ActiveX Programming Unleashed CD/AXU.iso/jgl_1_1/jgl_1_1.exe/src/OrderedMap.java

Java Source | 1996-09-10 | 15.1 KB | 474 lines

// Copyright(c) 1996 ObjectSpace, Inc.
// Portions Copyright(c) 1995, 1996 Hewlett-Packard Company.

package jgl;

import java.util.Dictionary;
import java.util.Enumeration;

/**
 * An OrderedMap is an associative container that manages a set of ordered key/value pairs.
 * The pairs are ordered by key, using a comparator. By default, a HashComparator is used,
 * which orders keys based on their hash value. By default, only one value may be associated with
 * a particular key. A OrderedMap's underlying data structure allows you to very efficiently
 * find all of the values associated with a particular key.
 * <p>
 * A OrderedMap is useful for implementing a collection of one-to-one or one-to-many mappings.
 * <p>
 * Strictly speaking, there is no reason why null is not a valid key. However, most
 * comparators (including the default HashComparator) will fail and throw an exception
 * if you attempt to add a null key because they cast the key to a class and then
 * activate one of its methods. It is perfectly possible to hand-craft a comparator
 * that will accept null as a valid key.
 * <p>
 * There are many different approaches that could be used to implementing an associative
 * container. For example, most of the older libraries used a hashing scheme for
 * positioning and retrieving items. This implementation use a data structure called a
 * red-black tree. A red-black tree is a binary search tree that uses an extra field in
 * every node to store the node's color. Red-black trees constrain the way that nodes may
 * be colored in such a way that the tree remains reasonably balanced. This property is
 * important for ensuring a good overall performance - red-black trees guarantee that the
 * worst case performance for the most common dynamic set operations is O(log N). One
 * conseqence of using a binary tree for storage of data is that the items remain in a
 * sorted order. This allows JGL users to iterate through an associative container and
 * access its elements in a sequenced manner. Each node of the red-black tree holds a
 * Pair( key, value ). The comparator is used to order the Pairs based only on their keys.
 * <p>
 * Insertion does not affect iterators or references.
 * <p>
 * Removal only invalidates the iterators and references to the removed elements.
 * <p>
 * @see jgl.OrderedMultimap
 * @see jgl.BinaryPredicate
 * @see jgl.examples.OrderedMapExamples
 * @version 1.1
 * @author ObjectSpace, Inc.
 */

public class OrderedMap extends Dictionary implements Container
  {
  Tree myTree;

  /**
   * Construct myself to be an empty OrderedMap that orders its keys based on
   * their hash value and does not allow duplicates.
   */
  public OrderedMap()
    {
    myTree = new Tree( true, false, this );
    }

  /**
   * Construct myself to be an empty OrderedMap that orders its keys based on
   * their hash value and conditionally allows duplicates.
   * @param allowDuplicates true if duplicates are allowed.
   */
  public OrderedMap( boolean allowDuplicates )
    {
    myTree = new Tree( true, allowDuplicates, this );
    }


  /**
   * Construct myself to be an empty OrderedMap that orders its keys using
   * a specified binary predicate and does not allow duplicates.
   * @param comparator The predicate for ordering keys.
   */
  public OrderedMap( BinaryPredicate comparator )
    {
    myTree = new Tree( true, false, comparator, this );
    }

  /**
   * Construct myself to be an empty OrderedMap that orders its keys using
   * a specified binary predicate and conditionally allows duplicates.
   * @param comparator The predicate for ordering keys.
   * @param allowDuplicates true if duplicates are allowed.
   */
  public OrderedMap( BinaryPredicate comparator, boolean allowDuplicates )
    {
    myTree = new Tree( true, allowDuplicates, comparator, this );
    }

  /**
   * Construct myself to be a shallow copy of an existing OrderedMap.
   * @param map The OrderedMap to copy.
   */
  public OrderedMap( OrderedMap map )
    {
    myTree = new Tree( map.myTree );
    }

  /**
   * Return true if duplicates are allowed.
   */
  public boolean allowsDuplicates()
    {
    return myTree.myInsertAlways;
    }

  /**
   * Return a shallow copy of myself.
   */
  public synchronized Object clone()
    {
    return new OrderedMap( this );
    }

  /**
   * Become a shallow copy of an existing OrderedMap.
   * @param map The OrderedMap that I shall become a shallow copy of.
   */
  public synchronized void copy( OrderedMap map )
    {
    myTree.copy( map.myTree );
    }

  /**
   * Return a string that describes me.
   */
  public synchronized String toString()
    {
    return Printing.toString( this, "OrderedMap" );
    }

  /**
   * Return an Enumeration of my values
   */
  public synchronized Enumeration elements()
    {
    return myTree.beginMap( OrderedMapIterator.VALUE );
    }

  /**
   * Return an iterator positioned at my first pair.
   */
  public synchronized ForwardIterator start()
    {
    return myTree.beginMap( OrderedMapIterator.PAIR );
    }

  /**
   * Return an iterator positioned immediately afer my last pair.
   */
  public synchronized ForwardIterator finish()
    {
    return myTree.endMap( OrderedMapIterator.PAIR );
    }

  /**
   * Return an iterator positioned at my first pair.
   */
  public synchronized OrderedMapIterator begin()
    {
    return myTree.beginMap( OrderedMapIterator.PAIR );
    }

  /**
   * Return an iterator positioned immediately after my last pair.
   */
  public synchronized OrderedMapIterator end()
    {
    return myTree.endMap( OrderedMapIterator.PAIR );
    }

  /**
   * Return true if I contain no entries.
   */
  public boolean isEmpty()
    {
    return myTree.size == 0;
    }

  /**
   * Return the number of entries that I contain.
   */
  public int size()
    {
    return myTree.size;
    }

  /**
   * Return the maximum number of entries that I can contain.
   */
  public int maxSize()
    {
    return myTree.maxSize();
    }

  /**
   * Return true if I'm equal to another object.
   * @param object The object to compare myself against.
   */
  public boolean equals( Object object )
    {
    return object instanceof OrderedMap && equals( (OrderedMap) object );
    }

  /**
   * Return true if I contain the same items in the same order as
   * another OrderedMap. Use equals() to compare the individual elements.
   * @param map The OrderedMap to compare myself against.
   */
  public synchronized boolean equals( OrderedMap map )
    {
    return Comparing.equal( this, map );
    }

  /**
   * Return my hash code for support of hashing containers
   */
  public int hashCode()
    {
    ForwardIterator start = myTree.beginMap( OrderedMapIterator.KEY );
    ForwardIterator end = myTree.endMap( OrderedMapIterator.KEY );
    return Hashing.orderedHash( start, end );
    }

  /**
   * Swap my contents with another OrderedMap.
   * @param map The OrderedMap that I will swap my contents with.
   */
  public synchronized void swap( OrderedMap map )
    {
    Tree tmp = myTree;
    myTree = map.myTree;
    map.myTree = tmp;
    }

  /**
   * Remove all of my elements.
   */
  public synchronized void clear()
    {
    myTree.clear();
    }

  /**
   * If I contain key/value pair(s) that matches a particular key,
   * remove them and return the value of the first key removed, otherwise return null.
   * @param key The key of the pair(s) to be removed.
   * @return The value that was removed or null if none.
   */
  public synchronized Object remove( Object key )
    {
    return myTree.remove( key );
    }

  /**
   * Remove the element at a particular position and return its value.
   * @param pos An Enumeration positioned at the element to remove.
   * @return The value that was removed or null if none.
   * @exception IllegalArgumentException is the Enumeration isn't an
   * OrderedMapIterator for this OrderedMap object.
   */
  public synchronized Object remove( Enumeration pos )
    {
    if( ! (pos instanceof OrderedMapIterator) )
      throw new IllegalArgumentException( "Enumeration not an OrderedMapIterator" );

    if( ((OrderedMapIterator)pos).myOrderedMap != this )
      throw new IllegalArgumentException( "Enumeration not for this OrderedMap" );

    TreeNode node = myTree.remove( ((OrderedMapIterator)pos).myNode );
    return ( node == null ? null : node.object );
    }

  /**
   * Remove the elements within a specified range, returning the first value
   * of the key in that range.
   * @param first An iterator positioned at the first element to remove.
   * @param last An iterator positioned immediately after the last element to remove.
   * @exception IllegalArgumentException is the Enumeration isn't an
   * OrderedMapIterator for this OrderedMap object.
   */
  public synchronized Object remove( Enumeration first, Enumeration last )
    {
    if( ( ! (first instanceof OrderedMapIterator) ) ||
        ( ! (last instanceof OrderedMapIterator) ) )
      throw new IllegalArgumentException( "Enumeration not an OrderedMapIterator" );

    if( ( ((OrderedMapIterator)first).myOrderedMap != this ) ||
        ( ((OrderedMapIterator)last).myOrderedMap != this ) )
      throw new IllegalArgumentException( "Enumeration not for this OrderedMap" );

    return myTree.remove( ((OrderedMapIterator)first).myNode,
                          ((OrderedMapIterator)last).myNode );
    }

  /**
   * Find a key/value pair based on its key and return its position.
   * If the pair is not found, return end().
   * @param object The object to locate.
   */
  public synchronized OrderedMapIterator find( Object key )
    {
    return new OrderedMapIterator( myTree, myTree.find( key ), this, OrderedMapIterator.PAIR );
    }

  /**
   * Return the number of key/value pairs that match a particular key.
   * @param key The key to match against.
   */
  public synchronized int count( Object key )
    {
    return myTree.count( key );
    }

  /**
   * Return the number of values that match a given object.
   * @param value The value to match against.
   */
  public synchronized int countValues( Object value )
    {
    return Counting.count( myTree.beginMap( OrderedMapIterator.VALUE ),
                           myTree.endMap( OrderedMapIterator.VALUE ),
                           value );
    }

  /**
   * Return an iterator positioned at the first location that a
   * pair with a specified key could be inserted without violating the ordering
   * criteria. If no such location is found, return an iterator positioned at end().
   * @param key The key.
   */
  public synchronized OrderedMapIterator lowerBound( Object key )
    {
    return new OrderedMapIterator( myTree, myTree.lowerBound( key ), this, OrderedMapIterator.PAIR );
    }

  /**
   * Return an iterator positioned at the last location that
   * a pair with a specified key could be inserted without violating the ordering
   * criteria. If no such location is found, return an iterator positioned at end().
   * @param key The key.
   */
  public synchronized OrderedMapIterator upperBound( Object key )
    {
    return new OrderedMapIterator( myTree, myTree.upperBound( key ), this, OrderedMapIterator.PAIR );
    }

  /**
   * Return my comparator.
   */
  public BinaryPredicate getComparator()
    {
    return myTree.myComparator;
    }

  /**
   * Return the value associated with key, or null if the key does not exist.
   * @param key The key to search against.
   */
  public synchronized Object get( Object key )
    {
    return myTree.get( key );
    }

  /**
   * If the key doesn't exist, associate the value with the key and return null,
   * otherwise replace the first value associated with the key and return the old value.
   * @param key The key.
   * @param value The value.
   * @exception java.lang.NullPointerException If the key or value is null.
   */
  public synchronized Object put( Object key, Object value )
    {
    if( key == null || value == null )
      throw new NullPointerException();

    InsertResult result = myTree.put( new Pair( key, value ) );

    if( result.ok )
      {
      return null;
      }
    else
      {
      Pair pair = (Pair) result.node.object;
      Object previous = pair.second;
      pair.second = value;
      return previous;
      }
    }

  /**
   * Assume that the specified object is a Pair whose first field is a key and whose
   * second field is a value. If the key doesn't exist or duplicates are allowed,
   * associate the value with the key and return null, otherwise don't modify the map and
   * return the current value associated with the key.
   * @param object The pair to add.
   * @exception java.lang.IllegalArgumentException If the object is not a Pair
   * @exception java.lang.NullPointerException If the object is null or if the first
   * or second items in the pair are null.
   */
  public Object add( Object object )
    {
    if( object == null )
      throw new NullPointerException();

    if ( !(object instanceof Pair) )
      throw new IllegalArgumentException( "object is not Pair" );

    if( ((Pair)object).first == null || ((Pair)object).second == null )
      throw new NullPointerException();

    Pair pair = (Pair) object;
    return add( pair.first, pair.second );
    }

  /**
   * If the key doesn't exist or duplicates are allowed, associate the value with the
   * key and return null, otherwise don't modify the map and return the current value
   * associated with the key.
   * @param key The key.
   * @param value The value.
   * @exception java.lang.NullPointerException If the key or value is null.
   */
  public Object add( Object key, Object value )
    {
    if( key == null || value == null )
      throw new NullPointerException();

    InsertResult result = myTree.insert( new Pair( key, value ) );
    return result.ok ? null : ((Pair) result.node.object).second;
    }

  /**
   * Return an Enumeration of all my keys.
   */
  public synchronized Enumeration keys()
    {
    return myTree.beginMap( OrderedMapIterator.KEY );
    }

  /**
   * Return an Enumeration of all my keys that are associated with a particular value.
   * @param value The value to match.
   */
  public synchronized Enumeration keys( Object value )
    {
    return myTree.keys( value ).elements();
    }

  /**
   * Return an Enumeration of all my values that are associated with a particular key.
   * @param key The key to match.
   */
  public synchronized Enumeration values( Object key )
    {
    return myTree.values( key ).elements();
    }

  /**
   * Return a pair of iterators whose first element is equal to
   * lowerBound() and whose second element is equal to upperBound().
   * @param object The object whose bounds are to be found.
   */
  public synchronized Range equalRange( Object object )
    {
    return new Range( lowerBound( object ), upperBound( object ) );
    }
  }