Tag: How to override equals() and hashCode() method in Java

When overriding the Equals() method, make sure the passed-in object is not null and can be cast to the type you are comparing . When overriding Equals(), you also need to override GetHashCode(), otherwise you get a compiler warning.

When class C overrides the equals method it must check that the object reference passes in is not null, that it is the same class (not a requirement, but typical), and that all the instance data is equal – including all superclass instance variables it inherited.

The String class overrides the equals method it inherited from the Object class and implemented logic to compare the two String objects character by character. The reason the equals method in the Object class does reference equality is because it does not know how to do anything else.

public boolean equals(Object ob) To override this method, it is usually necessary to override another method called hashCode. This is to fulfill the contract for the hashCode method as it says that objects which are equal must have equal hash codes.

StringBuilder/ StringBuffer does not override equals() and hashCode() method.

You must have to override both equals() and hashCode() method in Java , otherwise your value object will not be able to use as key object in HashMap because working of HashMap is based on equals() and hashCode to read more see , How HashMap works in Java.23 Eyl 2021