correct hashCode( ) method

[ankur rathi]

Ruels for correct implementation of hashCode() method :

1] if two object returning true with equals() method , then they should return same int with hashCode() method .

2] But the vice versa is not true . I mean two object may have same hash code but not returning true with equals() method .

Is this right ???

[Ray Stojonic]

Originally posted by rathi ji:
Is this right ???

Yes

[Tony Morris]

I mean two object may have same hash code but not returning true with equals() method .

Not only is it right, it is impossible for it to be wrong.
That is, if I created Integer.MAX_VALUE + 1 unique (equals returns false) instances your class, I am guaranteed a hash code collision.

In practice, it is quite simple to create a hash code collision.
I wrote a small application once to demonstrate that generating random 5 character Strings results in a collision about 3 times per second on my development machine. I wrote it because some twit was trying to use a String as a switch argument and claimed that "it works" if you call hashCode. This is despite the fact that the switch/case construct is evil in itself.
[ January 27, 2005: Message edited by: Tony Morris ]