Should be able to configure if I want to treat a given node as a leaf node

[j1ee]

There are 2 situations here (perhaps should be listed separately)

1. If I configure some collection as a leaf node, I want to be alerted of a change when the size of the collection changes but I do not want to be told if anything in the collection has changed.
2. If I am comparing objects of type A (which has a property named "b" of type B, which has various properties), I want to be able to configure "b" as a leaf node, so that if an property under b changes, the difference reported is that b has changed, rather than the property beneath b.

[SQiShER]

I have to think a little longer about your first situation but for your second one you can simply annotate the "b" property with @ObjectDiffProperty(equalsOnly = true) or do it programmatically via the Configuration object. This causes the object differ to check for differences by using the equals method of the property type instead of doing a deep comparison.

[j1ee]

Brilliant, cheers.
I suppose to check if the collection has not changed size, a new annotation to put on the collection to tell it what to use to compare if you don't want to rely on equals, such as @ObjectDiffProperty(compareMethod="size")? I see what you mean about wanting to think a little longer, as you want it general enough to keep the API nice and clean!

[SQiShER]

Yes, keeping the API nice and clean is pretty difficult. :-)

Collection diffing is the feature that could use the most improvements, because currently all Collections are more or less treated like Sets (having the same item twice in a list doesn't work properly, position changes don't get detected, etc.). Solving this requires some major changes to the API and it could end up making different strategies like the one you suggested very easy to implement. But I'm not yet sure how the API will look…

[SQiShER]

Back to your scenario: are you sure that size is a good measurement? What if one items gets replaced with another? Shouldn't that also count as a change?

[j1ee]

I agree that some people may want to compare more than just size, and that this is not a case of "job done" with regards to comparing collections, but for my specific case I only want to know if this size of the collection has changed.
I have done the following: #69
This allows you to specify the method called, and is not limited to collections. So you could compare by the result of size() on a collection, or by the result of some getter on a bean.

[SQiShER]

This sounds like a great solution! I never thought of that. I'll give it a try when I get home tonight.

[j1ee]

Brilliant :-) This is all covered by my pull request.