Java The Complete Reference, Seventh Edition

is made to add duplicate elements to a set. It does not define any additional methods of its

own.Setis a generic interface that has this declaration:

interface Set<E>

Here,Especifies the type of objects that the set will hold.

The SortedSet Interface

TheSortedSetinterface extendsSetand declares the behavior of a set sorted in ascending

order.SortedSetis a generic interface that has this declaration:

interface SortedSet<E>

Here,Especifies the type of objects that the set will hold.

In addition to those methods defined bySet, theSortedSetinterface declares the methods

summarized in Table 17-3. Several methods throw aNoSuchElementExceptionwhen no

items are contained in the invoking set. AClassCastExceptionis thrown when an object

is incompatible with the elements in a set. ANullPointerExceptionis thrown if an attempt is

made to use anullobject andnullis not allowed in the set. AnIllegalArgumentException

is thrown if an invalid argument is used.

SortedSetdefines several methods that make set processing more convenient. To obtain

the first object in the set, callfirst( ). To get the last element, uselast( ). You can obtain a subset

of a sorted set by callingsubSet( ), specifying the first and last object in the set. If you need

the subset that starts with the first element in the set, useheadSet( ). If you want the subset

that ends the set, usetailSet( ).

The NavigableSet Interface

TheNavigableSetinterface was added by Java SE 6. It extendsSortedSetand declares the

behavior of a collection that supports the retrieval of elements based on the closest match to

a given value or values.NavigableSetis a generic interface that has this declaration:

interface NavigableSet<E>

Here,Especifies the type of objects that the set will hold. In addition to the methods

that it inherits fromSortedSet,NavigableSetadds those summarized in Table 17-4. A

444 Part II: The Java Library

Method Description

Comparator<? super E> comparator( ) Returns the invoking sor ted set’s comparator. If the natural ordering

is used for this set,nullis returned.

E first( ) Returns the first element in the invoking sor ted set.

Sor tedSet<E> headSet(Eend) Returns aSortedSetcontaining those elements less thanendthat

are contained in the invoking sor ted set. Elements in the returned

sor ted set are also referenced by the invoking sor ted set.

E last( ) Returns the last element in the invoking sor ted set.

Sor tedSet<E> subSet(Estar t, Eend) Returns aSortedSetthat includes those elements betweenstar t

andend–1. Elements in the returned collection are also referenced

by the invoking object.

Sor tedSet<E> tailSet(Estar t) Returns aSortedSetthat contains those elements greater than or

equal tostar tthat are contained in the sor ted set. Elements in the

returned set are also referenced by the invoking object.

TABLE 17-3 The Methods Defined bySortedSet