HashMap
open class HashMap<K : Any!, V : Any!> : AbstractMap<K, V>, Cloneable, Serializable, MutableMap<K, V>
Known Direct Subclasses
| LinkedHashMap |
Hash table and linked list implementation of the Map interface, with well-defined encounter order.
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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 |
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Constructs an empty HashMap with the specified initial capacity and load factor.
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Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).
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Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).
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Constructs a new HashMap with the same mappings as the specified Map.
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| Public methods |
| open Unit |
Removes all of the mappings from this map.
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| open Any |
Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
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| open V? |
Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).
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| open 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.
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| open 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.
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| open Boolean |
Returns true if this map contains a mapping for the specified key.
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| open Boolean |
Returns true if this map contains a mapping for the specified key.
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| open Boolean |
Returns true if this map maps one or more keys to the specified value.
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| open Boolean |
Returns true if this map maps one or more keys to the specified value.
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| open Unit |
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| open V? |
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
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| open V? |
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
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| open V |
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| open Boolean |
Returns true if this map contains no key-value mappings.
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| open 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.
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| open static HashMap<K, V> |
Creates a new, empty HashMap suitable for the expected number of mappings.
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| open V? |
Associates the specified value with the specified key in this map.
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| open Unit |
Copies all of the mappings from the specified map to this map.
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| open V? |
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| open V? |
Removes the mapping for the specified key from this map if present.
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| open Boolean |
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| open V? |
Removes the mapping for the specified key from this map if present.
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| open Boolean |
replace(key: K, oldValue: V, newValue: V) |
| open V? |
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| open Unit |
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| Inherited functions |
From class AbstractMap
Boolean |
equals(other: Any?)
Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.
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Int |
hashCode()
Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's entrySet() view. This ensures that m1.equals(m2) implies that m1.hashCode()==m2.hashCode() for any two maps m1 and m2, as required by the general contract of Object#hashCode.
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String |
toString()
Returns a string representation of this map. The string representation consists of a list of key-value mappings in the order returned by the map's entrySet view's iterator, enclosed in braces ("{}"). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign ("=") followed by the associated value. Keys and values are converted to strings as by String#valueOf(Object).
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Public constructors
HashMap
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
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
HashMap()
Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).
HashMap
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
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
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
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) -> (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
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 -> 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 -> new HashSet<V>()).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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
keys
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
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
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.
