This week's giveaway is in the Spring forum.
We're giving away four copies of REST with Spring (video course) and have Eugen Paraschiv on-line!
See this thread for details.
The moose likes Beginning Java and the fly likes Doubt about hashcode() and equals()? Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login

Win a copy of REST with Spring (video course) this week in the Spring forum!
JavaRanch » Java Forums » Java » Beginning Java
Bookmark "Doubt about hashcode() and equals()?" Watch "Doubt about hashcode() and equals()?" New topic

Doubt about hashcode() and equals()?

Harivenkatesh Polnati

Joined: Mar 17, 2012
Posts: 25

Why always override hashcode() if overriding equals()?
Ashwini Kashyap
Ranch Hand

Joined: Aug 30, 2012
Posts: 90
If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
This is clearly stated in hashCode() description.

Please refer its Object class API here for more clarity.

Ashwini Kashyap
Winston Gutkowski

Joined: Mar 17, 2011
Posts: 8837

Harivenkatesh Polnati wrote:Why always override hashcode() if overriding equals()?

You don't have to do it, but it's basically good practise, because it ensures that your object will always work correctly in a hashed collection.

If you don't follow this rule - and that includes not just overriding hashCode(), but also ensuring that it's always in sync with equals() (ie, if you update equals(), you also need to update hashCode()) - you run the risk of someone using it in a HashMap or HashSet and having it behave very strangely.


Bats fly at night, 'cause they aren't we. And if we tried, we'd hit a tree -- Ogden Nash (or should've been).
Articles by Winston can be found here
I agree. Here's the link:
subject: Doubt about hashcode() and equals()?
It's not a secret anymore!