What are equals () and hashCode () overriding rules?

So all java classes have the hashcode() method by default. We can override these methods in our classes . Hashcode() is a method to return an unique integer which is used for indentifying the bucket where this object will be stored for hashing based collections like HashMap.

if a class overrides equals, it must override hashCode . when they are both overridden, equals and hashCode must use the same set of fields . if two objects are equal, then their hashCode values must be equal as well. if the object is immutable, then hashCode is a candidate for caching and lazy initialization.31 Ara 2021

If you don’t override hashcode() then the default implementation in Object class will be used by collections . This implementation gives different values for different objects, even if they are equal according to the equals() method.