NavigableSet
为了TreeSet做准备，增加了获取第一个，最后一个，小于x，大于x等节点的操作，以及正向和逆向的迭代器
package java.util;
public interface NavigableSet<E> extends SortedSet<E> {
/**
* Returns the greatest element in this set strictly less than the
* given element, or {@code null} if there is no such element.
*
* @param e the value to match
* @return the greatest element less than {@code e},
* or {@code null} if there is no such element
* @throws ClassCastException if the specified element cannot be
* compared with the elements currently in the set
* @throws NullPointerException if the specified element is null
* and this set does not permit null elements
*/
E lower(E e);
/**
* Returns the greatest element in this set less than or equal to
* the given element, or {@code null} if there is no such element.
*
* @param e the value to match
* @return the greatest element less than or equal to {@code e},
* or {@code null} if there is no such element
* @throws ClassCastException if the specified element cannot be
* compared with the elements currently in the set
* @throws NullPointerException if the specified element is null
* and this set does not permit null elements
*/
E floor(E e);
/**
* Returns the least element in this set greater than or equal to
* the given element, or {@code null} if there is no such element.
*
* @param e the value to match
* @return the least element greater than or equal to {@code e},
* or {@code null} if there is no such element
* @throws ClassCastException if the specified element cannot be
* compared with the elements currently in the set
* @throws NullPointerException if the specified element is null
* and this set does not permit null elements
*/
E ceiling(E e);
/**
* Returns the least element in this set strictly greater than the
* given element, or {@code null} if there is no such element.
*
* @param e the value to match
* @return the least element greater than {@code e},
* or {@code null} if there is no such element
* @throws ClassCastException if the specified element cannot be
* compared with the elements currently in the set
* @throws NullPointerException if the specified element is null
* and this set does not permit null elements
*/
E higher(E e);
/**
* Retrieves and removes the first (lowest) element,
* or returns {@code null} if this set is empty.
*
* @return the first element, or {@code null} if this set is empty
*/
E pollFirst();
/**
* Retrieves and removes the last (highest) element,
* or returns {@code null} if this set is empty.
*
* @return the last element, or {@code null} if this set is empty
*/
E pollLast();
/**
* Returns an iterator over the elements in this set, in ascending order.
*
* @return an iterator over the elements in this set, in ascending order
*/
Iterator<E> iterator();
/**
* 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 {@code remove} operation), the results of
* the iteration are undefined.
*
* <p>The returned set has an ordering equivalent to
* <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.
* The expression {@code s.descendingSet().descendingSet()} returns a
* view of {@code s} essentially equivalent to {@code s}.
*
* @return a reverse order view of this set
*/
NavigableSet<E> descendingSet();
/**
* Returns an iterator over the elements in this set, in descending order.
* Equivalent in effect to {@code descendingSet().iterator()}.
*
* @return an iterator over the elements in this set, in descending order
*/
Iterator<E> descendingIterator();
/**
* Returns a view of the portion of this set whose elements range from
* {@code fromElement} to {@code toElement}. If {@code fromElement} and
* {@code toElement} are equal, the returned set is empty unless {@code
* fromInclusive} and {@code toInclusive} 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.
*
* <p>The returned set will throw an {@code IllegalArgumentException}
* on an attempt to insert an element outside its range.
*
* @param fromElement low endpoint of the returned set
* @param fromInclusive {@code true} if the low endpoint
* is to be included in the returned view
* @param toElement high endpoint of the returned set
* @param toInclusive {@code true} if the high endpoint
* is to be included in the returned view
* @return a view of the portion of this set whose elements range from
* {@code fromElement}, inclusive, to {@code toElement}, exclusive
* @throws ClassCastException if {@code fromElement} and
* {@code 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 {@code fromElement} or
* {@code toElement} cannot be compared to elements currently in
* the set.
* @throws NullPointerException if {@code fromElement} or
* {@code toElement} is null and this set does
* not permit null elements
* @throws IllegalArgumentException if {@code fromElement} is
* greater than {@code toElement}; or if this set itself
* has a restricted range, and {@code fromElement} or
* {@code toElement} lies outside the bounds of the range.
*/
NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
E toElement, boolean toInclusive);
/**
* Returns a view of the portion of this set whose elements are less than
* (or equal to, if {@code inclusive} is true) {@code 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.
*
* <p>The returned set will throw an {@code IllegalArgumentException}
* on an attempt to insert an element outside its range.
*
* @param toElement high endpoint of the returned set
* @param inclusive {@code true} if the high endpoint
* is to be included in the returned view
* @return a view of the portion of this set whose elements are less than
* (or equal to, if {@code inclusive} is true) {@code toElement}
* @throws ClassCastException if {@code toElement} is not compatible
* with this set's comparator (or, if the set has no comparator,
* if {@code toElement} does not implement {@link Comparable}).
* Implementations may, but are not required to, throw this
* exception if {@code toElement} cannot be compared to elements
* currently in the set.
* @throws NullPointerException if {@code toElement} is null and
* this set does not permit null elements
* @throws IllegalArgumentException if this set itself has a
* restricted range, and {@code toElement} lies outside the
* bounds of the range
*/
NavigableSet<E> headSet(E toElement, boolean inclusive);
/**
* Returns a view of the portion of this set whose elements are greater
* than (or equal to, if {@code inclusive} is true) {@code 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.
*
* <p>The returned set will throw an {@code IllegalArgumentException}
* on an attempt to insert an element outside its range.
*
* @param fromElement low endpoint of the returned set
* @param inclusive {@code true} if the low endpoint
* is to be included in the returned view
* @return a view of the portion of this set whose elements are greater
* than or equal to {@code fromElement}
* @throws ClassCastException if {@code fromElement} is not compatible
* with this set's comparator (or, if the set has no comparator,
* if {@code fromElement} does not implement {@link Comparable}).
* Implementations may, but are not required to, throw this
* exception if {@code fromElement} cannot be compared to elements
* currently in the set.
* @throws NullPointerException if {@code fromElement} is null
* and this set does not permit null elements
* @throws IllegalArgumentException if this set itself has a
* restricted range, and {@code fromElement} lies outside the
* bounds of the range
*/
NavigableSet<E> tailSet(E fromElement, boolean inclusive);
/**
* {@inheritDoc}
*
* <p>Equivalent to {@code subSet(fromElement, true, toElement, false)}.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
SortedSet<E> subSet(E fromElement, E toElement);
/**
* {@inheritDoc}
*
* <p>Equivalent to {@code headSet(toElement, false)}.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
na */
SortedSet<E> headSet(E toElement);
/**
* {@inheritDoc}
*
* <p>Equivalent to {@code tailSet(fromElement, true)}.
*
* @throws ClassCastException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
SortedSet<E> tailSet(E fromElement);
}