java::util::AbstractMap Class Reference

Inheritance diagram for java::util::AbstractMap:

Inheritance graph
java::util::HashMapjava::util::TreeMapjava::util::Mapjava::lang::Interfacejava::lang::Object
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Collaboration diagram for java::util::AbstractMap:

Collaboration graph
java::util::Mapjava::lang::Interfacejava::lang::Object
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List of all members.


Detailed Description

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.

Author:
Josh Bloch
Version:
1.32, 12/03/01
See also:
Map

Collection

Since:
1.2

Public Member Functions

virtual jint size () const
 Returns the number of elements in this collection.
virtual jboolean isEmpty () const
 Returns true if this collection contains no elements.
virtual jboolean containsKey (const ObjectRef &key) const
 Returns true if this map contains a mapping for the specified key.
virtual jboolean containsValue (const ObjectRef &value) const
 Returns true if this map maps one or more keys to the specified value.
virtual ObjectRef get (const ObjectRef &key) const
 Returns the value to which this map maps the specified key.
virtual ObjectRef put (const ObjectRef &key, const ObjectRef &value)
 Associates the specified value with the specified key in this map (optional operation).
virtual ObjectRef remove (const ObjectRef &key)
 Removes the mapping for this key from this map if it is present (optional operation).
virtual void putAll (const Map &t)
 Copies all of the mappings from the specified map to this map (optional operation).
virtual void clear ()
 Removes all mappings from this map (optional operation).
virtual Ref< SetkeySet () const
 Returns a set view of the keys contained in this map.
virtual Ref< Collectionvalues () const
 Returns a collection view of the values contained in this map.
virtual jboolean equals (const Object &o) const
 Compares the specified object with this map for equality.
virtual jint hashCode () const
 Returns the hash code value for this map.
virtual String toString () const
 Returns a string representation of the object.

Protected Member Functions

 AbstractMap ()
 Sole constructor.

Classes

class  ImmutableEntry
class  SimpleEntry

Constructor & Destructor Documentation

java::util::AbstractMap::AbstractMap (  )  [protected]

Sole constructor.

(For invocation by subclass constructors, typically implicit.)


Member Function Documentation

virtual jint java::util::AbstractMap::size (  )  const [virtual]

Returns the number of elements in this collection.

If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Returns:
the number of elements in this collection

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual jboolean java::util::AbstractMap::isEmpty (  )  const [virtual]

Returns true if this collection contains no elements.

This implementation returns size() == 0.

Returns:
true if this collection contains no elements.

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual jboolean java::util::AbstractMap::containsKey ( const ObjectRef key  )  const [virtual]

Returns true if this map contains a mapping for the specified key.

More formally, returns true if and only if this map contains at a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Parameters:
key key whose presence in this map is to be tested.
Returns:
true if this map contains a mapping for the specified key.
Exceptions:
ClassCastException if the key is of an inappropriate type for this map (optional).
NullPointerException if the key is null and this map does not not permit null keys (optional).

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual jboolean java::util::AbstractMap::containsValue ( const ObjectRef value  )  const [virtual]

Returns true if this map maps one or more keys to the specified 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 the Map interface.

Parameters:
value value whose presence in this map is to be tested.
Returns:
true if this map maps one or more keys to the specified value.
Exceptions:
ClassCastException if the value is of an inappropriate type for this map (optional).
NullPointerException if the value is null and this map does not not permit null values (optional).

Implements java::util::Map.

Reimplemented in java::util::TreeMap.

virtual ObjectRef java::util::AbstractMap::get ( const ObjectRef key  )  const [virtual]

Returns the value to which this map maps the specified key.

Returns null if the map contains no mapping for this key. 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.

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.)

Parameters:
key key whose associated value is to be returned.
Returns:
the value to which this map maps the specified key, or null if the map contains no mapping for this key.
Exceptions:
ClassCastException if the key is of an inappropriate type for this map (optional).
NullPointerException key is null and this map does not not permit null keys (optional).
See also:
containsKey(Object)

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual ObjectRef java::util::AbstractMap::put ( const ObjectRef key,
const ObjectRef value 
) [virtual]

Associates the specified value with the specified key in this map (optional operation).

If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.))

Parameters:
key key with which the specified value is to be associated.
value value to be associated with the specified key.
Returns:
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.
Exceptions:
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.
IllegalArgumentException if some aspect of this key or value prevents it from being stored in this map.
NullPointerException this map does not permit null keys or values, and the specified key or value is null.

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual ObjectRef java::util::AbstractMap::remove ( const ObjectRef key  )  [virtual]

Removes the mapping for this key from this map if it is present (optional operation).

More formally, if this map contains a mapping from key k to value v such that (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 the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

Parameters:
key key whose mapping is to be removed from the map.
Returns:
previous value associated with specified key, or null if there was no mapping for key.
Exceptions:
ClassCastException if the key is of an inappropriate type for this map (optional).
NullPointerException if the key is null and this map does not not permit null keys (optional).
UnsupportedOperationException if the remove method is not supported by this map.

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual void java::util::AbstractMap::putAll ( const Map t  )  [virtual]

Copies all of the mappings from the specified map to this map (optional operation).

The effect of this call is equivalent to that of calling 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 unspecified if the specified map is modified while the operation is in progress.

Parameters:
t Mappings to be stored in this map.
Exceptions:
UnsupportedOperationException if the putAll method 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.
IllegalArgumentException some aspect of a key or value in the specified map prevents it from being stored in this map.
NullPointerException 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.

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual void java::util::AbstractMap::clear (  )  [virtual]

Removes all mappings from this map (optional operation).

Exceptions:
UnsupportedOperationException clear is not supported by this map.

Implements java::util::Map.

Reimplemented in java::util::HashMap, and java::util::TreeMap.

virtual Ref<Set> java::util::AbstractMap::keySet (  )  const [virtual]

Returns a 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, 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.

Returns:
a set view of the keys contained in this map.

Implements java::util::Map.

Reimplemented in java::util::TreeMap.

virtual Ref<Collection> java::util::AbstractMap::values (  )  const [virtual]

Returns a 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, 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.

Returns:
a collection view of the values contained in this map.

Implements java::util::Map.

Reimplemented in java::util::TreeMap.

virtual jboolean java::util::AbstractMap::equals ( const Object o  )  const [virtual]

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 t1 and t2 represent the same mappings if t1.entrySet().equals(t2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.

Parameters:
o object to be compared for equality with this map.
Returns:
true if the specified object is equal to this map.

Reimplemented from java::lang::Object.

Reimplemented in java::util::TreeMap.

virtual jint java::util::AbstractMap::hashCode (  )  const [virtual]

Returns the hash code value for this map.

The hash code of a map is defined to be the sum of the hashCodes of each entry in the map's entrySet view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.

Returns:
the hash code value for this map.

Reimplemented from java::lang::Object.

Reimplemented in java::util::TreeMap.

virtual String java::util::AbstractMap::toString (  )  const [virtual]

Returns a string representation of the object.

In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `</code>', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: <blockquote>

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 
</blockquote>

Returns:
a string representation of the object.

Reimplemented from java::lang::Object.

Reimplemented in java::util::TreeMap.


The documentation for this class was generated from the following file:
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