Package org.codehaus.plexus.util

Class FastMap<K,V>

java.lang.Object
org.codehaus.plexus.util.FastMap<K,V>
All Implemented Interfaces:
Serializable, Cloneable, Map<K,V>
public class FastMap<K,V> extends Object implements Map<K,V>, Cloneable, Serializable

This class represents a Map collection with real-time behavior. Unless the map's size exceeds its current capacity, no dynamic memory allocation is ever performed and response time is extremely fast and consistent.

Our benchmark indicates that FastMap.put(key, value) is up to 5x faster than java.util.HashMap.put(key, value). This difference is mostly due to the cost of the Map.Entry allocations that FastMap avoids by recycling its entries (see note below).

FastMap has a predictable iteration order, which is the order in which keys were inserted into the map (similar to java.util.LinkedHashMap collection class).

Applications may change the resizing policy of FastMap by overriding the sizeChanged() method. For example, to improve predictability, automatic resizing can be disabled.

This implementation is not synchronized. Multiple threads accessing or modifying the collection must be synchronized externally.

Note: To avoid dynamic memory allocations, FastMap maintains an internal pool of Map.Entry objects. The size of the pool is determined by the map's capacity. When an entry is removed from the map, it is automatically restored to the pool.

This class is public domain (not copyrighted).

Version:
5.3, October 31 2003
Author:
Jean-Marie Dautelle
See Also:

  • Constructor Details

    • FastMap

      public FastMap()
      Creates a FastMap with a capacity of 256 entries.

    • FastMap

      public FastMap(Map map)
      Creates a FastMap, copy of the specified Map. If the specified map is not an instance of FastMap, the newly created map has a capacity set to the specified map's size. The copy has the same order as the original, regardless of the original map's implementation: 
           TreeMap dictionary = ...;
     FastMap dictionaryLookup = new FastMap(dictionary);
      Parameters:
      map - the map whose mappings are to be placed in this map.

    • FastMap

      public FastMap(int capacity)
      Creates a FastMap with the specified capacity. Unless the capacity is exceeded, operations on this map do not allocate entries. For optimum performance, the capacity should be of the same order of magnitude or larger than the expected map's size.
      Parameters:
      capacity - the number of buckets in the hash table; it also defines the number of pre-allocated entries.

  • Method Details

    • size

      public int size()
      Returns the number of key-value mappings in this FastMap.
      Specified by:
      size in interface Map<K,V>
      Returns:
      this map's size.

    • capacity

      public int capacity()
      Returns the capacity of this FastMap. The capacity defines the number of buckets in the hash table, as well as the maximum number of entries the map may contain without allocating memory.
      Returns:
      this map's capacity.

    • isEmpty

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

    • containsKey

      public boolean containsKey(Object key)
      Indicates if this FastMap contains a mapping for the specified key.
      Specified by:
      containsKey in interface Map<K,V>
      Parameters:
      key - the key whose presence in this map is to be tested.
      Returns:
      true if this map contains a mapping for the specified key; false otherwise.
      Throws:
      NullPointerException - if the key is null.

    • containsValue

      public boolean containsValue(Object value)
      Indicates if this FastMap maps one or more keys to the specified value.
      Specified by:
      containsValue in interface Map<K,V>
      Parameters:
      value - the 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:
      NullPointerException - if the key is null.

    • get

      public V get(Object key)
      Returns the value to which this FastMap maps the specified key.
      Specified by:
      get in interface Map<K,V>
      Parameters:
      key - the key whose associated value is to be returned.
      Returns:
      the value to which this map maps the specified key, or null if there is no mapping for the key.
      Throws:
      NullPointerException - if key is null.

    • getEntry

      public Map.Entry getEntry(Object key)
      Returns the entry with the specified key.
      Parameters:
      key - the key whose associated entry is to be returned.
      Returns:
      the entry for the specified key or null if none.

    • put

      public Object put(Object key, Object value)
      Associates the specified value with the specified key in this FastMap. If the FastMap previously contained a mapping for this key, the old value is replaced.
      Specified by:
      put in interface Map<K,V>
      Parameters:
      key - the key with which the specified value is to be associated.
      value - the value to be associated with the specified key.
      Returns:
      the 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.
      Throws:
      NullPointerException - if the key is null.

    • putAll

      public void putAll(Map<? extends K,? extends V> map)
      Copies all of the mappings from the specified map to this FastMap.
      Specified by:
      putAll in interface Map<K,V>
      Parameters:
      map - the mappings to be stored in this map.
      Throws:
      NullPointerException - the specified map is null, or the specified map contains null keys.

    • remove

      public V remove(Object key)
      Removes the mapping for this key from this FastMap if present.
      Specified by:
      remove in interface Map<K,V>
      Parameters:
      key - the 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. A null return can also indicate that the map previously associated null with the specified key.
      Throws:
      NullPointerException - if the key is null.

    • clear

      public void clear()
      Removes all mappings from this FastMap.
      Specified by:
      clear in interface Map<K,V>

    • setCapacity

      public void setCapacity(int newCapacity)
      Changes the current capacity of this FastMap. If the capacity is increased, new entries are allocated and added to the pool. If the capacity is decreased, entries from the pool are deallocated (and are eventually garbage collected). The capacity also determined the number of buckets for the hash table.
      Parameters:
      newCapacity - the new capacity of this map.

    • clone

      public Object clone()
      Returns a shallow copy of this FastMap. The keys and the values themselves are not cloned.
      Overrides:
      clone in class Object
      Returns:
      a shallow copy of this map.

    • equals

      public boolean equals(Object obj)
      Compares the specified object with this FastMap for equality. Returns true if the given object is also a map and the two maps represent the same mappings (regardless of collection iteration order).
      Specified by:
      equals in interface Map<K,V>
      Overrides:
      equals in class Object
      Parameters:
      obj - the object to be compared for equality with this map.
      Returns:
      true if the specified object is equal to this map; false otherwise.

    • hashCode

      public int hashCode()
      Returns the hash code value for this FastMap.
      Specified by:
      hashCode in interface Map<K,V>
      Overrides:
      hashCode in class Object
      Returns:
      the hash code value for this map.

    • toString

      public String toString()
      Returns a String representation of this FastMap.
      Overrides:
      toString in class Object
      Returns:
      this.entrySet().toString();

    • values

      public Collection values()
      Returns a collection view of the values contained in this FastMap. 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.
      Specified by:
      values in interface Map<K,V>
      Returns:
      a collection view of the values contained in this map.

    • entrySet

      public Set entrySet()
      Returns a collection view of the mappings contained in this FastMap. Each element in the returned collection is a Map.Entry. 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.
      Specified by:
      entrySet in interface Map<K,V>
      Returns:
      a collection view of the mappings contained in this map.

    • keySet

      public Set keySet()
      Returns a set view of the keys contained in this FastMap. 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, Collection.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.

    • sizeChanged

      protected void sizeChanged()
      This methods is being called when the size of this FastMap has changed. The default behavior is to double the map's capacity when the map's size reaches the current map's capacity. Sub-class may override this method to implement custom resizing policies or to disable automatic resizing. For example: 
       Map fixedCapacityMap = new FastMap( 256 )
 {
     protected sizeChanged()
     {
         // Do nothing, automatic resizing disabled.
     }
 };
      See Also: