程序包 org.hibernate.internal.util.collections

类 BoundedConcurrentHashMap<K,​V>

  • 类型参数:
    K - the type of keys maintained by this map
    V - the type of mapped values
    所有已实现的接口:
    Serializable, ConcurrentMap<K,​V>, Map<K,​V>
    public class BoundedConcurrentHashMap<K,​V>
extends AbstractMap<K,​V>
implements ConcurrentMap<K,​V>, Serializable
    A hash table supporting full concurrency of retrievals and adjustable expected concurrency for updates. This class obeys the same functional specification as Hashtable, and includes versions of methods corresponding to each method of Hashtable. However, even though all operations are thread-safe, retrieval operations do not entail locking, and there is not any support for locking the entire table in a way that prevents all access. This class is fully interoperable with Hashtable in programs that rely on its thread safety but not on its synchronization details.

    Retrieval operations (including get) generally do not block, so may overlap with update operations (including put and remove). Retrievals reflect the results of the most recently completed update operations holding upon their onset. For aggregate operations such as putAll and clear, concurrent retrievals may reflect insertion or removal of only some entries. Similarly, Iterators and Enumerations return elements reflecting the state of the hash table at some point at or since the creation of the iterator/enumeration. They do not throw ConcurrentModificationException. However, iterators are designed to be used by only one thread at a time.

    The allowed concurrency among update operations is guided by the optional concurrencyLevel constructor argument (default 16), which is used as a hint for internal sizing. The table is internally partitioned to try to permit the indicated number of concurrent updates without contention. Because placement in hash tables is essentially random, the actual concurrency will vary. Ideally, you should choose a value to accommodate as many threads as will ever concurrently modify the table. Using a significantly higher value than you need can waste space and time, and a significantly lower value can lead to thread contention. But overestimates and underestimates within an order of magnitude do not usually have much noticeable impact. A value of one is appropriate when it is known that only one thread will modify and all others will only read. Also, resizing this or any other kind of hash table is a relatively slow operation, so, when possible, it is a good idea to provide estimates of expected table sizes in constructors.

    This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces.

    This class is copied from Infinispan, and was originally written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to the public domain, as explained at http://creativecommons.org/licenses/publicdomain

    Like Hashtable but unlike HashMap, this class does not allow null to be used as a key or value.

    作者:
    Doug Lea
    另请参阅:
    序列化表格

    • 构造器详细资料

      • BoundedConcurrentHashMap

        public BoundedConcurrentHashMap​(int capacity,
                                int concurrencyLevel,
                                BoundedConcurrentHashMap.Eviction evictionStrategy,
                                BoundedConcurrentHashMap.EvictionListener<K,​V> evictionListener)
        Creates a new, empty map with the specified maximum capacity, load factor and concurrency level.
        参数:
        capacity - is the upper bound capacity for the number of elements in this map
        concurrencyLevel - the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.
        evictionStrategy - the algorithm used to evict elements from this map
        evictionListener - the evicton listener callback to be notified about evicted elements
        抛出:
        IllegalArgumentException - if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.

      • BoundedConcurrentHashMap

        public BoundedConcurrentHashMap​(int capacity,
                                int concurrencyLevel)
        Creates a new, empty map with the specified maximum capacity, load factor, concurrency level and LRU eviction policy.
        参数:
        capacity - is the upper bound capacity for the number of elements in this map
        concurrencyLevel - the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.
        抛出:
        IllegalArgumentException - if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.

      • BoundedConcurrentHashMap

        public BoundedConcurrentHashMap​(int capacity,
                                int concurrencyLevel,
                                BoundedConcurrentHashMap.Eviction evictionStrategy)
        Creates a new, empty map with the specified maximum capacity, load factor, concurrency level and eviction strategy.
        参数:
        capacity - is the upper bound capacity for the number of elements in this map
        concurrencyLevel - the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.
        evictionStrategy - the algorithm used to evict elements from this map
        抛出:
        IllegalArgumentException - if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.

      • BoundedConcurrentHashMap

        public BoundedConcurrentHashMap​(int capacity)
        Creates a new, empty map with the specified maximum capacity, default concurrency level and LRU eviction policy.
        参数:
        capacity - is the upper bound capacity for the number of elements in this map
        抛出:
        IllegalArgumentException - if the initial capacity of elements is negative or the load factor is nonpositive
        从以下版本开始:
        1.6

      • BoundedConcurrentHashMap

        public BoundedConcurrentHashMap()
        Creates a new, empty map with the default maximum capacity

    • 方法详细资料

      • isEmpty

        public boolean isEmpty()
        Returns true if this map contains no key-value mappings.
        指定者:
        isEmpty 在接口中 Map<K,​V>
        覆盖:
        isEmpty 在类中 AbstractMap<K,​V>
        返回:
        true if this map contains no key-value mappings

      • size

        public int size()
        Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
        指定者:
        size 在接口中 Map<K,​V>
        覆盖:
        size 在类中 AbstractMap<K,​V>
        返回:
        the number of key-value mappings in this map

      • get

        public V get​(Object key)
        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 key.equals(k), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

        指定者:
        get 在接口中 Map<K,​V>
        覆盖:
        get 在类中 AbstractMap<K,​V>
        抛出:
        NullPointerException - if the specified key is null

      • containsKey

        public boolean containsKey​(Object key)
        Tests if the specified object is a key in this table.
        指定者:
        containsKey 在接口中 Map<K,​V>
        覆盖:
        containsKey 在类中 AbstractMap<K,​V>
        参数:
        key - possible key
        返回:
        true if and only if the specified object is a key in this table, as determined by the equals method; false otherwise.
        抛出:
        NullPointerException - if the specified key is null

      • containsValue

        public boolean containsValue​(Object value)
        Returns true if this map maps one or more keys to the specified value. Note: This method requires a full internal traversal of the hash table, and so is much slower than method containsKey.
        指定者:
        containsValue 在接口中 Map<K,​V>
        覆盖:
        containsValue 在类中 AbstractMap<K,​V>
        参数:
        value - value whose presence in this map is to be tested
        返回:
        true if this map maps one or more keys to the specified value
        抛出:
        NullPointerException - if the specified value is null

      • contains

        public boolean contains​(Object value)
        Legacy method testing if some key maps into the specified value in this table. This method is identical in functionality to containsValue(java.lang.Object), and exists solely to ensure full compatibility with class Hashtable, which supported this method prior to introduction of the Java Collections framework.
        参数:
        value - a value to search for
        返回:
        true if and only if some key maps to the value argument in this table as determined by the equals method; false otherwise
        抛出:
        NullPointerException - if the specified value is null

      • put

        public V put​(K key,
             V value)
        Maps the specified key to the specified value in this table. Neither the key nor the value can be null.

        The value can be retrieved by calling the get method with a key that is equal to the original key.

        指定者:
        put 在接口中 Map<K,​V>
        覆盖:
        put 在类中 AbstractMap<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 key, or null if there was no mapping for key
        抛出:
        NullPointerException - if the specified key or value is null

      • putIfAbsent

        public V putIfAbsent​(K key,
                     V value)
        指定者:
        putIfAbsent 在接口中 ConcurrentMap<K,​V>
        指定者:
        putIfAbsent 在接口中 Map<K,​V>
        返回:
        the previous value associated with the specified key, or null if there was no mapping for the key
        抛出:
        NullPointerException - if the specified key or value is null

      • putAll

        public void putAll​(Map<? extends K,​? extends V> m)
        Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified map.
        指定者:
        putAll 在接口中 Map<K,​V>
        覆盖:
        putAll 在类中 AbstractMap<K,​V>
        参数:
        m - mappings to be stored in this map

      • remove

        public V remove​(Object key)
        Removes the key (and its corresponding value) from this map. This method does nothing if the key is not in the map.
        指定者:
        remove 在接口中 Map<K,​V>
        覆盖:
        remove 在类中 AbstractMap<K,​V>
        参数:
        key - the key that needs to be removed
        返回:
        the previous value associated with key, or null if there was no mapping for key
        抛出:
        NullPointerException - if the specified key is null

      • replace

        public V replace​(K key,
                 V value)
        指定者:
        replace 在接口中 ConcurrentMap<K,​V>
        指定者:
        replace 在接口中 Map<K,​V>
        返回:
        the previous value associated with the specified key, or null if there was no mapping for the key
        抛出:
        NullPointerException - if the specified key or value is null

      • clear

        public void clear()
        Removes all of the mappings from this map.
        指定者:
        clear 在接口中 Map<K,​V>
        覆盖:
        clear 在类中 AbstractMap<K,​V>

      • keySet

        public Set<K> keySet()
        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. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

        The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

        指定者:
        keySet 在接口中 Map<K,​V>
        覆盖:
        keySet 在类中 AbstractMap<K,​V>

      • values

        public Collection<V> values()
        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. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

        The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

        指定者:
        values 在接口中 Map<K,​V>
        覆盖:
        values 在类中 AbstractMap<K,​V>

      • entrySet

        public Set<Map.Entry<K,​V>> entrySet()
        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. 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.

        The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

        指定者:
        entrySet 在接口中 Map<K,​V>
        指定者:
        entrySet 在类中 AbstractMap<K,​V>

      • keys

        public Enumeration<K> keys()
        Returns an enumeration of the keys in this table.
        返回:
        an enumeration of the keys in this table
        另请参阅:
        keySet()

      • elements

        public Enumeration<V> elements()
        Returns an enumeration of the values in this table.
        返回:
        an enumeration of the values in this table
        另请参阅:
        values()