ConcurrentMap

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Superinterfaces:

Map<K,V>

All Known Subinterfaces:

ConcurrentNavigableMap<K,V>

All Known Implementing Classes:

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.

Since:

1.5

Nested Class Summary
- Nested classes/interfaces inherited from interface java.util.Map
  Map.Entry<K,V>

Method Summary

All Methods

Instance Methods

Abstract Methods

Default Methods
Modifier and Type	Method and Description
`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.

Methods inherited from interface java.util.Map
clear, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, values

- Method Detail
  - 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.
    
    Specified by:
    
    getOrDefault in interface Map<K,V>
    
    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:
    
    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)
    
    Since:
    
    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.
    
    Specified by:
    
    forEach in interface Map<K,V>
    
    Parameters:
    
    action - The action to be performed for each entry
    
    Throws:
    
    NullPointerException - if the specified action is null
    
    Since:
    
    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.
    Specified by:
    
    putIfAbsent in interface Map<K,V>
    
    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:
    
    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.
    Specified by:
    
    remove in interface Map<K,V>
    
    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:
    
    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.
    Specified by:
    
    replace in interface Map<K,V>
    
    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:
    
    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.
    Specified by:
    
    replace in interface Map<K,V>
    
    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:
    
    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.
    
    Specified by:
    
    replaceAll in interface Map<K,V>
    
    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.
    
    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)
    
    Since:
    
    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); 
```
    Specified by:
    
    computeIfAbsent in interface Map<K,V>
    
    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:
    
    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
    
    Since:
    
    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.
    
    Specified by:
    
    computeIfPresent in interface Map<K,V>
    
    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:
    
    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
    
    Since:
    
    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.
    Specified by:
    
    compute in interface Map<K,V>
    
    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:
    
    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
    
    Since:
    
    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.
    Specified by:
    
    merge in interface Map<K,V>
    
    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 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:
    
    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
    
    Since:
    
    1.8

Interface ConcurrentMap<K,V>

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Method Summary

Methods inherited from interface java.util.Map

Method Detail

getOrDefault

forEach

putIfAbsent

remove

replace

replace

replaceAll

computeIfAbsent

computeIfPresent

compute

merge