Override hashCode where equals is overridden

[gayanW]

If two objects are equal according to the equals(Object), then calling
the hashCode method on each of the two objects must produce the same
integer result.

However we have classes in src/tests that overrides equals(Object)
without overriding the hashCode method. This overrides the missing
hashCode methods.

Fixes: #85

[cyrille-artho]

How about
return Integer.hashCode(value);
Directly using the data does not hash it.

[gayanW]

I returned data as it is a int. And Integer.hashCode(value) always return the passed value. Anyway it will be better to use Integer.hashCode(value)

[cyrille-artho]

This is functionally correct but Boolean.hashCode(b) is clearer and hides this implementation detail.

[cyrille-artho]

Again, I'd prefer Boolean.hashCode(b) unless there is a need to provide our own hash function.

[gayanW]

Thank you for the suggestions. I made the suggested changes. BTW is it okay to have the same hashCode for an instance of this class and its Integer counterpart. So for instance B(1) and Integer(1) will have the same hashCode.

[cyrille-artho]

If it is not required to have a different hash functions than the built-in ones, it is best to use the built-in hash functions. This makes it easier to understand the code and keeps us in sync with the Java base libraries. I'm actually a bit surprised the Integer.hashCode is this simple; this probably works well for hash tables but is quite a far cry from a cryptographically secure hash function, or even one that you could use to balance data across different servers. Gayan Weerakutti wrote:

…

***@***.**** commented on this pull request. --------------------------------------------------------------------------- In src/tests/TypeNameTest.java <#86 (comment)>: > @@ -45,6 +45,11 @@ public boolean equals(Object other) { return ((B) other).data == data; } + @OverRide + public int hashCode() { + return data; I returned |data| as it is a |int|. And Integer.hashCode(value) always return the passed |value|. Anyway it will be better to use |Integer.hashCode(value)| — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#86 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AG9eR3nVu-MmtGeCmU4eapEOI5GUz0HMks5t84usgaJpZM4UnyYf>.

-- Regards, Cyrille Artho - http://artho.com/ I love deadlines. I like the whooshing sound they make as they fly by. -- Douglas Adams

[cyrille-artho]

I think it's fine if there is a small int i which is not distinguished from a given boolean b by its hash value alone. A correct implementation of equals handles these cases for hash sets/maps.
Ideally, it would be very difficult to fine a given i whose hash code matches the one of a boolean, but it seems Java's hash functions are optimized for speed, not quality.