Interesting behavior when extending AbstractMap

[jonahaapala]

Me again!

I wanted to do some custom validation while I am deserializing part of my json payload that is a Map<String, Object>, so I had the idea to create my own Map object so I could override put() as an interception point. As an aside, I initially tried using reader.readMap() which takes in key and value readers, but I want to be able to quickly see if my Map experienced any errors during parsing as well as have access to the original values for reporting/diagnostics purposes. So my setup became something like this:

public class MyMap extends HashMap<String, Object> {
        ValidationError error = NONE;
        String sampleKey;

        @Override
        public Object put(String key, Object value) {
                if (/*key validation*/) { error = KEY_ERROR; sampleKey = key; }
                if (/*value validation*/) { error = VALUE_ERROR; sampleKey = key; }
                else { return super.put(key, value); }
        }
}

And this works! But I wanted to use the fast-utils Object2ObjectOpenHashMap instead, but switching to that did not work. I was able to work-around it by have MapMap extend AbstractMap<String, Object> and have MyMap have a delegate map, but I was wondering if there is a reason that you can't extend any valid Map implementation rather than just the ones provided by the Java runtime? This is not a huge deal, but I figured I'd see if it was something possible to add.