Re: hashCode

From:

Lew <lewbloch@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 28 Aug 2012 14:38:45 -0700 (PDT)

Message-ID:

<8e9daeec-8e40-48f2-8d48-88df8c39d671@googlegroups.com>

Patricia Shanahan wrote:

Lew wrote:

Patricia Shanahan wrote:

markspace wrote:
...

For example, in C, one can always hash based on memory address. In Java
we don't have that option, so hashcode() takes the place of the
intrinsic property of an address.

...
In Java we have System.identityHashCode() which provides an address-like
hash code for any object.

Which is simply a wrapper method for the 'Object#hashCode()' method.

Although that is the way round it is documented, they are both native
methods, and either could be a wrapper for the other, or they could both
be wrappers for a common native function.

Point taken. I should have said, "Which simply behaves indistinguishably from
the 'Object#hashCode()' method for its argument."

It being a literal wrapper is not important, only that it produces the same result
as 'Object#hashCode()' per its documentation.

Which latter in its Javadocs tells us that it's "typically implemented by converting
the internal address of the object into an integer".

All of which supports markspace's notion that the hash code is intended as a
sort-of address for programming purposes.

N.b., the promise of 'hashCode()' explicitly disallows using the result of
'System.identityHashCode()' as a guaranteed-unique object identifier.

--
Lew