Tree representation in java

Question

I am working on my thesis work that is relevant to the artificial intelligent domain.

I want to make a real time recommendation system so I need to represent the decisions with a tree.

My main question is how can I represent this tree in an efficient way? I want to mention that the tree will be traversing both bottom-up and up to bottom. Also the tree is not binary and the node that it has are quite many (over 100).

Right now I have create a node class like the above:

public class node {

    private String nodeName;
    private expectedValue ev;
    private boolean isLeaf;
    private boolean isRoot;
    private List<node> listOfChildren = new ArrayList<node>();
    private node parent;


    public node(String nodeName) {
        super();
        this.nodeName = nodeName;
    }


    public node(String nodeName, boolean isLeaf, boolean isRoot, List<node> listOfChildren, node parent) {
        super();
        this.nodeName = nodeName;
        this.isLeaf = isLeaf;
        this.isRoot = isRoot;
        this.listOfChildren = listOfChildren;
        this.parent = parent;
    }


    public void initializeNode(boolean isLeaf, boolean isRoot, List<node> listOfChildren, node parent) {
        this.isLeaf = isLeaf;
        this.isRoot = isRoot;
        this.listOfChildren = listOfChildren;
        this.parent = parent;
    }


    //getter and setter here......  
}

But I believe that it is not the most efficient way to represent a tree....

So, what is an efficient way to represent a tree in Java and is there a way to create the tree dynamically or do I have to initialise it one by one node?

Thank you!

I flagged it as 'too broad'/'opinion based' as there is no correct answer to your request. It also depends a lot on the exact requirements of the tree. Btw, you don't need "isLeaf" (listOfChildern.size() == 0) or "IsRoot" (parent == null). — Reinard
– Reinard, Commented Jan 7, 2016 at 11:49
Why do you "believe it is not the most efficient way to represent a tree"? What are some of the problems you see with it? — Dima
– Dima, Commented Jan 7, 2016 at 11:49
Possible duplicate of Tree implementation in Java (root, parents and children) — Rob Audenaerde
– Rob Audenaerde, Commented Jan 7, 2016 at 12:04
@Dima : Because of the fact that this system is going to run real time and also the tree has a lot of nodes, i believe that the overhead of the lists (for example list Of Children) is too big and it could be done in a more efficient and "elegant" way. — MixPap
– MixPap, Commented Jan 7, 2016 at 12:13
In order to elicit a most helpful answer, can you provide data / estimates on the relative frequency of operations (add, update, delete; possibly shuffle, reattach, etc.) on the nodes, possibly taking into account typical sequences of operations? Since the target is a recommendation system, optimizing for minimized query times might be the best way to go. — collapsar
– collapsar, Commented Jan 7, 2016 at 12:15

Idos · Accepted Answer · 2016-01-07 12:30:49Z

2

I think you don't need so many variables to be passed to your constructor. It could be much simpler. I would recommend to have a separate static inner class (nested class) for the Node. Also take advantage of java generics (<T>) Something like this:

public class MyTree<T> {

    private Node<T> root;

    public MyTree(T rootData) {
        root = new Node<T>();
        root.data = rootData;
        root.children = new ArrayList<Node<T>>();
    }

    public static class Node<T> {
        private T data;
        private Node<T> parent;
        private List<Node<T>> children;
    }
}

As a side note, there is a tree structure implemented in the JDK which you may use even without a swing interface. (javax.swing.tree TreeModel and TreeNode )

edited Jan 7, 2016 at 12:30

answered Jan 7, 2016 at 11:49

Idos

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4 Comments

smwikipedia Over a year ago

(This comment is irrelevant to the content of this reply.)The world is full of strangers. Why making an enemy rather than a friend. I am a bit over reacted to your comment today. Enjoy your journey in S.O. (Strange, I cannot @ you).

Idos Over a year ago

@smwikipedia you can delete the comments here :)

smwikipedia Over a year ago

@ldos They're educative. Let's keep them if it's not against the rules.

MixPap Over a year ago

@idos thank you for your answer. i was't aware of java generics (<T>) so i have to look further to it.

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