Specific syntax? java.util.regex.Pattern$Node

[lmhelp2]

Hi,

Thank you for reading my post :) .

I was considering the following package: "java.util.regex",
when I met the following thing:

- http://www.docjar.com/docs/api/java/util/regex/[B]Pattern$Node.html[/B]
- static class: [B]Pattern.Node[/B]
- java.util.regex.[B]Pattern$Node[/B]

and also for instance:

- http://www.docjar.com/docs/api/java/util/regex/[B]Pattern$Begin.html[/B]
- static final class: [B]Pattern.Begin[/B]
- java.util.regex.[B]Pattern$Begin[/B]

=> I am wondering what is that "dollar character" that appears above in
"Pattern$Node" or "Pattern$Begin".
Is this "$" character a character like any other one?
Or is it a specific construct... ?

=> What is "Pattern.Begin"?
Is it the name of a class with a dot character right in the middle of it?

=> Why do we have those two distinct forms of what appears to be the
same thing "Pattern.Begin" and "Pattern$Begin"?

Thank you for helping me.
All the best,
--
Lmhelp

[lmhelp2]

Hi again,

Someone in my office gave me a hint: "nested classes", "inner classes".
Ref. Nested Classes (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

Apparently, "Begin" would be an inner class of the class "Pattern"
which would be the outer class for "Begin".

We probably write "java.util.regex.Pattern$Begin" instead of
"java.util.regex.Pattern.Begin" not to think "java.util.regex.Pattern"
is a package name with a class "Begin" inside...

Sincerely,
--
Lmhelp