Package java.util

Class TreeSet<E>

java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractSet<E>
java.util.TreeSet<E>
All Implemented Interfaces:
Serializable, Cloneable, Iterable<E>, Collection<E>, NavigableSet<E>, Set<E>, SortedSet<E>
public class TreeSet<E>
extends AbstractSet<E>
implements NavigableSet<E>, Cloneable, Serializable
TreeSet is an implementation of SortedSet. All optional operations (adding and removing) are supported. The elements can be any objects which are comparable to each other either using their natural order or a specified Comparator.
Since:
1.2
See Also:
Serialized Form

  • Constructor Summary

    Constructors
    Constructor Description
    TreeSet()
    Constructs a new empty instance of TreeSet which uses natural ordering.
    TreeSet​(Collection<? extends E> collection)
    Constructs a new instance of TreeSet which uses natural ordering and containing the unique elements in the specified collection.
    TreeSet​(Comparator<? super E> comparator)
    Constructs a new empty instance of TreeSet which uses the specified comparator.
    TreeSet​(SortedSet<E> set)
    Constructs a new instance of TreeSet containing the elements of the specified SortedSet and using the same Comparator.

  • Method Summary

    Modifier and Type Method Description
    boolean add​(E object)
    Adds the specified object to this TreeSet.
    boolean addAll​(Collection<? extends E> collection)
    Adds the objects in the specified collection to this TreeSet.
    E ceiling​(E 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 elements from this TreeSet, leaving it empty.
    Object clone()
    Returns a new TreeSet with the same elements, size and comparator as this TreeSet.
    Comparator<? super E> comparator()
    Returns the comparator used to compare elements in this TreeSet.
    boolean contains​(Object object)
    Searches this TreeSet for the specified object.
    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.
    E first()
    Returns the first element in this set.
    E floor​(E 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 end)
    Returns a SortedSet of the specified portion of this TreeSet which contains elements less than the end element.
    NavigableSet<E> headSet​(E end, boolean endInclusive)
    Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.
    E higher​(E 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 TreeSet has no element, otherwise false.
    Iterator<E> iterator()
    Returns an Iterator on the elements of this TreeSet.
    E last()
    Returns the last element in this set.
    E lower​(E e)
    Returns the greatest element in this set strictly less than the given element, or null if there is no such element.
    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 object)
    Removes an occurrence of the specified object from this TreeSet.
    int size()
    Returns the number of elements in this TreeSet.
    NavigableSet<E> subSet​(E start, boolean startInclusive, E end, boolean endInclusive)
    Returns a view of the portion of this set whose elements range from fromElement to toElement.
    SortedSet<E> subSet​(E start, E end)
    Returns a SortedSet of the specified portion of this TreeSet which contains elements greater or equal to the start element but less than the end element.
    SortedSet<E> tailSet​(E start)
    Returns a SortedSet of the specified portion of this TreeSet which contains elements greater or equal to the start element.
    NavigableSet<E> tailSet​(E start, boolean startInclusive)
    Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement.

    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 Details

    • TreeSet

      public TreeSet()
      Constructs a new empty instance of TreeSet which uses natural ordering.

    • TreeSet

      public TreeSet​(Collection<? extends E> collection)
      Constructs a new instance of TreeSet which uses natural ordering and containing the unique elements in the specified collection.
      Parameters:
      collection - the collection of elements to add.
      Throws:
      ClassCastException - when an element in the collection does not implement the Comparable interface, or the elements in the collection cannot be compared.

    • TreeSet

      public TreeSet​(Comparator<? super E> comparator)
      Constructs a new empty instance of TreeSet which uses the specified comparator.
      Parameters:
      comparator - the comparator to use.

    • TreeSet

      public TreeSet​(SortedSet<E> set)
      Constructs a new instance of TreeSet containing the elements of the specified SortedSet and using the same Comparator.
      Parameters:
      set - the SortedSet of elements to add.

  • Method Details

    • add

      public boolean add​(E object)
      Adds the specified object to this TreeSet.
      Specified by:
      add in interface Collection<E>
      Specified by:
      add in interface Set<E>
      Overrides:
      add in class AbstractCollection<E>
      Parameters:
      object - the object to add.
      Returns:
      true when this TreeSet did not already contain the object, false otherwise.
      Throws:
      ClassCastException - when the object cannot be compared with the elements in this TreeSet.
      NullPointerException - when the object is null and the comparator cannot handle null.

    • addAll

      public boolean addAll​(Collection<? extends E> collection)
      Adds the objects in the specified collection to this TreeSet.
      Specified by:
      addAll in interface Collection<E>
      Specified by:
      addAll in interface Set<E>
      Overrides:
      addAll in class AbstractCollection<E>
      Parameters:
      collection - the collection of objects to add.
      Returns:
      true if this TreeSet was modified, false otherwise.
      Throws:
      ClassCastException - when an object in the collection cannot be compared with the elements in this TreeSet.
      NullPointerException - when an object in the collection is null and the comparator cannot handle null.

    • clear

      public void clear()
      Removes all elements from this TreeSet, leaving it empty.
      Specified by:
      clear in interface Collection<E>
      Specified by:
      clear in interface Set<E>
      Overrides:
      clear in class AbstractCollection<E>
      See Also:
      isEmpty(), size()

    • clone

      public Object clone()
      Returns a new TreeSet with the same elements, size and comparator as this TreeSet.
      Overrides:
      clone in class Object
      Returns:
      a shallow copy of this TreeSet.
      See Also:
      Cloneable

    • comparator

      public Comparator<? super E> comparator()
      Returns the comparator used to compare elements in this TreeSet.
      Specified by:
      comparator in interface SortedSet<E>
      Returns:
      a Comparator or null if the natural ordering is used

    • contains

      public boolean contains​(Object object)
      Searches this TreeSet for the specified object.
      Specified by:
      contains in interface Collection<E>
      Specified by:
      contains in interface Set<E>
      Overrides:
      contains in class AbstractCollection<E>
      Parameters:
      object - the object to search for.
      Returns:
      true if object is an element of this TreeSet, false otherwise.
      Throws:
      ClassCastException - when the object cannot be compared with the elements in this TreeSet.
      NullPointerException - when the object is null and the comparator cannot handle null.

    • isEmpty

      public boolean isEmpty()
      Returns true if this TreeSet has no element, otherwise false.
      Specified by:
      isEmpty in interface Collection<E>
      Specified by:
      isEmpty in interface Set<E>
      Overrides:
      isEmpty in class AbstractCollection<E>
      Returns:
      true if this TreeSet has no element.
      See Also:
      size()

    • iterator

      public Iterator<E> iterator()
      Returns an Iterator on the elements of this TreeSet.
      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<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 on the elements of this TreeSet.
      See Also:
      Iterator

    • descendingIterator

      public Iterator<E> descendingIterator()
      Returns an iterator over the elements in this set, in descending order. Equivalent in effect to descendingSet().iterator().
      Specified by:
      descendingIterator in interface NavigableSet<E>
      Returns:
      an iterator over the elements in this set, in descending order
      Since:
      1.6
      See Also:
      NavigableSet.descendingIterator()

    • remove

      public boolean remove​(Object object)
      Removes an occurrence of the specified object from this TreeSet.
      Specified by:
      remove in interface Collection<E>
      Specified by:
      remove in interface Set<E>
      Overrides:
      remove in class AbstractCollection<E>
      Parameters:
      object - the object to remove.
      Returns:
      true if this TreeSet was modified, false otherwise.
      Throws:
      ClassCastException - when the object cannot be compared with the elements in this TreeSet.
      NullPointerException - when the object is null and the comparator cannot handle null.

    • size

      public int size()
      Returns the number of elements in this TreeSet.
      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 TreeSet.

    • first

      public E first()
      Returns the first element in this set.
      Specified by:
      first in interface SortedSet<E>
      Returns:
      the first element.
      Throws:
      NoSuchElementException - when this TreeSet is empty

    • last

      public E last()
      Returns the last element in this set.
      Specified by:
      last in interface SortedSet<E>
      Returns:
      the last element.
      Throws:
      NoSuchElementException - when this TreeSet is empty

    • pollFirst

      public E pollFirst()
      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
      See Also:
      NavigableSet.pollFirst()

    • pollLast

      public E pollLast()
      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
      See Also:
      NavigableSet.pollLast()

    • higher

      public E higher​(E e)
      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
      Since:
      1.6
      See Also:
      NavigableSet.higher(java.lang.Object)

    • lower

      public E lower​(E e)
      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
      Since:
      1.6
      See Also:
      NavigableSet.lower(java.lang.Object)

    • ceiling

      public E ceiling​(E e)
      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
      Since:
      1.6
      See Also:
      NavigableSet.ceiling(java.lang.Object)

    • floor

      public E floor​(E e)
      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
      Since:
      1.6
      See Also:
      NavigableSet.floor(java.lang.Object)

    • descendingSet

      public NavigableSet<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 own remove operation), the results of the iteration are undefined.

      The returned set has an ordering equivalent to Collections.reverseOrder(comparator()). The expression s.descendingSet().descendingSet() returns a view of s essentially equivalent to s.

      Specified by:
      descendingSet in interface NavigableSet<E>
      Returns:
      a reverse order view of this set
      Since:
      1.6
      See Also:
      NavigableSet.descendingSet()

    • subSet

      public NavigableSet<E> subSet​(E start, boolean startInclusive, E end, boolean endInclusive)
      Returns a view of the portion of this set whose elements range from fromElement to toElement. If fromElement and toElement are equal, the returned set is empty unless fromExclusive and toExclusive are 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 IllegalArgumentException on an attempt to insert an element outside its range.

      Specified by:
      subSet in interface NavigableSet<E>
      Parameters:
      start - low endpoint of the returned set
      startInclusive - true if the low endpoint is to be included in the returned view
      end - high endpoint of the returned set
      endInclusive - true if 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, to toElement, exclusive
      Since:
      1.6
      See Also:
      NavigableSet.subSet(Object, boolean, Object, boolean)

    • headSet

      public NavigableSet<E> headSet​(E end, boolean endInclusive)
      Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is 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 IllegalArgumentException on an attempt to insert an element outside its range.

      Specified by:
      headSet in interface NavigableSet<E>
      Parameters:
      end - high endpoint of the returned set
      endInclusive - true if 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 inclusive is true) toElement
      Since:
      1.6
      See Also:
      NavigableSet.headSet(Object, boolean)

    • tailSet

      public NavigableSet<E> tailSet​(E start, boolean startInclusive)
      Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is 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 IllegalArgumentException on an attempt to insert an element outside its range.

      Specified by:
      tailSet in interface NavigableSet<E>
      Parameters:
      start - low endpoint of the returned set
      startInclusive - true if 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
      Since:
      1.6
      See Also:
      NavigableSet.tailSet(Object, boolean)

    • subSet

      public SortedSet<E> subSet​(E start, E end)
      Returns a SortedSet of the specified portion of this TreeSet which contains elements greater or equal to the start element but less than the end element. The returned SortedSet is backed by this TreeSet so changes to one are reflected by the other.
      Specified by:
      subSet in interface NavigableSet<E>
      Specified by:
      subSet in interface SortedSet<E>
      Parameters:
      start - the start element
      end - the end element
      Returns:
      a subset where the elements are greater or equal to start and less than end
      Throws:
      ClassCastException - when the start or end object cannot be compared with the elements in this TreeSet
      NullPointerException - when the start or end object is null and the comparator cannot handle null

    • headSet

      public SortedSet<E> headSet​(E end)
      Returns a SortedSet of the specified portion of this TreeSet which contains elements less than the end element. The returned SortedSet is backed by this TreeSet so changes to one are reflected by the other.
      Specified by:
      headSet in interface NavigableSet<E>
      Specified by:
      headSet in interface SortedSet<E>
      Parameters:
      end - the end element
      Returns:
      a subset where the elements are less than end
      Throws:
      ClassCastException - when the end object cannot be compared with the elements in this TreeSet
      NullPointerException - when the end object is null and the comparator cannot handle null

    • tailSet

      public SortedSet<E> tailSet​(E start)
      Returns a SortedSet of the specified portion of this TreeSet which contains elements greater or equal to the start element. The returned SortedSet is backed by this TreeSet so changes to one are reflected by the other.
      Specified by:
      tailSet in interface NavigableSet<E>
      Specified by:
      tailSet in interface SortedSet<E>
      Parameters:
      start - the start element
      Returns:
      a subset where the elements are greater or equal to start
      Throws:
      ClassCastException - when the start object cannot be compared with the elements in this TreeSet
      NullPointerException - when the start object is null and the comparator cannot handle null