Alex Herbert created NUMBERS-201:
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Summary: FP64 equals is not consistent with hashCode
Key: NUMBERS-201
URL: https://issues.apache.org/jira/browse/NUMBERS-201
Project: Commons Numbers
Issue Type: Bug
Components: field
Affects Versions: 1.1
Reporter: Alex Herbert
The FP64 class wraps a {{double}} so that it can be used as a field. The
implementation of {{equals}} uses Precision with an allowed difference of up to
2 ULP:
{code:java}
public boolean equals(Object other) {
if (other instanceof FP64) {
final FP64 o = (FP64) other;
return Precision.equals(value, o.value, 1);
}
return false;
}{code}
The hashCode is generated using Double.hashCode(value).
The result is that two objects that are equal can generate a different hash
code. This breaks the contract of Object.equals where two objects that are
equal have the same hash code.
Possible fixes:
# Use the equivalent of (({{{}Double)value).equals(o.value){}}} for a binary
equality check between values that is consistent with double.
# Document the class as having an equals method that is not consistent with
hash code.
I do not understand the requirement for using Precision. If a user has their
own tolerance for field equivalence then this should be left to them to set the
threshold. So I would recommend option 1.
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