Java Reference
In-Depth Information
<
formal_type_parameter_list
>
return_type identifier
(
para-
meter_list
)
The
formal_type_parameter_list
isthesameaswhenspecifyingageneric
type:itconsistsoftypeparameterswithoptionalbounds.Atypeparametercanappear
as the method's
return_type
, and type parameters can appear in the
paramet-
er_list
.Thecompilerinferstheactualtypeargumentsfromthecontextinwhichthe
method is invoked.
You'lldiscovermanyexamplesofgenericmethodsintheCollectionsFramework.For
example, its
java.util.Collections
class provides a
public static <T
extends Object & Comparable<? super T>> T min(Collection<?
extends T> coll)
method for returning the minimum element in the given
Collection
according to the ordering specified by the supplied
java.util.Comparator
instance.
Youcaneasilyconvert
copyList()
intoagenericmethodbyprefixingthereturn
typewith
<T>
andreplacingeachwildcardwith
T
.Theresultingmethodheaderis
<T>
void copyList(List<T> src, List<T> dest)
,and
Listing3-56
presents
itssourcecodeaspartofanapplicationthatcopiesa
List
of
Circle
toanother
List
of
Circle
.
Listing 3-56.
Declaring and using a
copyList()
generic method
import java.util.ArrayList;
import java.util.List;
class Circle
{
private double x, y, radius;
Circle(double x, double y, double radius)
{
this.x = x;
this.y = y;
this.radius = radius;
}
@Override
public String toString()
{
return "("+x+", "+y+", "+radius+")";
