Java Reference
In-Depth Information
Differences between
ArrayList<T>
and
Vector<T>
For most purposes,
ArrayList<T>
and
Vector<T>
are equivalent. There are only
minor differences between the classes. The methods that are in both classes are given
in Display 16.7 . The class
Vector<T>
has more methods than
ArrayList<T>
does;
these methods are not given in Display 16.7. However, most of the extra methods
are little more than alternate names for methods that are in both
ArrayList<T>
and
Vector<T>
. None of the methods in
Vector<T>
do anything that cannot easily be done
with an
ArrayList<T>
. The class
ArrayList<T>
is reputed to be more efficient than
Vector<T>
. The biggest difference between these two classes is that
ArrayList<T>
is newer than
Vector<T>
and was created as part of the Java collection framework,
whereas
Vector<T>
is an older class that was retrofitted with extra method names to
make it fit into the collection framework. You are encouraged to use
ArrayList<T>
rather than
Vector<T>
. However, a lot of existing code uses
Vector<T>
, so you should
be familiar with it.
1
Nonparameterized Version of the Collection Framework
★
Before version 5.0, Java did not have type parameters. So, the collection framework
consisted of ordinary classes and interfaces, such as
Collection
,
List
,
ArrayList
, and
so forth, all of which had no type parameters. Although this older collection framework
has been supplanted by the new, generic version, the old version's classes and interfaces,
without type parameters, are still in the standard libraries and in a lot of older code.
There is no longer any need for the older classes and interfaces that do not have type
parameters. They can sometimes be harder to use and are less versatile than the new,
generic classes with type parameters. You should not use the older classes and interfaces
without type parameters. However, you will often see them used in older code. When
reading older code, you will not go too far wrong in thinking of
Collection
as
meaning
Collection<Object>
,
ArrayList
as meaning
ArrayList<Object>
, and so
forth. This is not, strictly speaking, correct. For example, the classes
ArrayList
and
ArrayList<Object>
are not the same, but they are very similar.
1
The biggest difference between
Vector<T>
and
ArrayList<T>
classes is that
Vector<T>
objects are
synchronized
while
ArrayList<T>
objects are not. Synchronization is briefly discussed
in Chapter 19.
