This repository contains a Java implementation of a transform of a general list of objects depending onto another (and possibly other objects outside the scope you want to consider) into a data structure called a "leveled dependency tree". The key idea is to re-group the objects into groups, so called 'levels', where all objects in a given level only depend on objects in lower levels.

There are many situations in which a leveled dependency tree can save you a lot of headaches.

Consider a big (Java) programming project which consists of several Maven artifacts depending on one another. Probably you have some 'core' artifacts which are used by the other, more advanced, artifacts. When updating the core artifact, you need to propagate the updated version number into all artifacts that depend on the core artifact(s). However, your project is so large that also the other artifacts depend on one another. In order to update the whole project tree (rooted on the core artifacts) in an orderly manner, you would need to consider next the artifacts which only depend on the core artifact (and possibly some out-of-tree artifacts). If your project tree is sufficiently large, the complexity of which projects depend on which other projects prohibits keeping all these dependencies in your head at once.

This is where the leveled dependency tree comes in handy. It sorts the artifacts that belong to your project into "levels", where the first level only contains your core artifact(s) and successive levels only depend on artifacts on lower level(s). Thus, when updating the artifacts sorted by levels, you need to touch every artifact only exactly once to update it. Artifacts on the same level are mutually independent on each other, so you can parallelize the work required for updating a given level.

An example program to print the level structure for the netlib-java artifact is provided as MavenExample.java in this repository. The output looks as follows:

out-of-tree dependencies:
  net.sourceforge.f2j:arpack_combined_all:jar:0.1
  junit:junit:jar:4.11
  org.projectlombok:lombok:jar:1.12.2
level 1
  com.github.fommil.netlib:core:jar:1.1.2
  com.github.fommil:jniloader:jar:1.1
level 2
  com.github.fommil.netlib:native_ref-java:jar:1.1
  com.github.fommil.netlib:native_system-java:jar:1.1
level 3
  com.github.fommil.netlib:netlib-native_ref-osx-x86_64:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_ref-linux-x86_64:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_ref-linux-i686:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_ref-win-x86_64:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_ref-win-i686:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_ref-linux-armhf:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_system-osx-x86_64:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_system-linux-x86_64:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_system-linux-i686:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_system-linux-armhf:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_system-win-x86_64:jar:natives:1.1
  com.github.fommil.netlib:netlib-native_system-win-i686:jar:natives:1.1
level 4
  com.github.fommil.netlib:all:pom:1.1.2

When updating this project, you need to start with the artifacts core and jniloader before you can progress to native_*-java. Once these are done, you can go on with the netlib-native_*-* artifacts and finally, the all artifact can be built.

The corresponding dot graph is here:

The Xj3D framework is a big Java project, consisting of several thousands(?) of classes which are currently hosted as a monolithic source tree on SourceForge. Splitting this project up into seveval subproject would allow more fine-grained development and is actually considered by the project team. Using a leveled dependecy tree, the Xj3D classes could be split up into several Maven artifacts in an orderly manner.

This project is available on Maven Central with the following Maven coordinates:

<dependency>
	<groupId>de.labathome</groupId>
	<artifactId>LeveledDependencyTree</artifactId>
	<version>1.0.1</version>
</dependency>