abstractpublic class AbstractMap implements Map<K, V>(Code)
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 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.
< Parameters: K - > the type of keys maintained by this map< Parameters: V - > the type of mapped values author: Josh Bloch author: Neal Gafter version: 1.57, 06/12/07 See Also:Map See Also:Collection since: 1.2
Inner Class :public static class SimpleEntry implements Entry<K, V>,java.io.Serializable
Inner Class :public static class SimpleImmutableEntry implements Entry<K, V>,java.io.Serializable
This implementation returns a set that subclasses
AbstractSet .
The subclass's iterator method returns a "wrapper object" over this
map's entrySet() 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.
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.
Note that this implementation throws an
UnsupportedOperationException if the entrySet
does not support the clear operation.
throws: UnsupportedOperationException -
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 - throws: NullPointerException -
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 - throws: NullPointerException -
Compares the specified object with this map for equality. Returns
true if the given object is also a map and the two maps
represent the same mappings. More formally, two maps m1 and
m2 represent the same mappings if
m1.entrySet().equals(m2.entrySet()). This ensures that the
equals method works properly across different implementations
of the Map interface.
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.
Parameters: o - object to be compared for equality with this map true if the specified object is equal to this map
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 - throws: NullPointerException -
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
entrySet() view. This ensures that m1.equals(m2)
implies that m1.hashCode()==m2.hashCode() for any two maps
m1 and m2, as required by the general contract of
Object.hashCode .
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 void putAll(Map<? extends K, ? extends V> m)(Code)
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.
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 - throws: ClassCastException - throws: NullPointerException -
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 entrySet view's iterator, enclosed in braces
("{}"). Adjacent mappings are separated by the characters
", " (comma and space). Each key-value mapping is rendered as
the key followed by an equals sign ("=") followed by the
associated value. Keys and values are converted to strings as by
String.valueOf(Object) .
a string representation of this map
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.
