/* * @(#)AbstractMap.java 1.42 04/02/19 * * Copyright 2004 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 Map * interface, to minimize the effort required to implement this interface.
* * 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 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.
*
* This class is a member of the
*
* Java Collections Framework.
*
* @author Josh Bloch
* @author Neal Gafter
* @version 1.42, 02/19/04
* @see Map
* @see Collection
* @since 1.2
*/
public abstract class AbstractMap
*
* This implementation returns entrySet().size().
*
* @return the number of key-value mappings in this map.
*/
public int size() {
return entrySet().size();
}
/**
* Returns true if this map contains no key-value mappings.
*
* This implementation returns size() == 0.
*
* @return true if this map contains no key-value mappings.
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Returns true if this map maps one or more keys to this value.
* More formally, returns true if and only if this map contains
* at least one mapping to a value v such that (value==null ?
* v==null : value.equals(v)). This operation will probably require
* time linear in the map size for most implementations of map.
*
* 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.
*
* @param value value whose presence in this map is to be tested.
*
* @return true if this map maps one or more keys to this value.
*/
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.
*
* @param key key whose presence in this map is to be tested.
* @return true if this map contains a mapping for the specified
* key.
*
* @throws NullPointerException if the key is null and this map
* does not permit null keys.
*/
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.
*
* @param key key whose associated value is to be returned.
* @return the value to which this map maps the specified key.
*
* @throws NullPointerException if the key is null and this map
* does not permit null keys.
*
* @see #containsKey(Object)
*/
public V get(Object key) {
Iterator
*
* This implementation always throws an
* UnsupportedOperationException.
*
* @param key key with which the specified value is to be associated.
* @param value value to be associated with the specified key.
*
* @return previous value associated with specified key, or null
* if there was no mapping for key. (A null return can
* also indicate that the map previously associated null
* with the specified key, if the implementation supports
* null values.)
*
* @throws UnsupportedOperationException if the put operation is
* not supported by this map.
*
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map.
*
* @throws IllegalArgumentException if some aspect of this key or value *
* prevents it from being stored in this map.
*
* @throws NullPointerException if this map does not permit null
* keys or values, and the specified key or value is
* null.
*/
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
/**
* Removes the mapping for this key from this map if present (optional
* operation).
*
* 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.
*
* @param key key whose mapping is to be removed from the map.
* @return previous value associated with specified key, or null
* if there was no entry for key. (A null return can
* also indicate that the map previously associated null
* with the specified key, if the implementation supports
* null values.)
* @throws UnsupportedOperationException if the remove operation
* is not supported by this map.
*/
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.
*
* @param t mappings to be stored in this map.
*
* @throws UnsupportedOperationException if the putAll operation
* is not supported by this map.
*
* @throws ClassCastException if the class of a key or value in the
* specified map prevents it from being stored in this map.
*
* @throws IllegalArgumentException if some aspect of a key or value in
* the specified map prevents it from being stored in this map.
* @throws NullPointerException if the specified map is null, or if
* this map does not permit null keys or values, and the
* specified map contains null keys or values.
*/
public void putAll(Map extends K, ? extends V> t) {
Iterator extends Entry extends K, ? extends V>> i = t.entrySet().iterator();
while (i.hasNext()) {
Entry extends K, ? extends V> e = i.next();
put(e.getKey(), e.getValue());
}
}
/**
* Removes all mappings from this map (optional operation).
*
* This implementation calls entrySet().clear().
*
* Note that this implementation throws an
* UnsupportedOperationException if the entrySet
* does not support the clear 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
*
* 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.
*
* 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
*
* This implementation returns a collection that subclasses abstract
* collection. 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.
*
* @return a collection view of the values contained in this map.
*/
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 set; 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
* hashCode 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
*
* This implementation creates an empty string buffer, appends a left
* brace, and iterates over the map's entrySet view, appending
* the string representation of each map.entry in turn. After
* appending each entry except the last, the string ", " 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