程序包 java.util.concurrent

接口 ConcurrentMap<K,V>

类型参数:

K - the type of keys maintained by this map

V - the type of mapped values

所有超级接口:

Map<K,V>

所有已知子接口:

ConcurrentNavigableMap<K,V>

所有已知实现类:

ConcurrentHashMap, ConcurrentSkipListMap

public interface ConcurrentMap<K,V>
extends Map<K,V>

A Map providing thread safety and atomicity guarantees.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentMap as a key or value happen-before actions subsequent to the access or removal of that object from the ConcurrentMap in another thread.

This interface is a member of the Java Collections Framework.

从以下版本开始:

1.5

嵌套类概要

从接口继承的嵌套类/接口 java.util.Map

Map.Entry<K,V>

方法概要

限定符和类型	方法	说明
default V	compute(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).
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.
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.
default void	forEach(BiConsumer<? super K,? super V> action)	Performs the given action for each entry in this map until all entries have been processed or the action throws an exception.
default V	getOrDefault(Object key, V defaultValue)	Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.
default V	merge(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.
V	putIfAbsent(K key, V value)	If the specified key is not already associated with a value, associate it with the given value.
boolean	remove(Object key, Object value)	Removes the entry for a key only if currently mapped to a given value.
V	replace(K key, V value)	Replaces the entry for a key only if currently mapped to some value.
boolean	replace(K key, V oldValue, V newValue)	Replaces the entry for a key only if currently mapped to a given value.
default void	replaceAll(BiFunction<? super K,? super V,? extends V> function)	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.

从接口继承的方法 java.util.Map

clear, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, values

方法详细资料

getOrDefault

default V getOrDefault(Object key,
                       V defaultValue)

Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.

指定者:

getOrDefault 在接口中 Map<K,V>

参数:

key - the key whose associated value is to be returned

defaultValue - the default mapping of the key

返回:

the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key

抛出:

ClassCastException - if the key is of an inappropriate type for this map (optional)

NullPointerException - if the specified key is null and this map does not permit null keys (optional)

从以下版本开始:

1.8

forEach

default void forEach(BiConsumer<? super K,? super V> action)

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.

指定者:

forEach 在接口中 Map<K,V>

参数:

action - The action to be performed for each entry

抛出:

NullPointerException - if the specified action is null

从以下版本开始:

1.8

putIfAbsent

V putIfAbsent(K key,
              V value)

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

 
 if (!map.containsKey(key))
   return map.put(key, value);
 else
   return map.get(key);
 

except that the action is performed atomically.

指定者:

putIfAbsent 在接口中 Map<K,V>

参数:

key - key with which the specified value is to be associated

value - value to be associated with the specified key

返回:

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.)

抛出:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of the specified key or value prevents it from being stored in this map

NullPointerException - if the specified key or value is null, and this map does not permit null keys or values

IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map

remove

boolean remove(Object key,
               Object value)

Removes the entry for a key only if currently mapped to a given value. This is equivalent to

 
 if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
   map.remove(key);
   return true;
 } else
   return false;
 

except that the action is performed atomically.

指定者:

remove 在接口中 Map<K,V>

参数:

key - key with which the specified value is associated

value - value expected to be associated with the specified key

返回:

true if the value was removed

抛出:

UnsupportedOperationException - if the remove operation is not supported by this map

ClassCastException - if the key or value is of an inappropriate type for this map (optional)

NullPointerException - if the specified key or value is null, and this map does not permit null keys or values (optional)

replace

boolean replace(K key,
                V oldValue,
                V newValue)

Replaces the entry for a key only if currently mapped to a given value. This is equivalent to

 
 if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) {
   map.put(key, newValue);
   return true;
 } else
   return false;
 

except that the action is performed atomically.

指定者:

replace 在接口中 Map<K,V>

参数:

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

返回:

true if the value was replaced

抛出:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of a specified key or value prevents it from being stored in this map

NullPointerException - if a specified key or value is null, and this map does not permit null keys or values

IllegalArgumentException - if some property of a specified key or value prevents it from being stored in this map

replace

V replace(K key,
          V value)

Replaces the entry for a key only if currently mapped to some value. This is equivalent to

 
 if (map.containsKey(key)) {
   return map.put(key, value);
 } else
   return null;
 

except that the action is performed atomically.

指定者:

replace 在接口中 Map<K,V>

参数:

key - key with which the specified value is associated

value - value to be associated with the specified key

返回:

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.)

抛出:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of the specified key or value prevents it from being stored in this map

NullPointerException - if the specified key or value is null, and this map does not permit null keys or values

IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map

replaceAll

default void replaceAll(BiFunction<? super K,? super V,? extends V> function)

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.

指定者:

replaceAll 在接口中 Map<K,V>

参数:

function - the function to apply to each entry

抛出:

UnsupportedOperationException - if the set operation is not supported by this map's entry set iterator.

NullPointerException - if function or a replacement value is null, and this map does not permit null keys or values (optional)

ClassCastException - if a replacement value is of an inappropriate type for this map (optional)

IllegalArgumentException - if some property of a replacement value prevents it from being stored in this map (optional)

从以下版本开始:

1.8

computeIfAbsent

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 function returns null no mapping is recorded. If the 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);
 

指定者:

computeIfAbsent 在接口中 Map<K,V>

参数:

key - key with which the specified value is to be associated

mappingFunction - the function to compute a value

返回:

the current (existing or computed) value associated with the specified key, or null if the computed value is null

抛出:

UnsupportedOperationException - if the put operation is not supported by this map (optional)

ClassCastException - if the class of the specified key or value prevents it from being stored in this map (optional)

NullPointerException - if the specified key is null and this map does not support null keys, or the mappingFunction is null

从以下版本开始:

1.8

computeIfPresent

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 function returns null, the mapping is removed. If the function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

指定者:

computeIfPresent 在接口中 Map<K,V>

参数:

key - key with which the specified value is to be associated

remappingFunction - the function to compute a value

返回:

the new value associated with the specified key, or null if none

抛出:

UnsupportedOperationException - if the put operation is not supported by this map (optional)

ClassCastException - if the class of the specified key or value prevents it from being stored in this map (optional)

NullPointerException - if the specified key is null and this map does not support null keys, or the remappingFunction is null

从以下版本开始:

1.8

compute

default V compute(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 function returns null, the mapping is removed (or remains absent if initially absent). If the function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

指定者:

compute 在接口中 Map<K,V>

参数:

key - key with which the specified value is to be associated

remappingFunction - the function to compute a value

返回:

the new value associated with the specified key, or null if none

抛出:

UnsupportedOperationException - if the put operation is not supported by this map (optional)

ClassCastException - if the class of the specified key or value prevents it from being stored in this map (optional)

NullPointerException - if the specified key is null and this map does not support null keys, or the remappingFunction is null

从以下版本开始:

1.8

merge

default V merge(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 function returns null the mapping is removed. If the function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

指定者:

merge 在接口中 Map<K,V>

参数:

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 function to recompute a value if present

返回:

the new value associated with the specified key, or null if no value is associated with the key

抛出:

UnsupportedOperationException - if the put operation is not supported by this map (optional)

ClassCastException - if the class of the specified key or value prevents it from being stored in this map (optional)

NullPointerException - if the specified key is null and this map does not support null keys or the value or remappingFunction is null

从以下版本开始:

1.8