Java Reference
In-Depth Information
Unlike
List
,
Set
, and
Queue
,
Map
does not extend
Collection
. However, it
is possible to view a map as a
Collection
instance by calling
Map
's
keySet()
,
values()
, and
entrySet()
methods, which respectively return a
Set
of keys, a
Collection
of values, and a
Set
of key/value pair entries.
Note
The
values()
methodreturns
Collection
insteadof
Set
becausemul-
tiplekeyscanmaptothesamevalue,and
values()
wouldthenreturnmultiplecop-
ies of the same value.
The
Collection
viewsreturnedbythesemethods(recallthata
Set
isa
Collec-
tion
because
Set
extends
Collection
) provide the only means to iterate over a
lor
constants,
RED
,
GREEN
, and
BLUE
.
Listing 5-17.
A colorful enum
enum Color
{
RED(255, 0, 0),
GREEN(0, 255, 0),
BLUE(0, 0, 255);
private int r, g, b;
private Color(int r, int g, int b)
{
this.r = r;
this.g = g;
this.b = b;
}
@Override
public String toString()
{
return "r = "+r+", g = "+g+", b = "+b;
}
}