What is T , M , ... etc

Question

I have recently noticed a couple "tags" in the source code of Sun's classes. I say "tags" because they are always enclosed in '<' and '>'
An example is java.util.Date
public class Date
    implements java.io.Serializable, Cloneable, Comparable<Date>Notice the <Date> after Comparable.
Now, if we look at the source code for java.lang.Comparable we'll see following two lines:
public interface Comparable<T>
public int compareTo(T o);1. What is this <T> and what kind of object is the 'T' in the compareTo() method?
2. Is it similar to Templates in C++ ?
3. When was this implemented? Was it always there and I just didn't notice it all those years?
4. How can I use it in my programs?
I searched online for any kind of documentation about it, but I can't find anything.. Is it some kind of a mystic feature that we're not supposed to know about or did I miss something? :-)
Thank you for any kind of input.
Nick

Answer 1

1. What is this <T> and what kind of object is the 'T' in the compareTo() method?
You get to specify the class of T. For example, if you create a List<String>, then you have a List of strings, whereas List<Wakka> produces a list of wakkas.
2. Is it similar to Templates in C++ ?
In all the ways that have mattered to me when I have used them over the past year. The documentation on generics goes in depth about all kinds of nooks and crannies that I have never had reason or desire to explore, just like templates in C++. Does that make me a bad person? ;)
3. When was this implemented? Was it always there and I just didn't notice it all those years?
As of 1.5. Ooh, new and shiny!
4. How can I use it in my programs?
How, or why? I would take a look at some of the documentation on generics for syntax, and since you're somewhat familiar with templates in C++, you likely have an understanding of generics enough to make use of them. Maybe you'll even learn something I've gotten wrong here and/or been too lazy^H^H^H^H busy to discover on my own. :)
Hope this helps at least a little, maybe one of our more eloquent friends will jump in with something even more enlightening?
- Kyle