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[]";
}
}
}
}