In this mini Fragment, we introduce Joshua's eighth Item. This one is a doozy, probably one of the longest items in the group of the effective Java series, but most definitely quite important.

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Stay tuned for more items from our "Effective Java for Android developers" Fragment series.

Show Notes * Effective Java (2nd Edition) - Joshua Bloch

Obey the general contract when overriding equals

When to not override equals: * Each instance of the class is inherently unique. * You don't care whether the class provides a "logical equality" test. * A superclass has already overridden equals, and the superclass behavior is appropriate for this class.

The equals method implement an equivalence relation which states it must be: * Reflexive * Symmetric * Transitive * Consistent * For any non-null reference x, x.equals(null) must return false.

A recipe for a high-quality equals method is as such: * Use the == operator to check for references to this object. * Use the instanceof operator to check if the argument has the correct type * Cast to the correct type. * Check all field types and corresponding field types. * Finally, when done, ask yourself - is this method symmetric, transitive and consistent?

Caveats * Always override hashcode when you override equals * Don't be too clever! * Don't substitute another type for Object in the equals declaration.

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