[Springframework-developer] use java.util.Collections.EMPTY_LIST et. al. not new LinkedList()

[<ak...@sp...>]

Reading the sources trying to see if I can extract Spring's JDBC function=
ality away from its dependence on DataSource I noticed that quite a few m=
ethods that take optional List parameters substitute an empty LinkedList =
(via new LinkedList()) to methods on which they depend.

Which left me wondering: are those LinkedList instances ever written to -=
- they seem to not need to be, but I couldn't answer definitively without=
 significantly greater intimacy with Spring's code. 

So, if those are meant to be read-only, I'd encourage using java.util.Col=
lections.EMPTY_LIST instead (and similarly EMPTY_MAP and EMPTY_SET as nee=
ded).  Why?  3 reasons:

    1.  Better self-documenting code.  If a default parameter value is re=
ad-only, use a read-only (immutable) instance.  You still get the List se=
mantics and don't need null checks in the called methods.
    2.  It is faster.  Object creation ion the heap is orders of magnitud=
e slower than putting an object reference on the stack.
    3.  Uses less memory.  Small though they be, new objects still consum=
e resources.  And have to be garbage collected later -- which goes back t=
o point #2.

Seems like a win all-around.

=3D=3D Ee