java.lang.Object | ||
↳ | java.util.AbstractMap<K, V> | |
↳ | java.util.IdentityHashMap<K, V> |
IdentityHashMap is a variant on HashMap which tests equality by reference instead of equality by value. Basically, keys and values are compared for equality by checking if their references are equal rather than by calling the "equals" function.
Note: This class intentionally violates the general contract of Map
's on comparing objects by their equals
method.
IdentityHashMap uses open addressing (linear probing in particular) for collision resolution. This is different from HashMap which uses Chaining.
Like HashMap, IdentityHashMap is not thread safe, so access by multiple threads must be synchronized by an external mechanism such as Collections.synchronizedMap.
Public Constructors | |||||||||||
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Creates an IdentityHashMap with default expected maximum size.
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Creates an IdentityHashMap with the specified maximum size parameter.
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Creates an IdentityHashMap using the given map as initial values.
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Public Methods | |||||||||||
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Removes all elements from this map, leaving it empty.
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Returns a new IdentityHashMap with the same mappings and size as this
one.
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Returns whether this map contains the specified key.
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Returns whether this map contains the specified value.
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Returns a set containing all of the mappings in this map.
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Compares this map with other objects.
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Returns the value of the mapping with the specified key.
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Returns whether this IdentityHashMap has no elements.
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Returns a set of the keys contained in this map.
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Maps the specified key to the specified value.
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Copies all the mappings in the specified map to this map.
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Removes the mapping with the specified key from this map.
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Returns the number of mappings in this IdentityHashMap.
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Returns a collection of the values contained in this map.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.util.AbstractMap
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From class
java.lang.Object
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From interface
java.util.Map
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Creates an IdentityHashMap with default expected maximum size.
Creates an IdentityHashMap with the specified maximum size parameter.
maxSize | The estimated maximum number of entries that will be put in this map. |
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Creates an IdentityHashMap using the given map as initial values.
map | A map of (key,value) pairs to copy into the IdentityHashMap. |
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Returns a new IdentityHashMap with the same mappings and size as this one.
Returns whether this map contains the specified key.
key | the key to search for. |
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true
if this map contains the specified key,
false
otherwise.
Returns whether this map contains the specified value.
value | the value to search for. |
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true
if this map contains the specified value,
false
otherwise.
Returns a set containing all of the mappings in this map. Each mapping is
an instance of Map.Entry
. As the set is backed by this map,
changes in one will be reflected in the other.
Compares this map with other objects. This map is equal to another map is it represents the same set of mappings. With this map, two mappings are the same if both the key and the value are equal by reference. When compared with a map that is not an IdentityHashMap, the equals method is neither necessarily symmetric (a.equals(b) implies b.equals(a)) nor transitive (a.equals(b) and b.equals(c) implies a.equals(c)).
object | the object to compare to. |
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Returns the value of the mapping with the specified key.
key | the key. |
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Returns whether this IdentityHashMap has no elements.
true
if this IdentityHashMap has no elements,
false
otherwise.Returns a set of the keys contained in this map. The set is backed by this map so changes to one are reflected by the other. The set does not support adding.
Maps the specified key to the specified value.
key | the key. |
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value | the value. |
null
if there was no such mapping.
Copies all the mappings in the specified map to this map. These mappings will replace all mappings that this map had for any of the keys currently in the given map.
map | the map to copy mappings from. |
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NullPointerException | if map is null .
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Removes the mapping with the specified key from this map.
key | the key of the mapping to remove. |
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null
if no mapping
for the specified key was found.
Returns the number of mappings in this IdentityHashMap.
Returns a collection of the values contained in this map. The collection is backed by this map so changes to one are reflected by the other. The collection supports remove, removeAll, retainAll and clear operations, and it does not support add or addAll operations.
This method returns a collection which is the subclass of
AbstractCollection. The iterator method of this subclass returns a
"wrapper object" over the iterator of map's entrySet(). The size
method wraps the map's size method and the contains
method wraps
the map's containsValue method.
The collection is created when this method is called for the first time and returned in response to all subsequent calls. This method may return different collections when multiple concurrent calls occur, since no synchronization is performed.