Package com.globalmentor.collections

Class AbstractPurgeOnWriteReferenceValueMap<K,V,R extends Reference<V> & AbstractPurgeOnWriteReferenceValueMap.Keyed<K>>

java.lang.Object
com.globalmentor.collections.AbstractPurgeOnWriteReferenceValueMap<K,V,R>
Type Parameters:
K - The type of key.
V - The type of value.
R - The type of reference.
All Implemented Interfaces:
Map<K,V>
Direct Known Subclasses:
PurgeOnWriteSoftValueHashMap, PurgeOnWriteWeakValueHashMap
public abstract class AbstractPurgeOnWriteReferenceValueMap<K,V,R extends Reference<V> & AbstractPurgeOnWriteReferenceValueMap.Keyed<K>> extends Object implements Map<K,V>
A map that uses references to store map values. Cleared references are only purged when map write operations occur. null values are not supported.
Author:
Garret Wilson

  • Constructor Details

    • AbstractPurgeOnWriteReferenceValueMap

      public AbstractPurgeOnWriteReferenceValueMap(Map<K,R> map)
      Decorated map constructor.
      Parameters:
      map - The map being decorated.
      Throws:
      NullPointerException - if the given map is null.

  • Method Details

    • 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 .
      Specified by:
      size in interface Map<K,V>
      Returns:
      the number of key-value mappings in this map.

    • isEmpty

      public boolean isEmpty()
      Returns true if this map contains no key-value mappings.
      Specified by:
      isEmpty in interface Map<K,V>
      Returns:
      true if this map contains no key-value mappings.

    • containsKey

      public boolean containsKey(Object key)
      Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)
      Specified by:
      containsKey in interface Map<K,V>
      Parameters:
      key - key whose presence in this map is to be tested.
      Returns:
      true if this map contains a mapping for the specified key.
      Throws:
      ClassCastException - if the key is of an inappropriate type for this map (optional).
      NullPointerException - if the key is null and this map does not permit null keys (optional).

    • containsValue

      public boolean containsValue(Object value)
      Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.
      Specified by:
      containsValue in interface Map<K,V>
      Parameters:
      value - value whose presence in this map is to be tested.
      Returns:
      true if this map maps one or more keys to the specified value.
      Throws:
      ClassCastException - if the value is of an inappropriate type for this map (optional).
      NullPointerException - if the value is null and this map does not permit null values (optional).

    • get

      public V get(Object key)
      Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

      More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

      Specified by:
      get in interface Map<K,V>
      Parameters:
      key - key whose associated value is to be returned.
      Returns:
      the value to which this map maps the specified key, or null if the map contains no mapping for this key.
      Throws:
      ClassCastException - if the key is of an inappropriate type for this map (optional).
      NullPointerException - if the key is null and this map does not permit null keys (optional).
      See Also:

    • put

      public V put(K key, V value)
      Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.))
      Specified by:
      put 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:
      previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified 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.
      IllegalArgumentException - if some aspect of this key or value prevents it from being stored in this map.
      NullPointerException - if this map does not permit null keys or values, and the specified key or value is null.

    • remove

      public V remove(Object key)
      Removes the mapping for this key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

      Returns the value to which the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

      Specified by:
      remove in interface Map<K,V>
      Parameters:
      key - key whose mapping is to be removed from the map.
      Returns:
      previous value associated with specified key, or null if there was no mapping for key.
      Throws:
      ClassCastException - if the key is of an inappropriate type for this map (optional).
      NullPointerException - if the key is null and this map does not permit null keys (optional).
      UnsupportedOperationException - if the remove method is not supported by this map.

    • putAll

      public void putAll(Map<? extends K,? extends V> t)
      Copies all of the mappings from the specified map to this map (optional operation). The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is unspecified if the specified map is modified while the operation is in progress.
      Specified by:
      putAll in interface Map<K,V>
      Parameters:
      t - Mappings to be stored in this map.
      Throws:
      UnsupportedOperationException - if the putAll method is not supported by this map.
      ClassCastException - if the class of a key or value in the specified map prevents it from being stored in this map.
      IllegalArgumentException - some aspect of a key or value in the specified map prevents it from being stored in this map.
      NullPointerException - if the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values.

    • clear

      public void clear()
      Removes all mappings from this map (optional operation).
      Specified by:
      clear in interface Map<K,V>
      Throws:
      UnsupportedOperationException - clear is not supported by this map.

    • 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. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. 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.
      Specified by:
      keySet in interface Map<K,V>
      Returns:
      a set view of the keys contained in this map.

    • 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. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
      Specified by:
      values in interface Map<K,V>
      Returns:
      a collection view of the values contained in this map.

    • entrySet

      public Set<Map.Entry<K,V>> entrySet()
      Returns a set view of the mappings contained in this map. Each element in the returned set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. 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.
      Specified by:
      entrySet in interface Map<K,V>
      Returns:
      a set view of the mappings contained in this map.

    • equals

      public boolean equals(Object o)
      Compares the specified object with this map for equality. Returns true if the given object is also a map and the two Maps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.entrySet().equals(t2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.
      Specified by:
      equals in interface Map<K,V>
      Overrides:
      equals in class Object
      Parameters:
      o - object to be compared for equality with this map.
      Returns:
      true if the specified object is equal to this map.

    • hashCode

      public int hashCode()
      Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hashCodes of each entry in the map's entrySet view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.
      Specified by:
      hashCode in interface Map<K,V>
      Overrides:
      hashCode in class Object
      Returns:
      the hash code value for this map.
      See Also:

    • purge

      public void purge()
      Purges all enqueued references.

    • purgeExcept

      protected void purgeExcept(R exceptReference)
      Purges all enqueued references except for the given reference.
      Parameters:
      exceptReference - The reference not to purge, or null if all enqueued references should be purged.

    • createReference

      protected abstract R createReference(K key, V value, ReferenceQueue<V> referenceQueue)
      Creates the appropriate reference for associating the given value with the given key. The reference will be registered with the given queue.
      Parameters:
      key - The key with which the value is being associated.
      value - The value to be stored.
      referenceQueue - The queue with which the reference will be registered.
      Returns:
      A reference to the given value that also indicates the key being used.