ConcurrentLinkedHashMap (cayenne-doc: Cayenne Documentation 5.0-M2 API)
Description: declaration: package: org.apache.cayenne.util.concurrentlinkedhashmap, class: ConcurrentLinkedHashMap

# Class ConcurrentLinkedHashMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
org.apache.cayenne.util.concurrentlinkedhashmap.ConcurrentLinkedHashMap<K,V>

Type Parameters:
  `K` - the type of keys maintained by this map
  `V` - the type of mapped values

All Implemented Interfaces:
  `Serializable, ConcurrentMap<K,V>, Map<K,V>`

public class ConcurrentLinkedHashMap<K,V> extends AbstractMap<K,V> implements ConcurrentMap<K,V>, Serializable
A hash table supporting full concurrency of retrievals, adjustable expected concurrency for updates, and a maximum capacity to bound the map by. This implementation differs from `ConcurrentHashMap` in that it maintains a page replacement algorithm that is used to evict an entry when the map has exceeded its capacity. Unlike the `Java Collections Framework`, this map does not have a publicly visible constructor and instances are created through a `ConcurrentLinkedHashMap.Builder`.

An entry is evicted from the map when the `weighted capacity` exceeds its `maximum weighted capacity` threshold. A `Weigher` instance determines how many units of capacity that a value consumes. The default weigher assigns each value a weight of `1` to bound the map by the total number of key-value pairs. A map that holds collections may choose to weigh values by the number of elements in the collection and bound the map by the total number of elements that it contains. A change to a value that modifies its weight requires that an update operation is performed on the map.

An `EvictionListener` may be supplied for notification when an entry is evicted from the map. This listener is invoked on a caller's thread and will not block other threads from operating on the map. An implementation should be aware that the caller's thread will not expect long execution times or failures as a side effect of the listener being notified. Execution safety and a fast turn around time can be achieved by performing the operation asynchronously, such as by submitting a task to an `ExecutorService`.

The `concurrency level` determines the number of threads that can concurrently modify the table. Using a significantly higher or lower value than needed can waste space or lead to thread contention, but an estimate within an order of magnitude of the ideal value does not usually have a noticeable impact. Because placement in hash tables is essentially random, the actual concurrency will vary.

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. Unlike `LinkedHashMap`, this class does not provide predictable iteration order. A snapshot of the keys and entries may be obtained in ascending and descending order of retention.

See Also:
  - Serialized Form

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static final class`
  `ConcurrentLinkedHashMap.Builder<K,V>`
  A builder that creates `ConcurrentLinkedHashMap` instances.

  ### Nested classes/interfaces inherited from class AbstractMap

  `AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>`

  ### Nested classes/interfaces inherited from interface Map

  `Map.Entry<K,V>`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Set<K>`
  `ascendingKeySet()`
  Returns a unmodifiable snapshot `Set` view of the keys contained in this map.
  `Set<K>`
  `ascendingKeySetWithLimit(int limit)`
  Returns an unmodifiable snapshot `Set` view of the keys contained in this map.
  `Map<K,V>`
  `ascendingMap()`
  Returns an unmodifiable snapshot `Map` view of the mappings contained in this map.
  `Map<K,V>`
  `ascendingMapWithLimit(int limit)`
  Returns an unmodifiable snapshot `Map` view of the mappings contained in this map.
  `int`
  `capacity()`
  Retrieves the maximum weighted capacity of the map.
  `void`
  `clear()`
  `boolean`
  `containsKey(Object key)`
  `boolean`
  `containsValue(Object value)`
  `Set<K>`
  `descendingKeySet()`
  Returns an unmodifiable snapshot `Set` view of the keys contained in this map.
  `Set<K>`
  `descendingKeySetWithLimit(int limit)`
  Returns an unmodifiable snapshot `Set` view of the keys contained in this map.
  `Map<K,V>`
  `descendingMap()`
  Returns an unmodifiable snapshot `Map` view of the mappings contained in this map.
  `Map<K,V>`
  `descendingMapWithLimit(int limit)`
  Returns an unmodifiable snapshot `Map` view of the mappings contained in this map.
  `Set<Map.Entry<K,V>>`
  `entrySet()`
  `V`
  `get(Object key)`
  `boolean`
  `isEmpty()`
  `Set<K>`
  `keySet()`
  `V`
  `put(K key, V value)`
  `V`
  `putIfAbsent(K key, V value)`
  `V`
  `remove(Object key)`
  `boolean`
  `remove(Object key, Object value)`
  `V`
  `replace(K key, V value)`
  `boolean`
  `replace(K key, V oldValue, V newValue)`
  `void`
  `setCapacity(int capacity)`
  Sets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size.
  `int`
  `size()`
  `Collection<V>`
  `values()`
  `int`
  `weightedSize()`
  Returns the weighted size of this map.

  ### Methods inherited from class AbstractMap

  `clone, equals, hashCode, putAll, toString`

  ### Methods inherited from class Object

  `finalize, getClass, notify, notifyAll, wait, wait, wait`

  ### Methods inherited from interface ConcurrentMap

  `compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, replaceAll`

- ## Method Details

  - ### capacity

    public int capacity()
    Retrieves the maximum weighted capacity of the map.
    Returns:
      the maximum weighted capacity

  - ### setCapacity

    public void setCapacity(int capacity)
    Sets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size.
    Parameters:
      `capacity` - the maximum weighted capacity of the map
    Throws:
      `IllegalArgumentException` - if the capacity is negative

  - ### isEmpty

    public boolean isEmpty()
    Specified by:
      `isEmpty` in interface `Map<K,V>`
    Overrides:
      `isEmpty` in class `AbstractMap<K,V>`

  - ### size

    public int size()
    Specified by:
      `size` in interface `Map<K,V>`
    Overrides:
      `size` in class `AbstractMap<K,V>`

  - ### weightedSize

    public int weightedSize()
    Returns the weighted size of this map.
    Returns:
      the combined weight of the values in this map

  - ### clear

    public void clear()
    Specified by:
      `clear` in interface `Map<K,V>`
    Overrides:
      `clear` in class `AbstractMap<K,V>`

  - ### containsKey

    public boolean containsKey(Object key)
    Specified by:
      `containsKey` in interface `Map<K,V>`
    Overrides:
      `containsKey` in class `AbstractMap<K,V>`

  - ### containsValue

    public boolean containsValue(Object value)
    Specified by:
      `containsValue` in interface `Map<K,V>`
    Overrides:
      `containsValue` in class `AbstractMap<K,V>`

  - ### get

    public V get(Object key)
    Specified by:
      `get` in interface `Map<K,V>`
    Overrides:
      `get` in class `AbstractMap<K,V>`

  - ### put

    public V put(K key, V value)
    Specified by:
      `put` in interface `Map<K,V>`
    Overrides:
      `put` in class `AbstractMap<K,V>`

  - ### putIfAbsent

    public V putIfAbsent(K key, V value)
    Specified by:
      `putIfAbsent` in interface `ConcurrentMap<K,V>`
    Specified by:
      `putIfAbsent` in interface `Map<K,V>`

  - ### remove

    public V remove(Object key)
    Specified by:
      `remove` in interface `Map<K,V>`
    Overrides:
      `remove` in class `AbstractMap<K,V>`

  - ### remove

    public boolean remove(Object key, Object value)
    Specified by:
      `remove` in interface `ConcurrentMap<K,V>`
    Specified by:
      `remove` in interface `Map<K,V>`

  - ### replace

    public V replace(K key, V value)
    Specified by:
      `replace` in interface `ConcurrentMap<K,V>`
    Specified by:
      `replace` in interface `Map<K,V>`

  - ### replace

    public boolean replace(K key, V oldValue, V newValue)
    Specified by:
      `replace` in interface `ConcurrentMap<K,V>`
    Specified by:
      `replace` in interface `Map<K,V>`

  - ### keySet

    public Set<K> keySet()
    Specified by:
      `keySet` in interface `Map<K,V>`
    Overrides:
      `keySet` in class `AbstractMap<K,V>`

  - ### ascendingKeySet

    public Set<K> ascendingKeySet()
    Returns a unmodifiable snapshot `Set` view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

    Beware that, unlike in `keySet()`, obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

    Returns:
      an ascending snapshot view of the keys in this map

  - ### ascendingKeySetWithLimit

    public Set<K> ascendingKeySetWithLimit(int limit)
    Returns an unmodifiable snapshot `Set` view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

    Beware that, unlike in `keySet()`, obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

    Parameters:
      `limit` - the maximum size of the returned set
    Returns:
      a ascending snapshot view of the keys in this map
    Throws:
      `IllegalArgumentException` - if the limit is negative

  - ### descendingKeySet

    public Set<K> descendingKeySet()
    Returns an unmodifiable snapshot `Set` view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

    Beware that, unlike in `keySet()`, obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

    Returns:
      a descending snapshot view of the keys in this map

  - ### descendingKeySetWithLimit

    public Set<K> descendingKeySetWithLimit(int limit)
    Returns an unmodifiable snapshot `Set` view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

    Beware that, unlike in `keySet()`, obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

    Parameters:
      `limit` - the maximum size of the returned set
    Returns:
      a descending snapshot view of the keys in this map
    Throws:
      `IllegalArgumentException` - if the limit is negative

  - ### values

    public Collection<V> values()
    Specified by:
      `values` in interface `Map<K,V>`
    Overrides:
      `values` in class `AbstractMap<K,V>`

  - ### entrySet

    public Set<Map.Entry<K,V>> entrySet()
    Specified by:
      `entrySet` in interface `Map<K,V>`
    Specified by:
      `entrySet` in class `AbstractMap<K,V>`

  - ### ascendingMap

    public Map<K,V> ascendingMap()
    Returns an unmodifiable snapshot `Map` view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

    Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

    Returns:
      a ascending snapshot view of this map

  - ### ascendingMapWithLimit

    public Map<K,V> ascendingMapWithLimit(int limit)
    Returns an unmodifiable snapshot `Map` view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

    Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

    Parameters:
      `limit` - the maximum size of the returned map
    Returns:
      a ascending snapshot view of this map
    Throws:
      `IllegalArgumentException` - if the limit is negative

  - ### descendingMap

    public Map<K,V> descendingMap()
    Returns an unmodifiable snapshot `Map` view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

    Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

    Returns:
      a descending snapshot view of this map

  - ### descendingMapWithLimit

    public Map<K,V> descendingMapWithLimit(int limit)
    Returns an unmodifiable snapshot `Map` view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

    Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

    Parameters:
      `limit` - the maximum size of the returned map
    Returns:
      a descending snapshot view of this map
    Throws:
      `IllegalArgumentException` - if the limit is negative