To implement an unmodifiable map, the programmer needs only to extend this - * class and provide an implementation for the entrySet method, which - * returns a set-view of the map's mappings. Typically, the returned set - * will, in turn, be implemented atop AbstractSet. This set should - * not support the add or remove methods, and its iterator - * should not support the remove method. - * - *
To implement a modifiable map, the programmer must additionally override - * this class's put method (which otherwise throws an - * UnsupportedOperationException), and the iterator returned by - * entrySet().iterator() must additionally implement its - * remove method. - * - *
The programmer should generally provide a void (no argument) and map - * constructor, as per the recommendation in the Map interface - * specification. - * - *
The documentation for each non-abstract method 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. - * - *
This class is a member of the
- *
- * Java Collections Framework.
- *
- * @param This implementation returns entrySet().size().
- */
- public int size() {
- return entrySet().size();
- }
-
- /**
- * {@inheritDoc}
- *
- * This implementation returns size() == 0.
- */
- public boolean isEmpty() {
- return size() == 0;
- }
-
- /**
- * {@inheritDoc}
- *
- * This implementation iterates over entrySet() searching
- * for an entry with the specified value. If such an entry is found,
- * true is returned. If the iteration terminates without
- * finding such an entry, false 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 This implementation iterates over entrySet() searching
- * for an entry with the specified key. If such an entry is found,
- * true is returned. If the iteration terminates without
- * finding such an entry, false 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 This implementation iterates over entrySet() 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, null 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 This implementation always throws an
- * UnsupportedOperationException.
- *
- * @throws UnsupportedOperationException {@inheritDoc}
- * @throws ClassCastException {@inheritDoc}
- * @throws NullPointerException {@inheritDoc}
- * @throws IllegalArgumentException {@inheritDoc}
- */
- public V put(K key, V value) {
- throw new UnsupportedOperationException();
- }
-
- /**
- * {@inheritDoc}
- *
- * This implementation iterates over entrySet() searching for an
- * entry with the specified key. If such an entry is found, its value is
- * obtained with its getValue operation, the entry is removed
- * from the collection (and the backing map) with the iterator's
- * remove operation, and the saved value is returned. If the
- * iteration terminates without finding such an entry, null is
- * returned. Note that this implementation requires linear time in the
- * size of the map; many implementations will override this method.
- *
- * Note that this implementation throws an
- * UnsupportedOperationException if the entrySet
- * iterator does not support the remove 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 This implementation iterates over the specified map's
- * entrySet() collection, and calls this map's put
- * operation once for each entry returned by the iteration.
- *
- * Note that this implementation throws an
- * UnsupportedOperationException if this map does not support
- * the put operation and the specified map is nonempty.
- *
- * @throws UnsupportedOperationException {@inheritDoc}
- * @throws ClassCastException {@inheritDoc}
- * @throws NullPointerException {@inheritDoc}
- * @throws IllegalArgumentException {@inheritDoc}
- */
- public void putAll(Map m) {
- for (Map.Entry e : m.entrySet())
- put(e.getKey(), e.getValue());
- }
-
- /**
- * {@inheritDoc}
- *
- * This implementation calls entrySet().clear().
- *
- * Note that this implementation throws an
- * UnsupportedOperationException if the entrySet
- * does not support the clear 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 This implementation returns a set that subclasses {@link 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.
- *
- * 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 This implementation returns a collection that subclasses {@link
- * AbstractCollection}. 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
- * containsValue method.
- *
- * 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 This implementation first checks if the specified object is this map;
- * if so it returns true. Then, it checks if the specified
- * object is a map whose size is identical to the size of this map; if
- * not, it returns false. If so, it iterates over this map's
- * entrySet collection, and checks that the specified map
- * contains each mapping that this map contains. If the specified map
- * fails to contain such a mapping, false is returned. If the
- * iteration completes, true is returned.
- *
- * @param o object to be compared for equality with this map
- * @return true 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 This implementation iterates over entrySet(), calling
- * {@link Map.Entry#hashCode hashCode()} on each element (entry) in the
- * set, and adding up the results.
- *
- * @return the hash code value for this map
- * @see Map.Entry#hashCode()
- * @see Object#equals(Object)
- * @see Set#equals(Object)
- */
- public int hashCode() {
- int h = 0;
- Iterator
- * (e1.getKey()==null ?
- * e2.getKey()==null :
- * e1.getKey().equals(e2.getKey()))
- * &&
- * (e1.getValue()==null ?
- * e2.getValue()==null :
- * e1.getValue().equals(e2.getValue()))
- * This ensures that the {@code equals} method works properly across
- * different implementations of the {@code Map.Entry} interface.
- *
- * @param o object to be compared for equality with this map entry
- * @return {@code true} if the specified object is equal to this map
- * entry
- * @see #hashCode
- */
- 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());
- }
-
- /**
- * Returns the hash code value for this map entry. The hash code
- * of a map entry {@code e} is defined to be:
- * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
- * (e.getValue()==null ? 0 : e.getValue().hashCode())
- * This ensures that {@code e1.equals(e2)} implies that
- * {@code e1.hashCode()==e2.hashCode()} for any two Entries
- * {@code e1} and {@code e2}, as required by the general
- * contract of {@link Object#hashCode}.
- *
- * @return the hash code value for this map entry
- * @see #equals
- */
- 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 ("=")
- * 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 setValue. This class may be
- * convenient in methods that return thread-safe snapshots of
- * key-value mappings.
- *
- * @since 1.6
- */
- public static class SimpleImmutableEntry
- * (e1.getKey()==null ?
- * e2.getKey()==null :
- * e1.getKey().equals(e2.getKey()))
- * &&
- * (e1.getValue()==null ?
- * e2.getValue()==null :
- * e1.getValue().equals(e2.getValue()))
- * This ensures that the {@code equals} method works properly across
- * different implementations of the {@code Map.Entry} interface.
- *
- * @param o object to be compared for equality with this map entry
- * @return {@code true} if the specified object is equal to this map
- * entry
- * @see #hashCode
- */
- 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());
- }
-
- /**
- * Returns the hash code value for this map entry. The hash code
- * of a map entry {@code e} is defined to be:
- * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
- * (e.getValue()==null ? 0 : e.getValue().hashCode())
- * This ensures that {@code e1.equals(e2)} implies that
- * {@code e1.hashCode()==e2.hashCode()} for any two Entries
- * {@code e1} and {@code e2}, as required by the general
- * contract of {@link Object#hashCode}.
- *
- * @return the hash code value for this map entry
- * @see #equals
- */
- 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 ("=")
- * followed by the string representation of this entry's value.
- *
- * @return a String representation of this map entry
- */
- public String toString() {
- return key + "=" + value;
- }
-
- }
-
-}