Both Java and C# introduced generics after their first language release. However, there are differences in how the core libraries changed when generics was introduced. C#'s generics are not just compiler magic and so it was not possible to generify existing library classes without breaking backwards compatibility.
For example, in Java the existing Collections Framework was completely genericised. Java does not have both a generic and legacy non-generic version of the collections classes. In some ways this is much cleaner - if you need to use a collection in C# there is really very little reason to go with the non-generic version, but those legacy classes remain in place, cluttering up the landscape.
Another notable difference is the Enum classes in Java and C#. Java's Enum has this somewhat tortuous looking definition:
// java.lang.Enum Definition in Java
public abstract class Enum> implements Comparable, Serializable {
(see Angelika Langer's very clear explanation of exactly why this is so. Essentially, this means Java can give type safe access from a string to its Enum value:
// Parsing String to Enum in Java
Colour colour = Colour.valueOf("RED");
Compare this to C#'s version:
// Parsing String to Enum in C#
Colour colour = (Colour)Enum.Parse(typeof(Colour), "RED");
As Enum already existed in C# before generics was introduced to the language, the definition could not change without breaking existing code. So, like collections, it remains in the core libraries in this legacy state.
