On Oct 29, 2009, at 6:18 PM, glen e. p. ropella wrote:

> The point being, if you want to make the two things adhere to the same
> interface, then why are they different classes?  Is it solely for
> efficiency? Are there separate (functional requirement based) use  
> cases
> for mutables than for immutables?  Etc.

It's always been efficiency.

It's not uncommon either: for example, Obj-C has immutable and mutable  
versions of all of its basic data types.

Double2D is obviously the primary though, because its immutability  
means it doesn't break Java's hash tables (unlike say, the mutable  
java.awt.Point2D).

This is less of an issue with more efficient handling of allocations  
of small short-lived objects in Java, which is a priority for Sun now  
that all the boxing and unboxing is going on (ugh).  But it's still  
slower.

My goal then has been to try to make the Mutable classes *reasonably*  
compatible with the immutable classes without causing lots of  
confusion among people.

Sean