the jar file up to the parent directory   I then did  in the parent directory with the client java file    javac -cp  lt jarfile gt    java   the result is   cannot access MyClass bad class file  MyClass class  MyClass class  class file contains wrong class  com company product MyClass Please remove or make sure it appears in the correct subdirectory of the classpath    EDIT  I got the client code to compile and run if I used the fully qualified name for MyClass and compiled it in the parent directory   I am totally confused now     compiled with no classpath set - just   javac   java    in the parent directory - and it worked fine   I can get a test app to compile  but that is not going to cut it when i have to integrate it into the production code   Still looking for help   EDIT   Finally - not sure why it didn t work before - but I cleaned up all the files all over the directory structure and now it works     Thanks

User · Answer

Yes  this is a classpath issue   You need to tell the compiler and runtime that the directory where your  class files live is part of the CLASSPATH   The directory that you need to add is the parent of the  com  directory at the start of your package structure   You do this using the -classpath argument for both javac exe and java exe   Should also ask how the 3rd party classes you re using are packaged   If they re in a JAR  and I d recommend that you have them in one  you add the  jar file to the classpath   java -classpath   company jar foo bar baz YourClass   Google for  Java classpath    It ll find links like this   One more thing   import  isn t loading classes   All it does it save you typing   When you include an import statement  you don t have to use the fully-resolved class name in your code - you can type  Foo  instead of  com company thing Foo    That s all it s doing

User · Answer

It sounds like you are on the right track with your directory structure  When you compile the dependent code  specify the -classpath argument of javac  Use the parent directory of the com directory  where com  in turn  contains company thing YourClass class  So  when you do this   javac -classpath  lt parent gt  client java   The  lt parent gt  should be referring to the parent of com  If you are in com  it would be

User · Answer

Okay  just to clarify things that have already been posted  You should have the directory com  containing the directory company  containing the directory example  containing the file MyClass java  From the folder containing com  run     javac com company example MyClass java  Then     java com company example MyClass Hello from MyClass   These must both be done from the root of the source tree  Otherwise  javac and java won t be able to find any other packages  in fact  java wouldn t even be able to run MyClass   A short example I created the folders  quot testpackage quot  and  quot testpackage2 quot   Inside testpackage  I created TestPackageClass java containing the following code  package testpackage   import testpackage2 MyClass   public class TestPackageClass       public static void main String   args            System out println  quot Hello from testpackage TestPackageClass  quot            System out println  quot Now accessing  quot    MyClass NAME            Inside testpackage2  I created MyClass java containing the following code  package testpackage2  public class MyClass       public static String NAME    quot testpackage2 MyClass quot      From the directory containing the two new folders  I ran   C  examples javac testpackage   java  C  examples javac testpackage2   java  Then   C  examples java testpackage TestPackageClass Hello from testpackage TestPackageClass  Now accessing testpackage2 MyClass  Does that make things any clearer

User · Answer

You got a bunch of good answers  so I ll just throw out a suggestion   If you are going to be working on this project for more than 2 days  download eclipse or netbeans and build your project in there   If you are not normally a java programmer  then the help it will give you will be invaluable   It s not worth the 1 2 hour download install if you are only spending 2 hours on it   Both have hotkeys menu items to  Fix imports   with this you should never have to worry about imports again

User · Answer

Just add classpath entry   I mean your parent directory location  under System Variables and User Variables menu     Follow   Right Click My Computer Properties Advanced Environment Variables

User · Answer

The standard Java classloader is a stickler for directory structure  Each entry in the classpath is a directory or jar file  or zip file  really   which it then searches for the given class file  For example  if your classpath is    my jar   it will search for com example Foo in the following locations     com example  my jar  com example    That is  it will look in the subdirectory that has the  modified name  of the package  where     is replaced with the file separator   Also  it is noteworthy that you cannot nest  jar files

[java] Help with packages in java - import does not work

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