[java] Rule to check for double brace initialisation

[oowekyala]

Double brace initialisation is a pattern to initialise eg collections concisely. But it implicitly generates a new .class file, and the object holds a strong reference to the enclosing object...

Example:

 new ArrayList<String>() {{ addAll("a", "b", "c"); }};

I think, we could detect that for collections as a first step. But any instance initialiser in an anonymous class that calls only public methods of the object could be considered an instance of this code smell, if no methods are overridden.

[jsotuyod]

@oowekyala I strongly support this.