Can we make the trees serializable? about concurrent-trees HOT 3 OPEN

Yes this would be a good feature, I will look at adding support. Thanks.

Note: in the meantime, you could try the Kryo serialization library [1]. It can 
serialize objects which do not implement the Serializable interface. Let me 
know if it works!

[1] http://code.google.com/p/kryo/

Nope, Kryo doesn't work either. It complains about missing no-arg constructor 
on InvertedRadixTree when reading back.

Exception in thread "main" com.esotericsoftware.kryo.KryoException: Class 
cannot be created (missing no-arg constructor): 
com.googlecode.concurrenttrees.radixinverted.InvertedRadixTree
    at com.esotericsoftware.kryo.Kryo.newInstantiator(Kryo.java:1050)
    at com.esotericsoftware.kryo.Kryo.newInstance(Kryo.java:1062)
    at com.esotericsoftware.kryo.serializers.FieldSerializer.create(FieldSerializer.java:228)
    at com.esotericsoftware.kryo.serializers.FieldSerializer.read(FieldSerializer.java:217)
    at com.esotericsoftware.kryo.Kryo.readObject(Kryo.java:626)
...

You'll need to configure kryo to use objenesis to deserialize immutable 
objects: http://code.google.com/p/kryo/#Object_creation