Added in API level 19

ArrayMap

class ArrayMap<K : Any!, V : Any!> : MutableMap<K, V>
kotlin.Any
   ↳ android.util.ArrayMap

ArrayMap is a generic key->value mapping data structure that is designed to be more memory efficient than a traditional java.util.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

Create a new empty ArrayMap.
ArrayMap(map: ArrayMap<K, V>!)

Create a new ArrayMap with the mappings from the given ArrayMap.
ArrayMap(capacity: Int)

Create a new ArrayMap with a given initial capacity.
Public methods
Unit

Make the array map empty.
Boolean
containsAll(collection: MutableCollection<*>!)

Determine if the array map contains all of the keys in the given collection.
Boolean
containsKey(key: K)

Check whether a key exists in the array.
Boolean
containsValue(value: V)

Check whether a value exists in the array.
Unit
ensureCapacity(minimumCapacity: Int)

Ensure the array map can hold at least minimumCapacity items.
Boolean
equals(other: Any?)

Indicates whether some other object is "equal to" this one.
Unit
forEach(action: BiConsumer<in K, in V>)

Performs the given action for all elements in the stored order.
V?
get(key: K)

Retrieve a value from the array.
Int

Returns a hash code value for the object.
Int
indexOfKey(key: Any!)

Returns the index of a key in the set.
Int
indexOfValue(value: Any!)

Returns an index for which valueAt would return the specified value, or a negative number if no keys map to the specified value.
Boolean

Return true if the array map contains no items.
K
keyAt(index: Int)

Return the key at the given index in the array.
V?
put(key: K, value: V)

Add a new value to the array map.
Unit
putAll(array: ArrayMap<out K, out V>!)

Perform a put(java.lang.Object,java.lang.Object) of all key/value pairs in array
Unit
putAll(from: Map<out K, V>)

Perform a put(java.lang.Object,java.lang.Object) of all key/value pairs in map
V?
remove(key: K)

Remove an existing key from the array map.
Boolean
removeAll(collection: MutableCollection<*>!)

Remove all keys in the array map that exist in the given collection.
V
removeAt(index: Int)

Remove the key/value mapping at the given index.
Unit
replaceAll(function: BiFunction<in K, in V, out V>)

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: MutableCollection<*>!)

Remove all keys in the array map that do not exist in the given collection.
V
setValueAt(index: Int, value: V)

Set the value at a given index in the array.
String

Returns a string representation of the object.
V
valueAt(index: Int)

Return the value at the given index in the array.
Properties
MutableSet<MutableEntry<K, V>>

Return a java.util.Set for iterating over and interacting with all mappings in the array map.
MutableSet<K>

Return a java.util.Set for iterating over and interacting with all keys in the array map.
Int

Return the number of items in this array map.
MutableCollection<V>

Return a java.util.Collection for iterating over and interacting with all values in the array map.

Public constructors

ArrayMap

Added in API level 19
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

Added in API level 19
ArrayMap(map: ArrayMap<K, V>!)

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

ArrayMap

Added in API level 19
ArrayMap(capacity: Int)

Create a new ArrayMap with a given initial capacity.

Public methods

clear

Added in API level 19
fun clear(): Unit

Make the array map empty. All storage is released.

Exceptions
java.lang.UnsupportedOperationException if the clear operation is not supported by this map

containsAll

Added in API level 19
fun containsAll(collection: MutableCollection<*>!): Boolean

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

Parameters
collection MutableCollection<*>!: The collection whose contents are to be checked against.
Return
Boolean Returns true if this array map contains a key for every entry in collection, else returns false.

containsKey

Added in API level 19
fun containsKey(key: K): Boolean

Check whether a key exists in the array.

Parameters
key K: The key to search for.
Return
Boolean Returns true if the key exists, else false.
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (java.util.Collection#)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (java.util.Collection#)

containsValue

Added in API level 19
fun containsValue(value: V): Boolean

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

Parameters
value V: The value to search for.
Return
Boolean Returns true if the value exists, else false.
Exceptions
java.lang.ClassCastException if the value is of an inappropriate type for this map (java.util.Collection#)
java.lang.NullPointerException if the specified value is null and this map does not permit null values (java.util.Collection#)

ensureCapacity

Added in API level 19
fun ensureCapacity(minimumCapacity: Int): Unit

Ensure the array map can hold at least minimumCapacity items.

equals

Added in API level 19
fun equals(other: Any?): Boolean

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 return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

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
obj the reference object with which to compare.
o object to be compared for equality with this map
object This value may be null.
Return
Boolean true if the specified object is equal to this map

forEach

Added in API level 24
fun forEach(action: BiConsumer<in K, in V>): Unit

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<in K, in V>: The action to be performed for each element
Exceptions
java.lang.NullPointerException if the specified action is null
java.util.ConcurrentModificationException if an entry is found to be removed during iteration

get

Added in API level 19
fun get(key: K): V?

Retrieve a value from the array.

Parameters
key K: The key of the value to retrieve.
Return
V? Returns the value associated with the given key, or null if there is no such key.
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (java.util.Collection#)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (java.util.Collection#)

hashCode

Added in API level 19
fun hashCode(): Int

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by java.util.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 in equals 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 the hashCode 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 the hashCode 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.
Return
Int the hash code value for this map

indexOfKey

Added in API level 21
fun indexOfKey(key: Any!): Int

Returns the index of a key in the set.

Parameters
key Any!: The key to search for.
Return
Int Returns the index of the key if it exists, else a negative integer.

indexOfValue

Added in API level 29
fun indexOfValue(value: Any!): Int

Returns an index for which valueAt 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.

isEmpty

Added in API level 19
fun isEmpty(): Boolean

Return true if the array map contains no items.

Return
Boolean true if this map contains no key-value mappings

keyAt

Added in API level 19
fun keyAt(index: Int): K

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 android.os.Build.VERSION_CODES#P and earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting android.os.Build.VERSION_CODES#Q and later.

Parameters
index Int: The desired index, must be between 0 and size()-1.
Return
K Returns the key stored at the given index.

put

Added in API level 19
fun put(
    key: K, 
    value: V
): V?

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.
Return
V? Returns the old value that was stored for the given key, or null if there was no such key.
Exceptions
java.lang.UnsupportedOperationException if the put operation is not supported by this map
java.lang.ClassCastException if the class of the specified key or value prevents it from being stored in this map
java.lang.NullPointerException if the specified key or value is null and this map does not permit null keys or values
java.lang.IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map

putAll

Added in API level 19
fun putAll(array: ArrayMap<out K, out V>!): Unit

Perform a put(java.lang.Object,java.lang.Object) of all key/value pairs in array

Parameters
array ArrayMap<out K, out V>!: The array whose contents are to be retrieved.

putAll

Added in API level 19
fun putAll(from: Map<out K, V>): Unit

Perform a put(java.lang.Object,java.lang.Object) of all key/value pairs in map

Parameters
m mappings to be stored in this map
map The map whose contents are to be retrieved.
Exceptions
java.lang.UnsupportedOperationException if the putAll operation is not supported by this map
java.lang.ClassCastException if the class of a key or value in the specified map prevents it from being stored in this map
java.lang.NullPointerException if the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values
java.lang.IllegalArgumentException if some property of a key or value in the specified map prevents it from being stored in this map

remove

Added in API level 19
fun remove(key: K): V?

Remove an existing key from the array map.

Parameters
key K: The key of the mapping to remove.
Return
V? Returns the value that was stored under the key, or null if there was no such key.
Exceptions
java.lang.UnsupportedOperationException if the remove operation is not supported by this map
java.lang.ClassCastException if the key is of an inappropriate type for this map (java.util.Collection#)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (java.util.Collection#)

removeAll

Added in API level 19
fun removeAll(collection: MutableCollection<*>!): Boolean

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

Parameters
collection MutableCollection<*>!: The collection whose contents are to be used to remove keys.
Return
Boolean Returns true if any keys were removed from the array map, else false.

removeAt

Added in API level 19
fun removeAt(index: Int): V

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 android.os.Build.VERSION_CODES#P and earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting android.os.Build.VERSION_CODES#Q and later.

Parameters
index Int: The desired index, must be between 0 and size()-1.
Return
V Returns the value that was stored at this index.

replaceAll

Added in API level 24
fun replaceAll(function: BiFunction<in K, in V, out V>): Unit

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<in K, in V, out V>: The function to apply to each entry
Exceptions
java.lang.UnsupportedOperationException if the set operation is not supported by this map's entry set iterator.
java.lang.ClassCastException if the class of a replacement value prevents it from being stored in this map (java.util.Collection#)
java.lang.NullPointerException if the specified function is null, or if a replacement value is null and this map does not permit null values (java.util.Collection#)
java.lang.IllegalArgumentException if some property of a replacement value prevents it from being stored in this map (java.util.Collection#)
java.util.ConcurrentModificationException if an entry is found to be removed during iteration

retainAll

Added in API level 19
fun retainAll(collection: MutableCollection<*>!): Boolean

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

Parameters
collection MutableCollection<*>!: The collection whose contents are to be used to determine which keys to keep.
Return
Boolean Returns true if any keys were removed from the array map, else false.

setValueAt

Added in API level 19
fun setValueAt(
    index: Int, 
    value: V
): V

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 android.os.Build.VERSION_CODES#P and earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting android.os.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.
Return
V Returns the previous value at the given index.

toString

Added in API level 19
fun toString(): String

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.

Return
String a string representation of the object.

valueAt

Added in API level 19
fun valueAt(index: Int): V

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 android.os.Build.VERSION_CODES#P and earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting android.os.Build.VERSION_CODES#Q and later.

Parameters
index Int: The desired index, must be between 0 and size()-1.
Return
V Returns the value stored at the given index.

Properties

entries

Added in API level 19
val entries: MutableSet<MutableEntry<K, V>>

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 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 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.

Return
MutableSet<MutableEntry<K, V>> a set view of the mappings contained in this map

keys

Added in API level 19
val keys: MutableSet<K>

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 and allocates additional state information associated with the container that will remain for the life of the container.

Return
MutableSet<K> a set view of the keys contained in this map

size

Added in API level 19
val size: Int

Return the number of items in this array map.

Return
Int the number of key-value mappings in this map

values

Added in API level 19
val values: MutableCollection<V>

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 and allocates additional state information associated with the container that will remain for the life of the container.

Return
MutableCollection<V> a collection view of the values contained in this map