Why Java Collection Framework doesn't contain Tree and Graph

Question

I am familiar with Java Collection Framework which contains basic interfaces: Collection and Map. I am wondering why the Framework doesn\'t contain

Answer 1

I suspect that the answer is that it is a combination of two things:

• A generic tree or graph interface would be "feature poor".
• It is easier and more efficient to implement a tree or graph using fields to represent child and (if you need them) parent pointers.

Note that neither Apache commons or Google commons have generic graph or tree support. However, I did come across a couple of generic tree/graph hierarchies:

• The jsfcompounds project on JavaNet has the "com.truchsess.util" graph and tree framework.
• The OpenJGraph project (inactive) on SourceForge includes tree and graph libraries.