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Java Platform 1.2 |
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java.lang.Object | +--java.util.AbstractMap
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.
Map,
Collection| Constructor Summary | |
protected |
AbstractMap()
Sole constructor. |
| Method Summary | |
void |
clear()
Removes all mappings from this map (optional operation). |
boolean |
containsKey(Object key)
Returns true if this map contains a mapping for the specified key. |
boolean |
containsValue(Object value)
Returns true if this map maps one or more keys to this value. |
abstract Set |
entrySet()
Returns a set view of the mappings contained in this map. |
boolean |
equals(Object o)
Compares the specified object with this map for equality. |
Object |
get(Object key)
Returns the value to which this map maps the specified key. |
int |
hashCode()
Returns the hash code value for this map. |
boolean |
isEmpty()
Returns true if this map contains no key-value mappings. |
Set |
keySet()
Returns a Set view of the keys contained in this map. |
Object |
put(Object key,
Object value)
Associates the specified value with the specified key in this map (optional operation). |
void |
putAll(Map t)
Copies all of the mappings from the specified map to this map (optional operation). |
Object |
remove(Object key)
Removes the mapping for this key from this map if present (optional operation). |
int |
size()
Returns the number of key-value mappings in this map. |
String |
toString()
Returns a string representation of this map. |
Collection |
values()
Returns a collection view of the values contained in this map. |
| Methods inherited from class java.lang.Object |
clone,
finalize,
getClass,
notify,
notifyAll,
wait,
wait,
wait |
| Constructor Detail |
protected AbstractMap()
| Method Detail |
public int size()
This implementation returns entrySet().size().
public boolean isEmpty()
This implementation returns size() == 0.
public boolean containsValue(Object value)
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.
value - value whose presence in this map is to be tested.public boolean containsKey(Object key)
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.
key - key whose presence in this map is to be tested.public Object get(Object key)
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.
key - key whose associated value is to be returned.containsKey(Object)
public Object put(Object key,
Object value)
This implementation always throws an UnsupportedOperationException.
key - key with which the specified value is to be associated.value - value to be associated with the specified key.public Object remove(Object key)
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 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.
key - key whose mapping is to be removed from the map.public void putAll(Map t)
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.
t - mappings to be stored in this map.public void clear()
This implementation calls entrySet().clear().
public Set keySet()
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.
public Collection values()
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.
public abstract Set entrySet()
public boolean equals(Object o)
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 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.
o - object to be compared for equality with this map.public int hashCode()
This implementation iterates over entrySet(), calling hashCode on each element (entry) in the Collection, and adding up the results.
Map.Entry.hashCode(),
Object.hashCode(),
Object.equals(Object),
Set.equals(Object)public String toString()
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.
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Java Platform 1.2 |
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