Question

Is it possible to rewrite this C# code into java?

public interface IEnumerable<out T> : IEnumerable
{

    IEnumerator<T> GetEnumerator();
}

I have problem creating generic class with parameter T in its name. I also don’t know, how to solve out parameter, which Java don’t support. Anyone who is experienced in both platforms?

Answer 1

The out here isn’t for an out parameter in the normal sense – it’s expressing the fact that IEnumerable<T> is covariant in T. That allows you to say, for example:

IEnumerable<string> strings = new List<string>();
IEnumerable<object> objects = strings;

Java deals with generic variance very differently, basically. In fact, generics in Java are very different in general – look at the Java Generics FAQ for a lot more detail.

The near-equivalent of IEnumerable<T> in Java is Iterable<T> – you’d be far better off using that than copying IEnumerable<T> across. (For example, Iterable<T> has language support in Java in the form of the “enhanced for loop”.)