Package org.apache.directory.api.util

Class SynchronizedLRUMap

  • All Implemented Interfaces:
    Externalizable, Serializable, Cloneable, Map
    public final class SynchronizedLRUMap
extends SequencedHashMap
implements Externalizable

    An implementation of a Map which has a maximum size and uses a Least Recently Used algorithm to remove items from the Map when the maximum size is reached and new items are added.

    A synchronized version can be obtained with: Collections.synchronizedMap( theMapToSynchronize ) If it will be accessed by multiple threads, you _must_ synchronize access to this Map. Even concurrent get(Object) operations produce indeterminate behaviour.

    Unlike the Collections 1.0 version, this version of LRUMap does use a true LRU algorithm. The keys for all gets and puts are moved to the front of the list. LRUMap is now a subclass of SequencedHashMap, and the "LRU" key is now equivalent to LRUMap.getFirst().

    Since:
    Commons Collections 1.0
    Author:
    Apache Directory Project
    See Also:
    Serialized Form

    • Constructor Detail

      • SynchronizedLRUMap

        public SynchronizedLRUMap()
        Default constructor, primarily for the purpose of de-externalization. This constructors sets a default LRU limit of 100 keys, but this value may be overridden internally as a result of de-externalization.

      • SynchronizedLRUMap

        public SynchronizedLRUMap​(int maxSize)
        Create a new LRUMap with a maximum capacity of i. Once i capacity is achieved, subsequent gets and puts will push keys out of the map. See .
        Parameters:
        maxSize - Maximum capacity of the LRUMap

    • Method Detail

      • get

        public Object get​(Object key)

        Get the value for a key from the Map. The key will be promoted to the Most Recently Used position. Note that get(Object) operations will modify the underlying Collection. Calling get(Object) inside of an iteration over keys, values, etc. is currently unsupported.

        Specified by:
        get in interface Map
        Overrides:
        get in class SequencedHashMap
        Parameters:
        key - Key to retrieve
        Returns:
        Returns the value. Returns null if the key has a null value or if the key has no value.

      • put

        public Object put​(Object key,
                  Object value)

        Removes the key and its Object from the Map.

        (Note: this may result in the "Least Recently Used" object being removed from the Map. In that case, the removeLRU() method is called. See javadoc for removeLRU() for more details.)

        Specified by:
        put in interface Map
        Overrides:
        put in class SequencedHashMap
        Parameters:
        key - Key of the Object to add.
        value - Object to add
        Returns:
        Former value of the key

      • getMaximumSize

        public int getMaximumSize()
        Getter for property maximumSize.
        Returns:
        Value of property maximumSize.

      • setMaximumSize

        public void setMaximumSize​(int maximumSize)
        Setter for property maximumSize.
        Parameters:
        maximumSize - New value of property maximumSize.