treemap.java

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/*
 * @(#)TreeMap.java	1.50 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.util;

/**
 * Red-Black tree based implementation of the <tt>SortedMap</tt> interface.
 * This class guarantees that the map will be in ascending key order, sorted
 * according to the <i>natural order</i> for the key's class (see
 * <tt>Comparable</tt>), or by the comparator provided at creation time,
 * depending on which constructor is used.<p>
 *
 * This implementation provides guaranteed log(n) time cost for the
 * <tt>containsKey</tt>, <tt>get</tt>, <tt>put</tt> and <tt>remove</tt>
 * operations.  Algorithms are adaptations of those in Cormen, Leiserson, and
 * Rivest's <I>Introduction to Algorithms</I>.<p>
 *
 * Note that the ordering maintained by a sorted map (whether or not an
 * explicit comparator is provided) must be <i>consistent with equals</i> if
 * this sorted map is to correctly implement the <tt>Map</tt> interface.  (See
 * <tt>Comparable</tt> or <tt>Comparator</tt> for a precise definition of
 * <i>consistent with equals</i>.)  This is so because the <tt>Map</tt>
 * interface is defined in terms of the equals operation, but a map performs
 * all key comparisons using its <tt>compareTo</tt> (or <tt>compare</tt>)
 * method, so two keys that are deemed equal by this method are, from the
 * standpoint of the sorted map, equal.  The behavior of a sorted map
 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it
 * just fails to obey the general contract of the <tt>Map</tt> interface.<p>
 *
 * <b>Note that this implementation is not synchronized.</b> If multiple
 * threads access a map concurrently, and at least one of the threads modifies
 * the map structurally, it <i>must</i> be synchronized externally.  (A
 * structural modification is any operation that adds or deletes one or more
 * mappings; merely changing the value associated with an existing key is not
 * a structural modification.)  This is typically accomplished by
 * synchronizing on some object that naturally encapsulates the map.  If no
 * such object exists, the map should be "wrapped" using the
 * <tt>Collections.synchronizedMap</tt> method.  This is best done at creation
 * time, to prevent accidental unsynchronized access to the map: 
 * <pre>
 *     Map m = Collections.synchronizedMap(new TreeMap(...));
 * </pre><p>
 *
 * The iterators returned by all of this class's "collection view methods" are
 * <i>fail-fast</i>: if the map is structurally modified at any time after the
 * iterator is created, in any way except through the iterator's own
 * <tt>remove</tt> or <tt>add</tt> methods, the iterator throws a
 * <tt>ConcurrentModificationException</tt>.  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.
 *
 * <p>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 <tt>ConcurrentModificationException</tt> on a best-effort basis. 
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:   <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i><p>
 *
 * This class is a member of the 
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author  Josh Bloch and Doug Lea
 * @version 1.43, 02/02/00
 * @see Map
 * @see HashMap
 * @see Hashtable
 * @see Comparable
 * @see Comparator
 * @see Collection
 * @see Collections#synchronizedMap(Map)
 * @since 1.2
 */

public class TreeMap extends AbstractMap
                     implements SortedMap, Cloneable, java.io.Serializable
{
    /**
     * The Comparator used to maintain order in this TreeMap, or
     * null if this TreeMap uses its elements natural ordering.
     *
     * @serial
     */
    private Comparator comparator = null;

    private transient Entry root = null;

    /**
     * The number of entries in the tree
     */
    private transient int size = 0;

    /**
     * The number of structural modifications to the tree.
     */
    private transient int modCount = 0;

    private void incrementSize()   { modCount++; size++; }
    private void decrementSize()   { modCount++; size--; }

    /**
     * Constructs a new, empty map, sorted according to the keys' natural
     * order.  All keys inserted into the map must implement the
     * <tt>Comparable</tt> interface.  Furthermore, all such keys must be
     * <i>mutually comparable</i>: <tt>k1.compareTo(k2)</tt> must not throw a
     * ClassCastException for any elements <tt>k1</tt> and <tt>k2</tt> in the
     * map.  If the user attempts to put a key into the map that violates this
     * constraint (for example, the user attempts to put a string key into a
     * map whose keys are integers), the <tt>put(Object key, Object
     * value)</tt> call will throw a <tt>ClassCastException</tt>.
     *
     * @see Comparable
     */
    public TreeMap() {
    }

    /**
     * Constructs a new, empty map, sorted according to the given comparator.
     * All keys inserted into the map must be <i>mutually comparable</i> by
     * the given comparator: <tt>comparator.compare(k1, k2)</tt> must not
     * throw a <tt>ClassCastException</tt> for any keys <tt>k1</tt> and
     * <tt>k2</tt> in the map.  If the user attempts to put a key into the
     * map that violates this constraint, the <tt>put(Object key, Object
     * value)</tt> call will throw a <tt>ClassCastException</tt>.
     *
     * @param c the comparator that will be used to sort this map.  A
     *        <tt>null</tt> value indicates that the keys' <i>natural
     *        ordering</i> should be used.
     */
    public TreeMap(Comparator c) {
        this.comparator = c;
    }

    /**
     * Constructs a new map containing the same mappings as the given map,
     * sorted according to the keys' <i>natural order</i>.  All keys inserted
     * into the new map must implement the <tt>Comparable</tt> interface.
     * Furthermore, all such keys must be <i>mutually comparable</i>:
     * <tt>k1.compareTo(k2)</tt> must not throw a <tt>ClassCastException</tt>
     * for any elements <tt>k1</tt> and <tt>k2</tt> in the map.  This method
     * runs in n*log(n) time.
     *
     * @param  m the map whose mappings are to be placed in this map.
     * @throws ClassCastException the keys in t are not Comparable, or
     *         are not mutually comparable.
     * @throws NullPointerException if the specified map is null.
     */
    public TreeMap(Map m) {
        putAll(m);
    }

    /**
     * Constructs a new map containing the same mappings as the given
     * <tt>SortedMap</tt>, sorted according to the same ordering.  This method
     * runs in linear time.
     *
     * @param  m the sorted map whose mappings are to be placed in this map,
     *         and whose comparator is to be used to sort this map.
     * @throws NullPointerException if the specified sorted map is null.
     */
    public TreeMap(SortedMap m) {
        comparator = m.comparator();
        try {
            buildFromSorted(m.size(), m.entrySet().iterator(), null, null);
        } catch (java.io.IOException cannotHappen) {
        } catch (ClassNotFoundException cannotHappen) {
        }
    }


    // Query Operations

    /**
     * Returns the number of key-value mappings in this map.
     *
     * @return the number of key-value mappings in this map.
     */
    public int size() {
        return size;
    }

    /**
     * Returns <tt>true</tt> if this map contains a mapping for the specified
     * key.
     *
     * @param key key whose presence in this map is to be tested.
     * 
     * @return <tt>true</tt> if this map contains a mapping for the
     *            specified key.
     * @throws ClassCastException if the key cannot be compared with the keys
     *                  currently in the map.
     * @throws NullPointerException key is <tt>null</tt> and this map uses
     *                  natural ordering, or its comparator does not tolerate
     *            <tt>null</tt> keys.
     */
    public boolean containsKey(Object key) {
        return getEntry(key) != null;
    }

    /**
     * Returns <tt>true</tt> if this map maps one or more keys to the
     * specified value.  More formally, returns <tt>true</tt> if and only if
     * this map contains at least one mapping to a value <tt>v</tt> such
     * that <tt>(value==null ? v==null : value.equals(v))</tt>.  This
     * operation will probably require time linear in the Map size for most
     * implementations of Map.
     *
     * @param value value whose presence in this Map is to be tested.
     * @return  <tt>true</tt> if a mapping to <tt>value</tt> exists;
     *		<tt>false</tt> otherwise.
     * @since 1.2
     */
    public boolean containsValue(Object value) {
        return (root==null ? false :
                (value==null ? valueSearchNull(root)
                             : valueSearchNonNull(root, value)));
    }

    private boolean valueSearchNull(Entry n) {
        if (n.value == null)
            return true;

        // Check left and right subtrees for value
        return (n.left  != null && valueSearchNull(n.left)) ||
               (n.right != null && valueSearchNull(n.right));
    }

    private boolean valueSearchNonNull(Entry n, Object value) {
        // Check this node for the value
        if (value.equals(n.value))
            return true;

        // Check left and right subtrees for value
        return (n.left  != null && valueSearchNonNull(n.left, value)) ||
               (n.right != null && valueSearchNonNull(n.right, value));
    }

    /**
     * Returns the value to which this map maps the specified key.  Returns
     * <tt>null</tt> if the map contains no mapping for this key.  A return
     * value of <tt>null</tt> does not <i>necessarily</i> indicate that the
     * map contains no mapping for the key; it's also possible that the map
     * explicitly maps the key to <tt>null</tt>.  The <tt>containsKey</tt>
     * operation may be used to distinguish these two cases.
     *
     * @param key key whose associated value is to be returned.
     * @return the value to which this map maps the specified key, or
     *               <tt>null</tt> if the map contains no mapping for the key.
     * @throws    ClassCastException key cannot be compared with the keys
     *                  currently in the map.
     * @throws NullPointerException key is <tt>null</tt> and this map uses
     *                  natural ordering, or its comparator does not tolerate
     *                  <tt>null</tt> keys.
     * 
     * @see #containsKey(Object)
     */
    public Object get(Object key) {
        Entry p = getEntry(key);
        return (p==null ? null : p.value);
    }

    /**
     * Returns the comparator used to order this map, or <tt>null</tt> if this
     * map uses its keys' natural order.
     *
     * @return the comparator associated with this sorted map, or
     *                <tt>null</tt> if it uses its keys' natural sort method.
     */
    public Comparator comparator() {
        return comparator;
    }

    /**
     * Returns the first (lowest) key currently in this sorted map.
     *
     * @return the first (lowest) key currently in this sorted map.
     * @throws    NoSuchElementException Map is empty.
     */
    public Object firstKey() {
        return key(firstEntry());
    }

    /**
     * Returns the last (highest) key currently in this sorted map.
     *
     * @return the last (highest) key currently in this sorted map.
     * @throws    NoSuchElementException Map is empty.
     */
    public Object lastKey() {
        return key(lastEntry());
    }

    /**
     * Copies all of the mappings from the specified map to this map.  These
     * mappings replace any mappings that this map had for any of the keys
     * currently in the specified map.
     *
     * @param     map mappings to be stored in this map.
     * @throws    ClassCastException class of a key or value in the specified
     *                   map prevents it from being stored in this map.
     * 
     * @throws NullPointerException if the given map is <tt>null</tt> or
     *         this map does not permit <tt>null</tt> keys and a 
     *         key in the specified map is <tt>null</tt>.
     */
    public void putAll(Map map) {
        int mapSize = map.size();
        if (size==0 && mapSize!=0 && map instanceof SortedMap) {
            Comparator c = ((SortedMap)map).comparator();
            if (c == comparator || (c != null && c.equals(comparator))) {
              ++modCount;
              try {
                  buildFromSorted(mapSize, map.entrySet().iterator(),
                                  null, null);
              } catch (java.io.IOException cannotHappen) {
              } catch (ClassNotFoundException cannotHappen) {
              }
              return;
            }
        }
        super.putAll(map);
    }

    /**
     * Returns this map's entry for the given key, or <tt>null</tt> if the map
     * does not contain an entry for the key.
     *
     * @return this map's entry for the given key, or <tt>null</tt> if the map
     *                does not contain an entry for the key.
     * @throws ClassCastException if the key cannot be compared with the keys
     *                  currently in the map.
     * @throws NullPointerException key is <tt>null</tt> and this map uses
     *                  natural order, or its comparator does not tolerate *
     *                  <tt>null</tt> keys.
     */
    private Entry getEntry(Object key) {
        Entry p = root;
        while (p != null) {
            int cmp = compare(key,p.key);
            if (cmp == 0)
                return p;
            else if (cmp < 0)
                p = p.left;
            else
                p = p.right;
        }
        return null;
    }

    /**
     * Gets the entry corresponding to the specified key; if no such entry
     * exists, returns the entry for the least key greater than the specified
     * key; if no such entry exists (i.e., the greatest key in the Tree is less
     * than the specified key), returns <tt>null</tt>.
     */
    private Entry getCeilEntry(Object key) {
        Entry p = root;
        if (p==null)
            return null;

        while (true) {
            int cmp = compare(key, p.key);
            if (cmp == 0) {
                return p;
            } else if (cmp < 0) {
                if (p.left != null)
                    p = p.left;
                else
                    return p;
            } else {
                if (p.right != null) {
                    p = p.right;
                } else {
                    Entry parent = p.parent;
                    Entry ch = p;
                    while (parent != null && ch == parent.right) {
                        ch = parent;
                        parent = parent.parent;
                    }
                    return parent;
                }
            }
        }
    }

    /**
     * Returns the entry for the greatest key less than the specified key; if
     * no such entry exists (i.e., the least key in the Tree is greater than
     * the specified key), returns <tt>null</tt>.