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- Type Parameters:
- E- the type of elements maintained by this set
 - All Superinterfaces:
- Collection<E>,- Iterable<E>,- Set<E>,- SortedSet<E>
 - All Known Implementing Classes:
- ConcurrentSkipListSet,- TreeSet
 
 public interface NavigableSet<E> extends SortedSet<E> ASortedSetextended with navigation methods reporting closest matches for given search targets. Methodslower(E),floor(E),ceiling(E), andhigher(E)return elements respectively less than, less than or equal, greater than or equal, and greater than a given element, returningnullif there is no such element.A NavigableSetmay be accessed and traversed in either ascending or descending order. ThedescendingSet()method returns a view of the set with the senses of all relational and directional methods inverted. The performance of ascending operations and views is likely to be faster than that of descending ones. This interface additionally defines methodspollFirst()andpollLast()that return and remove the lowest and highest element, if one exists, else returningnull. MethodssubSet(E, boolean, E, boolean),headSet(E, boolean), andtailSet(E, boolean)differ from the like-namedSortedSetmethods in accepting additional arguments describing whether lower and upper bounds are inclusive versus exclusive. Subsets of anyNavigableSetmust implement theNavigableSetinterface.The return values of navigation methods may be ambiguous in implementations that permit nullelements. However, even in this case the result can be disambiguated by checkingcontains(null). To avoid such issues, implementations of this interface are encouraged to not permit insertion ofnullelements. (Note that sorted sets ofComparableelements intrinsically do not permitnull.)Methods subSet(E, E),headSet(E), andtailSet(E)are specified to returnSortedSetto allow existing implementations ofSortedSetto be compatibly retrofitted to implementNavigableSet, but extensions and implementations of this interface are encouraged to override these methods to returnNavigableSet.This interface is a member of the Java Collections Framework. - Since:
- 1.6
 
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Method SummaryAll Methods Instance Methods Abstract Methods Modifier and Type Method Description Eceiling(E e)Returns the least element in this set greater than or equal to the given element, ornullif there is no such element.Iterator<E>descendingIterator()Returns an iterator over the elements in this set, in descending order.NavigableSet<E>descendingSet()Returns a reverse order view of the elements contained in this set.Efloor(E e)Returns the greatest element in this set less than or equal to the given element, ornullif there is no such element.SortedSet<E>headSet(E toElement)Returns a view of the portion of this set whose elements are strictly less thantoElement.NavigableSet<E>headSet(E toElement, boolean inclusive)Returns a view of the portion of this set whose elements are less than (or equal to, ifinclusiveis true)toElement.Ehigher(E e)Returns the least element in this set strictly greater than the given element, ornullif there is no such element.Iterator<E>iterator()Returns an iterator over the elements in this set, in ascending order.Elower(E e)Returns the greatest element in this set strictly less than the given element, ornullif there is no such element.EpollFirst()Retrieves and removes the first (lowest) element, or returnsnullif this set is empty.EpollLast()Retrieves and removes the last (highest) element, or returnsnullif this set is empty.NavigableSet<E>subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)Returns a view of the portion of this set whose elements range fromfromElementtotoElement.SortedSet<E>subSet(E fromElement, E toElement)Returns a view of the portion of this set whose elements range fromfromElement, inclusive, totoElement, exclusive.SortedSet<E>tailSet(E fromElement)Returns a view of the portion of this set whose elements are greater than or equal tofromElement.NavigableSet<E>tailSet(E fromElement, boolean inclusive)Returns a view of the portion of this set whose elements are greater than (or equal to, ifinclusiveis true)fromElement.- 
Methods declared in interface java.util.CollectionparallelStream, removeIf, stream, toArray
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Methods declared in interface java.util.Setadd, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, remove, removeAll, retainAll, size, toArray, toArray
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Methods declared in interface java.util.SortedSetcomparator, first, last, spliterator
 
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Method Detail- 
lowerE lower(E e) Returns the greatest element in this set strictly less than the given element, ornullif there is no such element.- 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 does not permit null elements
 
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floorE floor(E e) Returns the greatest element in this set less than or equal to the given element, ornullif there is no such element.- 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 does not permit null elements
 
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ceilingE ceiling(E e) Returns the least element in this set greater than or equal to the given element, ornullif there is no such element.- 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 does not permit null elements
 
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higherE higher(E e) Returns the least element in this set strictly greater than the given element, ornullif there is no such element.- 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 does not permit null elements
 
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pollFirstE pollFirst() Retrieves and removes the first (lowest) element, or returnsnullif this set is empty.- Returns:
- the first element, or nullif this set is empty
 
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pollLastE pollLast() Retrieves and removes the last (highest) element, or returnsnullif this set is empty.- Returns:
- the last element, or nullif this set is empty
 
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iteratorIterator<E> iterator() Returns an iterator over the elements in this set, in ascending order.
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descendingSetNavigableSet<E> descendingSet() Returns 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.- Returns:
- a reverse order view of this set
 
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descendingIteratorIterator<E> descendingIterator() Returns an iterator over the elements in this set, in descending order. Equivalent in effect todescendingSet().iterator().- Returns:
- an iterator over the elements in this set, in descending order
 
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subSetNavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) Returns 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.- 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 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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headSetNavigableSet<E> headSet(E toElement, boolean inclusive) Returns 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.- 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 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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tailSetNavigableSet<E> tailSet(E fromElement, boolean inclusive) Returns 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.- 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 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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subSetSortedSet<E> subSet(E fromElement, E toElement) Returns 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- 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 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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headSetSortedSet<E> headSet(E toElement) Returns 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- 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 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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tailSetSortedSet<E> tailSet(E fromElement) Returns 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- 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 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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