Java Packages

These are some notes from a java/c class I took 

Package-filesystem corresponding

• Stay in the root when you compile (workspace for eclipse)
• The package hierarchy corresponds to where it's stored in the filesystem.
• For instance, mypackage.util is stored so mypackage java files are in the mypackage folder along with the util folder, but util java files are stored in util. 

Access-control

• Package and class inheritance relationships affect access control
• Java will only import what you use (from the import statement)
• First it looks in the package for class reference, then looks in import statement
• There are four possibilities:
  • same package, independent classes
  • same package, one is a subclass
  • different packages, independent classes
  • different packages, one is a subclass
• Four different methods of access control
  • public- any class can access this
  • package (default) - can be applied to class (like public)-- only accessible by those in package
  • private-only the class that houses these methods and fields can see them
  • protected-classes within a package can see them; through inheritance of another package you can inherit protected members
  • static-members that can be accessed without declaring an object
  • order of most restrictive to least restrictive - private, package, protected, public
• Packages
• you cannot declare an object of a class from another package, unless the class you are trying to declare is public
• if you do not declare the access for a field or method, it cannot be accessed from another package