abstractmap.java

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     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
     * does not support the <tt>clear</tt> operation.
     *
     * @throws    UnsupportedOperationException clear is not supported
     * 		  by this map.
     */
    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        keySet = null;
    transient volatile Collection values = null;

    /**
     * Returns a Set view of the keys contained in this map.  The Set is
     * backed by the map, so changes to the map are reflected in the Set,
     * and vice-versa.  (If the map is modified while an iteration over
     * the Set is in progress, the results of the iteration are undefined.)
     * The Set supports element removal, which removes the corresponding entry
     * from the map, via the Iterator.remove, Set.remove,  removeAll
     * retainAll, and clear operations.  It does not support the add or
     * addAll operations.<p>
     *
     * This implementation returns a Set that subclasses
     * AbstractSet.  The subclass's iterator method returns a "wrapper
     * object" over this map's entrySet() iterator.  The size method delegates
     * to this map's size method and the contains method delegates to this
     * map's containsKey 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.
     *
     * @return a Set view of the keys contained in this map.
     */
    public Set keySet() {
	if (keySet == null) {
	    keySet = new AbstractSet() {
		public Iterator iterator() {
		    return new Iterator() {
			private Iterator i = entrySet().iterator();

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

			public Object next() {
			    return ((Entry)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;
    }

    /**
     * Returns a collection view of the values contained in this map.  The
     * collection is backed by the map, so changes to the map are reflected in
     * the collection, and vice-versa.  (If the map is modified while an
     * iteration over the collection is in progress, the results of the
     * iteration are undefined.)  The collection supports element removal,
     * which removes the corresponding entry from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt> operations.
     * It does not support the <tt>add</tt> or <tt>addAll</tt> operations.<p>
     *
     * This implementation returns a collection that subclasses abstract
     * collection.  The subclass's iterator method returns a "wrapper object"
     * over this map's <tt>entrySet()</tt> iterator.  The size method
     * delegates to this map's size method and the contains method delegates
     * to this map's containsValue 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.
     *
     * @return a collection view of the values contained in this map.
     */
    public Collection values() {
	if (values == null) {
	    values = new AbstractCollection() {
		public Iterator iterator() {
		    return new Iterator() {
			private Iterator i = entrySet().iterator();

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

			public Object next() {
			    return ((Entry)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;
    }

    /**
     * Returns a set view of the mappings contained in this map.  Each element
     * in this set is a Map.Entry.  The set is backed by the map, so changes
     * to the map are reflected in the set, and vice-versa.  (If the map is
     * modified while an iteration over the set is in progress, the results of
     * the iteration are undefined.)  The set supports element removal, which
     * removes the corresponding entry from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
     * <tt>retainAll</tt> and <tt>clear</tt> operations.  It does not support
     * the <tt>add</tt> or <tt>addAll</tt> operations.
     *
     * @return a set view of the mappings contained in this map.
     */
    public abstract Set entrySet();


    // Comparison and hashing

    /**
     * Compares the specified object with this map for equality.  Returns
     * <tt>true</tt> if the given object is also a map and the two maps
     * represent the same mappings.  More formally, two maps <tt>t1</tt> and
     * <tt>t2</tt> represent the same mappings if
     * <tt>t1.keySet().equals(t2.keySet())</tt> and for every key <tt>k</tt>
     * in <tt>t1.keySet()</tt>, <tt> (t1.get(k)==null ? t2.get(k)==null :
     * t1.get(k).equals(t2.get(k))) </tt>.  This ensures that the
     * <tt>equals</tt> method works properly across different implementations
     * of the map interface.<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 set; if
     * not, it 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.
     *
     * @param o object to be compared for equality with this map.
     * @return <tt>true</tt> if the specified object is equal to this map.
     */
    public boolean equals(Object o) {
	if (o == this)
	    return true;

	if (!(o instanceof Map))
	    return false;
	Map t = (Map) o;
	if (t.size() != size())
	    return false;

        try {
            Iterator i = entrySet().iterator();
            while (i.hasNext()) {
                Entry e = (Entry) i.next();
                Object key = e.getKey();
                Object 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;
    }

    /**
     * Returns the hash code value for this map.  The hash code of a map is
     * defined to be the sum of the hash codes of each entry in the map's
     * <tt>entrySet()</tt> view.  This ensures that <tt>t1.equals(t2)</tt>
     * implies that <tt>t1.hashCode()==t2.hashCode()</tt> for any two maps
     * <tt>t1</tt> and <tt>t2</tt>, as required by the general contract of
     * Object.hashCode.<p>
     *
     * This implementation iterates over <tt>entrySet()</tt>, calling
     * <tt>hashCode</tt> on each element (entry) in the Collection, and adding
     * up the results.
     *
     * @return the hash code value for this map.
     * @see Map.Entry#hashCode()
     * @see Object#hashCode()
     * @see Object#equals(Object)
     * @see Set#equals(Object)
     */
    public int hashCode() {
	int h = 0;
	Iterator 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 i = entrySet().iterator();
        boolean hasNext = i.hasNext();
        while (hasNext) {
	    Entry e = (Entry) (i.next());
            Object key = e.getKey();
            Object value = e.getValue();
            buf.append((key == this ?  "(this Map)" : key) + "=" + 
                       (value == this ? "(this Map)": 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 result = (AbstractMap)super.clone();
        result.keySet = null;
        result.values = null;
        return result;
    }

    /**
     * This should be made public as soon as possible.  It greately simplifies
     * the task of implementing Map.
     */
    static class SimpleEntry implements Entry {
	Object key;
	Object value;

	public SimpleEntry(Object key, Object value) {
	    this.key   = key;
            this.value = value;
	}

	public SimpleEntry(Map.Entry e) {
	    this.key   = e.getKey();
            this.value = e.getValue();
	}

	public Object getKey() {
	    return key;
	}

	public Object getValue() {
	    return value;
	}

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

	public String toString() {
	    return key + "=" + value;
	}

        private static boolean eq(Object o1, Object o2) {
            return (o1 == null ? o2 == null : o1.equals(o2));
        }
    }
}