Mega Code Archive
MultiMap is a Java version of the C++ STL class std
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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**
*
* MultiMap is a Java version of the C++ STL class std::multimap. It allows
* users to associate more than one value with a unique key. Each key points
* to a collection of values that can be traversed independently of the map.
* The integrity of the map is such that it only protects the key values, not
* the values they point to.
* <br><br>
* All entries into the multimap are (Object, java.util.Collection), where
* each key object must be unique.
*
* @author Dan Jemiolo (danj)
*
*/
public final class MultiMap extends HashMap
{
private static final long serialVersionUID = -9145022530624375133L;
//
// The Collection class that holds the values
//
private Class _collectionClass = null;
//
// The number of KEYS in the map - we need to track this ourselves
// because size() is overridden to return the number of VALUES (the
// number of values is the sum of Collection.size()).
//
private int _keySize = 0;
/**
*
* The default constructor creates a new map using a HashSet as the
* value collection type.
*
* @see MultiMap#MultiMap(Class)
*
*/
public MultiMap()
{
this(HashSet.class);
}
/**
*
* @param collectionClass
* The Collection type to use for the map's values. The Class
* must be an implementation of java.util.Collection.
*
*/
public MultiMap(Class collectionClass)
{
_collectionClass = collectionClass;
}
public final void clear()
{
super.clear();
_keySize = 0;
}
/**
*
* @param value
*
* @return True if one or more of the keys in this map points to the
* given value.
*
*/
public final boolean containsValue(Object value)
{
Iterator i = values().iterator();
//
// look through each map entry's set of values to see if
// the given value is present
//
while (i.hasNext())
{
Collection values = (Collection)i.next();
if (values.contains(value))
return true;
}
return false;
}
/**
*
* @return The number of keys in the map, <b>not</b> the number of
* entries.
*
* @see #size()
*
*/
public final int keySetSize()
{
return _keySize;
}
/**
*
* Associates the value with the given key. If the key is not already in
* the map, it is added; otherwise, the value is simply added to the
* key's collection.
*
* @return The value reference on success or null if the value was
* already associated with the key.
*
*/
public final Object put(Object key, Object value)
{
Collection values = (Collection)get(key);
//
// if the key wasn't found - add it!
//
if (values == null)
{
values = (Collection)newInstance(_collectionClass);
super.put(key, values);
++_keySize;
}
//
// try to add the value to the key's set
//
boolean success = values.add(value);
return success ? value : null;
}
/**
*
* Invokes the Class.newInstance() method on the given Class.
*
* @param theClass
* The type to instantiate.
*
* @return An object of the given type, created with the default
* constructor. A RuntimeException is thrown if the object could not
* be created.
*
*/
public static Object newInstance(Class theClass)
{
try
{
return theClass.newInstance();
}
catch (InstantiationException error)
{
Object[] filler = { theClass };
String message = "ObjectCreationFailed";
throw new RuntimeException(message);
}
catch (IllegalAccessException error)
{
Object[] filler = { theClass };
String message = "DefaultConstructorHidden";
throw new RuntimeException(message);
}
}
/**
*
* Adds all of the entries in a generic map to the multimap.
* <br><br>
* NOTE: Because we cannot guarantee that the implementation of the
* base class putAll(Map) simply calls the put method in a loop, we must
* override it here to ensure this happens. Otherwise, HashMap might
* associate the values directly with the keys, breaking the unofficial
* key -> Collection system.
*
* @param map
* The Map to copy - this does not have to be another MultiMap.
*
*/
public final void putAll(Map map)
{
Set keys = map.keySet();
Iterator i = keys.iterator();
//
// if the argument is a multi-map, we want to add all of the
// values individually, otherwise each key will have a set
// of values whose only value is... the collection of values.
// that is, instead of key -> collection<value>, we'd have
// key -> collection<collection<value>>
//
if (map instanceof MultiMap)
{
while (i.hasNext())
{
Object key = i.next();
Object value = map.get(key);
Collection setOfValues = (Collection)value;
Iterator j = setOfValues.iterator();
while (j.hasNext())
put(key, j.next());
}
}
//
// it's a "normal" map - just add the name-value pairs
//
else
{
while (i.hasNext())
{
Object key = i.next();
put(key, map.get(key));
}
}
}
/**
*
* Removes <b>all</b> values associated with the given key.
*
* @param key
*
* @return The Collection of values previously associated with the key.
*
*/
public final Object remove(Object key)
{
Object value = super.remove(key);
--_keySize;
return value;
}
/**
*
* NOTE: This method takes O(n) time, where n is the number of keys in
* the map. It would be more efficient to keep a counter for the size,
* but this would require overriding more methods and dealing with the
* complicated issue of map integrity and entrySet(). This implementation
* is the most robust when you consider that all Maps allow users to
* modify their contents without using the interface directly.
*
* @return The sum of the sizes of all the map entries (value collections).
*
*/
public final int size()
{
Iterator i = values().iterator();
int count = 0;
//
// for each key, add the number of values to the count
//
while (i.hasNext())
{
Collection values = (Collection)i.next();
count += values.size();
}
return count;
}
}
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