Regarding LANG-411, the description mentions 2 parameters for each hash operation: the first a parameter to hold the type instance to be hashed, the second a hash multiplier.
Shouldn't there also be a way to define a specific hash constant value as well? Joshua Bloch refers to this value as the starting value for "result" in his examples and the HashCodeBuilder code maintains an internal field named: iTotal for this value. It doesn't seem to make sense to add a parameter to the hashing operations for a starting hash constant value, but it probably makes sense to add mutators that allow setting this value across any given type. For example: setIntHashConstant, setBoolHashConstant, setLongHashConstant, etc. Default values could be defined so that explicit hash constants are not required.