Re: Understanding an Enum Class Declaration

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 1 Oct 2010 12:54:15 -0700 (PDT)

Message-ID:

<c47cf478-a724-41af-ab68-13efe54383e8@d17g2000yqm.googlegroups.com>

KevinSimonson wrote:

Okay, I read the API section at "http://download.oracle.com/javase/6/
docs/api/java/util/EnumMap.html", and I think I understand it. But at
the very top of that page it says "java.util / Class EnumMap<K extends
Enum<K>,V>". What exactly does the "<K extends Enum<K>,V>" part
mean? I think it means that class <EnumMap> has two subtypes it's
based on, <K> and <V>, right? But what does the "Enum<K>" part mean?
Any pointers on this would be greatly appreciated.

Read up on generics.

The type parameters 'K' and 'V' represent the key and value types,
respectively, managed by any particular Map instance.

The "extends Enum<K>" part is an assertion that K is an enum type.

The whole declaration asserts that the Map deals with a key type 'K',
to be determined later that is an enum type, and a value type 'V', to
be determined later, that is some subtype of 'Object'.

Some of your questions, like what is a static initialization block,
relate to the basics of the Java language. Others have pointed you to
the tutorials. Read them.

--
Lew