Question

I have a quad tree* which I would like to use across several different machines. Calling the constructor (ie building the tree) takes a long time. I don’t want to build the tree each time I need to use it.

I am looking for a way to persist my tree in hard disk, send that to each node, and then quickly load it into memory so that I can perform lookups.

Can serialization help me with this? I know that I can serialize the tree, save it to disk then deserialize (that’s about all I know about serialization). To the best of my knowledge, the deserilization step needs a default constructor to build the tree. Since building the tree is computationally expensive, this is of no use to me.

Is there some way I can import the persisted tree without having to rebuild it each time?

*quad tree base code that I used: https://bitbucket.org/utcompling/textgrounder/src/f38150c7f33a/src/main/java/ags/utils/KdTree.java

Apologies if this is too basic, it’s closely related to: https://stackoverflow.com/questions/14701245/how-do-i-perform-kd-tree-lookups-in-hadoop

edit: So, it looks like the no-arg constructor of the least-inherited class is the one that will be called. Here’s my hirearchy:

abstract KDTree

QuadTree extends KdTree

SpecialQuadTree ( has an instance of QuadTree)

Now, I am only able to serialize SpecialQuadTree when I make everything Serializable (otherwise I’m getting NotSerizable or InvalidClassException no valid constructor):

abstract KDTree implements Serializable

QuadTree extends KdTree implements Serializable

SpecialQuadTree implements Serializable ( has an instance of QuadTree)

So, I suppose I can take the Serializable off the KdTree and then give it a do-nothing no-args constructor? That’s not easy, I didn’t write and don’t understand the KdTree class. I suppose I could subclass it, give the subclass a do-nothing no-args constructor, and inherit the QuadTree from that…

edit: Ok so, I have an abstract class
abstract KDTree implements Serializable

and from that I extend:
QuadTree extends KdTree implements Serializable

From all my experiments, I need to implement Serializable on both. Now,

public QuadTree() {
    super(2, 1000000);
    System.out.println("QuadTree no-args!");
}

and

protected KdTree(int dimensions, Integer sizeLimit) {
    System.out.println("KdTree, constructor!");

Since I never see it print out (aside from the initial construction…), I guess it’s all good.

Answer 1

To the best of my knowledge, the deserilization step needs a default constructor to build the tree

Not if you’re taking about Java Object Serialization it doesn’t.

it looks like the no-arg constructor of the least-inherited class is the one that will be called.

No. The no-args constructor of the nearest non-serializable base class is called.

I suppose I can take the Serializable off the KdTree and then give it a do-nothing no-args constructor?

Why? Just leave it alone.