Enthuware

It definitely compile with a warning !
The method set interest is not used ...

Thanks

I think you are talking about IDE generated warning. The javac compiler has nothing to do with it, which is what we care about for the purpose of this exam.

HTH,
Paul.

However, this behavior was changed in the TreeSet implementation recently and it throws a ClassCastException when you add the first element itself.

Was this changed in Java 7?

Not sure when exactly it was changed but for Java 7 the behavior is as described.

HTH,
Paul.

Ok. Thanks!

Ideally, when you add the first element, since there is nothing to compare this element to, there should be no exception.

If the first element added is-not-a Comparable, there should definitely be a ClassCastException? Since TreeSet only takes objects that are-a Comparable?

rianne wrote:Ideally, when you add the first element, since there is nothing to compare this element to, there should be no exception.

If the first element added is-not-a Comparable, there should definitely be a ClassCastException? Since TreeSet only takes objects that are-a Comparable?

A TreeSet is a Set and to satisfy the Set interface, it has to accept any Object as an argument to the add method. The method implementation can impose additional restriction (such as the argument must be a Comparable) only by checking the object (e.g. obj instanceof Comparable) and throwing an unchecked but this is a design decision. Some time prior to Java 7, they didn't do this. A TreeSet accepted any object. It threw an exception only when a comparison was required to be done.

HTH,
Paul.

I wonder if lack of compile time restriction of elements being Comparable is because of constructor with Comparator. If there was no such constructor generic type E could be bounded as E extends Comparable and this error would be moved to compile time.
Am I right?