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packages (Pakete)

Um Pakete mit gleichem Namen zu vermeiden, haben sich in der Java-Welt folgende Konvention für Paketnamen herausgebildet:2

  • Paketnamen bestehen nur aus Kleinbuchstaben und Unterstrichen (_), um sie von Klassen zu unterscheiden.
  • Paketnamen sind durch Punkte getrennt.
  • Der Anfang des Paketnamens wird durch die Organisation bestimmt, die sie erstellt.

Um den Paketnamen auf der Grundlage einer Organisation zu bestimmen, wird die URL der Organisation umgedreht.1 Beispielsweise wird aus der URL

https://pirckheimer-gymnasium.de/engine-pi

der Paketname:

de.pirckheimer_gymnasium.engine_pi

  1. https://docs.oracle.com/javase/specs/jls/se21/html/jls-6.html#d5e8762

    Package Names and Module Names

    Programmers should take steps to avoid the possibility of two published packages having the same name by choosing unique package names for packages that are widely distributed. This allows packages to be easily and automatically installed and catalogued. This section specifies a suggested convention for generating such unique package names. Implementations of the Java SE Platform are encouraged to provide automatic support for converting a set of packages from local and casual package names to the unique name format described here.

    If unique package names are not used, then package name conflicts may arise far from the point of creation of either of the conflicting packages. This may create a situation that is difficult or impossible for the user or programmer to resolve. The classes ClassLoader and ModuleLayer can be used to isolate packages with the same name from each other in those cases where the packages will have constrained interactions, but not in a way that is transparent to a naïve program.

    You form a unique package name by first having (or belonging to an organization that has) an Internet domain name, such as oracle.com. You then reverse this name, component by component, to obtain, in this example, com.oracle, and use this as a prefix for your package names, using a convention developed within your organization to further administer package names. Such a convention might specify that certain package name components be division, department, project, machine, or login names.

    Example 6.1-1. Unique Package Names

    com.nighthacks.scrabble.dictionary
org.openjdk.compiler.source.tree
net.jcip.annotations
edu.cmu.cs.bovik.cheese
gov.whitehouse.socks.mousefinder

    The first component of a unique package name is always written in all-lowercase ASCII letters and should be one of the top level domain names, such as com, edu, gov, mil, net, or org, or one of the English two-letter codes identifying countries as specified in ISO Standard 3166.

    In some cases, the Internet domain name may not be a valid package name. Here are some suggested conventions for dealing with these situations:

    • If the domain name contains a hyphen, or any other special character not allowed in an identifier (§3.8), convert it into an underscore.
    • If any of the resulting package name components are keywords (§3.9), append an underscore to them.
    • If any of the resulting package name components start with a digit, or any other character that is not allowed as an initial character of an identifier, have an underscore prefixed to the component.

    ↩

  2. https://www.baeldung.com/java-packages#1-naming-conventions

    3.1. Naming Conventions

    In order to avoid packages with the same name, we follow some naming conventions:

    • we define our package names in all lower case
    • package names are period-delimited
    • names are also determined by the company or organization that creates them

    To determine the package name based on an organization, we’ll typically start by reversing the company URL. After that, the naming convention is defined by the company and may include division names and project names.

    For example, to make a package out of www.baeldung.com, let’s reverse it:

    com.baeldung

    We can then further define sub-packages of this, like com.baeldung.packages or com.baeldung.packages.domain. ↩