GTree

Java tree, for general purpose. Functional approach.

Beware, it is not a binary tree

Features:

• Simple
• Iterable
• Modification: mapping, filtering, sorting
• Pretty-printing
• Different traversals - depth-first, breadth-first

Maven

<dependency>
    <groupId>org.jkee.gtree</groupId>
    <artifactId>gtree</artifactId>
    <version>0.64</version>
</dependency>

Builders

• Key builder
• Path builder

Examples

1. Build a tree from id - parentId mapping (adjacency list)

Assume you have objects like:

public class Entity {
    public final int id;
    public final int parentId;
    ...
}

And assume that id == 0 means no parent (e.g. root). KeyTreeBuilder will be the right choice.

1. Create a Funnel. Funnel is an object which knows how to extract id and parentId from your object.

   KeyTreeBuilder.Funnel<Integer, Entity> funnel = new KeyTreeBuilder.Funnel<Integer, Entity>() {
       @Override
       public Integer getKey(Entity node) {
           return node.id;
       }
   
       @Override
       public Integer getParentKey(Entity node) {
           //so lets take 0 as no parent
           if (node.parentId == 0) return null;
           return node.parentId;
       }
   };

2. Create a KeyTreeBuilder. Builder is stateless so you can create only one.

   KeyTreeBuilder<Integer, Entity> builder = new KeyTreeBuilder<Integer, Entity>(funnel);

3. Build a tree!

   Tree<Entity> tree = builder.buildTree(entities);

If you want a forest, or an Integer -> Tree<Entity> mapping, you can use .build method and get more results. Full example available here

2. Building url tree

Assume you have a batch of url and you want to build a tree structure. It's simple, really. All we need is the PathTreeBuilder.

1. Create a Funnel which knows how to extract a path from your object. In case of URL it will be a split by / (simplistically).

   PathTreeBuilder.Funnel<String, String> urlFunnel = new PathTreeBuilder.Funnel<String, String>() {
       @Override
       public List<String> getPath(String value) {
           return Lists.newArrayList(value.split("/"));
       }
   };

2. Create a PathTreeBuilder. Also stateless.

   PathTreeBuilder<String, String> builder = new PathTreeBuilder<String, String>(urlFunnel);

3. Build a tree! Actually, not a tree - a forest. There are no guarantees of root uniqueness.

   List<Tree<String>> build = builder.build(urls);

Full example available here