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what is hashcode and equals contract?

varinder mahajan
Ranch Hand

Joined: Jun 11, 2008
Posts: 47
what is hashcode and equals contract?


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marc weber
Sheriff

Joined: Aug 31, 2004
Posts: 11343

This is described in the API, under java.lang.Object's hashCode() method.


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Mario Razec
Greenhorn

Joined: Aug 01, 2008
Posts: 17
hi...
I understand that:

equals() using to comparison, refers to equivalence relations.
hashCode() is id number allocated to an object by JVM.
Contract: When you use equals() and hashCode() methods is necessary to override these methods

But checking please:
http://www.coderanch.com/t/269570/java-programmer-SCJP/certification/Let-discuss-hashcode-contract

http://www.javaworld.com/community/?q=node/1006
http://java.sun.com/developer/Books/effectivejava/Chapter3.pdf
arulk pillai
Author
Ranch Hand

Joined: May 31, 2007
Posts: 3223
The key thing to remember is that:

-- If two objects are equal then they should have the same hascode but the reverse is not true (i.e. If two objects have the same hashcode does not mean that they are equal)

-- You need to use the same attributes in your equals & hashCode methods


Look at the doco for further info.


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Sandeep Bhandari
Ranch Hand

Joined: Apr 16, 2004
Posts: 201
Besides checking about the implications of equals and hashcode values, the exam may simply ask that if you implement equals() method, which other method you should implement?


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