ArrayMap

Artifact: androidx.collection:collection

View Source

Added in 1.0.0

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Kotlin |Java

public class ArrayMap<K, V> extends SimpleArrayMap implements Map

java.lang.Object
↳	androidx.collection.SimpleArrayMap
	↳	androidx.collection.ArrayMap

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ArrayMap is a generic key->value mapping data structure that is designed to be more memory efficient than a traditional java.util.HashMap, this implementation is a version of the platform's android.util.ArrayMap that can be used on older versions of the platform. 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).

If you don't need the standard Java container APIs provided here (iterators etc), consider using SimpleArrayMap instead.

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.

NOTE: Consider using MutableScatterMap instead of this class. MutableScatterMap also avoids creating an extra object per entry but offers overall better performance characteristics. If a Map-like interface is required, please see asMap and asMutableMap.

Summary

Public constructors
ArrayMap()
ArrayMap(int capacity) Create a new ArrayMap with a given initial capacity.
ArrayMap(@Nullable SimpleArrayMap map) Create a new ArrayMap with the mappings from the given ArrayMap.

Public methods
boolean	containsAll(@NonNull Collection<Object> collection) Determine if the array map contains all of the keys in the given collection.
boolean	containsKey(@Nullable Object key) Check whether a key exists in the array.
boolean	containsValue(@Nullable Object value) Check whether a value exists in the array.
@NonNull Set<Map.Entry<K, V>>	entrySet() Return a java.util.Set for iterating over and interacting with all mappings in the array map.
V	get(@Nullable Object key) Retrieve a value from the array.
@NonNull Set<K>	keySet() Return a java.util.Set for iterating over and interacting with all keys in the array map.
void	putAll(@NonNull Map<K, V> map) Perform a put of all key/value pairs in map
V	remove(@Nullable Object key) Remove an existing key from the array map.
boolean	removeAll(@NonNull Collection<Object> collection) Remove all keys in the array map that exist in the given collection.
boolean	retainAll(@NonNull Collection<Object> collection) Remove all keys in the array map that do not exist in the given collection.
@NonNull Collection<V>	values() Return a java.util.Collection for iterating over and interacting with all values in the array map.

Inherited methods
From java.util.Map abstract void clear() V compute(K key, BiFunction<K, V, V> remappingFunction) V computeIfAbsent(K key, Function<K, V> mappingFunction) V computeIfPresent(K key, BiFunction<K, V, V> remappingFunction) static Map<K, V> <K, V> copyOf(Map<K, V> map) static Map.Entry<K, V> <K, V> entry(K k, V v) abstract boolean equals(Object p) void forEach(BiConsumer<K, V> action) V getOrDefault(Object key, V defaultValue) abstract int hashCode() abstract boolean isEmpty() V merge(K key, V value, BiFunction<V, V, V> remappingFunction) static Map<K, V> <K, V> of() static Map<K, V> <K, V> ofEntries(Map.Entry[] entries) abstract V put(K p, V p1) V putIfAbsent(K key, V value) boolean remove(Object key, Object value) V replace(K key, V value) boolean replace(K key, V oldValue, V newValue) void replaceAll(BiFunction<K, V, V> function) abstract int size()
From androidx.collection.SimpleArrayMap final int __restricted$indexOfValue(V value) void clear() Make the array map empty. void ensureCapacity(int minimumCapacity) Ensure the array map can hold at least minimumCapacity items. boolean equals(Object other) This implementation returns false if the object is not a Map or SimpleArrayMap, or if the maps have different sizes. V getOrDefault(Object key, V defaultValue) Retrieve a value from the array, or defaultValue if there is no mapping for the key. int hashCode() int indexOfKey(K key) Returns the index of a key in the set. 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. V put(K key, V value) Add a new value to the array map. void putAll(SimpleArrayMap<K, V> map) Perform a put of all key/value pairs in map V putIfAbsent(K key, V value) Add a new value to the array map only if the key does not already have a value or it is mapped to null. boolean remove(K key, V value) Remove an existing key from the array map only if it is currently mapped to value. V removeAt(int index) Remove the key/value mapping at the given index. V replace(K key, V value) Replace the mapping for key only if it is already mapped to a value. boolean replace(K key, V oldValue, V newValue) Replace the mapping for key only if it is already mapped to oldValue. 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. V valueAt(int index) Return the value at the given index in the array.

Public constructors

ArrayMap

Added in 1.0.0

public ArrayMap()

ArrayMap

Added in 1.0.0

public ArrayMap(int capacity)

Create a new ArrayMap with a given initial capacity.

ArrayMap

Added in 1.0.0

public ArrayMap(@Nullable SimpleArrayMap map)

Create a new ArrayMap with the mappings from the given ArrayMap.

Public methods

containsAll

Added in 1.0.0

public boolean containsAll(@NonNull Collection<Object> collection)

Determine if the array map contains all of the keys in the given collection.

Parameters
@NonNull Collection<Object> 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

Added in 1.5.0-alpha06

public boolean containsKey(@Nullable Object key)

Check whether a key exists in the array.

Parameters
@Nullable Object key	The key to search for. ** This must be the same type as K **

Returns
boolean	Returns true if the key exists, else false.

containsValue

Added in 1.5.0-alpha06

public boolean containsValue(@Nullable Object value)

Check whether a value exists in the array. This requires a linear search through the entire array.

Parameters
@Nullable Object value	The value to search for. ** This must be the same type as V **

Returns
boolean	Returns true if the value exists, else false.

entrySet

Added in 1.0.0

public @NonNull Set<Map.Entry<K, V>> entrySet()

Return a java.util.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.

Note:

the semantics of this Set are subtly different than that of a java.util.HashMap: 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.

get

Added in 1.5.0-alpha06

public V get(@Nullable Object key)

Retrieve a value from the array.

Parameters
@Nullable Object key	The key of the value to retrieve. ** This must be the same type as K **

Returns
V	Returns the value associated with the given key, or null if there is no such key.

keySet

Added in 1.0.0

public @NonNull Set<K> keySet()

Return a java.util.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.

putAll

Added in 1.0.0

public void putAll(@NonNull Map<K, V> map)

Perform a put of all key/value pairs in map

Parameters
@NonNull Map<K, V> map	The map whose contents are to be retrieved.

remove

Added in 1.5.0-alpha06

public V remove(@Nullable Object key)

Remove an existing key from the array map.

Parameters
@Nullable Object key	The key of the mapping to remove. ** This must be the same type as V **

Returns
V	Returns the value that was stored under the key, or null if there was no such key.

removeAll

Added in 1.0.0

public boolean removeAll(@NonNull Collection<Object> collection)

Remove all keys in the array map that exist in the given collection.

Parameters
@NonNull Collection<Object> 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.

retainAll

Added in 1.0.0

public boolean retainAll(@NonNull Collection<Object> collection)

Remove all keys in the array map that do not exist in the given collection.

Parameters
@NonNull Collection<Object> 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.

values

Added in 1.0.0

public @NonNull Collection<V> values()

Return a java.util.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.