Having mostly worked with C#, I tend to think in terms of C# features which aren't available in Java. After working extensively with Java over the last year, I've started to discover Java features that I wish were in C#. Below is a list of the ones that I'm aware of. Can anyone think of other Java language features which a person with a C# background may not realize exists?
The articles http://www.25hoursaday.com/CsharpVsJava.html and http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp give a very extensive list of differences between Java and C#, but I wonder whether I missed anything in the (very) long articles. I can also think of one feature (covariant return type) which I didn't see mentioned in either article.
Please limit answers to language or core library features which can't be effectively implemented by your own custom code or third party libraries.
Covariant return type - a method can be overridden by a method which returns a more specific type. Useful when implementing an interface or extending a class and you want a method to override a base method, but return a type more specific to your class.
Enums are classes - an enum is a full class in java, rather than a wrapper around a primitive like in .Net. Java allows you to define fields and methods on an enum.
Anonymous inner classes - define an anonymous class which implements a method. Although most of the use cases for this in Java are covered by delegates in .Net, there are some cases in which you really need to pass multiple callbacks as a group. It would be nice to have the choice of using an anonymous inner class.
Checked exceptions - I can see how this is useful in the context of common designs used with Java applications, but my experience with .Net has put me in a habit of using exceptions only for unrecoverable conditions. I.E. exceptions indicate a bug in the application and are only caught for the purpose of logging. I haven't quite come around to the idea of using exceptions for normal program flow.
strictfp - Ensures strict floating point arithmetic. I'm not sure what kind of applications would find this useful.
fields in interfaces - It's possible to declare fields in interfaces. I've never used this.
static imports - Allows one to use the static methods of a class without qualifying it with the class name. I just realized today that this feature exists. It sounds like a nice convenience.
