What is the need to override the equals and hashCode methods in Java?

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How can I decide when to use equals() and hashCode() efficiently?
Jan 2 in Java by Sushmita
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You must override hashCode() in every class that overrides equals(). Failure to do so will result in a violation of the general contract for Object.hashCode(), which will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable.

- from Effective Java, by Joshua Bloch

By defining equals() and hashCode(), you can improve the usability of your classes as keys in hash-based collections. As the API doc for hashCode explains: "This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable."

answered Jan 2 by Daisy
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