The problem

Hash-based containers call equals and hashCode on their elements and keys. Some types are not suitable for this even though their equals and hashCode methods are well-defined, for example because they are expensive to hash, or because instances that represent the same logical value don’t compare equal.

This check reports elements of hash-based Sets, and keys of hash-based Maps, Multimaps, and Multisets, whose types have been configured as unsuitable hash keys. Prefer keying on a stable identifier for the value, or using a non-hash-based container.

Options

• -XepOpt:DiscouragedHashKey:Types=com.example.Foo,com.example.Bar configures the types to report. Subtypes of the configured types are also reported.

Types whose equals methods are not meaningful, such as arrays or Collection, are handled by UndefinedEquals instead.

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("DiscouragedHashKey") to the enclosing element.