title: multiple classes and main method in Java, and packages, namespaces
body: <p>In Eclipse the .java file name must be the same as the class name. Is it true in any case or only for Eclipse? For the main method, it looks like the main function in C, but the question is, what if I have two classes both with their own main method and is it possible to link them together? In addition, can I write two classes in a single .java file? I'm using Eclipse in Windows, is it the same as the Linux version? </p>
  
  <p>For packages, my book tells me a package is sorta a directory. So to specify a package a file belongs to, do I just need to say "package my_pack"? Do I need to create a directory like /src/my_pack and place my .java file in it? </p>
  
  <p>Third, what is a namespace? What's its relationship with packages and classes? </p>