Matt, what you are putting into the outer HashMap is not the other HashMap, but the return value of the call to the inner put method (which is null in this case).
It *is* possible to do what you want to do (inserting a filled HashMap without first assigning it to a local variable), using an instance initializer:
The outer brace makes the HashMap an anonymous inner class, the inner brace is an instance initializer (kind of an "anonymous constructor").
That's quite an advanced trick, though, and I'm not sure how many people would say that it's good style...
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus