Added in API level 1

HashMap

open class HashMap<K : Any!, V : Any!> : AbstractMap<K, V>, Cloneable, Serializable, MutableMap<K, V>
kotlin.Any
   ↳ java.util.AbstractMap<K, V>
   ↳ java.util.HashMap

Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.) This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

This implementation provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets. Iteration over collection views requires time proportional to the "capacity" of the HashMap instance (the number of buckets) plus its size (the number of key-value mappings). Thus, it's very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important.

An instance of HashMap has two parameters that affect its performance: initial capacity and load factor. The capacity is the number of buckets in the hash table, and the initial capacity is simply the capacity at the time the hash table is created. The load factor is a measure of how full the hash table is allowed to get before its capacity is automatically increased. When the number of entries in the hash table exceeds the product of the load factor and the current capacity, the hash table is rehashed (that is, internal data structures are rebuilt) so that the hash table has approximately twice the number of buckets.

As a general rule, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values decrease the space overhead but increase the lookup cost (reflected in most of the operations of the HashMap class, including get and put). The expected number of entries in the map and its load factor should be taken into account when setting its initial capacity, so as to minimize the number of rehash operations. If the initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operations will ever occur.

If many mappings are to be stored in a HashMap instance, creating it with a sufficiently large capacity will allow the mappings to be stored more efficiently than letting it perform automatic rehashing as needed to grow the table. Note that using many keys with the same hashCode() is a sure way to slow down performance of any hash table. To ameliorate impact, when keys are Comparable, this class may use comparison order among keys to help break ties.

Note that this implementation is not synchronized. If multiple threads access a hash map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with a key that an instance already contains is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map:

Map m = Collections.synchronizedMap(new HashMap(...));

The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class is a member of the Java Collections Framework.

Summary

Public constructors
HashMap(initialCapacity: Int, loadFactor: Float)

Constructs an empty HashMap with the specified initial capacity and load factor.

HashMap(initialCapacity: Int)

Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).

Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).

HashMap(m: MutableMap<out K, out V>)

Constructs a new HashMap with the same mappings as the specified Map.

Public methods
open Unit

Removes all of the mappings from this map.

open Any

Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.

open V?
compute(key: K, remappingFunction: BiFunction<in K, in V?, out V?>)

Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).

open V
computeIfAbsent(key: K, mappingFunction: Function<in K, out V>)

If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into this map unless null.

open V?
computeIfPresent(key: K, remappingFunction: BiFunction<in K, in V, out V?>)

If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value.

open Boolean
containsKey(key: K)

Returns true if this map contains a mapping for the specified key.

open Boolean
containsKey(key: K)

Returns true if this map contains a mapping for the specified key.

open Boolean
containsValue(value: V)

Returns true if this map maps one or more keys to the specified value.

open Boolean
containsValue(value: V)

Returns true if this map maps one or more keys to the specified value.

open Unit
forEach(action: BiConsumer<in K, in V>)

open V?
get(key: K)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

open V?
get(key: K)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

open V
getOrDefault(key: K, defaultValue: V)

open Boolean

Returns true if this map contains no key-value mappings.

open V?
merge(key: K, value: V, remappingFunction: BiFunction<in V, in V, out V?>)

If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value.

open static HashMap<K, V>
newHashMap(numMappings: Int)

Creates a new, empty HashMap suitable for the expected number of mappings.

open V?
put(key: K, value: V)

Associates the specified value with the specified key in this map.

open Unit
putAll(from: Map<out K, V>)

Copies all of the mappings from the specified map to this map.

open V?
putIfAbsent(key: K, value: V)

open V?
remove(key: K)

Removes the mapping for the specified key from this map if present.

open Boolean
remove(key: K, value: V)

open V?
remove(key: K)

Removes the mapping for the specified key from this map if present.

open Boolean
replace(key: K, oldValue: V, newValue: V)

open V?
replace(key: K, value: V)

open Unit
replaceAll(function: BiFunction<in K, in V, out V>)

Inherited functions
Properties
open MutableSet<MutableEntry<K, V>>

Returns a Set view of the mappings contained in this map.

open MutableSet<K>

Returns a Set view of the keys contained in this map.

open Int

Returns the number of key-value mappings in this map.

open MutableCollection<V>

Returns a Collection view of the values contained in this map.

Public constructors

HashMap

Added in API level 1
HashMap(
    initialCapacity: Int,
    loadFactor: Float)

Constructs an empty HashMap with the specified initial capacity and load factor.

Parameters
initialCapacity Int: the initial capacity
loadFactor Float: the load factor
Exceptions
java.lang.IllegalArgumentException if the initial capacity is negative or the load factor is nonpositive

HashMap

Added in API level 1
HashMap(initialCapacity: Int)

Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).

Parameters
initialCapacity Int: the initial capacity.
Exceptions
java.lang.IllegalArgumentException if the initial capacity is negative.

HashMap

Added in API level 1
HashMap()

Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).

HashMap

Added in API level 1
HashMap(m: MutableMap<out K, out V>)

Constructs a new HashMap with the same mappings as the specified Map. The HashMap is created with default load factor (0.75) and an initial capacity sufficient to hold the mappings in the specified Map.

Parameters
m MutableMap<out K, out V>: the map whose mappings are to be placed in this map
Exceptions
java.lang.NullPointerException if the specified map is null

Public methods

clear

Added in API level 1
open fun clear(): Unit

Removes all of the mappings from this map. The map will be empty after this call returns.

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

clone

Added in API level 1
open fun clone(): Any

Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.

Return
Any a shallow copy of this map
Exceptions
java.lang.CloneNotSupportedException if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.

compute

Added in API level 24
open fun compute(
    key: K,
    remappingFunction: BiFunction<in K, in V?, out V?>
): V?

Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping). For example, to either create or append a String msg to a value mapping:

<code>map.compute(key, (k, v) -&gt; (v == null) ? msg : v.concat(msg))</code>
(Method merge() is often simpler to use for such purposes.)

If the remapping function returns null, the mapping is removed (or remains absent if initially absent). If the remapping function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

The remapping function should not modify this map during computation.

This method will, on a best-effort basis, throw a ConcurrentModificationException if it is detected that the remapping function modifies this map during computation.

Parameters
key K: key with which the specified value is to be associated
remappingFunction BiFunction<in K, in V?, out V?>: the remapping function to compute a value
Return
V? the new value associated with the specified key, or null if none
Exceptions
java.lang.NullPointerException if the specified key is null and this map does not support null keys, or the remappingFunction is null
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the class of the specified key or value prevents it from being stored in this map (optional)
java.lang.IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map (optional)
java.util.ConcurrentModificationException if it is detected that the remapping function modified this map

computeIfAbsent

Added in API level 24
open fun computeIfAbsent(
    key: K,
    mappingFunction: Function<in K, out V>
): V

If the specified key is not already associated with a value (or is mapped to null), attempts to compute its value using the given mapping function and enters it into this map unless null.

If the mapping function returns null, no mapping is recorded. If the mapping function itself throws an (unchecked) exception, the exception is rethrown, and no mapping is recorded. The most common usage is to construct a new object serving as an initial mapped value or memoized result, as in:

<code>map.computeIfAbsent(key, k -&gt; new Value(f(k)));
  </code>

Or to implement a multi-value map, Map<K,Collection<V>>, supporting multiple values per key:

<code>map.computeIfAbsent(key, k -&gt; new HashSet&lt;V&gt;()).add(v);
  </code>

The mapping function should not modify this map during computation.

This method will, on a best-effort basis, throw a ConcurrentModificationException if it is detected that the mapping function modifies this map during computation.

Parameters
key K: key with which the specified value is to be associated
mappingFunction Function<in K, out V>: the mapping function to compute a value
Return
V the current (existing or computed) value associated with the specified key, or null if the computed value is null
Exceptions
java.lang.NullPointerException if the specified key is null and this map does not support null keys, or the mappingFunction is null
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the class of the specified key or value prevents it from being stored in this map (optional)
java.lang.IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map (optional)
java.util.ConcurrentModificationException if it is detected that the mapping function modified this map

computeIfPresent

Added in API level 24
open fun computeIfPresent(
    key: K,
    remappingFunction: BiFunction<in K, in V, out V?>
): V?

If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value.

If the remapping function returns null, the mapping is removed. If the remapping function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

The remapping function should not modify this map during computation.

This method will, on a best-effort basis, throw a ConcurrentModificationException if it is detected that the remapping function modifies this map during computation.

Parameters
key K: key with which the specified value is to be associated
remappingFunction BiFunction<in K, in V, out V?>: the remapping function to compute a value
Return
V? the new value associated with the specified key, or null if none
Exceptions
java.lang.NullPointerException if the specified key is null and this map does not support null keys, or the remappingFunction is null
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the class of the specified key or value prevents it from being stored in this map (optional)
java.lang.IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map (optional)
java.util.ConcurrentModificationException if it is detected that the remapping function modified this map

containsKey

Added in API level 1
open fun containsKey(key: K): Boolean

Returns true if this map contains a mapping for the specified key.

Parameters
key K: The key whose presence in this map is to be tested
Return
Boolean true if this map contains a mapping for the specified key.
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

containsKey

Added in API level 1
open fun containsKey(key: K): Boolean

Returns true if this map contains a mapping for the specified key.

Parameters
key K: The key whose presence in this map is to be tested
Return
Boolean true if this map contains a mapping for the specified key.
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

containsValue

Added in API level 1
open fun containsValue(value: V): Boolean

Returns true if this map maps one or more keys to the specified value.

Parameters
value V: value whose presence in this map is to be tested
Return
Boolean true if this map maps one or more keys to the specified value
Exceptions
java.lang.ClassCastException if the value is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified value is null and this map does not permit null values (optional)

containsValue

Added in API level 1
open fun containsValue(value: V): Boolean

Returns true if this map maps one or more keys to the specified value.

Parameters
value V: value whose presence in this map is to be tested
Return
Boolean true if this map maps one or more keys to the specified value
Exceptions
java.lang.ClassCastException if the value is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified value is null and this map does not permit null values (optional)

forEach

Added in API level 24
open fun forEach(action: BiConsumer<in K, in V>): Unit
Parameters
action BiConsumer<in K, in V>: The action to be performed for each entry
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 1
open fun get(key: K): V?

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Parameters
key K: the key whose associated value is to be returned
Return
V? the value to which the specified key is mapped, or null if this map contains no mapping for the key
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

get

Added in API level 1
open fun get(key: K): V?

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Parameters
key K: the key whose associated value is to be returned
Return
V? the value to which the specified key is mapped, or null if this map contains no mapping for the key
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

getOrDefault

Added in API level 24
open fun getOrDefault(
    key: K,
    defaultValue: V
): V
Parameters
key K: the key whose associated value is to be returned
defaultValue V: the default mapping of the key
Return
V the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key
Exceptions
java.lang.ClassCastException if the key is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

isEmpty

Added in API level 1
open fun isEmpty(): Boolean

Returns true if this map contains no key-value mappings.

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

merge

Added in API level 24
open fun merge(
    key: K,
    value: V,
    remappingFunction: BiFunction<in V, in V, out V?>
): V?

If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value. Otherwise, replaces the associated value with the results of the given remapping function, or removes if the result is null. This method may be of use when combining multiple mapped values for a key. For example, to either create or append a String msg to a value mapping:

<code>map.merge(key, msg, String::concat)
  </code>

If the remapping function returns null, the mapping is removed. If the remapping function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

The remapping function should not modify this map during computation.

This method will, on a best-effort basis, throw a ConcurrentModificationException if it is detected that the remapping function modifies this map during computation.

Parameters
key K: key with which the resulting value is to be associated
value V: the non-null value to be merged with the existing value associated with the key or, if no existing value or a null value is associated with the key, to be associated with the key
remappingFunction BiFunction<in V, in V, out V?>: the remapping function to recompute a value if present
Return
V? the new value associated with the specified key, or null if no value is associated with the key
Exceptions
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the class of the specified key or value prevents it from being stored in this map (optional)
java.lang.IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map (optional)
java.lang.NullPointerException if the specified key is null and this map does not support null keys or the value or remappingFunction is null
java.util.ConcurrentModificationException if it is detected that the remapping function modified this map

newHashMap

open static fun <K : Any!, V : Any!> newHashMap(numMappings: Int): HashMap<K, V>

Creates a new, empty HashMap suitable for the expected number of mappings. The returned map uses the default load factor of 0.75, and its initial capacity is generally large enough so that the expected number of mappings can be added without resizing the map.

Parameters
numMappings Int: the expected number of mappings
<K> the type of keys maintained by the new map
<V> the type of mapped values
Return
HashMap<K, V> the newly created map
Exceptions
java.lang.IllegalArgumentException if numMappings is negative

put

Added in API level 1
open fun put(
    key: K,
    value: V
): V?

Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.

Parameters
key K: key with which the specified value is to be associated
value V: value to be associated with the specified key
Return
V? the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with 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 1
open fun putAll(from: Map<out K, V>): Unit

Copies all of the mappings from the specified map to this map. These mappings will replace any mappings that this map had for any of the keys currently in the specified map.

Parameters
m mappings to be stored in this map
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
java.lang.IllegalArgumentException if some property of a key or value in the specified map prevents it from being stored in this map

putIfAbsent

Added in API level 24
open fun putIfAbsent(
    key: K,
    value: V
): V?
Parameters
key K: key with which the specified value is to be associated
value V: value to be associated with the specified key
Return
V? the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)
Exceptions
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the key or value is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key or value is null, and this map does not permit null keys or values (optional)
java.lang.IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map (optional)

remove

Added in API level 1
open fun remove(key: K): V?

Removes the mapping for the specified key from this map if present.

Parameters
key K: key whose mapping is to be removed from the map
Return
V? the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with 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 (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

remove

Added in API level 24
open fun remove(
    key: K,
    value: V
): Boolean
Parameters
key K: key with which the specified value is associated
value V: value expected to be associated with the specified key
Return
Boolean true if the value was removed
Exceptions
java.lang.UnsupportedOperationException if the remove operation is not supported by this map (optional)
java.lang.ClassCastException if the key or value is of an inappropriate type for this map (optional)
java.lang.NullPointerException if the specified key or value is null, and this map does not permit null keys or values (optional)

remove

Added in API level 1
open fun remove(key: K): V?

Removes the mapping for the specified key from this map if present.

Parameters
key K: key whose mapping is to be removed from the map
Return
V? the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with 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 (optional)
java.lang.NullPointerException if the specified key is null and this map does not permit null keys (optional)

replace

Added in API level 24
open fun replace(
    key: K,
    oldValue: V,
    newValue: V
): Boolean
Parameters
key K: key with which the specified value is associated
oldValue V: value expected to be associated with the specified key
newValue V: value to be associated with the specified key
Return
Boolean true if the value was replaced
Exceptions
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the class of a specified key or value prevents it from being stored in this map
java.lang.NullPointerException if oldValue is null and this map does not permit null values (optional)
java.lang.IllegalArgumentException if some property of a specified key or value prevents it from being stored in this map

replace

Added in API level 24
open fun replace(
    key: K,
    value: V
): V?
Parameters
key K: key with which the specified value is associated
value V: value to be associated with the specified key
Return
V? the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)
Exceptions
java.lang.UnsupportedOperationException if the put operation is not supported by this map (optional)
java.lang.ClassCastException if the class of the specified key or value prevents it from being stored in this map (optional)
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

replaceAll

Added in API level 24
open fun replaceAll(function: BiFunction<in K, in V, out V>): Unit
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 a replacement value is of an inappropriate type for this map (optional)
java.lang.NullPointerException if function or a replacement value is null, and this map does not permit null keys or values (optional)
java.lang.IllegalArgumentException if some property of a replacement value prevents it from being stored in this map (optional)
java.util.ConcurrentModificationException if an entry is found to be removed during iteration

Properties

entries

Added in API level 1
open val entries: MutableSet<MutableEntry<K, V>>

Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

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

keys

Added in API level 1
open val keys: MutableSet<K>

Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

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

size

Added in API level 1
open val size: Int

Returns the number of key-value mappings in this map.

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

values

Added in API level 1
open val values: MutableCollection<V>

Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

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