java.util
Interface Map<K,V>
- SortedMap<K,V>
- AbstractMap<K,V>, Attributes, EnumMap<K,extends,Enum,K,V>, Gnu, GnuCallbacks, GnuCrypto, GnuSasl, HashMap<K,V>, Hashtable<K,V>, IdentityHashMap<K,V>, Jessie, LinkedHashMap<K,V>, LRUCache<K,V>, PrinterStateReasons, Properties, Provider, RenderingHints, TabularDataSupport, TreeMap<K,V>, UIDefaults, WeakHashMap<K,V>, WeakIdentityHashMap
An object that maps keys onto values. Keys cannot be duplicated. This
interface replaces the obsolete
Dictionary abstract class.
The map has three collection views, which are backed by the map
(modifications on one show up on the other): a set of keys, a collection
of values, and a set of key-value mappings. Some maps have a guaranteed
order, but not all do.
Note: Be careful about using mutable keys. Behavior is unspecified if
a key's comparison behavior is changed after the fact. As a corollary
to this rule, don't use a Map as one of its own keys or values, as it makes
hashCode and equals have undefined behavior.
All maps are recommended to provide a no argument constructor, which builds
an empty map, and one that accepts a Map parameter and copies the mappings
(usually by putAll), to create an equivalent map. Unfortunately, Java
cannot enforce these suggestions.
The map may be unmodifiable, in which case unsupported operations will
throw an UnsupportedOperationException. Note that some operations may be
safe, such as putAll(m) where m is empty, even if the operation would
normally fail with a non-empty argument.
static interface | Map.Entry- A map entry (key-value pair).
|
Set | V>> entrySet()- Returns a set view of the mappings in this Map.
|
void | clear()- Remove all entries from this Map (optional operation).
|
boolean | containsKey(Object key)- Returns true if this contains a mapping for the given key.
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boolean | containsValue(Object value)- Returns true if this contains at least one mapping with the given value.
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boolean | equals(Object o)- Compares the specified object with this map for equality.
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V | get(Object key)- Returns the value mapped by the given key.
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int | hashCode()- Returns the hash code for this map.
|
boolean | isEmpty()- Returns true if the map contains no mappings.
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Set | keySet()- Returns a set view of the keys in this Map.
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V | put(K key, V value)- Associates the given key to the given value (optional operation).
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void | putAll(extends K, V> m)- Copies all entries of the given map to this one (optional operation).
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V | remove(Object o)- Removes the mapping for this key if present (optional operation).
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int | size()- Returns the number of key-value mappings in the map.
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Collection | values()- Returns a collection (or bag) view of the values in this Map.
|
V>> entrySet
public SetV>> entrySet()
Returns a set view of the mappings in this Map. Each element in the
set is a Map.Entry. The set is backed by the map, so that changes in
one show up in the other. Modifications made while an iterator is
in progress cause undefined behavior. If the set supports removal,
these methods remove the underlying mapping from the map:
Iterator.remove, Set.remove,
removeAll, retainAll, and clear.
Element addition, via add or addAll, is
not supported via this set.
- the set view of all mapping entries
clear
public void clear()
Remove all entries from this Map (optional operation).
containsKey
public boolean containsKey(Object key)
Returns true if this contains a mapping for the given key.
key - the key to search for
- true if the map contains the key
containsValue
public boolean containsValue(Object value)
Returns true if this contains at least one mapping with the given value.
In other words, returns true if a value v exists where
(value == null ? v == null : value.equals(v)). This usually
requires linear time.
value - the value to search for
- true if the map contains the value
equals
public boolean equals(Object o)
Compares the specified object with this map for equality. Returns
true if the other object is a Map with the same mappings,
that is,
o instanceof Map && entrySet().equals(((Map) o).entrySet();
This allows comparison of maps, regardless of implementation.
- equals in interface Object
o - the object to be compared
- true if the object equals this map
get
public V get(Object key)
Returns the value mapped by the given key. Returns null if
there is no mapping. However, in Maps that accept null values, you
must rely on containsKey to determine if a mapping exists.
- the value associated with the key, or null if key not in map
hashCode
public int hashCode()
Returns the hash code for this map. This is the sum of all hashcodes
for each Map.Entry object in entrySet. This allows comparison of maps,
regardless of implementation, and satisfies the contract of
Object.hashCode.
- hashCode in interface Object
isEmpty
public boolean isEmpty()
Returns true if the map contains no mappings.
keySet
public Set keySet()
Returns a set view of the keys in this Map. The set is backed by the
map, so that changes in one show up in the other. Modifications made
while an iterator is in progress cause undefined behavior. If the set
supports removal, these methods remove the underlying mapping from
the map: Iterator.remove, Set.remove,
removeAll, retainAll, and clear.
Element addition, via add or addAll, is
not supported via this set.
put
public V put(K key,
V value) Associates the given key to the given value (optional operation). If the
map already contains the key, its value is replaced. Be aware that in
a map that permits null values, a null return does not
always imply that the mapping was created.
key - the key to mapvalue - the value to be mapped
- the previous value of the key, or null if there was no mapping
putAll
public void putAll(extends K,
V> m) Copies all entries of the given map to this one (optional operation). If
the map already contains a key, its value is replaced.
m - the mapping to load into this map
remove
public V remove(Object o)
Removes the mapping for this key if present (optional operation). If
the key is not present, this returns null. Note that maps which permit
null values may also return null if the key was removed.
- the value the key mapped to, or null if not present.
size
public int size()
Returns the number of key-value mappings in the map. If there are more
than Integer.MAX_VALUE mappings, return Integer.MAX_VALUE.
values
public Collection values()
Returns a collection (or bag) view of the values in this Map. The
collection is backed by the map, so that changes in one show up in
the other. Modifications made while an iterator is in progress cause
undefined behavior. If the collection supports removal, these methods
remove the underlying mapping from the map: Iterator.remove,
Collection.remove, removeAll,
retainAll, and clear. Element addition, via
add or addAll, is not supported via this
collection.
- the collection view of all values
Map.java: interface Map -- An object that maps keys to values
interface Map.Entry -- an Entry in a Map
Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.
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