java.util
Class TreeSet<E>

java.lang.Object
  java.util.AbstractCollection<E>
      java.util.AbstractSet<E>
          java.util.TreeSet<E>

Type Parameters: All Implemented Interfaces:

E - the type of elements maintained by this set Serializable , Cloneable , Iterable <E>, Collection <E>, Set <E>, SortedSet <E>

All Implemented Interfaces:

Serializable , Cloneable , Iterable <E>, Collection <E>, NavigableSet <E>, Set <E>, SortedSet <E>

public class TreeSet<E>
extends AbstractSet<E>
implements NavigableSetSortedSet<E>, Cloneable, Serializable

A NavigableSet implementation based on a TreeMap . The elements are ordered using their natural ordering , or by a Comparator provided at set creation time, depending on which constructor is used. This class implements the Set interface, backed by a TreeMap instance. This class guarantees that the sorted set will be in ascending element order, sorted according to the natural order of the elements (see Comparable ), or by the comparator provided at set creation time, depending on which constructor is used.

This implementation provides guaranteed log(n) time cost for the basic operations ( add , remove and contains ).

Note that the ordering maintained by a set (whether or not an explicit comparator is provided) must be consistent with equals if it is to correctly implement the Set interface. (See Comparable or Comparator for a precise definition of consistent with equals .) This is so because the Set interface is defined in terms of the equals operation, but a TreeSet instance performs all element key comparisons using its compareTo (or compare ) method, so two elements keys that are deemed equal by this method are, from the standpoint of the set, equal. The behavior of a set is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the Set interface.

Note that this implementation is not synchronized. If multiple threads access a tree set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the set. If no such object exists, the set should be "wrapped" using the Collections.synchronizedSortedSet Collections.synchronizedSet method. This is best done at creation time, to prevent accidental unsynchronized access to the set:

     SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
 

The iterators Iterators returned by this class's iterator method are fail-fast : if the set is modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException ConcurrentModificationException . Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class is a member of the Java Collections Framework .

Since:

1.2

See Also:

Collection , Set , HashSet , Comparable , Comparator , Collections.synchronizedSortedSet(SortedSet) , TreeMap , Serialized Form

Constructor Summary
TreeSet ()           Constructs a new, empty tree set, sorted according to the elements' natural ordering of its elements. order.
TreeSet ( Collection <? extends E           Constructs a new tree set containing the elements in the specified collection, sorted according to the elements' natural ordering order of its elements. .
TreeSet ( Comparator <? super E           Constructs a new, empty tree set, sorted according to the specified comparator.
TreeSet ( SortedSet < E           Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set. set, sorted according to the same ordering.

 

Method Summary
boolean	add ( E           Adds the specified element to this set if it is not already present.
boolean	addAll ( Collection <? extends E > c)           Adds all of the elements in the specified collection to this set.
E	ceiling ( E           Returns the least element in this set greater than or equal to the given element, or null if there is no such element.
void	clear ()           Removes all of the elements from this set.
Object	clone ()           Returns a shallow copy of this TreeSet instance.
Comparator <? super E	comparator ()           Returns the comparator used to order the elements in this sorted set, or null if this tree set uses the natural ordering its elements natural ordering.
boolean	contains ( Object  o)           Returns true if this set contains the specified element.
Iterator < E	descendingIterator first ()           Returns an iterator over the elements first (lowest) element currently in this set in descending order. sorted set.
E	first ()           Returns the first (lowest) element currently in this set.
SortedSet < E	headSet ( E           Returns a view of the portion of this set whose elements are strictly less than toElement .
E	floor ( E           Returns the greatest element in this set less than or equal to the given element, or null if there is no such element.
SortedSet < E	headSet ( E           Equivalent to navigableHeadSet(E) SortedSet interface.
E	higher ( E           Returns the least element in this set strictly greater than the given element, or null if there is no such element.
boolean	isEmpty ()           Returns true if this set contains no elements.
Iterator < E	iterator ()           Returns an iterator over the elements in this set in ascending order. set.
E	last ()           Returns the last (highest) element currently in this sorted set.
E	lower ( E           Returns the greatest element in this set strictly less than the given element, or null if there is no such element.
NavigableSet < E	navigableHeadSet ( E           Returns a view of the portion of this set whose elements are strictly less than toElement .
NavigableSet < E	navigableSubSet ( E  fromElement, E           Returns a view of the portion of this set whose elements range from fromElement , inclusive, to toElement , exclusive.
NavigableSet < E	navigableTailSet ( E           Returns a view of the portion of this set whose elements are greater than or equal to fromElement .
E	pollFirst ()           Retrieves and removes the first (lowest) element, or returns null if this set is empty.
E	pollLast ()           Retrieves and removes the last (highest) element, or returns null if this set is empty.
boolean	remove ( Object  o)           Removes the specified element from this set if it is present.
int	size ()           Returns the number of elements in this set (its cardinality).
SortedSet < E	subSet ( E  fromElement, E           Equivalent           Returns a view of the portion of this set whose elements range from fromElement , inclusive, to navigableSubSet(E, E) SortedSet toElement interface. , exclusive.
SortedSet < E	tailSet ( E           Equivalent           Returns a view of the portion of this set whose elements are greater than or equal to navigableTailSet(E) SortedSet fromElement interface. .

 

Methods inherited from class java.util. AbstractSet
equals , hashCode , removeAll

 

Methods inherited from class java.util. AbstractCollection
containsAll , retainAll , toArray , toArray , toString

 

Methods inherited from class java.lang. Object
finalize , getClass , notify , notifyAll , wait , wait , wait

 

Methods inherited from interface java.util. Set
containsAll , equals , hashCode , removeAll , retainAll , toArray , toArray

 

Constructor Detail

TreeSet

public TreeSet()

Constructs a new, empty tree set, sorted according to the elements' natural ordering of its elements. order. All elements inserted into the set must implement the Comparable Comparable interface. Furthermore, all such elements must be mutually comparable : e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the set. If the user attempts to add an element to the set that violates this constraint (for example, the user attempts to add a string element to a set whose elements are integers), the add(Object) call will throw a ClassCastException .

See Also:

Comparable

TreeSet

public TreeSet(Comparator<? super E> comparator) > c) 

Constructs a new, empty tree set, sorted according to the specified comparator. All elements inserted into the set must be mutually comparable by the specified comparator: comparator.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the set. If the user attempts to add an element to the set that violates this constraint, the add(Object) call will throw a ClassCastException .

Parameters:

comparator c - the comparator that will be used to order sort this set. If A null , the natural ordering of the elements will be used. value indicates that the elements' natural ordering should be used.

TreeSet

public TreeSet(Collection<? extends E> c)

Constructs a new tree set containing the elements in the specified collection, sorted according to the elements' natural ordering order of its elements. . All elements keys inserted into the set must implement the Comparable Comparable interface. Furthermore, all such elements keys must be mutually comparable : e1.compareTo(e2) k1.compareTo(k2) must not throw a ClassCastException for any elements e1 k1 and e2 k2 in the set.

Parameters:

c - collection whose The elements that will comprise the new set set.

Throws:

ClassCastException - if the elements keys in c the specified collection are not Comparable , comparable, or are not mutually comparable comparable.

NullPointerException - if the specified collection is null null.

TreeSet

public TreeSet(SortedSet<E> s)

Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set. set, sorted according to the same ordering.

Parameters:

s - sorted set whose elements will comprise the new set set.

Throws:

NullPointerException - if the specified sorted set is null null.

iterator

public Iterator<E> iterator()

Returns an iterator over the elements in this set set. The elements are returned in ascending order.

Specified by:

iterator in interface Iterable < E >

Specified by:

iterator in interface Collection < E >

Specified by:

iterator in interface NavigableSet < E >

Specified by:

iterator in interface Set < E >

Specified by:

iterator in class AbstractCollection < E >

Returns:

an iterator over the elements in this set in ascending order set.

descendingIterator

 
public Iterator< E> descendingIterator () 

Returns an iterator over the elements in this set in descending order.

Specified by:

descendingIterator in interface NavigableSet < E >

Returns:

an iterator over the elements in this set in descending order

Since:

1.6

size

public int size()

Returns the number of elements in this set (its cardinality).

Specified by:

size in interface Collection < E >

Specified by:

size in interface Set < E >

Specified by:

size in class AbstractCollection < E >

Returns:

the number of elements in this set (its cardinality) cardinality).

isEmpty

public boolean isEmpty()

Returns true if this set contains no elements.

Specified by:

isEmpty in interface Collection < E >

Specified by:

isEmpty in interface Set < E >

Overrides:

isEmpty in class AbstractCollection < E >

Returns:

true if this set contains no elements elements.

contains

public boolean contains(Object o)

Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that (o==null ? e==null : o.equals(e)) .

Specified by:

contains in interface Collection < E >

Specified by:

contains in interface Set < E >

Overrides:

contains in class AbstractCollection < E >

Parameters:

o - the object to be checked for containment in this set set.

Returns:

true if this set contains the specified element element.

Throws:

ClassCastException - if the specified object cannot be compared with the elements currently in the set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements set.

add

public boolean add(E e)  o) 

Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if the set contains no element e2 such that (e==null ? e2==null : e.equals(e2)) . If this set already contains the element, the call leaves the set unchanged and returns false .

Specified by:

add in interface Collection < E >

Specified by:

add in interface Set < E >

Overrides:

add in class AbstractCollection < E >

Parameters:

e o - element to be added to this set set.

Returns:

true if this the set did not already contain the specified element element.

Throws:

ClassCastException - if the specified object cannot be compared with the elements currently in this set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements set.

remove

public boolean remove(Object o)

Removes the specified element from this set if it is present. More formally, removes an element e such that (o==null ? e==null : o.equals(e)) , if this set contains such an element. Returns true if this set contained the element (or equivalently, if this set changed as a result of the call). (This set will not contain the element once the call returns.)

Specified by:

remove in interface Collection < E >

Specified by:

remove in interface Set < E >

Overrides:

remove in class AbstractCollection < E >

Parameters:

o - object to be removed from this set, if present present.

Returns:

true if this the set contained the specified element element.

Throws:

ClassCastException - if the specified object cannot be compared with the elements currently in this set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements set.

clear

public void clear()

Removes all of the elements from this set. The set will be empty after this call returns.

Specified by:

clear in interface Collection < E >

Specified by:

clear in interface Set < E >

Overrides:

clear in class AbstractCollection < E >

addAll

public boolean addAll(Collection<? extends E> c)

Adds all of the elements in the specified collection to this set.

Specified by:

addAll in interface Collection < E >

Specified by:

addAll in interface Set < E >

Overrides:

addAll in class AbstractCollection < E >

Parameters:

c - collection containing elements to be added to this set

Returns:

true if this set changed as a result of the call call.

Throws:

ClassCastException - if the elements provided cannot be compared with the elements currently in the set set.

NullPointerException - if the specified collection is null or if any element is null and this set uses natural ordering, or its comparator does not permit null elements - of the specified collection is null.

See Also:

AbstractCollection.add(Object)

navigableSubSet

 
public NavigableSet< E> navigableSubSet ( E fromElement,
 E toElement) 

Description copied from interface: NavigableSet

Returns a view of the portion of this set whose elements range from fromElement , inclusive, to toElement , exclusive. (If fromElement and toElement are equal, the returned set is empty.) The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Specified by:

navigableSubSet in interface NavigableSet < E >

Parameters:

fromElement - low endpoint (inclusive) of the returned set

toElement - high endpoint (exclusive) of the returned set

Returns:

a view of the portion of this set whose elements range from fromElement , inclusive, to toElement , exclusive

Throws:

ClassCastException - if fromElement and toElement cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromElement or toElement cannot be compared to elements currently in the set.

NullPointerException - if fromElement or toElement is null and this set uses natural ordering, or its comparator does not permit null elements

IllegalArgumentException - if fromElement is greater than toElement ; or if this set itself has a restricted range, and fromElement or toElement lies outside the bounds of the range.

Since:

1.6

navigableHeadSet

 
public NavigableSet< E> navigableHeadSet ( E toElement) 

Description copied from interface: NavigableSet

Returns a view of the portion of this set whose elements are strictly less than toElement . The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Specified by:

navigableHeadSet in interface NavigableSet < E >

Parameters:

toElement - high endpoint (exclusive) of the returned set

Returns:

a view of the portion of this set whose elements are strictly less than toElement

Throws:

ClassCastException - if toElement is not compatible with this set's comparator (or, if the set has no comparator, if toElement does not implement Comparable ). Implementations may, but are not required to, throw this exception if toElement cannot be compared to elements currently in the set.

NullPointerException - if toElement is null and this set uses natural ordering, or its comparator does not permit null elements

IllegalArgumentException - if this set itself has a restricted range, and toElement lies outside the bounds of the range

Since:

1.6

navigableTailSet

 
public NavigableSet< E> navigableTailSet ( E fromElement) 

Description copied from interface: NavigableSet

Returns a view of the portion of this set whose elements are greater than or equal to fromElement . The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Specified by:

navigableTailSet in interface NavigableSet < E >

Parameters:

fromElement - low endpoint (inclusive) of the returned set

Returns:

a view of the portion of this set whose elements are greater than or equal to fromElement

Throws:

ClassCastException - if fromElement is not compatible with this set's comparator (or, if the set has no comparator, if fromElement does not implement Comparable ). Implementations may, but are not required to, throw this exception if fromElement cannot be compared to elements currently in the set.

NullPointerException - if fromElement is null and this set uses natural ordering, or its comparator does not permit null elements

IllegalArgumentException - if this set itself has a restricted range, and fromElement lies outside the bounds of the range

Since:

1.6

subSet

public SortedSet<E> subSet(E fromElement,
                           E toElement)

Equivalent to navigableSubSet(E, E) but with a return type conforming to the SortedSet interface.

Returns a view of the portion of this set whose elements range from fromElement , inclusive, to toElement , exclusive. (If fromElement and toElement are equal, the returned sorted set is empty.) The returned sorted set is backed by this set, so changes in the returned sorted set are reflected in this set, and vice-versa. The returned sorted set supports all optional set operations that this set supports. Set operations.

The sorted set returned set by this method will throw an IllegalArgumentException on an attempt if the user attempts to insert an element outside its the specified range.

Note: this method always returns a half-open range (which includes its low endpoint but not its high endpoint). If you need a closed range (which includes both endpoints), and the element type allows for calculation of the successor of a specified value, merely request the subrange from lowEndpoint to successor(highEndpoint) . For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s from low to high , inclusive:

 SortedSet sub = s.subSet(low, high+"\0");
 

A similar technique can be used to generate an open range (which contains neither endpoint). The following idiom obtains a view containing all of the strings in s from low to high , exclusive:

 SortedSet sub = s.subSet(low+"\0", high);
 

Specified by:

subSet in interface SortedSet < E >

Parameters:

fromElement - low endpoint (inclusive) of the returned set subSet.

toElement - high endpoint (exclusive) of the returned set subSet.

Returns:

a view of the portion of this set whose elements range from fromElement , inclusive, to toElement , exclusive exclusive.

Throws:

ClassCastException - if fromElement and toElement cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromElement or toElement cannot be compared to elements currently in the set.

NullPointerException IllegalArgumentException - if fromElement or is greater than toElement is null and this set uses natural ordering, or its comparator does not permit null elements .

IllegalArgumentException NullPointerException - if fromElement is greater than or toElement ; or if this set itself has a restricted range, and is fromElement null or and this set uses natural order, or its comparator does not tolerate toElement null lies outside the bounds of the range elements.

headSet

public SortedSet<E> headSet(E toElement)

Equivalent to navigableHeadSet(E) but with a return type conforming to the Returns a view of the portion of this set whose elements are strictly less than SortedSet toElement interface. . The returned sorted set is backed by this set, so changes in the returned sorted set are reflected in this set, and vice-versa. The returned sorted set supports all optional set operations.

Returns a view of the portion of this set whose elements are strictly less than The sorted set returned by this method will throw an IllegalArgumentException if the user attempts to insert an element greater than or equal to toElement . The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an Note: this method always returns a view that does not contain its (high) endpoint. If you need a view that does contain this endpoint, and the element type allows for calculation of the successor of a specified value, merely request a headSet bounded by IllegalArgumentException successor(highEndpoint) on an attempt to insert an element outside its range. . For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s that are less than or equal to high :

SortedSet head = s.headSet(high+"\0"); 

Specified by:

headSet in interface SortedSet < E >

Parameters:

toElement - high endpoint (exclusive) of the returned set headSet.

Returns:

a view of the portion of this set whose elements are strictly less than toElement toElement.

Throws:

ClassCastException - if toElement is not compatible with this set's comparator (or, if the set has no comparator, if toElement does not implement Comparable does not implement Comparable ).

IllegalArgumentException ). Implementations may, but are not required to, throw this exception if - if this set is itself a subSet, headSet, or tailSet, and toElement cannot be compared to elements currently in the set. is not within the specified range of the subSet, headSet, or tailSet.

NullPointerException - if toElement is null and this set uses natural ordering, or its comparator does not permit null elements

IllegalArgumentException - if this set itself has a restricted range, and is toElement null lies outside the bounds of the range and this set uses natural ordering, or its comparator does not tolerate null elements.

tailSet

public SortedSet<E> tailSet(E fromElement)

Equivalent to navigableTailSet(E) but with a return type conforming to the Returns a view of the portion of this set whose elements are greater than or equal to SortedSet fromElement interface. . The returned sorted set is backed by this set, so changes in the returned sorted set are reflected in this set, and vice-versa. The returned sorted set supports all optional set operations.

Returns a view of the portion of this set whose elements are greater than or equal to The sorted set returned by this method will throw an IllegalArgumentException if the user attempts to insert an element less than fromElement . The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.

The returned set will throw an Note: this method always returns a view that contains its (low) endpoint. If you need a view that does not contain this endpoint, and the element type allows for calculation of the successor of a specified value, merely request a tailSet bounded by IllegalArgumentException successor(lowEndpoint) on an attempt to insert an element outside its range. . For example, suppose that s is a sorted set of strings. The following idiom obtains a view containing all of the strings in s that are strictly greater than low :

 SortedSet tail = s.tailSet(low+"\0");
 

Specified by:

tailSet in interface SortedSet < E >

Parameters:

fromElement - low endpoint (inclusive) of the returned set tailSet.

Returns:

a view of the portion of this set whose elements are greater than or equal to fromElement .

Throws:

ClassCastException - if fromElement is not compatible with this set's comparator (or, if the set has no comparator, if fromElement does not implement Comparable does not implement Comparable ).

IllegalArgumentException ). Implementations may, but are not required to, throw this exception if - if this set is itself a subSet, headSet, or tailSet, and fromElement cannot be compared to elements currently in the set. is not within the specified range of the subSet, headSet, or tailSet.

NullPointerException - if fromElement is null and this set uses natural ordering, or its comparator does not permit null elements

IllegalArgumentException - if this set itself has a restricted range, and is fromElement null lies outside the bounds of the range and this set uses natural ordering, or its comparator does not tolerate null elements.

comparator

public Comparator<? super E> comparator()

Description copied from interface: SortedSet

Returns the comparator used to order the elements in this sorted set, or null if this tree set uses the natural ordering of its elements. elements natural ordering.

Specified by:

comparator in interface SortedSet < E >

Returns:

the comparator used to order the elements in this sorted set, or null if this tree set uses the natural ordering of its elements natural ordering.

first

public E first()

Description copied from interface: SortedSet

Returns the first (lowest) element currently in this sorted set.

Specified by:

first in interface SortedSet < E >

Returns:

the first (lowest) element currently in this set sorted set.

Throws:

NoSuchElementException - if this sorted set is empty empty.

last

public E last()

Description copied from interface: SortedSet

Returns the last (highest) element currently in this sorted set.

Specified by:

last in interface SortedSet < E >

Returns:

the last (highest) element currently in this set sorted set.

Throws:

NoSuchElementException - if this sorted set is empty empty.

lower

 
public Elower ( E e) 

Description copied from interface: NavigableSet

Returns the greatest element in this set strictly less than the given element, or null if there is no such element.

Specified by:

lower in interface NavigableSet < E >

Parameters:

e - the value to match

Returns:

the greatest element less than e , or null if there is no such element

Throws:

ClassCastException - if the specified element cannot be compared with the elements currently in the set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements

Since:

1.6

floor

 
public Efloor ( E e) 

Description copied from interface: NavigableSet

Returns the greatest element in this set less than or equal to the given element, or null if there is no such element.

Specified by:

floor in interface NavigableSet < E >

Parameters:

e - the value to match

Returns:

the greatest element less than or equal to e , or null if there is no such element

Throws:

ClassCastException - if the specified element cannot be compared with the elements currently in the set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements

Since:

1.6

ceiling

 
public Eceiling ( E e) 

Description copied from interface: NavigableSet

Returns the least element in this set greater than or equal to the given element, or null if there is no such element.

Specified by:

ceiling in interface NavigableSet < E >

Parameters:

e - the value to match

Returns:

the least element greater than or equal to e , or null if there is no such element

Throws:

ClassCastException - if the specified element cannot be compared with the elements currently in the set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements

Since:

1.6

higher

 
public Ehigher ( E e) 

Description copied from interface: NavigableSet

Returns the least element in this set strictly greater than the given element, or null if there is no such element.

Specified by:

higher in interface NavigableSet < E >

Parameters:

e - the value to match

Returns:

the least element greater than e , or null if there is no such element

Throws:

ClassCastException - if the specified element cannot be compared with the elements currently in the set

NullPointerException - if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements

Since:

1.6

pollFirst

 
public EpollFirst () 

Description copied from interface: NavigableSet

Retrieves and removes the first (lowest) element, or returns null if this set is empty.

Specified by:

pollFirst in interface NavigableSet < E >

Returns:

the first element, or null if this set is empty

Since:

1.6

pollLast

 
public EpollLast () 

Description copied from interface: NavigableSet

Retrieves and removes the last (highest) element, or returns null if this set is empty.

Specified by:

pollLast in interface NavigableSet < E >

Returns:

the last element, or null if this set is empty

Since:

1.6

clone

public Object clone()

Returns a shallow copy of this TreeSet instance. (The elements themselves are not cloned.)

Overrides:

clone in class Object

Returns:

a shallow copy of this set set.

See Also:

Cloneable