ConcurrentMap
interface ConcurrentMap<K : Any!, V : Any!> : MutableMap<K, V>
java.util.concurrent.ConcurrentMap |
A Map
providing thread safety and atomicity guarantees.
To maintain the specified guarantees, default implementations of methods including putIfAbsent
inherited from Map
must be overridden by implementations of this interface. Similarly, implementations of the collections returned by methods keySet
, values
, and entrySet
must override methods such as removeIf
when necessary to preserve atomicity guarantees.
Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentMap
as a key or value happen-before actions subsequent to the access or removal of that object from the ConcurrentMap
in another thread.
This interface is a member of the Java Collections Framework.
Summary
Public methods | |
---|---|
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 |
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 |
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 Unit |
forEach(action: BiConsumer<in K, in V>) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. |
open V |
getOrDefault(key: K, defaultValue: V) Returns the value to which the specified key is mapped, or |
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. |
abstract V? |
putIfAbsent(key: K, value: V) If the specified key is not already associated with a value, associates it with the given value. |
abstract Boolean |
remove(key: K, value: V) Removes the entry for a key only if currently mapped to a given value. |
abstract Boolean |
replace(key: K, oldValue: V, newValue: V) Replaces the entry for a key only if currently mapped to a given value. |
abstract V? |
replace(key: K, value: V) Replaces the entry for a key only if currently mapped to some value. |
open 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. |
Public methods
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>
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.
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) |
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.
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) |
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.
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) |
forEach
open fun forEach(action: BiConsumer<in K, in V>): Unit
Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of entry set iteration (if an iteration order is specified.) Exceptions thrown by the action are relayed to the caller.
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 |
getOrDefault
open fun getOrDefault(
key: K,
defaultValue: V
): V
Returns the value to which the specified key is mapped, or defaultValue
if this map contains no mapping for the key.
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) |
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.
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 |
putIfAbsent
abstract fun putIfAbsent(
key: K,
value: V
): V?
If the specified key is not already associated with a value, associates it with the given value. This is equivalent to, for this map
:
<code>if (!map.containsKey(key)) return map.put(key, value); else return map.get(key);</code>
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 |
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 |
remove
abstract fun remove(
key: K,
value: V
): Boolean
Removes the entry for a key only if currently mapped to a given value. This is equivalent to, for this map
:
<code>if (map.containsKey(key) && Objects.equals(map.get(key), value)) { map.remove(key); return true; } else { return false; }</code>
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 |
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) |
replace
abstract fun replace(
key: K,
oldValue: V,
newValue: V
): Boolean
Replaces the entry for a key only if currently mapped to a given value. This is equivalent to, for this map
:
<code>if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) { map.put(key, newValue); return true; } else { return false; }</code>
Parameters | |
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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 |
java.lang.ClassCastException |
if the class of a specified key or value prevents it from being stored in this map |
java.lang.NullPointerException |
if a specified key or value is null, and this map does not permit null keys or values |
java.lang.IllegalArgumentException |
if some property of a specified key or value prevents it from being stored in this map |
replace
abstract fun replace(
key: K,
value: V
): V?
Replaces the entry for a key only if currently mapped to some value. This is equivalent to, for this map
:
<code>if (map.containsKey(key)) return map.put(key, value); else return null;</code>
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 |
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 |
replaceAll
open 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.
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.lang.NullPointerException |
if the specified function is null, or the specified replacement value is null, and this map does not permit null values |
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 |