> Here are four common pitfalls that can cause inconsistent behavior when overriding equals: 1. Defining equals with the wrong signature. 2. Changing equ

> Here are four common pitfalls that can cause inconsistent behavior when overriding equals: 1. Defining equals with the wrong signature. 2. Changing equals without also changing hashCode. 3. Defining equals in terms of mutable fields. 4. Failing to define equals as an equivalence relation. I have to call this a must read. Writing equals is straight forward, but there are are many ways to go wrong. In fact the article doesnt go far enough, because complex objects often have different levels of equality: Is it the same object, by UID or some immutable field? Is it equal by some subset of the contents? Is it equal by some classification or hierarchy? EDIT: by different kinds of equality, I mean such things as equalByContent for mutable fields or equalByLocation.