Thibault Kruse created MATH-1200:
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Summary: ObjectUtils should have type-safe equals method
Key: MATH-1200
URL: https://issues.apache.org/jira/browse/MATH-1200
Project: Commons Math
Issue Type: Improvement
Reporter: Thibault Kruse
Priority: Minor
Commonly implementation of Object.equals() perform an instanceof check before
casting and then comparing properties.
That means that any code like a.equals(b) does not imply any compile-time type
checking.
However it can be very desirable to check types at compiletime in many (though
not all) situations. E.g. consider this code:
Person a = getPersonViaX();
Person b = getPersonViaY();
assert !a.equals(b);
this code is typesafe at compiletime. If getPersonViaY() changes the return
type to something that does not extend Person, this will fail to compile.
Now consider this refactored:
assert !getPersonViaX().equals(getPersonViaY());
In this case the change to getPersonViaY() would go unnoticed, both at
compiletime AND at runtime (if equals merely returns false in the instanceof
check of the most common equals method design).
Based on this blogpost:
http://rickyclarkson.blogspot.de/2006/12/making-equalsobject-type-safe.html
I suggest a typesafe equals method for situations like above:
public static <T,U extends T> boolean equalT(T t,U u)
{
return t.equals(u);
}
and possible a typesafe notEquals method as well.
I am dispassionate about naming of the method, might as well be
typeSafeEquals() or whatever fits best into apache commons.
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