NavigableSet.java

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea and Josh Bloch with assistance from members of JCP
 * JSR-166 Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util;

/**
 * A {@link SortedSet} extended with navigation methods reporting
 * closest matches for given search targets. Methods {@link #lower},
 * {@link #floor}, {@link #ceiling}, and {@link #higher} return elements
 * respectively less than, less than or equal, greater than or equal,
 * and greater than a given element, returning {@code null} if there
 * is no such element.
 *
 * <p>A {@code NavigableSet} may be accessed and traversed in either
 * ascending or descending order.  The {@link #descendingSet} 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 methods {@link
 * #pollFirst} and {@link #pollLast} that return and remove the lowest
 * and highest element, if one exists, else returning {@code null}.
 * Methods
 * {@link #subSet(Object, boolean, Object, boolean) subSet(E, boolean, E, boolean)},
 * {@link #headSet(Object, boolean) headSet(E, boolean)}, and
 * {@link #tailSet(Object, boolean) tailSet(E, boolean)}
 * differ from the like-named {@code SortedSet} methods in accepting
 * additional arguments describing whether lower and upper bounds are
 * inclusive versus exclusive.  Subsets of any {@code NavigableSet}
 * must implement the {@code NavigableSet} interface.
 *
 * <p>The return values of navigation methods may be ambiguous in
 * implementations that permit {@code null} elements. However, even
 * in this case the result can be disambiguated by checking
 * {@code contains(null)}. To avoid such issues, implementations of
 * this interface are encouraged to <em>not</em> permit insertion of
 * {@code null} elements. (Note that sorted sets of {@link
 * Comparable} elements intrinsically do not permit {@code null}.)
 *
 * <p>Methods
 * {@link #subSet(Object, Object) subSet(E, E)},
 * {@link #headSet(Object) headSet(E)}, and
 * {@link #tailSet(Object) tailSet(E)}
 * are specified to return {@code SortedSet} to allow existing
 * implementations of {@code SortedSet} to be compatibly retrofitted to
 * implement {@code NavigableSet}, but extensions and implementations
 * of this interface are encouraged to override these methods to return
 * {@code NavigableSet}.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @author Doug Lea
 * @author Josh Bloch
 * @param <E> the type of elements maintained by this set
 * @since 1.6
 */
// 可导航的Set，要求Set必须有序，支持定位元素的起点/终点和前驱/后继，以及截取子视图
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
     */
    // 〖前驱〗获取遍历当前Set时形参e的前驱
    E lower(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
     */
    // 〖后继〗获取遍历当前Set时形参e的后继
    E higher(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
     */
    // 【前驱】获取遍历当前Set时形参e的前驱（包括e本身）
    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
     */
    // 【后继】获取遍历当前Set时形参e的后继（包括e本身）
    E ceiling(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
     */
    // 移除遍历当前Set时的首个元素（及其关联的内容）
    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
     */
    // 移除遍历当前Set时的最后一个元素（及其关联的内容）
    E pollLast();
    
    
    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code subSet(fromElement, true, toElement, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    // 获取【理论区间】为[fromElement, toElement)的Set
    SortedSet<E> subSet(E fromElement, E toElement);
    
    /**
     * 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.
     */
    // 获取【理论区间】为〖fromElement, toElement〗的Set，区间下限/上限是否为闭区间由fromInclusive和toInclusive参数决定
    NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive);
    
    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code headSet(toElement, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    // 获取【理论区间】上限为toElement(不包含)的Set
    SortedSet<E> headSet(E toElement);
    
    /**
     * 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
     */
    // 获取【理论区间】上限为toElement的Set，区间上限是否为闭区间由inclusive参数决定
    NavigableSet<E> headSet(E toElement, boolean inclusive);
    
    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code tailSet(fromElement, true)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    // 获取【理论区间】下限为fromElement(包含)的Set
    SortedSet<E> tailSet(E fromElement);
    
    /**
     * 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
     */
    // 获取【理论区间】下限为fromElement的Set，区间下限是否为闭区间由inclusive参数决定
    NavigableSet<E> tailSet(E fromElement, boolean inclusive);
    
    
    /**
     * 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
     * {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}{@code (comparator())}.
     * 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
     */
    // 获取【逆序】Set
    NavigableSet<E> descendingSet();
    
    
    /**
     * Returns an iterator over the elements in this set, in ascending order.
     *
     * @return an iterator over the elements in this set, in ascending order
     */
    // 返回当前Set的Iterator
    Iterator<E> iterator();
    
    /**
     * 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
     */
    // 返回【逆序】Set的Iterator
    Iterator<E> descendingIterator();
    
}