java.lang.Object | +--java.util.AbstractMapAll Implemented Interfaces:
AbstractMap() The main constructor, for use by subclasses. |
void | clear() Remove all entries from this Map (optional operation). |
java.lang.Object | clone() Create a shallow copy of this Map, no keys or values are copied. |
boolean | containsKey(java.lang.Object key) Returns true if this contains a mapping for the given key. |
boolean | containsValue(java.lang.Object value) Returns true if this contains at least one mapping with the given value. |
java.util.Set | entrySet() Returns a set view of the mappings in this Map. |
boolean | equals(java.lang.Object o) Compares the specified object with this map for equality. |
java.lang.Object | get(java.lang.Object key) Returns the value mapped by the given key. |
int | hashCode() Returns the hash code for this map. |
boolean | isEmpty() Returns true if the map contains no mappings. |
java.util.Set | keySet() Returns a set view of this map's keys. |
java.lang.Object | put(java.lang.Object key, java.lang.Object value) Associates the given key to the given value (optional operation). |
void | putAll(java.util.Map m) Copies all entries of the given map to this one (optional operation). |
java.lang.Object | remove(java.lang.Object key) Removes the mapping for this key if present (optional operation). |
int | size() Returns the number of key-value mappings in the map. |
java.lang.String | toString() Returns a String representation of this map. |
java.util.Collection | values() Returns a collection or bag view of this map's values. |
protected AbstractMap()
public void clear()
AbstractMap.clear
unless you want an infinite loop.
UnsupportedOperationException
- if entrySet().clear()
does not support clearing.protected Object clone()
super.clone()
.
CloneNotSupportedException
- if a subclass is not Cloneablepublic boolean containsKey(java.lang.Object key)
entrySet()
, returning true
if a match
is found, false
if the iteration ends. Many subclasses
can implement this more efficiently.
key
- the key to search forNullPointerException
- if key is null
but the map
does not permit null keyspublic boolean containsValue(java.lang.Object value)
entrySet()
, returning true
if a match
is found, false
if the iteration ends. A match is
defined as (value == null ? v == null : value.equals(v))
Subclasses are unlikely to implement this more efficiently.
value
- the value to search forpublic Set entrySet()
Iterator.remove
, Set.remove
,
removeAll
, retainAll
, and clear
.
Element addition is not supported via this set.
public boolean equals(java.lang.Object o)
true
if the other object is a Map with the same mappings,
that is,o instanceof Map && entrySet().equals(((Map) o).entrySet();
o
- the object to be comparedpublic Object get(java.lang.Object key)
null
if
there is no mapping. However, in Maps that accept null values, you
must rely on containsKey
to determine if a mapping exists.
This iteration takes linear time, searching entrySet().iterator() of
the key. Many implementations override this method.
key
- the key to look upNullPointerException
- if this map does not accept null keyspublic int hashCode()
public boolean isEmpty()
size() == 0
.
public Set keySet()
This implementation creates an AbstractSet, where the iterator wraps the entrySet iterator, size defers to the Map's size, and contains defers to the Map's containsKey. The set is created on first use, and returned on subsequent uses, although since no synchronization occurs, there is a slight possibility of creating two sets.
public Object put(java.lang.Object key, java.lang.Object value)
null
values, a null return does not always
imply that the mapping was created.
key
- the key to mapvalue
- the value to be mappedUnsupportedOperationException
- if the operation is not supportedClassCastException
- if the key or value is of the wrong typeIllegalArgumentException
- if something about this key or value
prevents it from existing in this mapNullPointerException
- if the map forbids null keys or valuespublic void putAll(java.util.Map m)
put
,
so it is not supported if puts are not.
m
- the mapping to load into this mapUnsupportedOperationException
- if the operation is not supportedClassCastException
- if a key or value is of the wrong typeIllegalArgumentException
- if something about a key or value
prevents it from existing in this mapNullPointerException
- if the map forbids null keys or values, or
if m
is null.public Object remove(java.lang.Object key)
remove
method.
It returns the result of getValue()
on the entry, if found,
or null if no entry is found. Note that maps which permit null values
may also return null if the key was removed. If the entrySet does not
support removal, this will also fail. This is O(n), so many
implementations override it for efficiency.
key
- the key to removeUnsupportedOperationException
- if deletion is unsupportedpublic int size()
entrySet().size()
.
public String toString()
getKey() + "=" + getValue()
), separated by a comma and
space (", "), and surrounded by braces ('{' and '}'). This implementation
uses a StringBuffer and iterates over the entrySet to build the String.
Note that this can fail with an exception if underlying keys or
values complete abruptly in toString().
public Collection values()
This implementation creates an AbstractCollection, where the iterator wraps the entrySet iterator, size defers to the Map's size, and contains defers to the Map's containsValue. The collection is created on first use, and returned on subsequent uses, although since no synchronization occurs, there is a slight possibility of creating two collections.
entrySet
(usually via an AbstractSet). To make it modifiable, also implementput
, and haveentrySet().iterator()
supportremove
.It is recommended that classes which extend this support at least the no-argument constructor, and a constructor which accepts another Map. Further methods in this class may be overridden if you have a more efficient implementation.