Java The Complete Reference, Seventh Edition

458 Part II: The Java Library

The EnumSet Class

EnumSetextendsAbstractSetand implementsSet. It is specifically for use with keys of an

enumtype. It is a generic class that has this declaration:

class EnumSet<E extends Enum<E>>

Here,Especifies the elements. Notice thatEmust extendEnum<E>, which enforces the

requirement that the elements must be of the specifiedenumtype.

EnumSetdefines no constructors. Instead, it uses the factory methods shown in Table 17-7

to create objects. All methods can throwNullPointerException. ThecopyOf( )andrange( )

methods can also throwIllegalArgumentException. Notice that theof( )method is overloaded

a number of times. This is in the interest of efficiency. Passing a known number of arguments

can be faster than using avarargparameter when the number of arguments is small.

Accessing a Collection via an Iterator

Often, you will want to cycle through the elements in a collection. For example, you might

want to display each element. One way to do this is to employ aniterator,which is an object

that implements either theIteratoror theListIteratorinterface.Iteratorenables you to cycle

through a collection, obtaining or removing elements.ListIteratorextendsIteratorto allow

Method Description

static <E extends Enum<E>>

EnumSet<E> allOf(Class<E>t)

Creates anEnumSetthat contains the elements in the

enumeration specified byt.

static <E extends Enum<E>> EnumSet<E>

complementOf(EnumSet<E>e)

Creates anEnumSetthat is comprised of those elements not

stored ine.

static <E extends Enum<E>>

EnumSet<E> copyOf(EnumSet<E>c)

Creates anEnumSetfrom the elements stored inc.

static <E extends Enum<E>>

EnumSet<E> copyOf(Collection<E>c)

Creates anEnumSetfrom the elements stored inc.

static <E extends Enum<E>>

EnumSet<E> noneOf(Class<E>t)

Creates anEnumSetthat contains the elements that are not in

the enumeration specified byt,which is an empty set by definition.

static <E extends Enum<E>>

EnumSet<E> of(Ev, E ...varargs)

Creates anEnumSetthat containsvand zero or more

additional enumeration values.

static <E extends Enum<E>>

EnumSet<E> of(Ev)

Creates anEnumSetthat containsv.

static <E extends Enum<E>>

EnumSet<E> of(Ev1, Ev2)

Creates anEnumSetthat containsv1andv2.

static <E extends Enum<E>>

EnumSet<E> of(Ev1, Ev2, Ev3)

Creates anEnumSetthat containsv1throughv3.

static <E extends Enum<E>>

EnumSet<E> of(Ev1, Ev2, Ev3, Ev4)

Creates anEnumSetthat containsv1throughv4.

static <E extends Enum<E>>

EnumSet<E> of(Ev1, Ev2, Ev3, Ev4,

Ev5)

Creates anEnumSetthat containsv1throughv5.

static <E extends Enum<E>>

EnumSet<E> range(Estar t, Eend)

Creates anEnumSetthat contains the elements in the range

specified bystar tandend.

TABLE 17-7 The Methods Defined byEnumSet