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JavaTM 2 Platform Std. Ed. v1.6.0
java.util
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Nested Class Summary | |
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static class |
AbstractMap.SimpleEntry<K,V>
An Entry maintaining a key and a value. |
static class |
AbstractMap.SimpleImmutableEntry<K,V>
An Entry maintaining an immutable key and value. |
Nested classes/interfaces inherited from interface java.util.Map |
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Map.Entry<K,V> |
Constructor Summary | |
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protected |
AbstractMap()
Sole constructor. |
Method Summary | |
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void |
clear()
Removes all of the mappings from this map (optional operation). |
protected Object |
clone()
Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned. |
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 the specified value. |
abstract Set<Map.Entry<K,V>> |
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. |
V |
get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. |
int |
hashCode()
Returns the hash code value for this map. |
boolean |
isEmpty()
Returns true if this map contains no key-value mappings. |
Set<K> |
keySet()
Returns a Set view of the keys contained in this map. |
V |
put(K key,
V value)
Associates the specified value with the specified key in this map (optional operation). |
void |
putAll(Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to this map (optional operation). |
V |
remove(Object key)
Removes the mapping for a key from this map if it is 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<V> |
values()
Returns a Collection view of the values contained in this map. |
Methods inherited from class java.lang.Object |
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finalize, getClass, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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protected AbstractMap()
Method Detail |
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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.
containsValue
in interface Map<K,V>
value
- value whose presence in this map is to be tested
ClassCastException
- if the value is of an inappropriate type for
this map (optional)
NullPointerException
- if the specified value is null and this
map does not permit null values (optional)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.
containsKey
in interface Map<K,V>
key
- key whose presence in this map is to be tested
ClassCastException
- if the key is of an inappropriate type for
this map (optional)
NullPointerException
- if the specified key is null and this map
does not permit null keys (optional)public V get(Object key)
null
if this map contains no mapping for the key.
More formally, if this map contains a mapping from a key
k
to a value v
such that (key==null ? k==null :
key.equals(k))
, then this method returns v
; otherwise
it returns null
. (There can be at most one such mapping.)
If this map permits null values, then a return value of
null
does not necessarily indicate that the map
contains no mapping for the key; it's also possible that the map
explicitly maps the key to null
. The containsKey
operation may be used to distinguish these two cases.
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
- the key whose associated value is to be returned
null
if this map contains no mapping for the key
ClassCastException
- if the key is of an inappropriate type for
this map (optional)
NullPointerException
- if the specified key is null and this map
does not permit null keys (optional)public V put(K key, V value)
m.containsKey(k)
would return
true.)
This implementation always throws an UnsupportedOperationException.
key
- key with which the specified value is to be associatedvalue
- value to be associated with the specified key
UnsupportedOperationException
- if the put operation
is not supported by this map
ClassCastException
- if the class of the specified key or value
prevents it from being stored in this map
NullPointerException
- if the specified key or value is null
and this map does not permit null keys or values
IllegalArgumentException
- if some property of the specified key
or value prevents it from being stored in this mappublic V remove(Object key)
(key==null ? k==null : key.equals(k))
, that mapping
is removed. (The map can contain at most one such mapping.)
Returns the value to which this map previously associated the key, or null if the map contained no mapping for the key.
If this map permits null values, then a return value of null does not necessarily indicate that the map contained no mapping for the key; it's also possible that the map explicitly mapped the key to null.
The map will not contain a mapping for the specified key once the call returns.
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.
key
- key whose mapping is to be removed from the map
UnsupportedOperationException
- if the remove operation
is not supported by this map
ClassCastException
- if the key is of an inappropriate type for
this map (optional)
NullPointerException
- if the specified key is null and this
map does not permit null keys (optional)public void putAll(Map<? extends K,? extends V> m)
put(k, v)
on this map once
for each mapping from key k to value v in the
specified map. The behavior of this operation is undefined if the
specified map is modified while the operation is in progress.
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.
m
- mappings to be stored in this map
UnsupportedOperationException
- if the putAll operation
is not supported by this map
ClassCastException
- if the class of a key or value in the
specified map prevents it from being stored in this map
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
IllegalArgumentException
- if some property of a key or value in
the specified map prevents it from being stored in this mappublic void clear()
This implementation calls entrySet().clear().
Note that this implementation throws an UnsupportedOperationException if the entrySet does not support the clear operation.
UnsupportedOperationException
- if the clear operation
is not supported by this mappublic Set<K> keySet()
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 (except through
the iterator's own remove operation), the results of
the iteration are undefined. The set supports element removal,
which removes the corresponding mapping from the map, via the
Iterator.remove, Set.remove,
removeAll, retainAll, and clear
operations. It does not support the add or addAll
operations.
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<V> values()
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
(except through the iterator's own remove operation),
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Collection.remove, removeAll,
retainAll and clear operations. It does not
support the add or addAll operations.
This implementation returns a collection that subclasses 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 abstract Set<Map.Entry<K,V>> entrySet()
Map
Set
view of the mappings 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 (except through
the iterator's own remove operation, or through the
setValue operation on a map entry returned by the
iterator) the results of the iteration are undefined. The set
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Set.remove, removeAll, retainAll and
clear operations. It does not support the
add or addAll operations.
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 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.
o
- object to be compared for equality with this map
Object.hashCode()
,
Hashtable
public int hashCode()
Object.hashCode()
.
This implementation iterates over entrySet(), calling
hashCode()
on each element (entry) in the
set, and adding up the results.
Map.Entry.hashCode()
,
Object.equals(Object)
,
Set.equals(Object)
public String toString()
String.valueOf(Object)
.
protected Object clone() throws CloneNotSupportedException
CloneNotSupportedException
- if the object's class does not
support the Cloneable
interface. Subclasses
that override the clone
method can also
throw this exception to indicate that an instance cannot
be cloned.Cloneable