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FlexDoc/Javadoc 2.0 Demo Java Doc |
Class ConcurrentHashMap<K,V>
java.util.concurrent.ConcurrentHashMap<K,V>
Type Parameters:
K - the type of keys maintained by this map
V - the type of mapped values
All Implemented Interfaces:
public class ConcurrentHashMap<K,V>
A hash table supporting full concurrency of retrievals and
high expected concurrency for updates. This class obeys the
same functional specification as
Hashtable, and
includes versions of methods corresponding to each method of
Hashtable. However, even though all operations are
thread-safe, retrieval operations do
not entail locking,
and there is
not any support for locking the entire table
in a way that prevents all access. This class is fully
interoperable with
Hashtable in programs that rely on its
thread safety but not on its synchronization details.
Retrieval operations (including get) generally do not
block, so may overlap with update operations (including put
and remove). Retrievals reflect the results of the most
recently completed update operations holding upon their
onset. (More formally, an update operation for a given key bears a
happens-before relation with any (non-null) retrieval for
that key reporting the updated value.) For aggregate operations
such as putAll and clear, concurrent retrievals may
reflect insertion or removal of only some entries. Similarly,
Iterators, Spliterators and Enumerations return elements reflecting the
state of the hash table at some point at or since the creation of the
iterator/enumeration. They do not throw ConcurrentModificationException.
However, iterators are designed to be used by only one thread at a time.
Bear in mind that the results of aggregate status methods including
size, isEmpty, and containsValue are typically
useful only when a map is not undergoing concurrent updates in other threads.
Otherwise the results of these methods reflect transient states
that may be adequate for monitoring or estimation purposes, but not
for program control.
The table is dynamically expanded when there are too many
collisions (i.e., keys that have distinct hash codes but fall into
the same slot modulo the table size), with the expected average
effect of maintaining roughly two bins per mapping (corresponding
to a 0.75 load factor threshold for resizing). There may be much
variance around this average as mappings are added and removed, but
overall, this maintains a commonly accepted time/space tradeoff for
hash tables. However, resizing this or any other kind of hash
table may be a relatively slow operation. When possible, it is a
good idea to provide a size estimate as an optional
initialCapacity constructor argument. An additional optional
loadFactor constructor argument provides a further means of
customizing initial table capacity by specifying the table density
to be used in calculating the amount of space to allocate for the
given number of elements. Also, for compatibility with previous
versions of this class, constructors may optionally specify an
expected concurrencyLevel as an additional hint for
internal sizing. Note that using many keys with exactly 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.
A Set projection of a ConcurrentHashMap may be created
(using newKeySet() or newKeySet(int)), or viewed
(using keySet(Object) when only keys are of interest, and the
mapped values are (perhaps transiently) not used or all take the
same mapping value.
A ConcurrentHashMap can be used as a scalable frequency map (a
form of histogram or multiset) by using LongAdder values and initializing via
computeIfAbsent. For example, to add a count
to a ConcurrentHashMap<String,LongAdder> freqs, you can use
freqs.computeIfAbsent(key, k -> new LongAdder()).increment();
This class and its views and iterators implement all of the
optional methods of the Map and Iterator
interfaces.
Like Hashtable but unlike HashMap, this class
does not allow null to be used as a key or value.
ConcurrentHashMaps support a set of sequential and parallel bulk
operations that, unlike most Stream methods, are designed
to be safely, and often sensibly, applied even with maps that are
being concurrently updated by other threads; for example, when
computing a snapshot summary of the values in a shared registry.
There are three kinds of operation, each with four forms, accepting
functions with keys, values, entries, and (key, value) pairs as
arguments and/or return values. Because the elements of a
ConcurrentHashMap are not ordered in any particular way, and may be
processed in different orders in different parallel executions, the
correctness of supplied functions should not depend on any
ordering, or on any other objects or values that may transiently
change while computation is in progress; and except for forEach
actions, should ideally be side-effect-free. Bulk operations on
Map.Entry objects do not support method setValue.
- forEach: Performs a given action on each element.
A variant form applies a given transformation on each element
before performing the action.
- search: Returns the first available non-null result of
applying a given function on each element; skipping further
search when a result is found.
- reduce: Accumulates each element. The supplied reduction
function cannot rely on ordering (more formally, it should be
both associative and commutative). There are five variants:
- Plain reductions. (There is not a form of this method for
(key, value) function arguments since there is no corresponding
return type.)
- Mapped reductions that accumulate the results of a given
function applied to each element.
- Reductions to scalar doubles, longs, and ints, using a
given basis value.
These bulk operations accept a parallelismThreshold
argument. Methods proceed sequentially if the current map size is
estimated to be less than the given threshold. Using a value of
Long.MAX_VALUE suppresses all parallelism. Using a value
of 1 results in maximal parallelism by partitioning into
enough subtasks to fully utilize the ForkJoinPool.commonPool() that is used for all parallel
computations. Normally, you would initially choose one of these
extreme values, and then measure performance of using in-between
values that trade off overhead versus throughput.
The concurrency properties of bulk operations follow
from those of ConcurrentHashMap: Any non-null result returned
from get(key) and related access methods bears a
happens-before relation with the associated insertion or
update. The result of any bulk operation reflects the
composition of these per-element relations (but is not
necessarily atomic with respect to the map as a whole unless it
is somehow known to be quiescent). Conversely, because keys
and values in the map are never null, null serves as a reliable
atomic indicator of the current lack of any result. To
maintain this property, null serves as an implicit basis for
all non-scalar reduction operations. For the double, long, and
int versions, the basis should be one that, when combined with
any other value, returns that other value (more formally, it
should be the identity element for the reduction). Most common
reductions have these properties; for example, computing a sum
with basis 0 or a minimum with basis MAX_VALUE.
Search and transformation functions provided as arguments
should similarly return null to indicate the lack of any result
(in which case it is not used). In the case of mapped
reductions, this also enables transformations to serve as
filters, returning null (or, in the case of primitive
specializations, the identity basis) if the element should not
be combined. You can create compound transformations and
filterings by composing them yourself under this "null means
there is nothing there now" rule before using them in search or
reduce operations.
Methods accepting and/or returning Entry arguments maintain
key-value associations. They may be useful for example when
finding the key for the greatest value. Note that "plain" Entry
arguments can be supplied using new
AbstractMap.SimpleEntry(k,v).
Bulk operations may complete abruptly, throwing an
exception encountered in the application of a supplied
function. Bear in mind when handling such exceptions that other
concurrently executing functions could also have thrown
exceptions, or would have done so if the first exception had
not occurred.
Speedups for parallel compared to sequential forms are common
but not guaranteed. Parallel operations involving brief functions
on small maps may execute more slowly than sequential forms if the
underlying work to parallelize the computation is more expensive
than the computation itself. Similarly, parallelization may not
lead to much actual parallelism if all processors are busy
performing unrelated tasks.
All arguments to all task methods must be non-null.
This class is a member of the
Java Collections Framework.
Since:
1.5
Author:
Doug Lea
See Also:
Nested Class Summary |
static class |
A view of a ConcurrentHashMap as a Set of keys, in
which additions may optionally be enabled by mapping to a
common value.
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Nested classes/interfaces inherited from class java.util. AbstractMap |
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Nested classes/interfaces inherited from interface java.util. Map |
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Constructor Summary |
Creates a new, empty map with the default initial table size (16).
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Creates a new, empty map with an initial table size
accommodating the specified number of elements without the need
to dynamically resize.
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Creates a new, empty map with an initial table size based on
the given number of elements (initialCapacity) and
initial table density (loadFactor).
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Creates a new, empty map with an initial table size based on
the given number of elements (initialCapacity), initial
table density (loadFactor), and number of concurrently
updating threads (concurrencyLevel).
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Creates a new map with the same mappings as the given map.
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Method Summary |
void |
Removes all of the mappings from this map.
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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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If the specified key is not already associated with a value,
attempts to compute its value using the given mapping function
and enters it into this map unless null.
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If the value for the specified key is present, attempts to
compute a new mapping given the key and its current mapped
value.
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boolean |
Tests if some key maps into the specified value in this table.
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boolean |
Tests if the specified object is a key in this table.
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boolean |
Returns true if this map maps one or more keys to the
specified value.
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Returns an enumeration of the values in this table.
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Returns a Set view of the mappings contained in this map.
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boolean |
Compares the specified object with this map for equality.
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void |
Performs the given action for each entry in this map until all entries
have been processed or the action throws an exception.
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void |
Performs the given action for each (key, value).
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Performs the given action for each non-null transformation
of each (key, value).
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void |
Performs the given action for each entry.
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Performs the given action for each non-null transformation
of each entry.
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void |
Performs the given action for each key.
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Performs the given action for each non-null transformation
of each key.
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void |
Performs the given action for each value.
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Performs the given action for each non-null transformation
of each value.
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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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Returns the value to which the specified key is mapped, or the
given default value if this map contains no mapping for the
key.
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int |
Returns the hash code value for this Map, i.e.,
the sum of, for each key-value pair in the map,
key.hashCode() ^ value.hashCode().
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boolean |
Returns true if this map contains no key-value mappings.
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Returns an enumeration of the keys in this table.
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Returns a Set view of the keys contained in this map.
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long |
Returns the number of mappings.
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If the specified key is not already associated with a
(non-null) value, associates it with the given value.
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Creates a new Set backed by a ConcurrentHashMap
from the given type to Boolean.TRUE.
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Creates a new Set backed by a ConcurrentHashMap
from the given type to Boolean.TRUE.
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Maps the specified key to the specified value in this table.
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void |
Copies all of the mappings from the specified map to this one.
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If the specified key is not already associated with a value (or is mapped
to null) associates it with the given value and returns
null, else returns the current value.
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Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, or null if none.
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Returns the result of accumulating all entries using the
given reducer to combine values, or null if none.
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Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
or null if none.
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double |
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
and the given basis as an identity value.
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int |
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
and the given basis as an identity value.
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long |
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
and the given basis as an identity value.
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Returns the result of accumulating all keys using the given
reducer to combine values, or null if none.
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Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, or
null if none.
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double |
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, and
the given basis as an identity value.
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int |
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, and
the given basis as an identity value.
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long |
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, and
the given basis as an identity value.
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double |
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, and the given basis as an identity value.
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int |
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, and the given basis as an identity value.
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long |
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, and the given basis as an identity value.
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Returns the result of accumulating all values using the
given reducer to combine values, or null if none.
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Returns the result of accumulating the given transformation
of all values using the given reducer to combine values, or
null if none.
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double |
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values,
and the given basis as an identity value.
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int |
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values,
and the given basis as an identity value.
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long |
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values,
and the given basis as an identity value.
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Removes the key (and its corresponding value) from this map.
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boolean |
Removes the entry for the specified key only if it is currently
mapped to the specified value.
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Replaces the entry for the specified key only if it is
currently mapped to some value.
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boolean |
Replaces the entry for the specified key only if currently
mapped to the specified value.
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void |
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.
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Returns a non-null result from applying the given search
function on each (key, value), or null if none.
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Returns a non-null result from applying the given search
function on each entry, or null if none.
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Returns a non-null result from applying the given search
function on each key, or null if none.
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Returns a non-null result from applying the given search
function on each value, or null if none.
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int |
Returns the number of key-value mappings in this map.
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Returns a string representation of this map.
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Returns a Collection view of the values contained in this map.
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Methods inherited from class java.lang. Object |
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Methods inherited from interface java.util. Map |
copyOf, entry, of, of, of, of, of, of, of, of, of, of, of, ofEntries |
public ConcurrentHashMap |
() |
Creates a new, empty map with the default initial table size (16).
public ConcurrentHashMap |
(int initialCapacity) |
Creates a new, empty map with an initial table size
accommodating the specified number of elements without the need
to dynamically resize.
Parameters:
initialCapacity - The implementation performs internal
sizing to accommodate this many elements.
Throws:
public ConcurrentHashMap |
( Map<? extends K,? extends V> m) |
Creates a new map with the same mappings as the given map.
Parameters:
m - the map
public ConcurrentHashMap |
(int initialCapacity, float loadFactor) |
Creates a new, empty map with an initial table size based on
the given number of elements (
initialCapacity) and
initial table density (
loadFactor).
Parameters:
initialCapacity - the initial capacity. The implementation
performs internal sizing to accommodate this many elements,
given the specified load factor.
loadFactor - the load factor (table density) for
establishing the initial table size
Throws:
Since:
1.6
public ConcurrentHashMap |
(int initialCapacity, float loadFactor, int concurrencyLevel) |
Creates a new, empty map with an initial table size based on
the given number of elements (
initialCapacity), initial
table density (
loadFactor), and number of concurrently
updating threads (
concurrencyLevel).
Parameters:
initialCapacity - the initial capacity. The implementation
performs internal sizing to accommodate this many elements,
given the specified load factor.
loadFactor - the load factor (table density) for
establishing the initial table size
concurrencyLevel - the estimated number of concurrently
updating threads. The implementation may use this value as
a sizing hint.
Throws:
Returns the number of key-value mappings in this map. If the
map contains more than
Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
Specified by:
Overrides:
Returns:
the number of key-value mappings in this map
public boolean isEmpty |
() |
Returns
true if this map contains no key-value mappings.
Specified by:
Overrides:
Returns:
true if this map contains no key-value mappings
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.equals(k),
then this method returns v; otherwise it returns
null. (There can be at most one such mapping.)
Specified by:
Overrides:
Parameters:
key - the key whose associated value is to be returned
Returns:
the value to which the specified key is mapped, or
null if this map contains no mapping for the key
Throws:
public boolean containsKey |
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Tests if the specified object is a key in this table.
Specified by:
Overrides:
Parameters:
key - possible key
Returns:
true if and only if the specified object
is a key in this table, as determined by the
equals method; false otherwise
Throws:
public boolean containsValue |
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Returns
true if this map maps one or more keys to the
specified value. Note: This method may require a full traversal
of the map, and is much slower than method
containsKey.
Specified by:
Overrides:
Parameters:
value - value whose presence in this map is to be tested
Returns:
true if this map maps one or more keys to the
specified value
Throws:
Maps the specified key to the specified value in this table.
Neither the key nor the value can be null.
The value can be retrieved by calling the get method
with a key that is equal to the original key.
Specified by:
Overrides:
Parameters:
key - key with which the specified value is to be associated
value - value to be associated with the specified key
Returns:
the previous value associated with key, or
null if there was no mapping for key
Throws:
public void putAll |
( Map<? extends K,? extends V> m) |
Copies all of the mappings from the specified map to this one.
These mappings replace any mappings that this map had for any of the
keys currently in the specified map.
Specified by:
Overrides:
Parameters:
m - mappings to be stored in this map
Removes the key (and its corresponding value) from this map.
This method does nothing if the key is not in the map.
Specified by:
Overrides:
Parameters:
key - the key that needs to be removed
Returns:
the previous value associated with key, or
null if there was no mapping for key
Throws:
Removes all of the mappings from this map.
Specified by:
Overrides:
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. The set supports element
removal, which removes the corresponding mapping from this map,
via the
Iterator.remove,
Set.remove,
removeAll,
retainAll, and
clear
operations. It does not support the
add or
addAll operations.
The view's iterators and spliterators are
weakly consistent.
The view's spliterator reports Spliterator.CONCURRENT,
Spliterator.DISTINCT, and Spliterator.NONNULL.
Specified by:
Overrides:
Returns:
the set view
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. The collection
supports element removal, which removes the corresponding
mapping from this map, via the
Iterator.remove,
Collection.remove,
removeAll,
retainAll, and
clear operations. It does not
support the
add or
addAll operations.
The view's iterators and spliterators are
weakly consistent.
The view's spliterator reports Spliterator.CONCURRENT
and Spliterator.NONNULL.
Specified by:
Overrides:
Returns:
the collection view
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. The set supports element
removal, which removes the corresponding mapping from the map,
via the
Iterator.remove,
Set.remove,
removeAll,
retainAll, and
clear
operations.
The view's iterators and spliterators are
weakly consistent.
The view's spliterator reports Spliterator.CONCURRENT,
Spliterator.DISTINCT, and Spliterator.NONNULL.
Specified by:
Overrides:
Returns:
the set view
Returns the hash code value for this
Map, i.e.,
the sum of, for each key-value pair in the map,
key.hashCode() ^ value.hashCode().
Specified by:
Overrides:
Returns:
the hash code value for this map
See Also:
Returns a string representation of this map. The string
representation consists of a list of key-value mappings (in no
particular order) 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.
Overrides:
Returns:
a string representation of this map
Compares the specified object with this map for equality.
Returns
true if the given object is a map with the same
mappings as this map. This operation may return misleading
results if either map is concurrently modified during execution
of this method.
Specified by:
Overrides:
Parameters:
o - object to be compared for equality with this map
Returns:
true if the specified object is equal to this map
See Also:
If the specified key is not already associated with a value (or is mapped
to
null) associates it with the given value and returns
null, else returns the current value.
Specified by:
Parameters:
key - key with which the specified value is to be associated
value - value to be associated with the specified key
Returns:
the previous value associated with the specified key,
or null if there was no mapping for the key
Throws:
Removes the entry for the specified key only if it is currently
mapped to the specified value.
Specified by:
Parameters:
key - key with which the specified value is associated
value - value expected to be associated with the specified key
Returns:
true if the value was removed
Throws:
public boolean replace |
( K key, V oldValue, V newValue) |
Replaces the entry for the specified key only if currently
mapped to the specified value.
Specified by:
Parameters:
key - key with which the specified value is associated
oldValue - value expected to be associated with the specified key
newValue - value to be associated with the specified key
Returns:
true if the value was replaced
Throws:
Replaces the entry for the specified key only if it is
currently mapped to some value.
Specified by:
Parameters:
key - key with which the specified value is associated
value - value to be associated with the specified key
Returns:
the previous value associated with the specified key,
or null if there was no mapping for the key
Throws:
Returns the value to which the specified key is mapped, or the
given default value if this map contains no mapping for the
key.
Specified by:
Parameters:
key - the key whose associated value is to be returned
defaultValue - the value to return if this map contains
no mapping for the given key
Returns:
the mapping for the key, if present; else the default value
Throws:
Description copied from interface:
Map
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.
Specified by:
Parameters:
action - The action to be performed for each entry
Description copied from interface:
Map
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.
Specified by:
Parameters:
function - the function to apply to each entry
|
( K key, Function<? super K,? extends V> mappingFunction) |
If the specified key is not already associated with a value,
attempts to compute its value using the given mapping function
and enters it into this map unless
null. The entire
method invocation is performed atomically. The supplied
function is invoked exactly once per invocation of this method
if the key is absent, else not at all. Some attempted update
operations on this map by other threads may be blocked while
computation is in progress, so the computation should be short
and simple.
The mapping function must not modify this map during computation.
Specified by:
Parameters:
key - key with which the specified value is to be associated
mappingFunction - the function to compute a value
Returns:
the current (existing or computed) value associated with
the specified key, or null if the computed value is null
Throws:
NullPointerException - if the specified key or mappingFunction
is null
IllegalStateException - if the computation detectably
attempts a recursive update to this map that would
otherwise never complete
RuntimeException - or Error if the mappingFunction does so,
in which case the mapping is left unestablished
public V computeIfPresent |
( K key, BiFunction<? super K,? super V,? extends V> remappingFunction) |
If the value for the specified key is present, attempts to
compute a new mapping given the key and its current mapped
value. The entire method invocation is performed atomically.
The supplied function is invoked exactly once per invocation of
this method if the key is present, else not at all. Some
attempted update operations on this map by other threads may be
blocked while computation is in progress, so the computation
should be short and simple.
The remapping function must not modify this map during computation.
Specified by:
Parameters:
key - key with which a value may be associated
remappingFunction - the function to compute a value
Returns:
the new value associated with the specified key, or null if none
Throws:
NullPointerException - if the specified key or remappingFunction
is null
IllegalStateException - if the computation detectably
attempts a recursive update to this map that would
otherwise never complete
RuntimeException - or Error if the remappingFunction does so,
in which case the mapping is unchanged
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( K key, BiFunction<? super K,? super V,? extends V> remappingFunction) |
Attempts to compute a mapping for the specified key and its
current mapped value (or
null if there is no current
mapping). The entire method invocation is performed atomically.
The supplied function is invoked exactly once per invocation of
this method. Some attempted update operations on this map by
other threads may be blocked while computation is in progress,
so the computation should be short and simple.
The remapping function must not modify this map during computation.
Specified by:
Parameters:
key - key with which the specified value is to be associated
remappingFunction - the function to compute a value
Returns:
the new value associated with the specified key, or null if none
Throws:
NullPointerException - if the specified key or remappingFunction
is null
IllegalStateException - if the computation detectably
attempts a recursive update to this map that would
otherwise never complete
RuntimeException - or Error if the remappingFunction does so,
in which case the mapping is unchanged
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( K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction) |
If the specified key is not already associated with a
(non-null) value, associates it with the given value.
Otherwise, replaces the value with the results of the given
remapping function, or removes if
null. The entire
method invocation is performed atomically. Some attempted
update operations on this map by other threads may be blocked
while computation is in progress, so the computation should be
short and simple, and must not attempt to update any other
mappings of this Map.
Specified by:
Parameters:
key - key with which the specified value is to be associated
value - the value to use if absent
remappingFunction - the function to recompute a value if present
Returns:
the new value associated with the specified key, or null if none
Throws:
Tests if some key maps into the specified value in this table.
Note that this method is identical in functionality to
containsValue(Object), and exists solely to ensure
full compatibility with class Hashtable,
which supported this method prior to introduction of the
Java Collections Framework.
Parameters:
value - a value to search for
Returns:
true if and only if some key maps to the
value argument in this table as
determined by the equals method;
false otherwise
Throws:
Returns an enumeration of the keys in this table.
Returns:
an enumeration of the keys in this table
See Also:
Returns an enumeration of the values in this table.
Returns:
an enumeration of the values in this table
See Also:
public long mappingCount |
() |
Returns the number of mappings. This method should be used
instead of
size() because a ConcurrentHashMap may
contain more mappings than can be represented as an int. The
value returned is an estimate; the actual count may differ if
there are concurrent insertions or removals.
Returns:
the number of mappings
Since:
1.8
Creates a new
Set backed by a ConcurrentHashMap
from the given type to
Boolean.TRUE.
Type Parameters:
K - the element type of the returned set
Returns:
the new set
Since:
1.8
Creates a new
Set backed by a ConcurrentHashMap
from the given type to
Boolean.TRUE.
Type Parameters:
K - the element type of the returned set
Parameters:
initialCapacity - The implementation performs internal
sizing to accommodate this many elements.
Returns:
the new set
Throws:
Since:
1.8
Returns a
Set view of the keys in this map, using the
given common mapped value for any additions (i.e.,
Collection.add(E) and
Collection.addAll(Collection)).
This is of course only appropriate if it is acceptable to use
the same value for all additions from this view.
Parameters:
mappedValue - the mapped value to use for any additions
Returns:
the set view
Throws:
public void forEach |
(long parallelismThreshold, BiConsumer<? super K,? super V> action) |
Performs the given action for each (key, value).
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
action - the action
Since:
1.8
|
(long parallelismThreshold, BiFunction<? super K,? super V,? extends U> transformer, Consumer<? super U> action) |
Performs the given action for each non-null transformation
of each (key, value).
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)
action - the action
Since:
1.8
|
(long parallelismThreshold, BiFunction<? super K,? super V,? extends U> searchFunction) |
Returns a non-null result from applying the given search
function on each (key, value), or null if none. Upon
success, further element processing is suppressed and the
results of any other parallel invocations of the search
function are ignored.
Type Parameters:
U - the return type of the search function
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
searchFunction - a function returning a non-null
result on success, else null
Returns:
a non-null result from applying the given search
function on each (key, value), or null if none
Since:
1.8
|
(long parallelismThreshold, BiFunction<? super K,? super V,? extends U> transformer, BiFunction<? super U,? super U,? extends U> reducer) |
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, or null if none.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all (key, value) pairs
Since:
1.8
public double reduceToDouble |
|
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all (key, value) pairs
Since:
1.8
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all (key, value) pairs
Since:
1.8
Returns the result of accumulating the given transformation
of all (key, value) pairs using the given reducer to
combine values, and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all (key, value) pairs
Since:
1.8
public void forEachKey |
(long parallelismThreshold, Consumer<? super K> action) |
Performs the given action for each key.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
action - the action
Since:
1.8
public < U> void forEachKey |
(long parallelismThreshold, Function<? super K,? extends U> transformer, Consumer<? super U> action) |
Performs the given action for each non-null transformation
of each key.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)
action - the action
Since:
1.8
|
(long parallelismThreshold, Function<? super K,? extends U> searchFunction) |
Returns a non-null result from applying the given search
function on each key, or null if none. Upon success,
further element processing is suppressed and the results of
any other parallel invocations of the search function are
ignored.
Type Parameters:
U - the return type of the search function
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
searchFunction - a function returning a non-null
result on success, else null
Returns:
a non-null result from applying the given search
function on each key, or null if none
Since:
1.8
|
(long parallelismThreshold, BiFunction<? super K,? super K,? extends K> reducer) |
Returns the result of accumulating all keys using the given
reducer to combine values, or null if none.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
reducer - a commutative associative combining function
Returns:
the result of accumulating all keys using the given
reducer to combine values, or null if none
Since:
1.8
|
(long parallelismThreshold, Function<? super K,? extends U> transformer, BiFunction<? super U,? super U,? extends U> reducer) |
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, or
null if none.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all keys
Since:
1.8
public double reduceKeysToDouble |
|
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, and
the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all keys
Since:
1.8
public long reduceKeysToLong |
|
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, and
the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all keys
Since:
1.8
public int reduceKeysToInt |
|
Returns the result of accumulating the given transformation
of all keys using the given reducer to combine values, and
the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all keys
Since:
1.8
public void forEachValue |
(long parallelismThreshold, Consumer<? super V> action) |
Performs the given action for each value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
action - the action
Since:
1.8
public < U> void forEachValue |
(long parallelismThreshold, Function<? super V,? extends U> transformer, Consumer<? super U> action) |
Performs the given action for each non-null transformation
of each value.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)
action - the action
Since:
1.8
public < U> U searchValues |
(long parallelismThreshold, Function<? super V,? extends U> searchFunction) |
Returns a non-null result from applying the given search
function on each value, or null if none. Upon success,
further element processing is suppressed and the results of
any other parallel invocations of the search function are
ignored.
Type Parameters:
U - the return type of the search function
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
searchFunction - a function returning a non-null
result on success, else null
Returns:
a non-null result from applying the given search
function on each value, or null if none
Since:
1.8
|
(long parallelismThreshold, BiFunction<? super V,? super V,? extends V> reducer) |
Returns the result of accumulating all values using the
given reducer to combine values, or null if none.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
reducer - a commutative associative combining function
Returns:
the result of accumulating all values
Since:
1.8
public < U> U reduceValues |
(long parallelismThreshold, Function<? super V,? extends U> transformer, BiFunction<? super U,? super U,? extends U> reducer) |
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values, or
null if none.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all values
Since:
1.8
public double reduceValuesToDouble |
|
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values,
and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all values
Since:
1.8
public long reduceValuesToLong |
|
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values,
and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all values
Since:
1.8
public int reduceValuesToInt |
|
Returns the result of accumulating the given transformation
of all values using the given reducer to combine values,
and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all values
Since:
1.8
Performs the given action for each entry.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
action - the action
Since:
1.8
public < U> void forEachEntry |
|
Performs the given action for each non-null transformation
of each entry.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case the action is not applied)
action - the action
Since:
1.8
public < U> U searchEntries |
|
Returns a non-null result from applying the given search
function on each entry, or null if none. Upon success,
further element processing is suppressed and the results of
any other parallel invocations of the search function are
ignored.
Type Parameters:
U - the return type of the search function
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
searchFunction - a function returning a non-null
result on success, else null
Returns:
a non-null result from applying the given search
function on each entry, or null if none
Since:
1.8
Returns the result of accumulating all entries using the
given reducer to combine values, or null if none.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
reducer - a commutative associative combining function
Returns:
the result of accumulating all entries
Since:
1.8
public < U> U reduceEntries |
|
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
or null if none.
Type Parameters:
U - the return type of the transformer
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element, or null if there is no transformation (in
which case it is not combined)
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all entries
Since:
1.8
public double reduceEntriesToDouble |
|
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all entries
Since:
1.8
public long reduceEntriesToLong |
|
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all entries
Since:
1.8
public int reduceEntriesToInt |
|
Returns the result of accumulating the given transformation
of all entries using the given reducer to combine values,
and the given basis as an identity value.
Parameters:
parallelismThreshold - the (estimated) number of elements
needed for this operation to be executed in parallel
transformer - a function returning the transformation
for an element
basis - the identity (initial default value) for the reduction
reducer - a commutative associative combining function
Returns:
the result of accumulating the given transformation
of all entries
Since:
1.8
|
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