在项目当中，经常出现需要根据Key值获取value；而且要求根据value获取key值，其实在commons-collections包中已经提供了此集合类。就是DualHashBidiMap类。
（官方API：http://commons.apache.org/proper/commons-collections/apidocs/org/apache/commons/collections4/BidiMap.html）
其用法如下：
/** * BidiMap，双向Map，可以通过key找到value， 也可以通过value找到key，<br> * 注意：BidiMap中key不能重复，value也不可以。 * * 实现思路为：使用了两个Map，其中一个作为Key-Value使用，另外一个在put时，<br/> * 把value做为key，key作为value。<br/> * 当根据key查询value时，使用第一个map，此时和普通Map一样；<br/> * 当根据value查询key时，使用第二个map，也即查询的key就是put时的value值。 * * 使用此Map需要引入commons-collections的jar包 * @auther <a href="mailto:g2room@163.com">天涯</a> * May 31, 2013 2:32:55 PM */ public static void bidiMap() { // 第一种用法，和Map用法一样 // 此时实际创建了两个临时Map，分别记录key-value和value-key // 根据key查询value时，使用key-value的map； // 根据value查询key时，使用value-key的map。 DualHashBidiMap dualHashBidiMap = new DualHashBidiMap(); dualHashBidiMap.put("success", "成功"); dualHashBidiMap.put("fail", "失败"); dualHashBidiMap.put("wait", "等待"); System.out.println("根据Key获取Value: fail = " + dualHashBidiMap.get("fail")); System.out.println("根据Value获取Key: 等待 = " + dualHashBidiMap.getKey("等待")); Map<String, String> student1 = new HashMap<String, String>(); student1.put("name", "张三"); student1.put("score", "83"); student1.put("sex", "男"); // 第二种用法，让已有的Map也能通过value查找到key // 此时实际创建了两个临时Map，分别记录key-value和value-key // 但传入的Map会复制到临时的第一个Map里面 // 根据key查询value时，使用key-value的map； // 根据value查询key时，使用value-key的map。 dualHashBidiMap = new DualHashBidiMap(student1); System.out.println("根据Key获取Value: name = " + dualHashBidiMap.get("name")); System.out.println("根据Value获取Key: 男 = " + dualHashBidiMap.getKey("男")); }
输出结果如下：
根据Key获取Value: fail = 失败
根据Value获取Key: 等待 = wait
根据Key获取Value: name = 张三
根据Value获取Key: 男 = sex
DualHashBidiMap实现源码如下：
/* * 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. */ package org.apache.commons.collections.bidimap; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; import java.util.HashMap; import java.util.Map; import org.apache.commons.collections.BidiMap; /** * Implementation of <code>BidiMap</code> that uses two <code>HashMap</code> instances. * <p> * Two <code>HashMap</code> instances are used in this class. * This provides fast lookups at the expense of storing two sets of map entries. * Commons Collections would welcome the addition of a direct hash-based * implementation of the <code>BidiMap</code> interface. * <p> * NOTE: From Commons Collections 3.1, all subclasses will use <code>HashMap</code> * and the flawed <code>createMap</code> method is ignored. * * @since Commons Collections 3.0 * @version $Id: DualHashBidiMap.java 646777 2008-04-10 12:33:15Z niallp $ * * @author Matthew Hawthorne * @author Stephen Colebourne */ public class DualHashBidiMap extends AbstractDualBidiMap implements Serializable { /** Ensure serialization compatibility */ private static final long serialVersionUID = 721969328361808L; /** * Creates an empty <code>HashBidiMap</code>. */ public DualHashBidiMap() { super(new HashMap(), new HashMap()); } /** * Constructs a <code>HashBidiMap</code> and copies the mappings from * specified <code>Map</code>. * * @param map the map whose mappings are to be placed in this map */ public DualHashBidiMap(Map map) { super(new HashMap(), new HashMap()); putAll(map); } /** * Constructs a <code>HashBidiMap</code> that decorates the specified maps. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @param inverseBidiMap the inverse BidiMap */ protected DualHashBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) { super(normalMap, reverseMap, inverseBidiMap); } /** * Creates a new instance of this object. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @param inverseBidiMap the inverse BidiMap * @return new bidi map */ protected BidiMap createBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) { return new DualHashBidiMap(normalMap, reverseMap, inverseBidiMap); } // Serialization //----------------------------------------------------------------------- private void writeObject(ObjectOutputStream out) throws IOException { out.defaultWriteObject(); out.writeObject(maps[0]); } private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { in.defaultReadObject(); maps[0] = new HashMap(); maps[1] = new HashMap(); Map map = (Map) in.readObject(); putAll(map); } }
其抽象类AbstractDualBidiMap实现源码如下：
/* * 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. */ package org.apache.commons.collections.bidimap; import java.util.Collection; import java.util.Iterator; import java.util.Map; import java.util.Set; import org.apache.commons.collections.BidiMap; import org.apache.commons.collections.MapIterator; import org.apache.commons.collections.ResettableIterator; import org.apache.commons.collections.collection.AbstractCollectionDecorator; import org.apache.commons.collections.iterators.AbstractIteratorDecorator; import org.apache.commons.collections.keyvalue.AbstractMapEntryDecorator; /** * Abstract <code>BidiMap</code> implemented using two maps. * <p> * An implementation can be written simply by implementing the * <code>createMap</code> method. * * @see DualHashBidiMap * @see DualTreeBidiMap * @since Commons Collections 3.0 * @version $Id: AbstractDualBidiMap.java 646777 2008-04-10 12:33:15Z niallp $ * * @author Matthew Hawthorne * @author Stephen Colebourne */ public abstract class AbstractDualBidiMap implements BidiMap { /** * Delegate map array. The first map contains standard entries, and the * second contains inverses. */ protected transient final Map[] maps = new Map[2]; /** * Inverse view of this map. */ protected transient BidiMap inverseBidiMap = null; /** * View of the keys. */ protected transient Set keySet = null; /** * View of the values. */ protected transient Collection values = null; /** * View of the entries. */ protected transient Set entrySet = null; /** * Creates an empty map, initialised by <code>createMap</code>. * <p> * This constructor remains in place for deserialization. * All other usage is deprecated in favour of * {@link #AbstractDualBidiMap(Map, Map)}. */ protected AbstractDualBidiMap() { super(); maps[0] = createMap(); maps[1] = createMap(); } /** * Creates an empty map using the two maps specified as storage. * <p> * The two maps must be a matching pair, normal and reverse. * They will typically both be empty. * <p> * Neither map is validated, so nulls may be passed in. * If you choose to do this then the subclass constructor must populate * the <code>maps[]</code> instance variable itself. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @since Commons Collections 3.1 */ protected AbstractDualBidiMap(Map normalMap, Map reverseMap) { super(); maps[0] = normalMap; maps[1] = reverseMap; } /** * Constructs a map that decorates the specified maps, * used by the subclass <code>createBidiMap</code> implementation. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @param inverseBidiMap the inverse BidiMap */ protected AbstractDualBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) { super(); maps[0] = normalMap; maps[1] = reverseMap; this.inverseBidiMap = inverseBidiMap; } /** * Creates a new instance of the map used by the subclass to store data. * <p> * This design is deeply flawed and has been deprecated. * It relied on subclass data being used during a superclass constructor. * * @return the map to be used for internal storage * @deprecated For constructors, use the new two map constructor. * For deserialization, populate the maps array directly in readObject. */ protected Map createMap() { return null; } /** * Creates a new instance of the subclass. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @param inverseMap this map, which is the inverse in the new map * @return the inverse map */ protected abstract BidiMap createBidiMap(Map normalMap, Map reverseMap, BidiMap inverseMap); // Map delegation //----------------------------------------------------------------------- public Object get(Object key) { return maps[0].get(key); } public int size() { return maps[0].size(); } public boolean isEmpty() { return maps[0].isEmpty(); } public boolean containsKey(Object key) { return maps[0].containsKey(key); } public boolean equals(Object obj) { return maps[0].equals(obj); } public int hashCode() { return maps[0].hashCode(); } public String toString() { return maps[0].toString(); } // BidiMap changes //----------------------------------------------------------------------- public Object put(Object key, Object value) { if (maps[0].containsKey(key)) { maps[1].remove(maps[0].get(key)); } if (maps[1].containsKey(value)) { maps[0].remove(maps[1].get(value)); } final Object obj = maps[0].put(key, value); maps[1].put(value, key); return obj; } public void putAll(Map map) { for (Iterator it = map.entrySet().iterator(); it.hasNext();) { Map.Entry entry = (Map.Entry) it.next(); put(entry.getKey(), entry.getValue()); } } public Object remove(Object key) { Object value = null; if (maps[0].containsKey(key)) { value = maps[0].remove(key); maps[1].remove(value); } return value; } public void clear() { maps[0].clear(); maps[1].clear(); } public boolean containsValue(Object value) { return maps[1].containsKey(value); } // BidiMap //----------------------------------------------------------------------- /** * Obtains a <code>MapIterator</code> over the map. * The iterator implements <code>ResetableMapIterator</code>. * This implementation relies on the entrySet iterator. * <p> * The setValue() methods only allow a new value to be set. * If the value being set is already in the map, an IllegalArgumentException * is thrown (as setValue cannot change the size of the map). * * @return a map iterator */ public MapIterator mapIterator() { return new BidiMapIterator(this); } public Object getKey(Object value) { return maps[1].get(value); } public Object removeValue(Object value) { Object key = null; if (maps[1].containsKey(value)) { key = maps[1].remove(value); maps[0].remove(key); } return key; } public BidiMap inverseBidiMap() { if (inverseBidiMap == null) { inverseBidiMap = createBidiMap(maps[1], maps[0], this); } return inverseBidiMap; } // Map views //----------------------------------------------------------------------- /** * Gets a keySet view of the map. * Changes made on the view are reflected in the map. * The set supports remove and clear but not add. * * @return the keySet view */ public Set keySet() { if (keySet == null) { keySet = new KeySet(this); } return keySet; } /** * Creates a key set iterator. * Subclasses can override this to return iterators with different properties. * * @param iterator the iterator to decorate * @return the keySet iterator */ protected Iterator createKeySetIterator(Iterator iterator) { return new KeySetIterator(iterator, this); } /** * Gets a values view of the map. * Changes made on the view are reflected in the map. * The set supports remove and clear but not add. * * @return the values view */ public Collection values() { if (values == null) { values = new Values(this); } return values; } /** * Creates a values iterator. * Subclasses can override this to return iterators with different properties. * * @param iterator the iterator to decorate * @return the values iterator */ protected Iterator createValuesIterator(Iterator iterator) { return new ValuesIterator(iterator, this); } /** * Gets an entrySet view of the map. * Changes made on the set are reflected in the map. * The set supports remove and clear but not add. * <p> * The Map Entry setValue() method only allow a new value to be set. * If the value being set is already in the map, an IllegalArgumentException * is thrown (as setValue cannot change the size of the map). * * @return the entrySet view */ public Set entrySet() { if (entrySet == null) { entrySet = new EntrySet(this); } return entrySet; } /** * Creates an entry set iterator. * Subclasses can override this to return iterators with different properties. * * @param iterator the iterator to decorate * @return the entrySet iterator */ protected Iterator createEntrySetIterator(Iterator iterator) { return new EntrySetIterator(iterator, this); } //----------------------------------------------------------------------- /** * Inner class View. */ protected static abstract class View extends AbstractCollectionDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** * Constructs a new view of the BidiMap. * * @param coll the collection view being decorated * @param parent the parent BidiMap */ protected View(Collection coll, AbstractDualBidiMap parent) { super(coll); this.parent = parent; } public boolean removeAll(Collection coll) { if (parent.isEmpty() || coll.isEmpty()) { return false; } boolean modified = false; Iterator it = iterator(); while (it.hasNext()) { if (coll.contains(it.next())) { it.remove(); modified = true; } } return modified; } public boolean retainAll(Collection coll) { if (parent.isEmpty()) { return false; } if (coll.isEmpty()) { parent.clear(); return true; } boolean modified = false; Iterator it = iterator(); while (it.hasNext()) { if (coll.contains(it.next()) == false) { it.remove(); modified = true; } } return modified; } public void clear() { parent.clear(); } } //----------------------------------------------------------------------- /** * Inner class KeySet. */ protected static class KeySet extends View implements Set { /** * Constructs a new view of the BidiMap. * * @param parent the parent BidiMap */ protected KeySet(AbstractDualBidiMap parent) { super(parent.maps[0].keySet(), parent); } public Iterator iterator() { return parent.createKeySetIterator(super.iterator()); } public boolean contains(Object key) { return parent.maps[0].containsKey(key); } public boolean remove(Object key) { if (parent.maps[0].containsKey(key)) { Object value = parent.maps[0].remove(key); parent.maps[1].remove(value); return true; } return false; } } /** * Inner class KeySetIterator. */ protected static class KeySetIterator extends AbstractIteratorDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The last returned key */ protected Object lastKey = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param iterator the iterator to decorate * @param parent the parent map */ protected KeySetIterator(Iterator iterator, AbstractDualBidiMap parent) { super(iterator); this.parent = parent; } public Object next() { lastKey = super.next(); canRemove = true; return lastKey; } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } Object value = parent.maps[0].get(lastKey); super.remove(); parent.maps[1].remove(value); lastKey = null; canRemove = false; } } //----------------------------------------------------------------------- /** * Inner class Values. */ protected static class Values extends View implements Set { /** * Constructs a new view of the BidiMap. * * @param parent the parent BidiMap */ protected Values(AbstractDualBidiMap parent) { super(parent.maps[0].values(), parent); } public Iterator iterator() { return parent.createValuesIterator(super.iterator()); } public boolean contains(Object value) { return parent.maps[1].containsKey(value); } public boolean remove(Object value) { if (parent.maps[1].containsKey(value)) { Object key = parent.maps[1].remove(value); parent.maps[0].remove(key); return true; } return false; } } /** * Inner class ValuesIterator. */ protected static class ValuesIterator extends AbstractIteratorDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The last returned value */ protected Object lastValue = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param iterator the iterator to decorate * @param parent the parent map */ protected ValuesIterator(Iterator iterator, AbstractDualBidiMap parent) { super(iterator); this.parent = parent; } public Object next() { lastValue = super.next(); canRemove = true; return lastValue; } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } super.remove(); // removes from maps[0] parent.maps[1].remove(lastValue); lastValue = null; canRemove = false; } } //----------------------------------------------------------------------- /** * Inner class EntrySet. */ protected static class EntrySet extends View implements Set { /** * Constructs a new view of the BidiMap. * * @param parent the parent BidiMap */ protected EntrySet(AbstractDualBidiMap parent) { super(parent.maps[0].entrySet(), parent); } public Iterator iterator() { return parent.createEntrySetIterator(super.iterator()); } public boolean remove(Object obj) { if (obj instanceof Map.Entry == false) { return false; } Map.Entry entry = (Map.Entry) obj; Object key = entry.getKey(); if (parent.containsKey(key)) { Object value = parent.maps[0].get(key); if (value == null ? entry.getValue() == null : value.equals(entry.getValue())) { parent.maps[0].remove(key); parent.maps[1].remove(value); return true; } } return false; } } /** * Inner class EntrySetIterator. */ protected static class EntrySetIterator extends AbstractIteratorDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The last returned entry */ protected Map.Entry last = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param iterator the iterator to decorate * @param parent the parent map */ protected EntrySetIterator(Iterator iterator, AbstractDualBidiMap parent) { super(iterator); this.parent = parent; } public Object next() { last = new MapEntry((Map.Entry) super.next(), parent); canRemove = true; return last; } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } // store value as remove may change the entry in the decorator (eg.TreeMap) Object value = last.getValue(); super.remove(); parent.maps[1].remove(value); last = null; canRemove = false; } } /** * Inner class MapEntry. */ protected static class MapEntry extends AbstractMapEntryDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** * Constructor. * @param entry the entry to decorate * @param parent the parent map */ protected MapEntry(Map.Entry entry, AbstractDualBidiMap parent) { super(entry); this.parent = parent; } public Object setValue(Object value) { Object key = MapEntry.this.getKey(); if (parent.maps[1].containsKey(value) && parent.maps[1].get(value) != key) { throw new IllegalArgumentException("Cannot use setValue() when the object being set is already in the map"); } parent.put(key, value); final Object oldValue = super.setValue(value); return oldValue; } } /** * Inner class MapIterator. */ protected static class BidiMapIterator implements MapIterator, ResettableIterator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The iterator being wrapped */ protected Iterator iterator; /** The last returned entry */ protected Map.Entry last = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param parent the parent map */ protected BidiMapIterator(AbstractDualBidiMap parent) { super(); this.parent = parent; this.iterator = parent.maps[0].entrySet().iterator(); } public boolean hasNext() { return iterator.hasNext(); } public Object next() { last = (Map.Entry) iterator.next(); canRemove = true; return last.getKey(); } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } // store value as remove may change the entry in the decorator (eg.TreeMap) Object value = last.getValue(); iterator.remove(); parent.maps[1].remove(value); last = null; canRemove = false; } public Object getKey() { if (last == null) { throw new IllegalStateException("Iterator getKey() can only be called after next() and before remove()"); } return last.getKey(); } public Object getValue() { if (last == null) { throw new IllegalStateException("Iterator getValue() can only be called after next() and before remove()"); } return last.getValue(); } public Object setValue(Object value) { if (last == null) { throw new IllegalStateException("Iterator setValue() can only be called after next() and before remove()"); } if (parent.maps[1].containsKey(value) && parent.maps[1].get(value) != last.getKey()) { throw new IllegalArgumentException("Cannot use setValue() when the object being set is already in the map"); } return parent.put(last.getKey(), value); } public void reset() { iterator = parent.maps[0].entrySet().iterator(); last = null; canRemove = false; } public String toString() { if (last != null) { return "MapIterator[" + getKey() + "=" + getValue() + "]"; } else { return "MapIterator[]"; } } } }
/* * 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 * * * 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. */package org.apache.commons.collections.bidimap;import java.util.Collection;import java.util.Iterator;import java.util.Map;import java.util.Set;import org.apache.commons.collections.BidiMap;import org.apache.commons.collections.MapIterator;import org.apache.commons.collections.ResettableIterator;import org.apache.commons.collections.collection.AbstractCollectionDecorator;import org.apache.commons.collections.iterators.AbstractIteratorDecorator;import org.apache.commons.collections.keyvalue.AbstractMapEntryDecorator;/** * Abstract <code>BidiMap</code> implemented using two maps. * <p> * An implementation can be written simply by implementing the * <code>createMap</code> method. * * @see DualHashBidiMap * @see DualTreeBidiMap * @since Commons Collections 3.0 * @version $Id: AbstractDualBidiMap.java 646777 2008-04-10 12:33:15Z niallp $ * * @author Matthew Hawthorne * @author Stephen Colebourne */public abstract class AbstractDualBidiMap implements BidiMap { /** * Delegate map array. The first map contains standard entries, and the * second contains inverses. */ protected transient final Map[] maps = new Map[2]; /** * Inverse view of this map. */ protected transient BidiMap inverseBidiMap = null; /** * View of the keys. */ protected transient Set keySet = null; /** * View of the values. */ protected transient Collection values = null; /** * View of the entries. */ protected transient Set entrySet = null; /** * Creates an empty map, initialised by <code>createMap</code>. * <p> * This constructor remains in place for deserialization. * All other usage is deprecated in favour of * {@link #AbstractDualBidiMap(Map, Map)}. */ protected AbstractDualBidiMap() { super(); maps[0] = createMap(); maps[1] = createMap(); } /** * Creates an empty map using the two maps specified as storage. * <p> * The two maps must be a matching pair, normal and reverse. * They will typically both be empty. * <p> * Neither map is validated, so nulls may be passed in. * If you choose to do this then the subclass constructor must populate * the <code>maps[]</code> instance variable itself. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @since Commons Collections 3.1 */ protected AbstractDualBidiMap(Map normalMap, Map reverseMap) { super(); maps[0] = normalMap; maps[1] = reverseMap; } /** * Constructs a map that decorates the specified maps, * used by the subclass <code>createBidiMap</code> implementation. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @param inverseBidiMap the inverse BidiMap */ protected AbstractDualBidiMap(Map normalMap, Map reverseMap, BidiMap inverseBidiMap) { super(); maps[0] = normalMap; maps[1] = reverseMap; this.inverseBidiMap = inverseBidiMap; } /** * Creates a new instance of the map used by the subclass to store data. * <p> * This design is deeply flawed and has been deprecated. * It relied on subclass data being used during a superclass constructor. * * @return the map to be used for internal storage * @deprecated For constructors, use the new two map constructor. * For deserialization, populate the maps array directly in readObject. */ protected Map createMap() { return null; } /** * Creates a new instance of the subclass. * * @param normalMap the normal direction map * @param reverseMap the reverse direction map * @param inverseMap this map, which is the inverse in the new map * @return the inverse map */ protected abstract BidiMap createBidiMap(Map normalMap, Map reverseMap, BidiMap inverseMap); // Map delegation //----------------------------------------------------------------------- public Object get(Object key) { return maps[0].get(key); } public int size() { return maps[0].size(); } public boolean isEmpty() { return maps[0].isEmpty(); } public boolean containsKey(Object key) { return maps[0].containsKey(key); } public boolean equals(Object obj) { return maps[0].equals(obj); } public int hashCode() { return maps[0].hashCode(); } public String toString() { return maps[0].toString(); } // BidiMap changes //----------------------------------------------------------------------- public Object put(Object key, Object value) { if (maps[0].containsKey(key)) { maps[1].remove(maps[0].get(key)); } if (maps[1].containsKey(value)) { maps[0].remove(maps[1].get(value)); } final Object obj = maps[0].put(key, value); maps[1].put(value, key); return obj; } public void putAll(Map map) { for (Iterator it = map.entrySet().iterator(); it.hasNext();) { Map.Entry entry = (Map.Entry) it.next(); put(entry.getKey(), entry.getValue()); } } public Object remove(Object key) { Object value = null; if (maps[0].containsKey(key)) { value = maps[0].remove(key); maps[1].remove(value); } return value; } public void clear() { maps[0].clear(); maps[1].clear(); } public boolean containsValue(Object value) { return maps[1].containsKey(value); } // BidiMap //----------------------------------------------------------------------- /** * Obtains a <code>MapIterator</code> over the map. * The iterator implements <code>ResetableMapIterator</code>. * This implementation relies on the entrySet iterator. * <p> * The setValue() methods only allow a new value to be set. * If the value being set is already in the map, an IllegalArgumentException * is thrown (as setValue cannot change the size of the map). * * @return a map iterator */ public MapIterator mapIterator() { return new BidiMapIterator(this); } public Object getKey(Object value) { return maps[1].get(value); } public Object removeValue(Object value) { Object key = null; if (maps[1].containsKey(value)) { key = maps[1].remove(value); maps[0].remove(key); } return key; } public BidiMap inverseBidiMap() { if (inverseBidiMap == null) { inverseBidiMap = createBidiMap(maps[1], maps[0], this); } return inverseBidiMap; } // Map views //----------------------------------------------------------------------- /** * Gets a keySet view of the map. * Changes made on the view are reflected in the map. * The set supports remove and clear but not add. * * @return the keySet view */ public Set keySet() { if (keySet == null) { keySet = new KeySet(this); } return keySet; } /** * Creates a key set iterator. * Subclasses can override this to return iterators with different properties. * * @param iterator the iterator to decorate * @return the keySet iterator */ protected Iterator createKeySetIterator(Iterator iterator) { return new KeySetIterator(iterator, this); } /** * Gets a values view of the map. * Changes made on the view are reflected in the map. * The set supports remove and clear but not add. * * @return the values view */ public Collection values() { if (values == null) { values = new Values(this); } return values; } /** * Creates a values iterator. * Subclasses can override this to return iterators with different properties. * * @param iterator the iterator to decorate * @return the values iterator */ protected Iterator createValuesIterator(Iterator iterator) { return new ValuesIterator(iterator, this); } /** * Gets an entrySet view of the map. * Changes made on the set are reflected in the map. * The set supports remove and clear but not add. * <p> * The Map Entry setValue() method only allow a new value to be set. * If the value being set is already in the map, an IllegalArgumentException * is thrown (as setValue cannot change the size of the map). * * @return the entrySet view */ public Set entrySet() { if (entrySet == null) { entrySet = new EntrySet(this); } return entrySet; } /** * Creates an entry set iterator. * Subclasses can override this to return iterators with different properties. * * @param iterator the iterator to decorate * @return the entrySet iterator */ protected Iterator createEntrySetIterator(Iterator iterator) { return new EntrySetIterator(iterator, this); } //----------------------------------------------------------------------- /** * Inner class View. */ protected static abstract class View extends AbstractCollectionDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** * Constructs a new view of the BidiMap. * * @param coll the collection view being decorated * @param parent the parent BidiMap */ protected View(Collection coll, AbstractDualBidiMap parent) { super(coll); this.parent = parent; } public boolean removeAll(Collection coll) { if (parent.isEmpty() || coll.isEmpty()) { return false; } boolean modified = false; Iterator it = iterator(); while (it.hasNext()) { if (coll.contains(it.next())) { it.remove(); modified = true; } } return modified; } public boolean retainAll(Collection coll) { if (parent.isEmpty()) { return false; } if (coll.isEmpty()) { parent.clear(); return true; } boolean modified = false; Iterator it = iterator(); while (it.hasNext()) { if (coll.contains(it.next()) == false) { it.remove(); modified = true; } } return modified; } public void clear() { parent.clear(); } } //----------------------------------------------------------------------- /** * Inner class KeySet. */ protected static class KeySet extends View implements Set { /** * Constructs a new view of the BidiMap. * * @param parent the parent BidiMap */ protected KeySet(AbstractDualBidiMap parent) { super(parent.maps[0].keySet(), parent); } public Iterator iterator() { return parent.createKeySetIterator(super.iterator()); } public boolean contains(Object key) { return parent.maps[0].containsKey(key); } public boolean remove(Object key) { if (parent.maps[0].containsKey(key)) { Object value = parent.maps[0].remove(key); parent.maps[1].remove(value); return true; } return false; } } /** * Inner class KeySetIterator. */ protected static class KeySetIterator extends AbstractIteratorDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The last returned key */ protected Object lastKey = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param iterator the iterator to decorate * @param parent the parent map */ protected KeySetIterator(Iterator iterator, AbstractDualBidiMap parent) { super(iterator); this.parent = parent; } public Object next() { lastKey = super.next(); canRemove = true; return lastKey; } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } Object value = parent.maps[0].get(lastKey); super.remove(); parent.maps[1].remove(value); lastKey = null; canRemove = false; } } //----------------------------------------------------------------------- /** * Inner class Values. */ protected static class Values extends View implements Set { /** * Constructs a new view of the BidiMap. * * @param parent the parent BidiMap */ protected Values(AbstractDualBidiMap parent) { super(parent.maps[0].values(), parent); } public Iterator iterator() { return parent.createValuesIterator(super.iterator()); } public boolean contains(Object value) { return parent.maps[1].containsKey(value); } public boolean remove(Object value) { if (parent.maps[1].containsKey(value)) { Object key = parent.maps[1].remove(value); parent.maps[0].remove(key); return true; } return false; } } /** * Inner class ValuesIterator. */ protected static class ValuesIterator extends AbstractIteratorDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The last returned value */ protected Object lastValue = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param iterator the iterator to decorate * @param parent the parent map */ protected ValuesIterator(Iterator iterator, AbstractDualBidiMap parent) { super(iterator); this.parent = parent; } public Object next() { lastValue = super.next(); canRemove = true; return lastValue; } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } super.remove(); // removes from maps[0] parent.maps[1].remove(lastValue); lastValue = null; canRemove = false; } } //----------------------------------------------------------------------- /** * Inner class EntrySet. */ protected static class EntrySet extends View implements Set { /** * Constructs a new view of the BidiMap. * * @param parent the parent BidiMap */ protected EntrySet(AbstractDualBidiMap parent) { super(parent.maps[0].entrySet(), parent); } public Iterator iterator() { return parent.createEntrySetIterator(super.iterator()); } public boolean remove(Object obj) { if (obj instanceof Map.Entry == false) { return false; } Map.Entry entry = (Map.Entry) obj; Object key = entry.getKey(); if (parent.containsKey(key)) { Object value = parent.maps[0].get(key); if (value == null ? entry.getValue() == null : value.equals(entry.getValue())) { parent.maps[0].remove(key); parent.maps[1].remove(value); return true; } } return false; } } /** * Inner class EntrySetIterator. */ protected static class EntrySetIterator extends AbstractIteratorDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The last returned entry */ protected Map.Entry last = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param iterator the iterator to decorate * @param parent the parent map */ protected EntrySetIterator(Iterator iterator, AbstractDualBidiMap parent) { super(iterator); this.parent = parent; } public Object next() { last = new MapEntry((Map.Entry) super.next(), parent); canRemove = true; return last; } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } // store value as remove may change the entry in the decorator (eg.TreeMap) Object value = last.getValue(); super.remove(); parent.maps[1].remove(value); last = null; canRemove = false; } } /** * Inner class MapEntry. */ protected static class MapEntry extends AbstractMapEntryDecorator { /** The parent map */ protected final AbstractDualBidiMap parent; /** * Constructor. * @param entry the entry to decorate * @param parent the parent map */ protected MapEntry(Map.Entry entry, AbstractDualBidiMap parent) { super(entry); this.parent = parent; } public Object setValue(Object value) { Object key = MapEntry.this.getKey(); if (parent.maps[1].containsKey(value) && parent.maps[1].get(value) != key) { throw new IllegalArgumentException("Cannot use setValue() when the object being set is already in the map"); } parent.put(key, value); final Object oldValue = super.setValue(value); return oldValue; } } /** * Inner class MapIterator. */ protected static class BidiMapIterator implements MapIterator, ResettableIterator { /** The parent map */ protected final AbstractDualBidiMap parent; /** The iterator being wrapped */ protected Iterator iterator; /** The last returned entry */ protected Map.Entry last = null; /** Whether remove is allowed at present */ protected boolean canRemove = false; /** * Constructor. * @param parent the parent map */ protected BidiMapIterator(AbstractDualBidiMap parent) { super(); this.parent = parent; this.iterator = parent.maps[0].entrySet().iterator(); } public boolean hasNext() { return iterator.hasNext(); } public Object next() { last = (Map.Entry) iterator.next(); canRemove = true; return last.getKey(); } public void remove() { if (canRemove == false) { throw new IllegalStateException("Iterator remove() can only be called once after next()"); } // store value as remove may change the entry in the decorator (eg.TreeMap) Object value = last.getValue(); iterator.remove(); parent.maps[1].remove(value); last = null; canRemove = false; } public Object getKey() { if (last == null) { throw new IllegalStateException("Iterator getKey() can only be called after next() and before remove()"); } return last.getKey(); } public Object getValue() { if (last == null) { throw new IllegalStateException("Iterator getValue() can only be called after next() and before remove()"); } return last.getValue(); } public Object setValue(Object value) { if (last == null) { throw new IllegalStateException("Iterator setValue() can only be called after next() and before remove()"); } if (parent.maps[1].containsKey(value) && parent.maps[1].get(value) != last.getKey()) { throw new IllegalArgumentException("Cannot use setValue() when the object being set is already in the map"); } return parent.put(last.getKey(), value); } public void reset() { iterator = parent.maps[0].entrySet().iterator(); last = null; canRemove = false; } public String toString() { if (last != null) { return "MapIterator[" + getKey() + "=" + getValue() +"]"; } else { return "MapIterator[]"; } } } }