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FlexDoc/Javadoc 2.0 Demo Java Doc |
Interface Map<K,V>
Type Parameters:
K - the type of keys maintained by this map
V - the type of mapped values
All Known Subinterfaces:
All Known Implementing Classes:
AbstractMap,
ConcurrentHashMap,
ConcurrentSkipListMap,
EnumMap,
HashMap,
Hashtable,
IdentityHashMap,
LinkedHashMap,
Properties,
TreeMap,
WeakHashMap
public interface Map<K,V>
An object that maps keys to values. A map cannot contain duplicate keys;
each key can map to at most one value.
This interface takes the place of the Dictionary class, which
was a totally abstract class rather than an interface.
The Map interface provides three collection views, which
allow a map's contents to be viewed as a set of keys, collection of values,
or set of key-value mappings. The order of a map is defined as
the order in which the iterators on the map's collection views return their
elements. Some map implementations, like the TreeMap class, make
specific guarantees as to their order; others, like the HashMap
class, do not.
Note: great care must be exercised if mutable objects are used as map
keys. The behavior of a map is not specified if the value of an object is
changed in a manner that affects equals comparisons while the
object is a key in the map. A special case of this prohibition is that it
is not permissible for a map to contain itself as a key. While it is
permissible for a map to contain itself as a value, extreme caution is
advised: the equals and hashCode methods are no longer
well defined on such a map.
All general-purpose map implementation classes should provide two
"standard" constructors: a void (no arguments) constructor which creates an
empty map, and a constructor with a single argument of type Map,
which creates a new map with the same key-value mappings as its argument.
In effect, the latter constructor allows the user to copy any map,
producing an equivalent map of the desired class. There is no way to
enforce this recommendation (as interfaces cannot contain constructors) but
all of the general-purpose map implementations in the JDK comply.
The "destructive" methods contained in this interface, that is, the
methods that modify the map on which they operate, are specified to throw
UnsupportedOperationException if this map does not support the
operation. If this is the case, these methods may, but are not required
to, throw an UnsupportedOperationException if the invocation would
have no effect on the map. For example, invoking the putAll(Map)
method on an unmodifiable map may, but is not required to, throw the
exception if the map whose mappings are to be "superimposed" is empty.
Some map implementations have restrictions on the keys and values they
may contain. For example, some implementations prohibit null keys and
values, and some have restrictions on the types of their keys. Attempting
to insert an ineligible key or value throws an unchecked exception,
typically NullPointerException or ClassCastException.
Attempting to query the presence of an ineligible key or value may throw an
exception, or it may simply return false; some implementations will exhibit
the former behavior and some will exhibit the latter. More generally,
attempting an operation on an ineligible key or value whose completion
would not result in the insertion of an ineligible element into the map may
throw an exception or it may succeed, at the option of the implementation.
Such exceptions are marked as "optional" in the specification for this
interface.
Many methods in Collections Framework interfaces are defined
in terms of the equals method. For
example, the specification for the containsKey(Object key) method says: "returns true if and
only if this map contains a mapping for a key k such that
(key==null ? k==null : key.equals(k))." This specification should
not be construed to imply that invoking Map.containsKey
with a non-null argument key will cause key.equals(k) to
be invoked for any key k. Implementations are free to
implement optimizations whereby the equals invocation is avoided,
for example, by first comparing the hash codes of the two keys. (The
Object.hashCode() specification guarantees that two objects with
unequal hash codes cannot be equal.) More generally, implementations of
the various Collections Framework interfaces are free to take advantage of
the specified behavior of underlying Object methods wherever the
implementor deems it appropriate.
Some map operations which perform recursive traversal of the map may fail
with an exception for self-referential instances where the map directly or
indirectly contains itself. This includes the clone(),
equals(), hashCode() and toString() methods.
Implementations may optionally handle the self-referential scenario, however
most current implementations do not do so.
The Map.of,
Map.ofEntries, and
Map.copyOf
static factory methods provide a convenient way to create unmodifiable maps.
The Map
instances created by these methods have the following characteristics:
- They are unmodifiable. Keys and values
cannot be added, removed, or updated. Calling any mutator method on the Map
will always cause UnsupportedOperationException to be thrown.
However, if the contained keys or values are themselves mutable, this may cause the
Map to behave inconsistently or its contents to appear to change.
- They disallow null keys and values. Attempts to create them with
null keys or values result in NullPointerException.
- They are serializable if all keys and values are serializable.
- They reject duplicate keys at creation time. Duplicate keys
passed to a static factory method result in IllegalArgumentException.
- The iteration order of mappings is unspecified and is subject to change.
- They are value-based.
Programmers should treat instances that are equal
as interchangeable and should not use them for synchronization, or
unpredictable behavior may occur. For example, in a future release,
synchronization may fail. Callers should make no assumptions
about the identity of the returned instances. Factories are free to
create new instances or reuse existing ones.
- They are serialized as specified on the
Serialized Form
page.
This interface is a member of the
Java Collections Framework.
Since:
1.2
Author:
Josh Bloch
See Also:
Nested Class Summary |
static interface |
A map entry (key-value pair).
|
Method Summary |
void |
Removes all of the mappings from this map (optional operation).
|
|
Attempts to compute a mapping for the specified key and its current
mapped value (or null if there is no current mapping).
|
|
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 value for the specified key is present and non-null, attempts to
compute a new mapping given the key and its current mapped value.
|
boolean |
Returns true if this map contains a mapping for the specified
key.
|
boolean |
Returns true if this map maps one or more keys to the
specified value.
|
|
|
|
Returns an unmodifiable Map.Entry containing the given key and value.
|
|
Returns a Set view of the mappings contained in this map.
|
boolean |
Compares the specified object with this map for equality.
|
default void |
Performs the given action for each entry in this map until all entries
have been processed or the action throws an exception.
|
|
Returns the value to which the specified key is mapped,
or null if this map contains no mapping for the key.
|
|
Returns the value to which the specified key is mapped, or
defaultValue if this map contains no mapping for the key.
|
int |
Returns the hash code value for this map.
|
boolean |
Returns true if this map contains no key-value mappings.
|
|
Returns a Set view of the keys contained in this map.
|
|
If the specified key is not already associated with a value or is
associated with null, associates it with the given non-null value.
|
|
Returns an unmodifiable map containing zero mappings.
|
|
Returns an unmodifiable map containing a single mapping.
|
|
Returns an unmodifiable map containing two mappings.
|
|
Returns an unmodifiable map containing three mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4)
Returns an unmodifiable map containing four mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5)
Returns an unmodifiable map containing five mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6)
Returns an unmodifiable map containing six mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7)
Returns an unmodifiable map containing seven mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8)
Returns an unmodifiable map containing eight mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9)
Returns an unmodifiable map containing nine mappings.
|
|
of( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10)
Returns an unmodifiable map containing ten mappings.
|
|
Returns an unmodifiable map containing keys and values extracted from the given entries.
|
|
Associates the specified value with the specified key in this map
(optional operation).
|
void |
Copies all of the mappings from the specified map to this map
(optional operation).
|
|
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.
|
|
Removes the mapping for a key from this map if it is present
(optional operation).
|
default boolean |
Removes the entry for the specified key only if it is currently
mapped to the specified value.
|
|
Replaces the entry for the specified key only if it is
currently mapped to some value.
|
default boolean |
Replaces the entry for the specified key only if currently
mapped to the specified value.
|
default 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.
|
int |
Returns the number of key-value mappings in this map.
|
|
Returns a Collection view of the values contained in this map.
|
Returns the number of key-value mappings in this map. If the
map contains more than
Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
Returns:
the number of key-value mappings in this map
Returns
true if this map contains no key-value mappings.
Returns:
true if this map contains no key-value mappings
Returns
true if this map contains a mapping for the specified
key. More formally, returns
true if and only if
this map contains a mapping for a key
k such that
Objects.equals(key, k). (There can be
at most one such mapping.)
Parameters:
key - key whose presence in this map is to be tested
Returns:
true if this map contains a mapping for the specified
key
Throws:
Returns
true if this map maps one or more keys to the
specified value. More formally, returns
true if and only if
this map contains at least one mapping to a value
v such that
Objects.equals(value, v). This operation
will probably require time linear in the map size for most
implementations of the
Map interface.
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:
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
Objects.equals(key, k),
then this method returns v; otherwise
it returns null. (There can be at most one such mapping.)
If this map permits null values, then 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 - 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:
Associates the specified value with the specified key in this map
(optional operation). If the map previously contained a mapping for
the key, the old value is replaced by the specified value. (A map
m is said to contain a mapping for a key
k if and only
if
m.containsKey(k) would return
true.)
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.
(A null return can also indicate that the map
previously associated null with key,
if the implementation supports null values.)
Throws:
Removes the mapping for a key from this map if it is present
(optional operation). More formally, if this map contains a mapping
from key
k to value
v such that
Objects.equals(key, k), that mapping
is removed. (The map can contain at most one such mapping.)
Returns the value to which this map previously associated the key,
or null if the map contained no mapping for the key.
If this map permits null values, then a return value of
null does not necessarily indicate that the map
contained no mapping for the key; it's also possible that the map
explicitly mapped the key to null.
The map will not contain a mapping for the specified key once the
call returns.
Parameters:
key - key whose mapping is to be removed from the map
Returns:
the previous value associated with key, or
null if there was no mapping for key.
Throws:
void putAll |
( Map<? extends K,? extends V> m) |
Copies all of the mappings from the specified map to this map
(optional operation). The effect of this call is equivalent to that
of calling
put(k, v) on this map once
for each mapping from key
k to value
v in the
specified map. The behavior of this operation is undefined if the
specified map is modified while the operation is in progress.
Parameters:
m - mappings to be stored in this map
Throws:
UnsupportedOperationException - if the
putAll operation
is not supported by this map
ClassCastException - if the class of a key or value in the
specified map prevents it from being stored in this map
NullPointerException - if the specified map is null, or if
this map does not permit null keys or values, and the
specified map contains null keys or values
IllegalArgumentException - if some property of a key or value in
the specified map prevents it from being stored in this map
Removes all of the mappings from this map (optional operation).
The map will be empty after this call returns.
Throws:
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.
Returns:
a set view of the keys contained in this map
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.
Returns:
a collection view of the values contained in this map
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.
Returns:
a set view of the mappings contained in this map
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.
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:
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().
Overrides:
Returns:
the hash code value for this map
See Also:
Returns the value to which the specified key is mapped, or
defaultValue if this map contains no mapping for the key.
Implementation Requirements:
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
Parameters:
key - the key whose associated value is to be returned
defaultValue - the default mapping of the key
Returns:
the value to which the specified key is mapped, or
defaultValue if this map contains no mapping for the key
Throws:
Since:
1.8
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.
Implementation Requirements:
The default implementation is equivalent to, for this
map:
for (Map.Entry<K, V> entry : map.entrySet())
action.accept(entry.getKey(), entry.getValue());
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
Parameters:
action - The action to be performed for each entry
Throws:
Since:
1.8
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.
Implementation Requirements:
The default implementation is equivalent to, for this map:
for (Map.Entry<K, V> entry : map.entrySet())
entry.setValue(function.apply(entry.getKey(), entry.getValue()));
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
Parameters:
function - the function to apply to each entry
Throws:
UnsupportedOperationException - if the
set operation
is not supported by this map's entry set iterator.
ClassCastException - if the class of a replacement value
prevents it from being stored in this map
NullPointerException - if the specified function is null, or the
specified replacement value is null, and this map does not permit null
values
Since:
1.8
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.
Implementation Requirements:
The default implementation is equivalent to, for this
map:
V v = map.get(key);
if (v == null)
v = map.put(key, value);
return v;
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
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.
(A null return can also indicate that the map
previously associated null with the key,
if the implementation supports null values.)
Throws:
Since:
1.8
Removes the entry for the specified key only if it is currently
mapped to the specified value.
Implementation Requirements:
The default implementation is equivalent to, for this
map:
if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
map.remove(key);
return true;
} else
return false;
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
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:
Since:
1.8
default boolean replace |
( K key, V oldValue, V newValue) |
Replaces the entry for the specified key only if currently
mapped to the specified value.
Implementation Requirements:
The default implementation is equivalent to, for this
map:
if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) {
map.put(key, newValue);
return true;
} else
return false;
The default implementation does not throw NullPointerException
for maps that do not support null values if oldValue is null unless
newValue is also null.
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
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:
Since:
1.8
Replaces the entry for the specified key only if it is
currently mapped to some value.
Implementation Requirements:
The default implementation is equivalent to, for this
map:
if (map.containsKey(key)) {
return map.put(key, value);
} else
return null;
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties.
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.
(A null return can also indicate that the map
previously associated null with the key,
if the implementation supports null values.)
Throws:
Since:
1.8
default V computeIfAbsent |
( K key, Function<? super K,? extends V> mappingFunction) |
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:
map.computeIfAbsent(key, k -> new Value(f(k)));
Or to implement a multi-value map, Map<K,Collection<V>>,
supporting multiple values per key:
map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
The mapping function should not modify this map during computation.
Implementation Requirements:
The default implementation is equivalent to the following steps for this
map, then returning the current value or
null if now
absent:
if (map.get(key) == null) {
V newValue = mappingFunction.apply(key);
if (newValue != null)
map.put(key, newValue);
}
The default implementation makes no guarantees about detecting if the
mapping function modifies this map during computation and, if
appropriate, reporting an error. Non-concurrent implementations should
override this method and, on a best-effort basis, throw a
ConcurrentModificationException if it is detected that the
mapping function modifies this map during computation. Concurrent
implementations should override this method and, on a best-effort basis,
throw an IllegalStateException if it is detected that the
mapping function modifies this map during computation and as a result
computation would never complete.
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties. In particular, all implementations of
subinterface ConcurrentMap must document
whether the mapping function is applied once atomically only if the value
is not present.
Parameters:
key - key with which the specified value is to be associated
mappingFunction - the mapping 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 is null and
this map does not support null keys, or the mappingFunction
is null
Since:
1.8
default V computeIfPresent |
( K key, BiFunction<? super K,? super V,? extends V> remappingFunction) |
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.
Implementation Requirements:
The default implementation is equivalent to performing the following
steps for this
map, then returning the current value or
null if now absent:
if (map.get(key) != null) {
V oldValue = map.get(key);
V newValue = remappingFunction.apply(key, oldValue);
if (newValue != null)
map.put(key, newValue);
else
map.remove(key);
}
The default implementation makes no guarantees about detecting if the
remapping function modifies this map during computation and, if
appropriate, reporting an error. Non-concurrent implementations should
override this method and, on a best-effort basis, throw a
ConcurrentModificationException if it is detected that the
remapping function modifies this map during computation. Concurrent
implementations should override this method and, on a best-effort basis,
throw an IllegalStateException if it is detected that the
remapping function modifies this map during computation and as a result
computation would never complete.
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties. In particular, all implementations of
subinterface ConcurrentMap must document
whether the remapping function is applied once atomically only if the
value is not present.
Parameters:
key - key with which the specified value is to be associated
remappingFunction - the remapping function to compute a value
Returns:
the new value associated with the specified key, or null if none
Throws:
NullPointerException - if the specified key is null and
this map does not support null keys, or the
remappingFunction is null
Since:
1.8
|
( 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). For
example, to either create or append a
String msg to a value
mapping:
map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))
(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.
Implementation Requirements:
The default implementation is equivalent to performing the following
steps for this
map:
V oldValue = map.get(key);
V newValue = remappingFunction.apply(key, oldValue);
if (newValue != null) {
map.put(key, newValue);
} else if (oldValue != null || map.containsKey(key)) {
map.remove(key);
}
return newValue;
The default implementation makes no guarantees about detecting if the
remapping function modifies this map during computation and, if
appropriate, reporting an error. Non-concurrent implementations should
override this method and, on a best-effort basis, throw a
ConcurrentModificationException if it is detected that the
remapping function modifies this map during computation. Concurrent
implementations should override this method and, on a best-effort basis,
throw an IllegalStateException if it is detected that the
remapping function modifies this map during computation and as a result
computation would never complete.
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties. In particular, all implementations of
subinterface ConcurrentMap must document
whether the remapping function is applied once atomically only if the
value is not present.
Parameters:
key - key with which the specified value is to be associated
remappingFunction - the remapping function to compute a value
Returns:
the new value associated with the specified key, or null if none
Throws:
NullPointerException - if the specified key is null and
this map does not support null keys, or the
remappingFunction is null
Since:
1.8
|
( K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction) |
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:
map.merge(key, msg, String::concat)
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.
Implementation Requirements:
The default implementation is equivalent to performing the following
steps for this
map, then returning the current value or
null if absent:
V oldValue = map.get(key);
V newValue = (oldValue == null) ? value :
remappingFunction.apply(oldValue, value);
if (newValue == null)
map.remove(key);
else
map.put(key, newValue);
The default implementation makes no guarantees about detecting if the
remapping function modifies this map during computation and, if
appropriate, reporting an error. Non-concurrent implementations should
override this method and, on a best-effort basis, throw a
ConcurrentModificationException if it is detected that the
remapping function modifies this map during computation. Concurrent
implementations should override this method and, on a best-effort basis,
throw an IllegalStateException if it is detected that the
remapping function modifies this map during computation and as a result
computation would never complete.
The default implementation makes no guarantees about synchronization
or atomicity properties of this method. Any implementation providing
atomicity guarantees must override this method and document its
concurrency properties. In particular, all implementations of
subinterface ConcurrentMap must document
whether the remapping function is applied once atomically only if the
value is not present.
Parameters:
key - key with which the resulting value is to be associated
value - 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 - the remapping function to recompute a value if
present
Returns:
the new value associated with the specified key, or null if no
value is associated with the key
Throws:
Since:
1.8
Returns an unmodifiable map containing zero mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Returns:
an empty Map
Since:
9
Returns an unmodifiable map containing a single mapping.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the mapping's key
v1 - the mapping's value
Returns:
a Map containing the specified mapping
Throws:
Since:
9
Returns an unmodifiable map containing two mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3) |
Returns an unmodifiable map containing three mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) |
Returns an unmodifiable map containing four mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) |
Returns an unmodifiable map containing five mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
k5 - the fifth mapping's key
v5 - the fifth mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6) |
Returns an unmodifiable map containing six mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
k5 - the fifth mapping's key
v5 - the fifth mapping's value
k6 - the sixth mapping's key
v6 - the sixth mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7) |
Returns an unmodifiable map containing seven mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
k5 - the fifth mapping's key
v5 - the fifth mapping's value
k6 - the sixth mapping's key
v6 - the sixth mapping's value
k7 - the seventh mapping's key
v7 - the seventh mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8) |
Returns an unmodifiable map containing eight mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
k5 - the fifth mapping's key
v5 - the fifth mapping's value
k6 - the sixth mapping's key
v6 - the sixth mapping's value
k7 - the seventh mapping's key
v7 - the seventh mapping's value
k8 - the eighth mapping's key
v8 - the eighth mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) |
Returns an unmodifiable map containing nine mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
k5 - the fifth mapping's key
v5 - the fifth mapping's value
k6 - the sixth mapping's key
v6 - the sixth mapping's value
k7 - the seventh mapping's key
v7 - the seventh mapping's value
k8 - the eighth mapping's key
v8 - the eighth mapping's value
k9 - the ninth mapping's key
v9 - the ninth mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
|
( K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) |
Returns an unmodifiable map containing ten mappings.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
k1 - the first mapping's key
v1 - the first mapping's value
k2 - the second mapping's key
v2 - the second mapping's value
k3 - the third mapping's key
v3 - the third mapping's value
k4 - the fourth mapping's key
v4 - the fourth mapping's value
k5 - the fifth mapping's key
v5 - the fifth mapping's value
k6 - the sixth mapping's key
v6 - the sixth mapping's value
k7 - the seventh mapping's key
v7 - the seventh mapping's value
k8 - the eighth mapping's key
v8 - the eighth mapping's value
k9 - the ninth mapping's key
v9 - the ninth mapping's value
k10 - the tenth mapping's key
v10 - the tenth mapping's value
Returns:
a Map containing the specified mappings
Throws:
Since:
9
Returns an unmodifiable map containing keys and values extracted from the given entries.
The entries themselves are not stored in the map.
See
Unmodifiable Maps for details.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
entries - Map.Entrys containing the keys and values from which the map is populated
Returns:
a Map containing the specified mappings
Throws:
Since:
9
See Also:
Returns an unmodifiable
Map.Entry containing the given key and value.
These entries are suitable for populating
Map instances using the
Map.ofEntries() method.
The
Entry instances created by this method have the following characteristics:
- They disallow null keys and values. Attempts to create them using a null
key or value result in NullPointerException.
- They are unmodifiable. Calls to Entry.setValue()
on a returned Entry result in UnsupportedOperationException.
- They are not serializable.
- They are value-based.
Programmers should treat instances that are equal
as interchangeable and should not use them for synchronization, or
unpredictable behavior may occur. For example, in a future release,
synchronization may fail. Callers should make no assumptions
about the identity of the returned instances. This method is free to
create new instances or reuse existing ones.
Type Parameters:
K - the key's type
V - the value's type
Parameters:
k - the key
v - the value
Returns:
an Entry containing the specified key and value
Throws:
Since:
9
See Also:
|
( Map<? extends K,? extends V> map) |
Returns an
unmodifiable Map containing the entries
of the given Map. The given Map must not be null, and it must not contain any
null keys or values. If the given Map is subsequently modified, the returned
Map will not reflect such modifications.
Implementation Note:
If the given Map is an
unmodifiable Map,
calling copyOf will generally not create a copy.
Type Parameters:
K - the
Map's key type
V - the Map's value type
Parameters:
map - a Map from which entries are drawn, must be non-null
Returns:
a Map containing the entries of the given Map
Throws:
Since:
10
|
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