Streems

Read me first

This project is licensed under the Apache Software License, version 2. See the LICENSE file at the root of the project for more details.

This project requires Java 8.

The current version is 0.2.0:

dependencies {
    compile(group: "com.github.javachat", name: "streems", version: "0.1.0");
}

Another package exists which provides a way to reuse a TreeTraverer from Guava (see below):

dependencies {
    compile(group: "com.github.javachat", name: "streems-guava", version: "0.1.0");
}

What this is

This library provides a Stream interface over n-ary trees.

The idea was inspired by Guava's TreeTraverser. Since Guava is aimed at Java 7 or less, its traversal methods return instances of Iterables, not Streams. This package provides such a functionality.

The different traversals of an n-ary tree

An example is provided by the javadoc of TreeTraverser; we will reproduce it here:

For example, the tree

          h
        / | \
       /  e  \
      d       g
     /|\      |
    / | \     f
   a  b  c       

can be iterated over in preorder (hdabcegf), postorder (abcdefgh), or
breadth-first order (hdegabcf).

Usage

You provide a class which gives access to its immediate children, in order, using either of:

• a Stream,
• an Iterator,
• an Iterable,
• or an array.

You can then use this API to traverse instances of the class as an n-ary tree in any order: preorder, postorder or breadth first.

For instance:

final Stream<MyNode> stream
    = Streems.traverse(myNode, MyNode::children, Traversal.PREORDER);

Notes about the returned Streams...

The underlying Spliterator will always have the same characteristics: ORDERED and NONNULL:

• ORDERED is obvious... After all, you choose the traversal order and you expect nodes to be returned in that order;
• NONNULL because it is a requirement (you cannot attempt to get any children from a null node).