Re: How do I set up CollapsableHashtable to take parameters?
Lew <l...@nospam.lewscanon.com> wrote:
Where did you learn about Hashtable and Enumeration anyway?
They were replaced in 2000.
phillip.s.powell@gmail.com wrote:
You asked me the times where I learned about Hashtable and
Enumeration, so I am obliging you.
Joshua Cranmer wrote:
His question was "where", not "when" -- "where" indicating the source
from which you used Hashtable/Enumeration.
Pardon my confusing presentation. Yes, I did mean "where".
This is no reflection on Phillip - I am trying to track down how people are
being trained to use something that was replaced nine years ago, really before
Java's growth in popularity.
Phillip's question about why two different implementations of Map behave
differently is really very apt. It holds one of the secrets to effective API
use, especially the collections API.
If you compare implementations of collections such as List, like ArrayList vs.
LinkedList, you will find differences even for the same methods. For example,
get( int index ) takes constant time in ArrayList, but requires time
proportional to the list size for LinkedList if the index is near the middle
of the list.
You will also find that LinkedList has many methods that ArrayList does not.
This is a major advantage of interfaces - LinkedList is a List, but it also is
a Queue, and a Deque since J 1.6. These are other interfaces that LinkedList
implements.
A class is allowed to have methods that come from no interface, although in
some styles of programming that is a Bad Thing to do.
In the case of Hashtable, it has methods that do not belong to Map or any part
of the collections API, and the methods it implements differ from the same
methods in other Map implementations. So it has a method "keys()" that is not
part of Map, and it has a method "keySet()" that is part of Map. (The modern
equivalent of "keys()" is "keySet().iterator()".) Hashtable's "keySet()"
behaves differently from HashMap's. (Threads tutorial.)
Something that "is-a" Map can "be-a" something else, too.
-- Lew