ArrayMap
public
final
class
ArrayMap
extends Object
implements
Map<K, V>
java.lang.Object | |
↳ | android.util.ArrayMap<K, V> |
ArrayMap is a generic key->value mapping data structure that is
designed to be more memory efficient than a traditional HashMap
.
It keeps its mappings in an array data structure -- an integer array of hash
codes for each item, and an Object array of the key/value pairs. This allows it to
avoid having to create an extra object for every entry put in to the map, and it
also tries to control the growth of the size of these arrays more aggressively
(since growing them only requires copying the entries in the array, not rebuilding
a hash map).
Note that this implementation is not intended to be appropriate for data structures that may contain large numbers of items. It is generally slower than a traditional HashMap, since lookups require a binary search and adds and removes require inserting and deleting entries in the array. For containers holding up to hundreds of items, the performance difference is not significant, less than 50%.
Because this container is intended to better balance memory use, unlike most other standard Java containers it will shrink its array as items are removed from it. Currently you have no control over this shrinking -- if you set a capacity and then remove an item, it may reduce the capacity to better match the current size. In the future an explicit call to set the capacity should turn off this aggressive shrinking behavior.
This structure is NOT thread-safe.
Summary
Public constructors | |
---|---|
ArrayMap()
Create a new empty ArrayMap. |
|
ArrayMap(int capacity)
Create a new ArrayMap with a given initial capacity. |
|
ArrayMap(ArrayMap<K, V> map)
Create a new ArrayMap with the mappings from the given ArrayMap. |
Public methods | |
---|---|
void
|
clear()
Make the array map empty. |
boolean
|
containsAll(Collection<?> collection)
Determine if the array map contains all of the keys in the given collection. |
boolean
|
containsKey(Object key)
Check whether a key exists in the array. |
boolean
|
containsValue(Object value)
Check whether a value exists in the array. |
void
|
ensureCapacity(int minimumCapacity)
Ensure the array map can hold at least minimumCapacity items. |
Set<Entry<K, V>>
|
entrySet()
Return a |
boolean
|
equals(Object object)
Indicates whether some other object is "equal to" this one. This implementation returns false if the object is not a map, or if the maps have different sizes. |
void
|
forEach(BiConsumer<? super K, ? super V> action)
Performs the given action for all elements in the stored order. |
V
|
get(Object key)
Retrieve a value from the array. |
int
|
hashCode()
Returns a hash code value for the object. |
int
|
indexOfKey(Object key)
Returns the index of a key in the set. |
int
|
indexOfValue(Object value)
Returns an index for which |
boolean
|
isEmpty()
Return true if the array map contains no items. |
K
|
keyAt(int index)
Return the key at the given index in the array. |
Set<K>
|
keySet()
Return a |
V
|
put(K key, V value)
Add a new value to the array map. |
void
|
putAll(ArrayMap<? extends K, ? extends V> array)
Perform a |
void
|
putAll(Map<? extends K, ? extends V> map)
Perform a |
V
|
remove(Object key)
Remove an existing key from the array map. |
boolean
|
removeAll(Collection<?> collection)
Remove all keys in the array map that exist in the given collection. |
V
|
removeAt(int index)
Remove the key/value mapping at the given index. |
void
|
replaceAll(BiFunction<? super K, ? super V, ? extends V> function)
Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception. |
boolean
|
retainAll(Collection<?> collection)
Remove all keys in the array map that do not exist in the given collection. |
V
|
setValueAt(int index, V value)
Set the value at a given index in the array. |
int
|
size()
Return the number of items in this array map. |
String
|
toString()
Returns a string representation of the object. This implementation composes a string by iterating over its mappings. |
V
|
valueAt(int index)
Return the value at the given index in the array. |
Collection<V>
|
values()
Return a |
Inherited methods | |
---|---|
Public constructors
ArrayMap
public ArrayMap ()
Create a new empty ArrayMap. The default capacity of an array map is 0, and will grow once items are added to it.
ArrayMap
public ArrayMap (int capacity)
Create a new ArrayMap with a given initial capacity.
Parameters | |
---|---|
capacity |
int |
ArrayMap
public ArrayMap (ArrayMap<K, V> map)
Create a new ArrayMap with the mappings from the given ArrayMap.
Parameters | |
---|---|
map |
ArrayMap |
Public methods
containsAll
public boolean containsAll (Collection<?> collection)
Determine if the array map contains all of the keys in the given collection.
Parameters | |
---|---|
collection |
Collection : The collection whose contents are to be checked against. |
Returns | |
---|---|
boolean |
Returns true if this array map contains a key for every entry in collection, else returns false. |
containsKey
public boolean containsKey (Object key)
Check whether a key exists in the array.
Parameters | |
---|---|
key |
Object : The key to search for. |
Returns | |
---|---|
boolean |
Returns true if the key exists, else false. |
containsValue
public boolean containsValue (Object value)
Check whether a value exists in the array. This requires a linear search through the entire array.
Parameters | |
---|---|
value |
Object : The value to search for. |
Returns | |
---|---|
boolean |
Returns true if the value exists, else false. |
ensureCapacity
public void ensureCapacity (int minimumCapacity)
Ensure the array map can hold at least minimumCapacity items.
Parameters | |
---|---|
minimumCapacity |
int |
entrySet
public Set<Entry<K, V>> entrySet ()
Return a Set
for iterating over and interacting with all mappings
in the array map.
Note: this is a very inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.
Note:
the semantics of this Set are subtly different than that of aHashMap
: most important,
the Map.Entry
object returned by its iterator is a single
object that exists for the entire iterator, so you can not hold on to it
after calling Iterator.next
.
Returns | |
---|---|
Set<Entry<K, V>> |
a set view of the mappings contained in this map |
equals
public boolean equals (Object object)
Indicates whether some other object is "equal to" this one.
The equals
method implements an equivalence relation
on non-null object references:
- It is reflexive: for any non-null reference value
x
,x.equals(x)
should returntrue
. - It is symmetric: for any non-null reference values
x
andy
,x.equals(y)
should returntrue
if and only ify.equals(x)
returnstrue
. - It is transitive: for any non-null reference values
x
,y
, andz
, ifx.equals(y)
returnstrue
andy.equals(z)
returnstrue
, thenx.equals(z)
should returntrue
. - It is consistent: for any non-null reference values
x
andy
, multiple invocations ofx.equals(y)
consistently returntrue
or consistently returnfalse
, provided no information used inequals
comparisons on the objects is modified. - For any non-null reference value
x
,x.equals(null)
should returnfalse
.
An equivalence relation partitions the elements it operates on into equivalence classes; all the members of an equivalence class are equal to each other. Members of an equivalence class are substitutable for each other, at least for some purposes.
This implementation returns false if the object is not a map, or if the maps have different sizes. Otherwise, for each key in this map, values of both maps are compared. If the values for any key are not equal, the method returns false, otherwise it returns true.
Parameters | |
---|---|
object |
Object : This value may be null . |
Returns | |
---|---|
boolean |
true if this object is the same as the obj
argument; false otherwise. |
forEach
public void forEach (BiConsumer<? super K, ? super V> action)
Performs the given action for all elements in the stored order. This implementation overrides
the default implementation to avoid iterating using the entrySet()
and iterates in
the key-value order consistent with keyAt(int)
and valueAt(int)
.
Parameters | |
---|---|
action |
BiConsumer : The action to be performed for each element |
get
public V get (Object key)
Retrieve a value from the array.
Parameters | |
---|---|
key |
Object : The key of the value to retrieve. |
Returns | |
---|---|
V |
Returns the value associated with the given key, or null if there is no such key. |
hashCode
public int hashCode ()
Returns a hash code value for the object. This method is
supported for the benefit of hash tables such as those provided by
HashMap
.
The general contract of hashCode
is:
- Whenever it is invoked on the same object more than once during
an execution of a Java application, the
hashCode
method must consistently return the same integer, provided no information used inequals
comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. - If two objects are equal according to the
equals
method, then calling thehashCode
method on each of the two objects must produce the same integer result. - It is not required that if two objects are unequal
according to the
equals
method, then calling thehashCode
method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
Returns | |
---|---|
int |
a hash code value for this object. |
indexOfKey
public int indexOfKey (Object key)
Returns the index of a key in the set.
Parameters | |
---|---|
key |
Object : The key to search for. |
Returns | |
---|---|
int |
Returns the index of the key if it exists, else a negative integer. |
indexOfValue
public int indexOfValue (Object value)
Returns an index for which valueAt(int)
would return the
specified value, or a negative number if no keys map to the
specified value.
Beware that this is a linear search, unlike lookups by key,
and that multiple keys can map to the same value and this will
find only one of them.
Parameters | |
---|---|
value |
Object |
Returns | |
---|---|
int |
isEmpty
public boolean isEmpty ()
Return true if the array map contains no items.
Returns | |
---|---|
boolean |
true if this map contains no key-value mappings |
keyAt
public K keyAt (int index)
Return the key at the given index in the array.
For indices outside of the range 0...size()-1
, the behavior is undefined for
apps targeting Build.VERSION_CODES.P
and earlier, and an
ArrayIndexOutOfBoundsException
is thrown for apps targeting
Build.VERSION_CODES.Q
and later.
Parameters | |
---|---|
index |
int : The desired index, must be between 0 and size() -1. |
Returns | |
---|---|
K |
Returns the key stored at the given index. |
keySet
public Set<K> keySet ()
Return a Set
for iterating over and interacting with all keys
in the array map.
Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.
Returns | |
---|---|
Set<K> |
a set view of the keys contained in this map |
put
public V put (K key, V value)
Add a new value to the array map.
Parameters | |
---|---|
key |
K : The key under which to store the value. If
this key already exists in the array, its value will be replaced. |
value |
V : The value to store for the given key. |
Returns | |
---|---|
V |
Returns the old value that was stored for the given key, or null if there was no such key. |
putAll
public void putAll (ArrayMap<? extends K, ? extends V> array)
Perform a put(java.lang.Object, java.lang.Object)
of all key/value pairs in array
Parameters | |
---|---|
array |
ArrayMap : The array whose contents are to be retrieved. |
putAll
public void putAll (Map<? extends K, ? extends V> map)
Perform a put(java.lang.Object, java.lang.Object)
of all key/value pairs in map
Parameters | |
---|---|
map |
Map : The map whose contents are to be retrieved. |
remove
public V remove (Object key)
Remove an existing key from the array map.
Parameters | |
---|---|
key |
Object : The key of the mapping to remove. |
Returns | |
---|---|
V |
Returns the value that was stored under the key, or null if there was no such key. |
removeAll
public boolean removeAll (Collection<?> collection)
Remove all keys in the array map that exist in the given collection.
Parameters | |
---|---|
collection |
Collection : The collection whose contents are to be used to remove keys. |
Returns | |
---|---|
boolean |
Returns true if any keys were removed from the array map, else false. |
removeAt
public V removeAt (int index)
Remove the key/value mapping at the given index.
For indices outside of the range 0...size()-1
, the behavior is undefined for
apps targeting Build.VERSION_CODES.P
and earlier, and an
ArrayIndexOutOfBoundsException
is thrown for apps targeting
Build.VERSION_CODES.Q
and later.
Parameters | |
---|---|
index |
int : The desired index, must be between 0 and size() -1. |
Returns | |
---|---|
V |
Returns the value that was stored at this index. |
replaceAll
public void replaceAll (BiFunction<? super K, ? super V, ? extends V> function)
Replaces each entry's value with the result of invoking the given function on that entry
until all entries have been processed or the function throws an exception. Exceptions thrown
by the function are relayed to the caller. This implementation overrides
the default implementation to avoid iterating using the entrySet()
and iterates in
the key-value order consistent with keyAt(int)
and valueAt(int)
.
Parameters | |
---|---|
function |
BiFunction : The function to apply to each entry |
retainAll
public boolean retainAll (Collection<?> collection)
Remove all keys in the array map that do not exist in the given collection.
Parameters | |
---|---|
collection |
Collection : The collection whose contents are to be used to determine which
keys to keep. |
Returns | |
---|---|
boolean |
Returns true if any keys were removed from the array map, else false. |
setValueAt
public V setValueAt (int index, V value)
Set the value at a given index in the array.
For indices outside of the range 0...size()-1
, the behavior is undefined for
apps targeting Build.VERSION_CODES.P
and earlier, and an
ArrayIndexOutOfBoundsException
is thrown for apps targeting
Build.VERSION_CODES.Q
and later.
Parameters | |
---|---|
index |
int : The desired index, must be between 0 and size() -1. |
value |
V : The new value to store at this index. |
Returns | |
---|---|
V |
Returns the previous value at the given index. |
size
public int size ()
Return the number of items in this array map.
Returns | |
---|---|
int |
the number of key-value mappings in this map |
toString
public String toString ()
Returns a string representation of the object.
This implementation composes a string by iterating over its mappings. If this map contains itself as a key or a value, the string "(this Map)" will appear in its place.
Returns | |
---|---|
String |
a string representation of the object. |
valueAt
public V valueAt (int index)
Return the value at the given index in the array.
For indices outside of the range 0...size()-1
, the behavior is undefined for
apps targeting Build.VERSION_CODES.P
and earlier, and an
ArrayIndexOutOfBoundsException
is thrown for apps targeting
Build.VERSION_CODES.Q
and later.
Parameters | |
---|---|
index |
int : The desired index, must be between 0 and size() -1. |
Returns | |
---|---|
V |
Returns the value stored at the given index. |
values
public Collection<V> values ()
Return a Collection
for iterating over and interacting with all values
in the array map.
Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.
Returns | |
---|---|
Collection<V> |
a collection view of the values contained in this map |