@ThreadSafe public final class ConcurrentLinkedHashMap extends AbstractMap
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 Builder.
An entry is evicted from the map when the weighted capacity exceeds its maximum weighted capacity threshold. A EntryWeigher determines how many units of capacity that an entry 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.
- the type of keys maintained by this map
- the type of mapped valuesModifiers | Name | Description |
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static class |
ConcurrentLinkedHashMap.Builder |
A builder that creates ConcurrentLinkedHashMap instances. |
Type Params | Return Type | Name and description |
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Set<K> |
ascendingKeySet() Returns a unmodifiable snapshot Set view of the keys contained in this map. |
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Set<K> |
ascendingKeySetWithLimit(int limit) Returns an unmodifiable snapshot Set view of the keys contained in this map. |
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Map<K, V> |
ascendingMap() Returns an unmodifiable snapshot Map view of the mappings contained in this map. |
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Map<K, V> |
ascendingMapWithLimit(int limit) Returns an unmodifiable snapshot Map view of the mappings contained in this map. |
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long |
capacity() Retrieves the maximum weighted capacity of the map. |
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void |
clear() |
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boolean |
containsKey(Object key) |
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boolean |
containsValue(Object value) |
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Set<K> |
descendingKeySet() Returns an unmodifiable snapshot Set view of the keys contained in this map. |
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Set<K> |
descendingKeySetWithLimit(int limit) Returns an unmodifiable snapshot Set view of the keys contained in this map. |
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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. |
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Set<Entry<K, V>> |
entrySet() |
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V |
get(Object key) |
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V |
getQuietly(Object key) 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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boolean |
isEmpty() |
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Set<K> |
keySet() |
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V |
put(K key, V value) |
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V |
putIfAbsent(K key, V value) |
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V |
remove(Object key) |
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boolean |
remove(Object key, Object value) |
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V |
replace(K key, V value) |
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boolean |
replace(K key, V oldValue, V newValue) |
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void |
setCapacity(long capacity) Sets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size. |
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int |
size() |
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Collection<V> |
values() |
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long |
weightedSize() Returns the weighted size of this map. |
Methods inherited from class | Name |
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class AbstractMap |
remove, get, put, equals, toString, values, hashCode, clear, isEmpty, size, entrySet, putAll, containsKey, containsValue, keySet, wait, wait, wait, getClass, notify, notifyAll, remove, replace, replace, replaceAll, merge, putIfAbsent, compute, forEach, computeIfAbsent, getOrDefault, computeIfPresent |
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 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.
limit
- the maximum size of the returned setReturns 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 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.
limit
- the maximum size of the returned mapRetrieves the maximum weighted capacity of the map.
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 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.
limit
- the maximum size of the returned setReturns 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 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.
limit
- the maximum size of the returned map Returns the value to which the specified key is mapped, or null
if this map contains no mapping for the key. This method differs from
get(Object) in that it does not record the operation with the
page replacement policy.
key
- the key whose associated value is to be returnednull
if this map contains no mapping for the keySets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size.
capacity
- the maximum weighted capacity of the mapReturns the weighted size of this map.