Ok good points. But in order to have a useful interface I think we will
have to specify the equals methods. I believe, but you can correct me
if I'm wrong, that .equals is frequently used.
Jesse
Martin Desruisseaux wrote:
Jesse Eichar a écrit :
I agree with you for the most part Martin. But if you look at some
implementations of equals, such as java.util.AbstractList, you will
find that it checks only that the object implements the interface and
only uses public methods to determine equality.
Yes, but they can do that because the equals(...) behavior for a List
is part of the specification. I mean, the java.util.List interface
explains exactly how the equals(...) method must behave for all
java.util.List implementations, including java.util.AbstractList:
http://java.sun.com/j2se/1.5.0/docs/api/java/util/List.html#equals(java.lang.Object)
My point was:
- If we want to check for interface, then the *interface* should have
an equals(...) method with a javadoc that explain exactly how the
comparaison must be done for all implementations of that interface.
This is what Sun do for collections like List and Set.
- When the equals(...) behavior is not part of the specification,
then looking for implementation is just a conservative approach
for making sure that symmetry is enforced.
Just relying on public methods to determine equality is not enough.
Look for example at java.util.Collection: does the order of elements
matter? Element order matter if the collection is actually a
java.util.List, but doesn't matter (and should be ignored) if the
collection is actually a java.util.Set. This kind of details must be
part of the specification of the equals(...) method in interfaces, if
we want to look for interfaces only in equals(...).
I'm not against checking for interfaces in the equals(...) method. I
just said that if we want to do so, we shoud add an equals(...) method
in interfaces and explain there what this method should compare
exactly for all implementations.
Martin.
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