java/util/AbstractMap.java

/*
 * %W% %E%
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;
import java.util.Map.Entry;

/**
 * This class provides a skeletal implementation of the <tt>Map</tt>
 * interface, to minimize the effort required to implement this interface.
 *
 * <p>To implement an unmodifiable map, the programmer needs only to extend this
 * class and provide an implementation for the <tt>entrySet</tt> method, which
 * returns a set-view of the map's mappings.  Typically, the returned set
 * will, in turn, be implemented atop <tt>AbstractSet</tt>.  This set should
 * not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
 * should not support the <tt>remove</tt> method.
 *
 * <p>To implement a modifiable map, the programmer must additionally override
 * this class's <tt>put</tt> method (which otherwise throws an
 * <tt>UnsupportedOperationException</tt>), and the iterator returned by
 * <tt>entrySet().iterator()</tt> must additionally implement its
 * <tt>remove</tt> method.
 *
 * <p>The programmer should generally provide a void (no argument) and map
 * constructor, as per the recommendation in the <tt>Map</tt> interface
 * specification.
 *
 * <p>The documentation for each non-abstract methods in this class describes its
 * implementation in detail.  Each of these methods may be overridden if the
 * map being implemented admits a more efficient implementation.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 *
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @version %I%, %G%
 * @see Map
 * @see Collection
 * @since 1.2
 */

public abstract class AbstractMap<K,V> implements Map<K,V> {
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected AbstractMap() {
    }

    // Query Operations

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns <tt>entrySet().size()</tt>.
     */
    public int size() {
        return entrySet().size();
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns <tt>size() == 0</tt>.
     */
    public boolean isEmpty() {
        return size() == 0;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation iterates over <tt>entrySet()</tt> searching
     * for an entry with the specified value.  If such an entry is found,
     * <tt>true</tt> is returned.  If the iteration terminates without
     * finding such an entry, <tt>false</tt> is returned.  Note that this
     * implementation requires linear time in the size of the map.
     *
     * @throws ClassCastException   {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean containsValue(Object value) {
        Iterator<Entry<K,V>> i = entrySet().iterator();
        if (value==null) {
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                if (e.getValue()==null)
                    return true;
            }
        } else {
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                if (value.equals(e.getValue()))
                    return true;
            }
        }
        return false;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation iterates over <tt>entrySet()</tt> searching
     * for an entry with the specified key.  If such an entry is found,
     * <tt>true</tt> is returned.  If the iteration terminates without
     * finding such an entry, <tt>false</tt> is returned.  Note that this
     * implementation requires linear time in the size of the map; many
     * implementations will override this method.
     *
     * @throws ClassCastException   {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean containsKey(Object key) {
        Iterator<Map.Entry<K,V>> i = entrySet().iterator();
        if (key==null) {
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                if (e.getKey()==null)
                    return true;
            }
        } else {
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                if (key.equals(e.getKey()))
                    return true;
            }
        }
        return false;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation iterates over <tt>entrySet()</tt> searching
     * for an entry with the specified key.  If such an entry is found,
     * the entry's value is returned.  If the iteration terminates without
     * finding such an entry, <tt>null</tt> is returned.  Note that this
     * implementation requires linear time in the size of the map; many
     * implementations will override this method.
     *
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     */
    public V get(Object key) {
        Iterator<Entry<K,V>> i = entrySet().iterator();
        if (key==null) {
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                if (e.getKey()==null)
                    return e.getValue();
            }
        } else {
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                if (key.equals(e.getKey()))
                    return e.getValue();
            }
        }
        return null;
    }


    // Modification Operations

    /**
     * {@inheritDoc}
     *
     * <p>This implementation always throws an
     * <tt>UnsupportedOperationException</tt>.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public V put(K key, V value) {
        throw new UnsupportedOperationException();
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation iterates over <tt>entrySet()</tt> searching for an
     * entry with the specified key.  If such an entry is found, its value is
     * obtained with its <tt>getValue</tt> operation, the entry is removed
     * from the collection (and the backing map) with the iterator's
     * <tt>remove</tt> operation, and the saved value is returned.  If the
     * iteration terminates without finding such an entry, <tt>null</tt> is
     * returned.  Note that this implementation requires linear time in the
     * size of the map; many implementations will override this method.
     *
     * <p>Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
     * iterator does not support the <tt>remove</tt> method and this map
     * contains a mapping for the specified key.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     */
    public V remove(Object key) {
        Iterator<Entry<K,V>> i = entrySet().iterator();
        Entry<K,V> correctEntry = null;
        if (key==null) {
            while (correctEntry==null && i.hasNext()) {
                Entry<K,V> e = i.next();
                if (e.getKey()==null)
                    correctEntry = e;
            }
        } else {
            while (correctEntry==null && i.hasNext()) {
                Entry<K,V> e = i.next();
                if (key.equals(e.getKey()))
                    correctEntry = e;
            }
        }

        V oldValue = null;
        if (correctEntry !=null) {
            oldValue = correctEntry.getValue();
            i.remove();
        }
        return oldValue;
    }


    // Bulk Operations

    /**
     * {@inheritDoc}
     *
     * <p>This implementation iterates over the specified map's
     * <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>
     * operation once for each entry returned by the iteration.
     *
     * <p>Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if this map does not support
     * the <tt>put</tt> operation and the specified map is nonempty.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    public void putAll(Map<? extends K, ? extends V> m) {
        Iterator<? extends Entry<? extends K, ? extends V>> i = m.entrySet().iterator();
        while (i.hasNext()) {
            Entry<? extends K, ? extends V> e = i.next();
            put(e.getKey(), e.getValue());
        }
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation calls <tt>entrySet().clear()</tt>.
     *
     * <p>Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
     * does not support the <tt>clear</tt> operation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     */
    public void clear() {
        entrySet().clear();
    }


    // Views

    /**
     * Each of these fields are initialized to contain an instance of the
     * appropriate view the first time this view is requested.  The views are
     * stateless, so there's no reason to create more than one of each.
     */
    transient volatile Set<K>        keySet = null;
    transient volatile Collection<V> values = null;

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns a set that subclasses {@link AbstractSet}.
     * The subclass's iterator method returns a "wrapper object" over this
     * map's <tt>entrySet()</tt> iterator.  The <tt>size</tt> method
     * delegates to this map's <tt>size</tt> method and the
     * <tt>contains</tt> method delegates to this map's
     * <tt>containsKey</tt> method.
     *
     * <p>The set is created the first time this method is called,
     * and returned in response to all subsequent calls.  No synchronization
     * is performed, so there is a slight chance that multiple calls to this
     * method will not all return the same set.
     */
    public Set<K> keySet() {
        if (keySet == null) {
            keySet = new AbstractSet<K>() {
                public Iterator<K> iterator() {
                    return new Iterator<K>() {
                        private Iterator<Entry<K,V>> i = entrySet().iterator();

                        public boolean hasNext() {
                            return i.hasNext();
                        }

                        public K next() {
                            return i.next().getKey();
                        }

                        public void remove() {
                            i.remove();
                        }
                    };
                }

                public int size() {
                    return AbstractMap.this.size();
                }

                public boolean contains(Object k) {
                    return AbstractMap.this.containsKey(k);
                }
            };
        }
        return keySet;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns a collection that subclasses {@link
     * AbstractCollection}.  The subclass's iterator method returns a
     * "wrapper object" over this map's <tt>entrySet()</tt> iterator.
     * The <tt>size</tt> method delegates to this map's <tt>size</tt>
     * method and the <tt>contains</tt> method delegates to this map's
     * <tt>containsValue</tt> method.
     *
     * <p>The collection is created the first time this method is called, and
     * returned in response to all subsequent calls.  No synchronization is
     * performed, so there is a slight chance that multiple calls to this
     * method will not all return the same collection.
     */
    public Collection<V> values() {
        if (values == null) {
            values = new AbstractCollection<V>() {
                public Iterator<V> iterator() {
                    return new Iterator<V>() {
                        private Iterator<Entry<K,V>> i = entrySet().iterator();

                        public boolean hasNext() {
                            return i.hasNext();
                        }

                        public V next() {
                            return i.next().getValue();
                        }

                        public void remove() {
                            i.remove();
                        }
                    };
                }

                public int size() {
                    return AbstractMap.this.size();
                }

                public boolean contains(Object v) {
                    return AbstractMap.this.containsValue(v);
                }
            };
        }
        return values;
    }

    public abstract Set<Entry<K,V>> entrySet();


    // Comparison and hashing

    /**
     * {@inheritDoc}
     *
     * <p>This implementation first checks if the specified object is this map;
     * if so it returns <tt>true</tt>.  Then, it checks if the specified
     * object is a map whose size is identical to the size of this map; if
     * not, it returns <tt>false</tt>.  If so, it iterates over this map's
     * <tt>entrySet</tt> collection, and checks that the specified map
     * contains each mapping that this map contains.  If the specified map
     * fails to contain such a mapping, <tt>false</tt> is returned.  If the
     * iteration completes, <tt>true</tt> is returned.
     */
    public boolean equals(Object o) {
        if (o == this)
            return true;

        if (!(o instanceof Map))
            return false;
        Map<K,V> t = (Map<K,V>) o;
        if (t.size() != size())
            return false;

        try {
            Iterator<Entry<K,V>> i = entrySet().iterator();
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
                K key = e.getKey();
                V value = e.getValue();
                if (value == null) {
                    if (!(t.get(key)==null && t.containsKey(key)))
                        return false;
                } else {
                    if (!value.equals(t.get(key)))
                        return false;
                }
            }
        } catch (ClassCastException unused) {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }

        return true;
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation iterates over <tt>entrySet()</tt>, calling
     * <tt>hashCode()</tt> on each element (entry) in the set, and
     * adding up the results.
     *
     * @see Map.Entry#hashCode()
     * @see Object#hashCode()
     * @see Object#equals(Object)
     * @see Set#equals(Object)
     */
    public int hashCode() {
        int h = 0;
        Iterator<Entry<K,V>> i = entrySet().iterator();
        while (i.hasNext())
            h += i.next().hashCode();
        return h;
    }

    /**
     * Returns a string representation of this map.  The string representation
     * consists of a list of key-value mappings in the order returned by the
     * map's <tt>entrySet</tt> view's iterator, enclosed in braces
     * (<tt>"{}"</tt>).  Adjacent mappings are separated by the characters
     * <tt>", "</tt> (comma and space).  Each key-value mapping is rendered as
     * the key followed by an equals sign (<tt>"="</tt>) followed by the
     * associated value.  Keys and values are converted to strings as by
     * <tt>String.valueOf(Object)</tt>.<p>
     *
     * This implementation creates an empty string buffer, appends a left
     * brace, and iterates over the map's <tt>entrySet</tt> view, appending
     * the string representation of each <tt>map.entry</tt> in turn.  After
     * appending each entry except the last, the string <tt>", "</tt> is
     * appended.  Finally a right brace is appended.  A string is obtained
     * from the stringbuffer, and returned.
     *
     * @return a String representation of this map.
     */
    public String toString() {
        StringBuffer buf = new StringBuffer();
        buf.append("{");

        Iterator<Entry<K,V>> i = entrySet().iterator();
        boolean hasNext = i.hasNext();
        while (hasNext) {
            Entry<K,V> e = i.next();
            K key = e.getKey();
            V value = e.getValue();
            if (key == this)
                buf.append("(this Map)");
            else
                buf.append(key);
            buf.append("=");
            if (value == this)
                buf.append("(this Map)");
            else
                buf.append(value);
            hasNext = i.hasNext();
            if (hasNext)
                buf.append(", ");
        }

        buf.append("}");
        return buf.toString();
    }

    /**
     * Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys
     * and values themselves are not cloned.
     *
     * @return a shallow copy of this map
     */
    protected Object clone() throws CloneNotSupportedException {
        AbstractMap<K,V> result = (AbstractMap<K,V>)super.clone();
        result.keySet = null;
        result.values = null;
        return result;
    }

    /**
     * Utility method for SimpleEntry and SimpleImmutableEntry.
     * Test for equality, checking for nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null ? o2 == null : o1.equals(o2));
    }

    // Implementation Note: SimpleEntry and SimpleImmutableEntry
    // are distinct unrelated classes, even though they share
    // some code. Since you can't add or subtract final-ness
    // of a field in a subclass, they can't share representations,
    // and the amount of duplicated code is too small to warrant
    // exposing a common abstract class.


    /**
     * An Entry maintaining a key and a value.  The value may be
     * changed using the <tt>setValue</tt> method.  This class
     * facilitates the process of building custom map
     * implementations. For example, it may be convenient to return
     * arrays of <tt>SimpleEntry</tt> instances in method
     * <tt>Map.entrySet().toArray</tt>
     */
    public static class SimpleEntry<K,V> implements Entry<K,V> {
        private final K key;
        private V value;

        /**
         * Creates an entry representing a mapping from the specified
         * key to the specified value.
         *
         * @param key the key represented by this entry
         * @param value the value represented by this entry
         */
        public SimpleEntry(K key, V value) {
            this.key   = key;
            this.value = value;
        }

        /**
         * Creates an entry representing the same mapping as the
         * specified entry.
         *
         * @param entry the entry to copy.
         */
        public SimpleEntry(Entry<? extends K, ? extends V> entry) {
            this.key   = entry.getKey();
            this.value = entry.getValue();
        }

        /**
         * Returns the key corresponding to this entry.
         *
         * @return the key corresponding to this entry
         */
        public K getKey() {
            return key;
        }

        /**
         * Returns the value corresponding to this entry.
         *
         * @return the value corresponding to this entry
         */
        public V getValue() {
            return value;
        }

        /**
         * Replaces the value corresponding to this entry with the specified
         * value.
         *
         * @param value new value to be stored in this entry
         * @return the old value corresponding to the entry
         */
        public V setValue(V value) {
            V oldValue = this.value;
            this.value = value;
            return oldValue;
        }

        public boolean equals(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry e = (Map.Entry)o;
            return eq(key, e.getKey()) && eq(value, e.getValue());
        }

        public int hashCode() {
            return ((key   == null)   ? 0 :   key.hashCode()) ^
                   ((value == null)   ? 0 : value.hashCode());
        }

        /**
         * Returns a String representation of this map entry.  This
         * implementation returns the string representation of this
         * entry's key followed by the equals character ("<tt>=</tt>")
         * followed by the string representation of this entry's value.
         *
         * @return a String representation of this map entry
         */
        public String toString() {
            return key + "=" + value;
        }

    }

    /**
     * An Entry maintaining an immutable key and value, This class
     * does not support method <tt>setValue</tt>.  This class may be
     * convenient in methods that return thread-safe snapshots of
     * key-value mappings.
     */
    public static class SimpleImmutableEntry<K,V> implements Entry<K,V> {
        private final K key;
        private final V value;

        /**
         * Creates an entry representing a mapping from the specified
         * key to the specified value.
         *
         * @param key the key represented by this entry
         * @param value the value represented by this entry
         */
        public SimpleImmutableEntry(K key, V value) {
            this.key   = key;
            this.value = value;
        }

        /**
         * Creates an entry representing the same mapping as the
         * specified entry.
         *
         * @param entry the entry to copy
         */
        public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
            this.key   = entry.getKey();
            this.value = entry.getValue();
        }

        /**
         * Returns the key corresponding to this entry.
         *
         * @return the key corresponding to this entry
         */
        public K getKey() {
            return key;
        }

        /**
         * Returns the value corresponding to this entry.
         *
         * @return the value corresponding to this entry
         */
        public V getValue() {
            return value;
        }

        /**
         * Replaces the value corresponding to this entry with the specified
         * value (optional operation).  This implementation simply throws
         * <tt>UnsupportedOperationException</tt>, as this class implements
         * an <i>immutable</i> map entry.
         *
         * @param value new value to be stored in this entry
         * @return (Does not return)
         * @throws UnsupportedOperationException always
         */
        public V setValue(V value) {
            throw new UnsupportedOperationException();
        }

        public boolean equals(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry e = (Map.Entry)o;
            return eq(key, e.getKey()) && eq(value, e.getValue());
        }

        public int hashCode() {
            return ((key   == null)   ? 0 :   key.hashCode()) ^
                   ((value == null)   ? 0 : value.hashCode());
        }

        /**
         * Returns a String representation of this map entry.  This
         * implementation returns the string representation of this
         * entry's key followed by the equals character ("<tt>=</tt>")
         * followed by the string representation of this entry's value.
         *
         * @return a String representation of this map entry
         */
        public String toString() {
            return key + "=" + value;
        }

    }

}
Revision:	1.10
Committed:	Mon May 16 05:03:18 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.9:	+6 -6 lines
Log Message:	doc fixes
#	Content
1	/*
2	* %W% %E%
3	*
4	* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	*/
7
8	package java.util;
9	import java.util.Map.Entry;
10
11	/**
12	* This class provides a skeletal implementation of the <tt>Map</tt>
13	* interface, to minimize the effort required to implement this interface.
14	*
15	* <p>To implement an unmodifiable map, the programmer needs only to extend this
16	* class and provide an implementation for the <tt>entrySet</tt> method, which
17	* returns a set-view of the map's mappings. Typically, the returned set
18	* will, in turn, be implemented atop <tt>AbstractSet</tt>. This set should
19	* not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
20	* should not support the <tt>remove</tt> method.
21	*
22	* <p>To implement a modifiable map, the programmer must additionally override
23	* this class's <tt>put</tt> method (which otherwise throws an
24	* <tt>UnsupportedOperationException</tt>), and the iterator returned by
25	* <tt>entrySet().iterator()</tt> must additionally implement its
26	* <tt>remove</tt> method.
27	*
28	* <p>The programmer should generally provide a void (no argument) and map
29	* constructor, as per the recommendation in the <tt>Map</tt> interface
30	* specification.
31	*
32	* <p>The documentation for each non-abstract methods in this class describes its
33	* implementation in detail. Each of these methods may be overridden if the
34	* map being implemented admits a more efficient implementation.
35	*
36	* <p>This class is a member of the
37	* <a href="{@docRoot}/../guide/collections/index.html">
38	* Java Collections Framework</a>.
39	*
40	* @param <K> the type of keys maintained by this map
41	* @param <V> the type of mapped values
42	*
43	* @author Josh Bloch
44	* @author Neal Gafter
45	* @version %I%, %G%
46	* @see Map
47	* @see Collection
48	* @since 1.2
49	*/
50
51	public abstract class AbstractMap<K,V> implements Map<K,V> {
52	/**
53	* Sole constructor. (For invocation by subclass constructors, typically
54	* implicit.)
55	*/
56	protected AbstractMap() {
57	}
58
59	// Query Operations
60
61	/**
62	* {@inheritDoc}
63	*
64	* <p>This implementation returns <tt>entrySet().size()</tt>.
65	*/
66	public int size() {
67	return entrySet().size();
68	}
69
70	/**
71	* {@inheritDoc}
72	*
73	* <p>This implementation returns <tt>size() == 0</tt>.
74	*/
75	public boolean isEmpty() {
76	return size() == 0;
77	}
78
79	/**
80	* {@inheritDoc}
81	*
82	* <p>This implementation iterates over <tt>entrySet()</tt> searching
83	* for an entry with the specified value. If such an entry is found,
84	* <tt>true</tt> is returned. If the iteration terminates without
85	* finding such an entry, <tt>false</tt> is returned. Note that this
86	* implementation requires linear time in the size of the map.
87	*
88	* @throws ClassCastException {@inheritDoc}
89	* @throws NullPointerException {@inheritDoc}
90	*/
91	public boolean containsValue(Object value) {
92	Iterator<Entry<K,V>> i = entrySet().iterator();
93	if (value==null) {
94	while (i.hasNext()) {
95	Entry<K,V> e = i.next();
96	if (e.getValue()==null)
97	return true;
98	}
99	} else {
100	while (i.hasNext()) {
101	Entry<K,V> e = i.next();
102	if (value.equals(e.getValue()))
103	return true;
104	}
105	}
106	return false;
107	}
108
109	/**
110	* {@inheritDoc}
111	*
112	* <p>This implementation iterates over <tt>entrySet()</tt> searching
113	* for an entry with the specified key. If such an entry is found,
114	* <tt>true</tt> is returned. If the iteration terminates without
115	* finding such an entry, <tt>false</tt> is returned. Note that this
116	* implementation requires linear time in the size of the map; many
117	* implementations will override this method.
118	*
119	* @throws ClassCastException {@inheritDoc}
120	* @throws NullPointerException {@inheritDoc}
121	*/
122	public boolean containsKey(Object key) {
123	Iterator<Map.Entry<K,V>> i = entrySet().iterator();
124	if (key==null) {
125	while (i.hasNext()) {
126	Entry<K,V> e = i.next();
127	if (e.getKey()==null)
128	return true;
129	}
130	} else {
131	while (i.hasNext()) {
132	Entry<K,V> e = i.next();
133	if (key.equals(e.getKey()))
134	return true;
135	}
136	}
137	return false;
138	}
139
140	/**
141	* {@inheritDoc}
142	*
143	* <p>This implementation iterates over <tt>entrySet()</tt> searching
144	* for an entry with the specified key. If such an entry is found,
145	* the entry's value is returned. If the iteration terminates without
146	* finding such an entry, <tt>null</tt> is returned. Note that this
147	* implementation requires linear time in the size of the map; many
148	* implementations will override this method.
149	*
150	* @throws ClassCastException {@inheritDoc}
151	* @throws NullPointerException {@inheritDoc}
152	*/
153	public V get(Object key) {
154	Iterator<Entry<K,V>> i = entrySet().iterator();
155	if (key==null) {
156	while (i.hasNext()) {
157	Entry<K,V> e = i.next();
158	if (e.getKey()==null)
159	return e.getValue();
160	}
161	} else {
162	while (i.hasNext()) {
163	Entry<K,V> e = i.next();
164	if (key.equals(e.getKey()))
165	return e.getValue();
166	}
167	}
168	return null;
169	}
170
171
172	// Modification Operations
173
174	/**
175	* {@inheritDoc}
176	*
177	* <p>This implementation always throws an
178	* <tt>UnsupportedOperationException</tt>.
179	*
180	* @throws UnsupportedOperationException {@inheritDoc}
181	* @throws ClassCastException {@inheritDoc}
182	* @throws NullPointerException {@inheritDoc}
183	* @throws IllegalArgumentException {@inheritDoc}
184	*/
185	public V put(K key, V value) {
186	throw new UnsupportedOperationException();
187	}
188
189	/**
190	* {@inheritDoc}
191	*
192	* <p>This implementation iterates over <tt>entrySet()</tt> searching for an
193	* entry with the specified key. If such an entry is found, its value is
194	* obtained with its <tt>getValue</tt> operation, the entry is removed
195	* from the collection (and the backing map) with the iterator's
196	* <tt>remove</tt> operation, and the saved value is returned. If the
197	* iteration terminates without finding such an entry, <tt>null</tt> is
198	* returned. Note that this implementation requires linear time in the
199	* size of the map; many implementations will override this method.
200	*
201	* <p>Note that this implementation throws an
202	* <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
203	* iterator does not support the <tt>remove</tt> method and this map
204	* contains a mapping for the specified key.
205	*
206	* @throws UnsupportedOperationException {@inheritDoc}
207	* @throws ClassCastException {@inheritDoc}
208	* @throws NullPointerException {@inheritDoc}
209	*/
210	public V remove(Object key) {
211	Iterator<Entry<K,V>> i = entrySet().iterator();
212	Entry<K,V> correctEntry = null;
213	if (key==null) {
214	while (correctEntry==null && i.hasNext()) {
215	Entry<K,V> e = i.next();
216	if (e.getKey()==null)
217	correctEntry = e;
218	}
219	} else {
220	while (correctEntry==null && i.hasNext()) {
221	Entry<K,V> e = i.next();
222	if (key.equals(e.getKey()))
223	correctEntry = e;
224	}
225	}
226
227	V oldValue = null;
228	if (correctEntry !=null) {
229	oldValue = correctEntry.getValue();
230	i.remove();
231	}
232	return oldValue;
233	}
234
235
236	// Bulk Operations
237
238	/**
239	* {@inheritDoc}
240	*
241	* <p>This implementation iterates over the specified map's
242	* <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>
243	* operation once for each entry returned by the iteration.
244	*
245	* <p>Note that this implementation throws an
246	* <tt>UnsupportedOperationException</tt> if this map does not support
247	* the <tt>put</tt> operation and the specified map is nonempty.
248	*
249	* @throws UnsupportedOperationException {@inheritDoc}
250	* @throws ClassCastException {@inheritDoc}
251	* @throws NullPointerException {@inheritDoc}
252	* @throws IllegalArgumentException {@inheritDoc}
253	*/
254	public void putAll(Map<? extends K, ? extends V> m) {
255	Iterator<? extends Entry<? extends K, ? extends V>> i = m.entrySet().iterator();
256	while (i.hasNext()) {
257	Entry<? extends K, ? extends V> e = i.next();
258	put(e.getKey(), e.getValue());
259	}
260	}
261
262	/**
263	* {@inheritDoc}
264	*
265	* <p>This implementation calls <tt>entrySet().clear()</tt>.
266	*
267	* <p>Note that this implementation throws an
268	* <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
269	* does not support the <tt>clear</tt> operation.
270	*
271	* @throws UnsupportedOperationException {@inheritDoc}
272	*/
273	public void clear() {
274	entrySet().clear();
275	}
276
277
278	// Views
279
280	/**
281	* Each of these fields are initialized to contain an instance of the
282	* appropriate view the first time this view is requested. The views are
283	* stateless, so there's no reason to create more than one of each.
284	*/
285	transient volatile Set<K> keySet = null;
286	transient volatile Collection<V> values = null;
287
288	/**
289	* {@inheritDoc}
290	*
291	* <p>This implementation returns a set that subclasses {@link AbstractSet}.
292	* The subclass's iterator method returns a "wrapper object" over this
293	* map's <tt>entrySet()</tt> iterator. The <tt>size</tt> method
294	* delegates to this map's <tt>size</tt> method and the
295	* <tt>contains</tt> method delegates to this map's
296	* <tt>containsKey</tt> method.
297	*
298	* <p>The set is created the first time this method is called,
299	* and returned in response to all subsequent calls. No synchronization
300	* is performed, so there is a slight chance that multiple calls to this
301	* method will not all return the same set.
302	*/
303	public Set<K> keySet() {
304	if (keySet == null) {
305	keySet = new AbstractSet<K>() {
306	public Iterator<K> iterator() {
307	return new Iterator<K>() {
308	private Iterator<Entry<K,V>> i = entrySet().iterator();
309
310	public boolean hasNext() {
311	return i.hasNext();
312	}
313
314	public K next() {
315	return i.next().getKey();
316	}
317
318	public void remove() {
319	i.remove();
320	}
321	};
322	}
323
324	public int size() {
325	return AbstractMap.this.size();
326	}
327
328	public boolean contains(Object k) {
329	return AbstractMap.this.containsKey(k);
330	}
331	};
332	}
333	return keySet;
334	}
335
336	/**
337	* {@inheritDoc}
338	*
339	* <p>This implementation returns a collection that subclasses {@link
340	* AbstractCollection}. The subclass's iterator method returns a
341	* "wrapper object" over this map's <tt>entrySet()</tt> iterator.
342	* The <tt>size</tt> method delegates to this map's <tt>size</tt>
343	* method and the <tt>contains</tt> method delegates to this map's
344	* <tt>containsValue</tt> method.
345	*
346	* <p>The collection is created the first time this method is called, and
347	* returned in response to all subsequent calls. No synchronization is
348	* performed, so there is a slight chance that multiple calls to this
349	* method will not all return the same collection.
350	*/
351	public Collection<V> values() {
352	if (values == null) {
353	values = new AbstractCollection<V>() {
354	public Iterator<V> iterator() {
355	return new Iterator<V>() {
356	private Iterator<Entry<K,V>> i = entrySet().iterator();
357
358	public boolean hasNext() {
359	return i.hasNext();
360	}
361
362	public V next() {
363	return i.next().getValue();
364	}
365
366	public void remove() {
367	i.remove();
368	}
369	};
370	}
371
372	public int size() {
373	return AbstractMap.this.size();
374	}
375
376	public boolean contains(Object v) {
377	return AbstractMap.this.containsValue(v);
378	}
379	};
380	}
381	return values;
382	}
383
384	public abstract Set<Entry<K,V>> entrySet();
385
386
387	// Comparison and hashing
388
389	/**
390	* {@inheritDoc}
391	*
392	* <p>This implementation first checks if the specified object is this map;
393	* if so it returns <tt>true</tt>. Then, it checks if the specified
394	* object is a map whose size is identical to the size of this map; if
395	* not, it returns <tt>false</tt>. If so, it iterates over this map's
396	* <tt>entrySet</tt> collection, and checks that the specified map
397	* contains each mapping that this map contains. If the specified map
398	* fails to contain such a mapping, <tt>false</tt> is returned. If the
399	* iteration completes, <tt>true</tt> is returned.
400	*/
401	public boolean equals(Object o) {
402	if (o == this)
403	return true;
404
405	if (!(o instanceof Map))
406	return false;
407	Map<K,V> t = (Map<K,V>) o;
408	if (t.size() != size())
409	return false;
410
411	try {
412	Iterator<Entry<K,V>> i = entrySet().iterator();
413	while (i.hasNext()) {
414	Entry<K,V> e = i.next();
415	K key = e.getKey();
416	V value = e.getValue();
417	if (value == null) {
418	if (!(t.get(key)==null && t.containsKey(key)))
419	return false;
420	} else {
421	if (!value.equals(t.get(key)))
422	return false;
423	}
424	}
425	} catch (ClassCastException unused) {
426	return false;
427	} catch (NullPointerException unused) {
428	return false;
429	}
430
431	return true;
432	}
433
434	/**
435	* {@inheritDoc}
436	*
437	* <p>This implementation iterates over <tt>entrySet()</tt>, calling
438	* <tt>hashCode()</tt> on each element (entry) in the set, and
439	* adding up the results.
440	*
441	* @see Map.Entry#hashCode()
442	* @see Object#hashCode()
443	* @see Object#equals(Object)
444	* @see Set#equals(Object)
445	*/
446	public int hashCode() {
447	int h = 0;
448	Iterator<Entry<K,V>> i = entrySet().iterator();
449	while (i.hasNext())
450	h += i.next().hashCode();
451	return h;
452	}
453
454	/**
455	* Returns a string representation of this map. The string representation
456	* consists of a list of key-value mappings in the order returned by the
457	* map's <tt>entrySet</tt> view's iterator, enclosed in braces
458	* (<tt>"{}"</tt>). Adjacent mappings are separated by the characters
459	* <tt>", "</tt> (comma and space). Each key-value mapping is rendered as
460	* the key followed by an equals sign (<tt>"="</tt>) followed by the
461	* associated value. Keys and values are converted to strings as by
462	* <tt>String.valueOf(Object)</tt>.<p>
463	*
464	* This implementation creates an empty string buffer, appends a left
465	* brace, and iterates over the map's <tt>entrySet</tt> view, appending
466	* the string representation of each <tt>map.entry</tt> in turn. After
467	* appending each entry except the last, the string <tt>", "</tt> is
468	* appended. Finally a right brace is appended. A string is obtained
469	* from the stringbuffer, and returned.
470	*
471	* @return a String representation of this map.
472	*/
473	public String toString() {
474	StringBuffer buf = new StringBuffer();
475	buf.append("{");
476
477	Iterator<Entry<K,V>> i = entrySet().iterator();
478	boolean hasNext = i.hasNext();
479	while (hasNext) {
480	Entry<K,V> e = i.next();
481	K key = e.getKey();
482	V value = e.getValue();
483	if (key == this)
484	buf.append("(this Map)");
485	else
486	buf.append(key);
487	buf.append("=");
488	if (value == this)
489	buf.append("(this Map)");
490	else
491	buf.append(value);
492	hasNext = i.hasNext();
493	if (hasNext)
494	buf.append(", ");
495	}
496
497	buf.append("}");
498	return buf.toString();
499	}
500
501	/**
502	* Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys
503	* and values themselves are not cloned.
504	*
505	* @return a shallow copy of this map
506	*/
507	protected Object clone() throws CloneNotSupportedException {
508	AbstractMap<K,V> result = (AbstractMap<K,V>)super.clone();
509	result.keySet = null;
510	result.values = null;
511	return result;
512	}
513
514	/**
515	* Utility method for SimpleEntry and SimpleImmutableEntry.
516	* Test for equality, checking for nulls.
517	*/
518	private static boolean eq(Object o1, Object o2) {
519	return (o1 == null ? o2 == null : o1.equals(o2));
520	}
521
522	// Implementation Note: SimpleEntry and SimpleImmutableEntry
523	// are distinct unrelated classes, even though they share
524	// some code. Since you can't add or subtract final-ness
525	// of a field in a subclass, they can't share representations,
526	// and the amount of duplicated code is too small to warrant
527	// exposing a common abstract class.
528
529
530	/**
531	* An Entry maintaining a key and a value. The value may be
532	* changed using the <tt>setValue</tt> method. This class
533	* facilitates the process of building custom map
534	* implementations. For example, it may be convenient to return
535	* arrays of <tt>SimpleEntry</tt> instances in method
536	* <tt>Map.entrySet().toArray</tt>
537	*/
538	public static class SimpleEntry<K,V> implements Entry<K,V> {
539	private final K key;
540	private V value;
541
542	/**
543	* Creates an entry representing a mapping from the specified
544	* key to the specified value.
545	*
546	* @param key the key represented by this entry
547	* @param value the value represented by this entry
548	*/
549	public SimpleEntry(K key, V value) {
550	this.key = key;
551	this.value = value;
552	}
553
554	/**
555	* Creates an entry representing the same mapping as the
556	* specified entry.
557	*
558	* @param entry the entry to copy.
559	*/
560	public SimpleEntry(Entry<? extends K, ? extends V> entry) {
561	this.key = entry.getKey();
562	this.value = entry.getValue();
563	}
564
565	/**
566	* Returns the key corresponding to this entry.
567	*
568	* @return the key corresponding to this entry
569	*/
570	public K getKey() {
571	return key;
572	}
573
574	/**
575	* Returns the value corresponding to this entry.
576	*
577	* @return the value corresponding to this entry
578	*/
579	public V getValue() {
580	return value;
581	}
582
583	/**
584	* Replaces the value corresponding to this entry with the specified
585	* value.
586	*
587	* @param value new value to be stored in this entry
588	* @return the old value corresponding to the entry
589	*/
590	public V setValue(V value) {
591	V oldValue = this.value;
592	this.value = value;
593	return oldValue;
594	}
595
596	public boolean equals(Object o) {
597	if (!(o instanceof Map.Entry))
598	return false;
599	Map.Entry e = (Map.Entry)o;
600	return eq(key, e.getKey()) && eq(value, e.getValue());
601	}
602
603	public int hashCode() {
604	return ((key == null) ? 0 : key.hashCode()) ^
605	((value == null) ? 0 : value.hashCode());
606	}
607
608	/**
609	* Returns a String representation of this map entry. This
610	* implementation returns the string representation of this
611	* entry's key followed by the equals character ("<tt>=</tt>")
612	* followed by the string representation of this entry's value.
613	*
614	* @return a String representation of this map entry
615	*/
616	public String toString() {
617	return key + "=" + value;
618	}
619
620	}
621
622	/**
623	* An Entry maintaining an immutable key and value, This class
624	* does not support method <tt>setValue</tt>. This class may be
625	* convenient in methods that return thread-safe snapshots of
626	* key-value mappings.
627	*/
628	public static class SimpleImmutableEntry<K,V> implements Entry<K,V> {
629	private final K key;
630	private final V value;
631
632	/**
633	* Creates an entry representing a mapping from the specified
634	* key to the specified value.
635	*
636	* @param key the key represented by this entry
637	* @param value the value represented by this entry
638	*/
639	public SimpleImmutableEntry(K key, V value) {
640	this.key = key;
641	this.value = value;
642	}
643
644	/**
645	* Creates an entry representing the same mapping as the
646	* specified entry.
647	*
648	* @param entry the entry to copy
649	*/
650	public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
651	this.key = entry.getKey();
652	this.value = entry.getValue();
653	}
654
655	/**
656	* Returns the key corresponding to this entry.
657	*
658	* @return the key corresponding to this entry
659	*/
660	public K getKey() {
661	return key;
662	}
663
664	/**
665	* Returns the value corresponding to this entry.
666	*
667	* @return the value corresponding to this entry
668	*/
669	public V getValue() {
670	return value;
671	}
672
673	/**
674	* Replaces the value corresponding to this entry with the specified
675	* value (optional operation). This implementation simply throws
676	* <tt>UnsupportedOperationException</tt>, as this class implements
677	* an <i>immutable</i> map entry.
678	*
679	* @param value new value to be stored in this entry
680	* @return (Does not return)
681	* @throws UnsupportedOperationException always
682	*/
683	public V setValue(V value) {
684	throw new UnsupportedOperationException();
685	}
686
687	public boolean equals(Object o) {
688	if (!(o instanceof Map.Entry))
689	return false;
690	Map.Entry e = (Map.Entry)o;
691	return eq(key, e.getKey()) && eq(value, e.getValue());
692	}
693
694	public int hashCode() {
695	return ((key == null) ? 0 : key.hashCode()) ^
696	((value == null) ? 0 : value.hashCode());
697	}
698
699	/**
700	* Returns a String representation of this map entry. This
701	* implementation returns the string representation of this
702	* entry's key followed by the equals character ("<tt>=</tt>")
703	* followed by the string representation of this entry's value.
704	*
705	* @return a String representation of this map entry
706	*/
707	public String toString() {
708	return key + "=" + value;
709	}
710
711	}
712
713	}