Java Reference
In-Depth Information
21.15. The Legacy Collection Types
The collection frameworkthe interfaces and classes described in this
chapter, and shown in
Figure 21-1
on page
568
has not always been a
part of the package
java.util
, but that package has always contained
some other collections. Most are superseded by the new collection types.
Even so, they are not deprecated because they are in widespread use in
existing code and will continue to be used until programs shift over to the
new types. You are therefore likely to encounter these
legacy collections
so you should learn about them, including their relationship to the newer
collection types. The legacy collections consist of the following types:
•
Enumeration
Analogous to
Iterator
.
•
Vector
Analogous to
ArrayList
, maintains an ordered list of ele-
ments that are stored in an underlying array.
•
Stack
A subclass of
Vector
that adds methods to push and pop ele-
ments so that you can treat the vector by using the terms normal
to a stack.
•
Dictionary
Analogous to the
Map
interface, although
Dictionary
is an
abstract class, not an interface.
[4]
[4]
Dictionary
is not an interface because it predates the addition of interfaces to
the language, which gives you some idea of how old these legacy collections are.
•
Hashtable
Analogous to
HashMap
.
•
Properties
A subclass of
Hashtable
. Maintains a map of key/value
pairs where the keys and values are strings. If a key is not found in
a properties object a "default" properties object can be searched.
Of these types, only
Properties
is in active useit is used to contain system
properties, as described in "
System Properties
"
on page
663
and by some
applications to store configuration data. We describe the other legacy
collections by contrasting them with their analogous types. We then de-
