将类添加到包中

Question

I am studying java packages. I successfully created a package pack that contained single .class file Hello.class. Now I want to add another class file into the same package. I named the new java class as Goodbye.java and compiled it into the same directory "pack" via

javac -d ./bin Goodbye.java

command. bin directory contains pack directory. The I compile test.java file containing main function via

javac -cp ./bin test.java

command. Compilation works fine. But when I enter

java test 

command. I get

Hello, world
Exception in thread "main" java.lang.NoClassDefFoundError: pack/Goodbye
at test.main(test.java:9)
Caused by: java.lang.ClassNotFoundException: pack.Goodbye
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
... 1 more

Can anybody explain what I did wrong in this case? I am working on ubuntu 14.04 and doing everything in the terminal.

Both Hello.java and Goodbye.java files are located in

/home/username/apps/src 

directory. Corresponding class files are inside

/home/username/apps/bin/pack

directory. pack directory was created by

javac -d ./bin 

command. Contents of the Hello.java file

package pack;
public class Hello
{
    public static void HelloMessage()
    {
        System.out.println("hello, world");
    }
}

It works ok. For its corresponding class file gets loaded Contents of Goodbye.java file is

package pack;
public class Goodbye
{
    public static void message()
    {
        System.out.println("bye");
    }
}

test.java file which imports the package is located at /home/username/apps directory. It has the following lines of code

import pack.*;
public class test
{
    public static void main(String args[])
    {
        Hello.HelloMessage();
        Goodbye.message();
    }
}

Any help is highly appreciated.

Answer 1

My understanding of your class files is like the following tree:

/home/username/apps/bin
                     |
                     +-- pack
                     |     |
                     |     +--- Hello.class
                     |     |
                     |     +--- Goodbye.class
                     |
                     +-- test.class

Then go to /home/username/apps/bin and call

java -cp . test

With -cp you add the current directory to search for classes. This should always be the root of your packages. Then refer to your main class.

BTW: According to the Java naming conventions , class names should start with a capital letter, like Test .

Update : Updated the class file location.

Answer 2

You need to set classpath of two locations because you have class files in two different locations:

1. /home/username/apps/ (test.class available in this location)
2. /home/username/apps/src/bin (pack.Hello.class and pack.Goodbye.class available in this location)

You can do it by using -cp option of javac command. You need to put semicolon between more than one classpaths like below:

java -cp .;./bin test