Java Reference
In-Depth Information
developing among programmers for the class
ArrayList
. There are some differences
between the classes
Vector
and
ArrayList
, but the differences involve material we
have not covered. If you encounter the class
Vector
in somebody's code, chances are
the class
Vector
could be replaced by the class
ArrayList
, which would require at
most cosmetic changes in the code.
1
Parameterized Classes and Generics
The class
ArrayList
is a
parameterized class
. It has a parameter, which we have
been denoting
Base_Type
, that can be replaced by any reference type to obtain a class
for
ArrayList
s with the specified base type.
ArrayList
is just a class that somebody
defined (and placed in the standard Java library package
java.util
), so you should
also be able to define these kinds of classes. Starting with version 5.0, Java allows
class definitions with parameters for types. These classes that have type parameters
are called parameterized class or
generic definitions
or, more simply,
generics
. You
already know how to use classes with a type parameter, because we have been using the
parameterized class
ArrayList
. In Section 14.2, we will show you how to write your
own parameterized classes.
parameterized
class
generics
PITFALL: Nonparameterized
ArrayList
and
Vector
Classes
The
ArrayList
and
Vector
classes we discussed in this section have a type parameter
for the base type. There are also
ArrayList
and
Vector
classes with no parameter
for the base type. (They have base type
Object
.) These
ArrayList
and
Vector
classes without type parameters are left over from earlier versions of Java. When
checking details in the Java documentation, be sure you get the documentation for the
ArrayList
and
Vector
classes that have a type parameter. Using notation we introduce
in Section 14.2, the versions with type parameters are usually written as
ArrayList<E>
and
Vector<E>
or as
ArrayList<T>
and
Vector<T>
in the Java documentation.
■
14.2
Generics
You can have this dish prepared with any type of meat or fish.
Entry on a restaurant menu
Starting with version 5.0, Java allows class definitions that contain a parameter (or
parameters) for a type (or types). In this section, we teach you how to write class
definitions that contain a type parameter.
1
The biggest difference between the
Vector
and
ArrayList
classes is that
Vectors
are
synchronized
whereas
ArrayLists
are not. However, synchronization is a topic that we do not cover and is not
relevant to the kinds of programming we are doing.
