Java Reference
In-Depth Information
20.1
Introduction
20.2
Motivation for Generic Methods
20.3
Generic Methods: Implementation
and Compile-Time Translation
20.4
Additional Compile-Time Translation
Issues: Methods That Use a Type
Parameter as the Return Type
20.5
Overloading Generic Methods
20.6
Generic Classes
20.7
Raw Types
20.8
Wildcards in Methods That Accept
Type Parameters
20.9
Wrap-Up
Summary | Self-Review Exercises | Answers to Self-Review Exercises | Exercises
You've used existing generic methods and classes in Chapters 7 and 16. In this chapter,
you'll learn how to write your own.
It would be nice if we could write a single
sort
method to sort the elements in an
Integer
array, a
String
array or an array of any type that supports ordering (i.e., its ele-
ments can be compared). It would also be nice if we could write a single
Stack
class that
could be used as a
Stack
of integers, a
Stack
of floating-point numbers, a
Stack
of
String
s
or a
Stack
of any other type. It would be even nicer if we could detect type mismatches at
compile time
—known as
compile-time type safety
. For example, if a
Stack
should store
only integers, an attempt to push a
String
onto that
Stack
should issue a
compilation
error.
This chapter discusses
generics
—specifically
generic methods
and
generic classes
—which
provide the means to create the type-safe general models mentioned above.
Overloaded methods are often used to perform
similar
operations on
different
types of
data. To motivate generic methods, let's begin with an example (Fig. 20.1) containing
overloaded
printArray
methods (lines 22-29, 32-39 and 42-49) that print the
String
representations of the elements of an
Integer
array, a
Double
array and a
Character
array,
respectively. We could have used arrays of primitive types
int
,
double
and
char
. We're
using arrays of the type-wrapper classes to set up our generic method example, because
only
reference types can be used to specify generic types in generic methods and classes
.
1
// Fig. 20.1: OverloadedMethods.java
2
// Printing array elements using overloaded methods.
3
4
public class
OverloadedMethods
5
{
6
public static void
main(String[] args)
7
{
8
// create arrays of Integer, Double and Character
9
Integer[] integerArray = {
1
,
2
,
3
,
4
,
5
,
6
};
10
Double[] doubleArray = {
1.1
,
2.2
,
3.3
,
4.4
,
5.5
,
6.6
,
7.7
};
11
Character[] characterArray = {
'H'
,
'E'
,
'L'
,
'L'
,
'O'
};
Fig. 20.1
|
Printing array elements using overloaded methods. (Part 1 of 2.)
