Class TreeSet<E>
- Type Parameters:
- E- the type of elements maintained by this set
- All Implemented Interfaces:
- Serializable,- Cloneable,- Iterable<E>,- Collection<E>,- NavigableSet<E>,- SequencedCollection<E>,- SequencedSet<E>,- Set<E>,- SortedSet<E>
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 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 comparisons using its compareTo (or
 compare) method, so two elements 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
 method.  This is best done at creation time, to prevent accidental
 unsynchronized access to the set: 
SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
The 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.
 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.
 
The addFirst and addLast methods of this class
 throw UnsupportedOperationException. The encounter order of elements is determined
 by the comparison method; therefore, explicit positioning is not supported.
 
This class is a member of the Java Collections Framework.
- Since:
- 1.2
- See Also:
- 
Constructor SummaryConstructorsConstructorDescriptionTreeSet()Constructs a new, empty tree set, sorted according to the natural ordering of its elements.TreeSet(Collection<? extends E> c) Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements.TreeSet(Comparator<? super E> comparator) Constructs a new, empty tree set, sorted according to the specified comparator.Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.
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Method SummaryModifier and TypeMethodDescriptionbooleanAdds the specified element to this set if it is not already present.booleanaddAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this set.voidThrowsUnsupportedOperationException.voidThrowsUnsupportedOperationException.Returns the least element in this set greater than or equal to the given element, ornullif there is no such element.voidclear()Removes all of the elements from this set.clone()Returns a shallow copy of thisTreeSetinstance.Comparator<? super E> Returns the comparator used to order the elements in this set, ornullif this set uses the natural ordering of its elements.booleanReturnstrueif this set contains the specified element.Returns an iterator over the elements in this set in descending order.Returns a reverse order view of the elements contained in this set.first()Returns the first (lowest) element currently in this set.Returns the greatest element in this set less than or equal to the given element, ornullif there is no such element.Returns a view of the portion of this set whose elements are strictly less thantoElement.Returns a view of the portion of this set whose elements are less than (or equal to, ifinclusiveis true)toElement.Returns the least element in this set strictly greater than the given element, ornullif there is no such element.booleanisEmpty()Returnstrueif this set contains no elements.iterator()Returns an iterator over the elements in this set in ascending order.last()Returns the last (highest) element currently in this set.Returns the greatest element in this set strictly less than the given element, ornullif there is no such element.Retrieves and removes the first (lowest) element, or returnsnullif this set is empty (optional operation).pollLast()Retrieves and removes the last (highest) element, or returnsnullif this set is empty (optional operation).booleanRemoves the specified element from this set if it is present.intsize()Returns the number of elements in this set (its cardinality).Creates a late-binding and fail-fastSpliteratorover the elements in this set.Returns a view of the portion of this set whose elements range fromfromElementtotoElement.Returns a view of the portion of this set whose elements range fromfromElement, inclusive, totoElement, exclusive.Returns a view of the portion of this set whose elements are greater than or equal tofromElement.Returns a view of the portion of this set whose elements are greater than (or equal to, ifinclusiveis true)fromElement.Methods declared in class java.util.AbstractSetequals, hashCode, removeAllMethods declared in class java.util.AbstractCollectioncontainsAll, retainAll, toArray, toArray, toStringMethods declared in interface java.util.CollectionparallelStream, removeIf, stream, toArrayMethods declared in interface java.util.NavigableSetremoveFirst, removeLast, reversed
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Constructor Details- 
TreeSetpublic TreeSet()Constructs a new, empty tree set, sorted according to the natural ordering of its elements. All elements inserted into the set must implement theComparableinterface. Furthermore, all such elements must be mutually comparable:e1.compareTo(e2)must not throw aClassCastExceptionfor any elementse1ande2in 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), theaddcall will throw aClassCastException.
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TreeSetConstructs 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 aClassCastExceptionfor any elementse1ande2in the set. If the user attempts to add an element to the set that violates this constraint, theaddcall will throw aClassCastException.- Parameters:
- comparator- the comparator that will be used to order this set. If- null, the natural ordering of the elements will be used.
 
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TreeSetConstructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements. All elements inserted into the set must implement theComparableinterface. Furthermore, all such elements must be mutually comparable:e1.compareTo(e2)must not throw aClassCastExceptionfor any elementse1ande2in the set.- Parameters:
- c- collection whose elements will comprise the new set
- Throws:
- ClassCastException- if the elements in- care not- Comparable, or are not mutually comparable
- NullPointerException- if the specified collection is null
 
- 
TreeSetConstructs a new tree set containing the same elements and using the same ordering as the specified sorted set.- Parameters:
- s- sorted set whose elements will comprise the new set
- Throws:
- NullPointerException- if the specified sorted set is null
 
 
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Method Details- 
iteratorReturns an iterator over the elements in this set in ascending order.- Specified by:
- iteratorin interface- Collection<E>
- Specified by:
- iteratorin interface- Iterable<E>
- Specified by:
- iteratorin interface- NavigableSet<E>
- Specified by:
- iteratorin interface- Set<E>
- Specified by:
- iteratorin class- AbstractCollection<E>
- Returns:
- an iterator over the elements in this set in ascending order
 
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descendingIteratorReturns an iterator over the elements in this set in descending order.- Specified by:
- descendingIteratorin interface- NavigableSet<E>
- Returns:
- an iterator over the elements in this set in descending order
- Since:
- 1.6
 
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descendingSetDescription copied from interface:NavigableSetReturns a reverse order view of the elements contained in this set. The descending set is backed by this set, so changes to the set are reflected in the descending set, and vice-versa. If either set is modified while an iteration over either set is in progress (except through the iterator's ownremoveoperation), the results of the iteration are undefined.The returned set has an ordering equivalent to Collections.reverseOrder(comparator()). The expressions.descendingSet().descendingSet()returns a view ofsessentially equivalent tos.- Specified by:
- descendingSetin interface- NavigableSet<E>
- Returns:
- a reverse order view of this set
- Since:
- 1.6
 
- 
size
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isEmptypublic boolean isEmpty()Returnstrueif this set contains no elements.- Specified by:
- isEmptyin interface- Collection<E>
- Specified by:
- isEmptyin interface- Set<E>
- Overrides:
- isEmptyin class- AbstractCollection<E>
- Returns:
- trueif this set contains no elements
 
- 
containsReturnstrueif this set contains the specified element. More formally, returnstrueif and only if this set contains an elementesuch thatObjects.equals(o, e).- Specified by:
- containsin interface- Collection<E>
- Specified by:
- containsin interface- Set<E>
- Overrides:
- containsin class- AbstractCollection<E>
- Parameters:
- o- object to be checked for containment in this set
- Returns:
- trueif this set contains the specified 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
 
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addAdds the specified element to this set if it is not already present. More formally, adds the specified elementeto this set if the set contains no elemente2such thatObjects.equals(e, e2). If this set already contains the element, the call leaves the set unchanged and returnsfalse.- Specified by:
- addin interface- Collection<E>
- Specified by:
- addin interface- Set<E>
- Overrides:
- addin class- AbstractCollection<E>
- Parameters:
- e- element to be added to this set
- Returns:
- trueif this set did not already contain the specified 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
 
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removeRemoves the specified element from this set if it is present. More formally, removes an elementesuch thatObjects.equals(o, e), if this set contains such an element. Returnstrueif 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:
- removein interface- Collection<E>
- Specified by:
- removein interface- Set<E>
- Overrides:
- removein class- AbstractCollection<E>
- Parameters:
- o- object to be removed from this set, if present
- Returns:
- trueif this set contained the specified 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
 
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clearpublic void clear()Removes all of the elements from this set. The set will be empty after this call returns.- Specified by:
- clearin interface- Collection<E>
- Specified by:
- clearin interface- Set<E>
- Overrides:
- clearin class- AbstractCollection<E>
 
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addAllAdds all of the elements in the specified collection to this set.- Specified by:
- addAllin interface- Collection<E>
- Specified by:
- addAllin interface- Set<E>
- Overrides:
- addAllin class- AbstractCollection<E>
- Parameters:
- c- collection containing elements to be added to this set
- Returns:
- trueif this set changed as a result of the call
- Throws:
- ClassCastException- if the elements provided cannot be compared with the elements currently in the 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
- See Also:
 
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subSetpublic NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) Description copied from interface:NavigableSetReturns a view of the portion of this set whose elements range fromfromElementtotoElement. IffromElementandtoElementare equal, the returned set is empty unlessfromInclusiveandtoInclusiveare both true. 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 IllegalArgumentExceptionon an attempt to insert an element outside its range.- Specified by:
- subSetin interface- NavigableSet<E>
- Parameters:
- fromElement- low endpoint of the returned set
- fromInclusive-- trueif the low endpoint is to be included in the returned view
- toElement- high endpoint of the returned set
- toInclusive-- trueif the high endpoint is to be included in the returned view
- Returns:
- a view of the portion of this set whose elements range from
         fromElement, inclusive, totoElement, exclusive
- Throws:
- ClassCastException- if- fromElementand- toElementcannot 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- fromElementor- toElementcannot be compared to elements currently in the set.
- NullPointerException- if- fromElementor- toElementis null and this set uses natural ordering, or its comparator does not permit null elements
- IllegalArgumentException- if- fromElementis greater than- toElement; or if this set itself has a restricted range, and- fromElementor- toElementlies outside the bounds of the range.
- Since:
- 1.6
 
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headSetDescription copied from interface:NavigableSetReturns a view of the portion of this set whose elements are less than (or equal to, ifinclusiveis true)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 IllegalArgumentExceptionon an attempt to insert an element outside its range.- Specified by:
- headSetin interface- NavigableSet<E>
- Parameters:
- toElement- high endpoint of the returned set
- inclusive-- trueif the high endpoint is to be included in the returned view
- Returns:
- a view of the portion of this set whose elements are less than
         (or equal to, if inclusiveis true)toElement
- Throws:
- ClassCastException- if- toElementis not compatible with this set's comparator (or, if the set has no comparator, if- toElementdoes not implement- Comparable). Implementations may, but are not required to, throw this exception if- toElementcannot be compared to elements currently in the set.
- NullPointerException- if- toElementis 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- toElementlies outside the bounds of the range
- Since:
- 1.6
 
- 
tailSetDescription copied from interface:NavigableSetReturns a view of the portion of this set whose elements are greater than (or equal to, ifinclusiveis true)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 IllegalArgumentExceptionon an attempt to insert an element outside its range.- Specified by:
- tailSetin interface- NavigableSet<E>
- Parameters:
- fromElement- low endpoint of the returned set
- inclusive-- trueif the low endpoint is to be included in the returned view
- Returns:
- a view of the portion of this set whose elements are greater
         than or equal to fromElement
- Throws:
- ClassCastException- if- fromElementis not compatible with this set's comparator (or, if the set has no comparator, if- fromElementdoes not implement- Comparable). Implementations may, but are not required to, throw this exception if- fromElementcannot be compared to elements currently in the set.
- NullPointerException- if- fromElementis 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- fromElementlies outside the bounds of the range
- Since:
- 1.6
 
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subSetDescription copied from interface:NavigableSetReturns a view of the portion of this set whose elements range fromfromElement, inclusive, totoElement, exclusive. (IffromElementandtoElementare 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 IllegalArgumentExceptionon an attempt to insert an element outside its range.Equivalent to subSet(fromElement, true, toElement, false).- Specified by:
- subSetin interface- NavigableSet<E>
- Specified by:
- subSetin interface- SortedSet<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, totoElement, exclusive
- Throws:
- ClassCastException- if- fromElementand- toElementcannot 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- fromElementor- toElementcannot be compared to elements currently in the set.
- NullPointerException- if- fromElementor- toElementis null and this set uses natural ordering, or its comparator does not permit null elements
- IllegalArgumentException- if- fromElementis greater than- toElement; or if this set itself has a restricted range, and- fromElementor- toElementlies outside the bounds of the range
 
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headSetDescription copied from interface:NavigableSetReturns a view of the portion of this set whose elements are strictly less thantoElement. 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 IllegalArgumentExceptionon an attempt to insert an element outside its range.Equivalent to headSet(toElement, false).- Specified by:
- headSetin interface- NavigableSet<E>
- Specified by:
- headSetin interface- SortedSet<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- toElementis not compatible with this set's comparator (or, if the set has no comparator, if- toElementdoes not implement- Comparable). Implementations may, but are not required to, throw this exception if- toElementcannot be compared to elements currently in the set.
- NullPointerException- if- toElementis 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- toElementlies outside the bounds of the range
 
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tailSetDescription copied from interface:NavigableSetReturns a view of the portion of this set whose elements are greater than or equal tofromElement. 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 IllegalArgumentExceptionon an attempt to insert an element outside its range.Equivalent to tailSet(fromElement, true).- Specified by:
- tailSetin interface- NavigableSet<E>
- Specified by:
- tailSetin interface- SortedSet<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- fromElementis not compatible with this set's comparator (or, if the set has no comparator, if- fromElementdoes not implement- Comparable). Implementations may, but are not required to, throw this exception if- fromElementcannot be compared to elements currently in the set.
- NullPointerException- if- fromElementis 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- fromElementlies outside the bounds of the range
 
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comparatorDescription copied from interface:SortedSetReturns the comparator used to order the elements in this set, ornullif this set uses the natural ordering of its elements.- Specified by:
- comparatorin interface- SortedSet<E>
- Returns:
- the comparator used to order the elements in this set,
         or nullif this set uses the natural ordering of its elements
 
- 
first
- 
last
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lowerDescription copied from interface:NavigableSetReturns the greatest element in this set strictly less than the given element, ornullif there is no such element.- Specified by:
- lowerin interface- NavigableSet<E>
- Parameters:
- e- the value to match
- Returns:
- the greatest element less than e, ornullif 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
 
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floorDescription copied from interface:NavigableSetReturns the greatest element in this set less than or equal to the given element, ornullif there is no such element.- Specified by:
- floorin interface- NavigableSet<E>
- Parameters:
- e- the value to match
- Returns:
- the greatest element less than or equal to e, ornullif 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
 
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ceilingDescription copied from interface:NavigableSetReturns the least element in this set greater than or equal to the given element, ornullif there is no such element.- Specified by:
- ceilingin interface- NavigableSet<E>
- Parameters:
- e- the value to match
- Returns:
- the least element greater than or equal to e, ornullif 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
 
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higherDescription copied from interface:NavigableSetReturns the least element in this set strictly greater than the given element, ornullif there is no such element.- Specified by:
- higherin interface- NavigableSet<E>
- Parameters:
- e- the value to match
- Returns:
- the least element greater than e, ornullif 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
 
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pollFirstDescription copied from interface:NavigableSetRetrieves and removes the first (lowest) element, or returnsnullif this set is empty (optional operation).- Specified by:
- pollFirstin interface- NavigableSet<E>
- Returns:
- the first element, or nullif this set is empty
- Since:
- 1.6
 
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pollLastDescription copied from interface:NavigableSetRetrieves and removes the last (highest) element, or returnsnullif this set is empty (optional operation).- Specified by:
- pollLastin interface- NavigableSet<E>
- Returns:
- the last element, or nullif this set is empty
- Since:
- 1.6
 
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addFirstThrowsUnsupportedOperationException. The encounter order induced by this set's comparison method determines the position of elements, so explicit positioning is not supported.- Specified by:
- addFirstin interface- SequencedCollection<E>
- Specified by:
- addFirstin interface- SortedSet<E>
- Parameters:
- e- the element to be added
- Throws:
- UnsupportedOperationException- always
- Since:
- 21
 
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addLastThrowsUnsupportedOperationException. The encounter order induced by this set's comparison method determines the position of elements, so explicit positioning is not supported.- Specified by:
- addLastin interface- SequencedCollection<E>
- Specified by:
- addLastin interface- SortedSet<E>
- Parameters:
- e- the element to be added.
- Throws:
- UnsupportedOperationException- always
- Since:
- 21
 
- 
clone
- 
spliteratorCreates a late-binding and fail-fastSpliteratorover the elements in this set.The SpliteratorreportsSpliterator.SIZED,Spliterator.DISTINCT,Spliterator.SORTED, andSpliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values.The spliterator's comparator (see Spliterator.getComparator()) isnullif the tree set's comparator (seecomparator()) isnull. Otherwise, the spliterator's comparator is the same as or imposes the same total ordering as the tree set's comparator.- Specified by:
- spliteratorin interface- Collection<E>
- Specified by:
- spliteratorin interface- Iterable<E>
- Specified by:
- spliteratorin interface- Set<E>
- Specified by:
- spliteratorin interface- SortedSet<E>
- Returns:
- a Spliteratorover the elements in this set
- Since:
- 1.8
 
 
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