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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.collections4.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.collections4.BoundedMap;
import org.apache.commons.collections4.KeyValue;
import org.apache.commons.collections4.OrderedMap;
import org.apache.commons.collections4.OrderedMapIterator;
import org.apache.commons.collections4.ResettableIterator;
import org.apache.commons.collections4.iterators.SingletonIterator;
import org.apache.commons.collections4.keyvalue.TiedMapEntry;

/**
 * A Map implementation that holds a single item and is fixed size.
 * 

* 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 put or setValue methods can change * the value associated with the key. *

* 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 succeed if the key specified is the same as the * singleton key. *

* The key and value can be obtained by: *

    *
  • normal Map methods and views *
  • the MapIterator, see {@link #mapIterator()} *
  • the KeyValue interface (just cast - no object creation) *
* * @since 3.1 * @version $Id: SingletonMap.java 1686855 2015-06-22 13:00:27Z tn $ */ public class SingletonMap implements OrderedMap, BoundedMap, KeyValue, Serializable, Cloneable { /** Serialization version */ private static final long serialVersionUID = -8931271118676803261L; /** Singleton key */ private final K key; /** Singleton value */ private V value; /** * Constructor that creates a map of null to null. */ 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(final K key, final V value) { super(); this.key = key; this.value = value; } /** * Constructor specifying the key and value as a KeyValue. * * @param keyValue the key value pair to use */ public SingletonMap(final KeyValue keyValue) { super(); this.key = keyValue.getKey(); this.value = keyValue.getValue(); } /** * Constructor specifying the key and value as a MapEntry. * * @param mapEntry the mapEntry to use */ public SingletonMap(final 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(final Map map) { super(); if (map.size() != 1) { throw new IllegalArgumentException("The map size must be 1"); } final Map.Entry entry = map.entrySet().iterator().next(); this.key = entry.getKey(); this.value = entry.getValue(); } // KeyValue //----------------------------------------------------------------------- /** * Gets the key. * * @return the key */ public K getKey() { return key; } /** * Gets the value. * * @return the value */ public V getValue() { return value; } /** * Sets the value. * * @param value the new value to set * @return the old value */ public V setValue(final V value) { final V 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 V get(final 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(final 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(final Object value) { return isEqualValue(value); } //----------------------------------------------------------------------- /** * Puts a key-value mapping into this map where the key must match the existing key. *

* 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 V put(final K key, final V 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. *

* 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(final Map map) { switch (map.size()) { case 0: return; case 1: final Map.Entry 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 V remove(final Object key) { throw new UnsupportedOperationException(); } /** * Unsupported operation. */ public void clear() { throw new UnsupportedOperationException(); } //----------------------------------------------------------------------- /** * Gets the entrySet view of the map. * Changes made via setValue affect this map. * To simply iterate through the entries, use {@link #mapIterator()}. * * @return the entrySet view */ public Set> entrySet() { final Map.Entry entry = new TiedMapEntry(this, getKey()); return Collections.singleton(entry); } /** * Gets the unmodifiable keySet view of the map. * Changes made to the view affect this map. * To simply iterate through the keys, use {@link #mapIterator()}. * * @return the keySet view */ public Set keySet() { return Collections.singleton(key); } /** * Gets the unmodifiable values view of the map. * Changes made to the view affect this map. * To simply iterate through the values, use {@link #mapIterator()}. * * @return the values view */ public Collection values() { return new SingletonValues(this); } /** * {@inheritDoc} */ public OrderedMapIterator mapIterator() { return new SingletonMapIterator(this); } /** * Gets the first (and only) key in the map. * * @return the key */ public K firstKey() { return getKey(); } /** * Gets the last (and only) key in the map. * * @return the key */ public K lastKey() { return getKey(); } /** * Gets the next key after the key specified, always null. * * @param key the next key * @return null always */ public K nextKey(final K key) { return null; } /** * Gets the previous key before the key specified, always null. * * @param key the next key * @return null always */ public K previousKey(final K key) { return null; } //----------------------------------------------------------------------- /** * Compares the specified key to the stored key. * * @param key the key to compare * @return true if equal */ protected boolean isEqualKey(final Object key) { return key == null ? getKey() == null : key.equals(getKey()); } /** * Compares the specified value to the stored value. * * @param value the value to compare * @return true if equal */ protected boolean isEqualValue(final Object value) { return value == null ? getValue() == null : value.equals(getValue()); } //----------------------------------------------------------------------- /** * SingletonMapIterator. */ static class SingletonMapIterator implements OrderedMapIterator, ResettableIterator { private final SingletonMap parent; private boolean hasNext = true; private boolean canGetSet = false; SingletonMapIterator(final SingletonMap parent) { super(); this.parent = parent; } public boolean hasNext() { return hasNext; } public K next() { if (hasNext == false) { throw new NoSuchElementException(AbstractHashedMap.NO_NEXT_ENTRY); } hasNext = false; canGetSet = true; return parent.getKey(); } public boolean hasPrevious() { return hasNext == false; } public K previous() { if (hasNext == true) { throw new NoSuchElementException(AbstractHashedMap.NO_PREVIOUS_ENTRY); } hasNext = true; return parent.getKey(); } public void remove() { throw new UnsupportedOperationException(); } public K getKey() { if (canGetSet == false) { throw new IllegalStateException(AbstractHashedMap.GETKEY_INVALID); } return parent.getKey(); } public V getValue() { if (canGetSet == false) { throw new IllegalStateException(AbstractHashedMap.GETVALUE_INVALID); } return parent.getValue(); } public V setValue(final V value) { if (canGetSet == false) { throw new IllegalStateException(AbstractHashedMap.SETVALUE_INVALID); } return parent.setValue(value); } public void reset() { hasNext = true; } @Override public String toString() { if (hasNext) { return "Iterator[]"; } return "Iterator[" + getKey() + "=" + getValue() + "]"; } } /** * Values implementation for the SingletonMap. * This class is needed as values is a view that must update as the map updates. */ static class SingletonValues extends AbstractSet implements Serializable { private static final long serialVersionUID = -3689524741863047872L; private final SingletonMap parent; SingletonValues(final SingletonMap parent) { super(); this.parent = parent; } @Override public int size() { return 1; } @Override public boolean isEmpty() { return false; } @Override public boolean contains(final Object object) { return parent.containsValue(object); } @Override public void clear() { throw new UnsupportedOperationException(); } @Override public Iterator iterator() { return new SingletonIterator(parent.getValue(), false); } } //----------------------------------------------------------------------- /** * Clones the map without cloning the key or value. * * @return a shallow clone */ @Override @SuppressWarnings("unchecked") public SingletonMap clone() { try { return (SingletonMap) super.clone(); } catch (final CloneNotSupportedException ex) { throw new InternalError(); } } /** * Compares this map with another. * * @param obj the object to compare to * @return true if equal */ @Override public boolean equals(final Object obj) { if (obj == this) { return true; } if (obj instanceof Map == false) { return false; } final Map other = (Map) obj; if (other.size() != 1) { return false; } final Map.Entry entry = other.entrySet().iterator().next(); return isEqualKey(entry.getKey()) && isEqualValue(entry.getValue()); } /** * Gets the standard Map hashCode. * * @return the hash code defined in the Map interface */ @Override public int hashCode() { return (getKey() == null ? 0 : getKey().hashCode()) ^ (getValue() == null ? 0 : getValue().hashCode()); } /** * Gets the map as a String. * * @return a string version of the map */ @Override public String toString() { return new StringBuilder(128) .append('{') .append(getKey() == this ? "(this Map)" : getKey()) .append('=') .append(getValue() == this ? "(this Map)" : getValue()) .append('}') .toString(); } }





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