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Java: Always override equals?

should I override equals function for any class that I create?

even for very simple classes which only contains some very simple attributes and by equals I need every single attribute of it to be equal?

Answer 1

should I override equals function for any class that I create?

Override equals if (and only if) the object “represents some data”, i.e. if it models something such as Person, Car or RecipieIngredient (these typically end up in collections etc). Don’t override equals for other types of classes, for example LoginServlet or DatabaseUtil.

Remember to always override hashCode whenever you override equals.

(A natural follow-up question:) What happens if I don’t override equals and hashCode?

Any two objects will be considered unequal unless they are the exact same object.

[…] I need every single attribute of it to be equal?

Typically yes. It depends on how you define your notion of equality. Note that for reference types, you can reuse/delegate to that objects implementation of equals (and hashCode) when implementing your own.

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