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From "Thibault Kruse (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LANG-1084) ObjectUtils should have type-safe equals() method
Date Wed, 28 Jan 2015 16:01:34 GMT
Thibault Kruse created LANG-1084:
------------------------------------

             Summary: ObjectUtils should have type-safe equals() method
                 Key: LANG-1084
                 URL: https://issues.apache.org/jira/browse/LANG-1084
             Project: Commons Lang
          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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