HashMap

HashMap

HashMap()

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

HashMap

HashMap(initialCapacity: Int)

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

HashMap

HashMap(
    initialCapacity: Int, 
    loadFactor: Float)

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

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.

clear

open fun clear(): Unit

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

clone

open fun clone(): Any

Returns a shallow copy of this HashMap instance: the keys and values themselves are not 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) -&gt; (v == null) ? msg : v.concat(msg))</code>

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.

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 -&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.

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.

containsKey

open fun containsKey(key: K): Boolean

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

containsKey

open fun containsKey(key: K): Boolean

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

containsValue

open fun containsValue(value: V): Boolean

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

containsValue

open fun containsValue(value: V): Boolean

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

forEach

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

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.

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.

getOrDefault

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

isEmpty

open fun isEmpty(): Boolean

Returns 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.

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.

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.

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.

putIfAbsent

open fun putIfAbsent(
    key: K, 
    value: V
): V?

remove

open fun remove(key: K): V?

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

remove

open fun remove(
    key: K, 
    value: V
): Boolean

remove

open fun remove(key: K): V?

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

replace

open fun replace(
    key: K, 
    value: V
): V?

replace

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

replaceAll

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

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.

size

open val size: Int

Returns 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.