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overriding hashcode and equals.

Aneek Banerjee
Ranch Hand

Joined: Jun 20, 2012
Posts: 61

Is it always necessary to override hashcode if I try to override equals?
Matthew Brown

Joined: Apr 06, 2010
Posts: 4512

You should do, yes. The contract says that if two objects are equal then they should have the same hash code (but not necessarily the other way round). So if you redefine equals() you should redefine hashCode() to match.
Jeanne Boyarsky
author & internet detective

Joined: May 26, 2003
Posts: 31551

Not "you should.". You "must."

The JavaDoc says
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.

If you don't override hashCode when you've overwritten equals, you will get unpredictable behavior at times. T he only exception is when you "overwrite" equals with:

Do you know why this is a special case?

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subject: overriding hashcode and equals.