singletonmap.java

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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.
 */
package org.apache.commons.collections.map;

import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import org.apache.commons.collections.BoundedMap;
import org.apache.commons.collections.KeyValue;
import org.apache.commons.collections.MapIterator;
import org.apache.commons.collections.OrderedMap;
import org.apache.commons.collections.OrderedMapIterator;
import org.apache.commons.collections.ResettableIterator;
import org.apache.commons.collections.iterators.SingletonIterator;
import org.apache.commons.collections.keyvalue.TiedMapEntry;

/**
 * A <code>Map</code> implementation that holds a single item and is fixed size.
 * <p>
 * The single key/value pair is specified at creation.
 * The map is fixed size so any action that would change the size is disallowed.
 * However, the <code>put</code> or <code>setValue</code> methods can <i>change</i>
 * the value associated with the key.
 * <p>
 * If trying to remove or clear the map, an UnsupportedOperationException is thrown.
 * If trying to put a new mapping into the map, an  IllegalArgumentException is thrown.
 * The put method will only suceed if the key specified is the same as the 
 * singleton key.
 * <p>
 * The key and value can be obtained by:
 * <ul>
 * <li>normal Map methods and views
 * <li>the <code>MapIterator</code>, see {@link #mapIterator()}
 * <li>the <code>KeyValue</code> interface (just cast - no object creation)
 * </ul>
 * 
 * @since Commons Collections 3.1
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Stephen Colebourne
 */
public class SingletonMap
        implements OrderedMap, BoundedMap, KeyValue, Serializable, Cloneable {

    /** Serialization version */
    private static final long serialVersionUID = -8931271118676803261L;

    /** Singleton key */
    private final Object key;
    /** Singleton value */
    private Object value;

    /**
     * Constructor that creates a map of <code>null</code> to <code>null</code>.
     */
    public SingletonMap() {
        super();
        this.key = null;
    }

    /**
     * Constructor specifying the key and value.
     *
     * @param key  the key to use
     * @param value  the value to use
     */
    public SingletonMap(Object key, Object value) {
        super();
        this.key = key;
        this.value = value;
    }

    /**
     * Constructor specifying the key and value as a <code>KeyValue</code>.
     *
     * @param keyValue  the key value pair to use
     */
    public SingletonMap(KeyValue keyValue) {
        super();
        this.key = keyValue.getKey();
        this.value = keyValue.getValue();
    }

    /**
     * Constructor specifying the key and value as a <code>MapEntry</code>.
     *
     * @param mapEntry  the mapEntry to use
     */
    public SingletonMap(Map.Entry mapEntry) {
        super();
        this.key = mapEntry.getKey();
        this.value = mapEntry.getValue();
    }

    /**
     * Constructor copying elements from another map.
     *
     * @param map  the map to copy, must be size 1
     * @throws NullPointerException if the map is null
     * @throws IllegalArgumentException if the size is not 1
     */
    public SingletonMap(Map map) {
        super();
        if (map.size() != 1) {
            throw new IllegalArgumentException("The map size must be 1");
        }
        Map.Entry entry = (Map.Entry) map.entrySet().iterator().next();
        this.key = entry.getKey();
        this.value = entry.getValue();
    }

    // KeyValue
    //-----------------------------------------------------------------------
    /**
     * Gets the key.
     *
     * @return the key 
     */
    public Object getKey() {
        return key;
    }

    /**
     * Gets the value.
     *
     * @return the value
     */
    public Object getValue() {
        return value;
    }

    /**
     * Sets the value.
     *
     * @param value  the new value to set
     * @return the old value
     */
    public Object setValue(Object value) {
        Object old = this.value;
        this.value = value;
        return old;
    }

    // BoundedMap
    //-----------------------------------------------------------------------
    /**
     * Is the map currently full, always true.
     *
     * @return true always
     */
    public boolean isFull() {
        return true;
    }

    /**
     * Gets the maximum size of the map, always 1.
     * 
     * @return 1 always
     */
    public int maxSize() {
        return 1;
    }

    // Map
    //-----------------------------------------------------------------------
    /**
     * Gets the value mapped to the key specified.
     * 
     * @param key  the key
     * @return the mapped value, null if no match
     */
    public Object get(Object key) {
        if (isEqualKey(key)) {
            return value;
        }
        return null;
    }

    /**
     * Gets the size of the map, always 1.
     * 
     * @return the size of 1
     */
    public int size() {
        return 1;
    }

    /**
     * Checks whether the map is currently empty, which it never is.
     * 
     * @return false always
     */
    public boolean isEmpty() {
        return false;
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether the map contains the specified key.
     * 
     * @param key  the key to search for
     * @return true if the map contains the key
     */
    public boolean containsKey(Object key) {
        return (isEqualKey(key));
    }

    /**
     * Checks whether the map contains the specified value.
     * 
     * @param value  the value to search for
     * @return true if the map contains the key
     */
    public boolean containsValue(Object value) {
        return (isEqualValue(value));
    }

    //-----------------------------------------------------------------------
    /**
     * Puts a key-value mapping into this map where the key must match the existing key.
     * <p>
     * An IllegalArgumentException is thrown if the key does not match as the map
     * is fixed size.
     * 
     * @param key  the key to set, must be the key of the map
     * @param value  the value to set
     * @return the value previously mapped to this key, null if none
     * @throws IllegalArgumentException if the key does not match
     */
    public Object put(Object key, Object value) {
        if (isEqualKey(key)) {
            return setValue(value);
        }
        throw new IllegalArgumentException("Cannot put new key/value pair - Map is fixed size singleton");
    }

    /**
     * Puts the values from the specified map into this map.
     * <p>
     * The map must be of size 0 or size 1.
     * If it is size 1, the key must match the key of this map otherwise an
     * IllegalArgumentException is thrown.
     * 
     * @param map  the map to add, must be size 0 or 1, and the key must match
     * @throws NullPointerException if the map is null
     * @throws IllegalArgumentException if the key does not match
     */
    public void putAll(Map map) {
        switch (map.size()) {
            case 0:
                return;
            
            case 1:
                Map.Entry entry = (Map.Entry) map.entrySet().iterator().next();
                put(entry.getKey(), entry.getValue());
                return;
            
            default:
                throw new IllegalArgumentException("The map size must be 0 or 1");
        }
    }

    /**
     * Unsupported operation.
     * 
     * @param key  the mapping to remove
     * @return the value mapped to the removed key, null if key not in map
     * @throws UnsupportedOperationException always
     */
    public Object remove(Object key) {
        throw new UnsupportedOperationException();
    }

    /**
     * Unsupported operation.
     */
    public void clear() {