如何使用javac编译java包结构

Question

I am trying to compile (from the command line) a java package that imports another package of my own. I was following a tutorial online but it seems that I get an error when I try to compile the final java file (CallPackage.java).

Here is the file structure:

+ test_directory (contains CallPackage.java)
   -> importpackage
       -> subpackage (contains HelloWorld.java)

Here is CallPackage.java:

/// CallPackage.java
import importpackage.subpackage.*;
class CallPackage{
  public static void main(String[] args){
  HelloWorld h2=new HelloWorld();
  h2.show();
  }
}

and here is HelloWorld.java:

///HelloWorld.java

package importpackage.subpackage;

public class HelloWorld {
  public void show(){
  System.out.println("This is the function of the class HelloWorld!!");
  }
}

Attempted Steps

1. Go to the subpackage and compile HelloWorld.java with $javac HelloWorld.java .
2. Go to test_directory and compile CallPackage.java with $javac CallPackage.java .

This gives me an error on the last command:

CallPackage.java:1: package importpackage.subpackage does not exist
import importpackage.subpackage.*;
^
CallPackage.java:4: cannot find symbol
symbol  : class HelloWorld
location: class CallPackage
  HelloWorld h2=new HelloWorld();
  ^
CallPackage.java:4: cannot find symbol
symbol  : class HelloWorld
location: class CallPackage
  HelloWorld h2=new HelloWorld();
                    ^
3 errors

How can I compile both packages? Thanks so much for any help!

Answer 1

The issue was that the class path needs to be set for each command (javac and java):

Attempted Steps

1. instead of going to subpackage, compile HelloWorld.java from the top_level:

   $javac -cp . importpackage/subpackage/HelloWorld.java

2. compile CallPackage.java in the same way:

   $javac -cp . CallPackage.java

3. run the file using the class path also:

   $java -cp . CallPackage

NOTE : running "$java CallPackage" will give an error "Error: Could not find or load main class CallPackage"

In summary, during each step, the class path must be specified. It worked after running it as such.

Answer 2

Same situation to me. And I came to take over it by compiling classes at the same time.
For example, here is my project:

+ beerV1
   -> classes
   -> src
         -> com
              -> example
                   -> model
                        -> BeerExpert.java
                   -> web
                        -> BeerSelect.java

BeerExpert.java:

package com.example.model;
import ...

public class BeerExpert{
    ...
}

BeerSelect.java:

package com.example.web;
import com.example.model.*;
import ...

public class BeerSelect {
      ...
}

As you can see: BeerSelect.java is trying to import classes in package.
At the first time, I compiled BeerExert.java first by command:

--> javac -d classes src/com/example/model/BeerExpert.java

Then:
--> javac -d classes src/com/example/web/BeerSelect.java

And the result was:
-->... error: package com.example.model does not exist

So, I knew that compiling multiple classes separately will not work in this case.

After suffering on google, I found this very simple way to solve the problem:
Just compile all at once:

--> javac -d classes src/com/example/model/BeerExpert.java src/com/example/web/BeerSelect.java 

Finally, here is what I got:

 + beerV1
           -> classes
                 -> com
                      -> example
                           -> model
                                -> BeerExpert.class
                           -> web
                                -> BeerSelect.class
           -> src
                 -> com
                      -> example
                           -> model
                                -> BeerExpert.java
                           -> web
                                -> BeerSelect.java

Hope that helps.

Answer 3

Are you sure importpackage/subpackage is in your classpath?

-cp path or -classpath path

Specify where to find user class files, and (optionally) annotation processors and source files. This class path overrides the user class path in the CLASSPATH environment variable. If neither CLASSPATH, -cp nor -classpath is specified, the user class path consists of the current directory. See Setting the Class Path for more details.

If the -sourcepath option is not specified, the user class path is also searched for source files.

If the -processorpath option is not specified, the class path is also searched for annotation processors.

http://docs.oracle.com/javase/7/docs/technotes/tools/windows/javac.html

Answer 4

It's an old topic but Google has led me to this site. For the completness, I'd like to add one bit to @Vĩnh Thụy Trần's answer on how to run the main class after compiling it into a custom folder. While it looks trivial now it took me some time to get it right.

In order to run your project, you also need to specify a path to the classes:

java -classpath <directory> your.package.name.classname

or

java -cp <directory> your.package.name.classname

Taking Vĩnh Thụy Trần's example again, the command would look like this:

java -cp classes com.example.web.BeerSelect

I hope it will help someone as I spent some time figuring it out.

Answer 5

(1)first compile the code

javac -d importpackage.subpackage.HelloWorld

(2) and then compile the CallPackage.java

javac CallPackage.java

Answer 6

delete your package folder (after pasting you code to some other folder) and then locate to the folder in cmd where you current code is and try javac -d . Helloworld.java (this will create the Helloworldclass and subpackage as well) and try same for you mainfunction code ie Callpackage.java after compiling to run the code try java Callpackage