Class IdentityMap<K,​V>


  • public class IdentityMap<K,​V>
    extends java.lang.Object
    An unordered map that uses identity comparison for keys. This implementation is a cuckoo hash map using 3 hashes (if table size is less than 2^16) or 4 hashes (if table size is greater than or equal to 2^16), random walking, and a small stash for problematic keys Null keys are not allowed. Null values are allowed. No allocation is done except when growing the table size.
    4
    This map performs very fast get, containsKey, and remove (typically O(1), worst case O(log(n))). Put may be a bit slower, depending on hash collisions. Load factors greater than 0.91 greatly increase the chances the map will have to rehash to the next higher POT size.
    • Field Detail

      • size

        public int size
      • keyTable

        K[] keyTable
      • valueTable

        V[] valueTable
      • capacity

        int capacity
      • stashSize

        int stashSize
      • loadFactor

        private float loadFactor
      • hashShift

        private int hashShift
      • mask

        private int mask
      • threshold

        private int threshold
      • stashCapacity

        private int stashCapacity
      • pushIterations

        private int pushIterations
      • bigTable

        private boolean bigTable
    • Constructor Detail

      • IdentityMap

        public IdentityMap()
        Creates a new map with an initial capacity of 32 and a load factor of 0.8. This map will hold 25 items before growing the backing table.
      • IdentityMap

        public IdentityMap​(int initialCapacity)
        Creates a new map with a load factor of 0.8. This map will hold initialCapacity * 0.8 items before growing the backing table.
      • IdentityMap

        public IdentityMap​(int initialCapacity,
                           float loadFactor)
        Creates a new map with the specified initial capacity and load factor. This map will hold initialCapacity * loadFactor items before growing the backing table.
    • Method Detail

      • put

        public V put​(K key,
                     V value)
      • putResize

        private void putResize​(K key,
                               V value)
        Skips checks for existing keys.
      • push

        private void push​(K insertKey,
                          V insertValue,
                          int index1,
                          K key1,
                          int index2,
                          K key2,
                          int index3,
                          K key3,
                          int index4,
                          K key4)
      • putStash

        private void putStash​(K key,
                              V value)
      • get

        public V get​(K key)
      • get

        public V get​(K key,
                     V defaultValue)
      • getStash

        private V getStash​(K key,
                           V defaultValue)
      • remove

        public V remove​(K key)
      • removeStash

        V removeStash​(K key)
      • removeStashIndex

        void removeStashIndex​(int index)
      • shrink

        public void shrink​(int maximumCapacity)
        Reduces the size of the backing arrays to be the specified capacity or less. If the capacity is already less, nothing is done. If the map contains more items than the specified capacity, nothing is done.
      • clear

        public void clear​(int maximumCapacity)
        Clears the map and reduces the size of the backing arrays to be the specified capacity if they are larger.
      • clear

        public void clear()
      • containsValue

        public boolean containsValue​(java.lang.Object value,
                                     boolean identity)
        Returns true if the specified value is in the map. Note this traverses the entire map and compares every value, which may be an expensive operation.
        Parameters:
        identity - If true, uses == to compare the specified value with values in the map. If false, uses Object.equals(Object).
      • containsKey

        public boolean containsKey​(K key)
      • containsKeyStash

        private boolean containsKeyStash​(K key)
      • findKey

        public K findKey​(java.lang.Object value,
                         boolean identity)
        Returns the key for the specified value, or null if it is not in the map. Note this traverses the entire map and compares every value, which may be an expensive operation.
        Parameters:
        identity - If true, uses == to compare the specified value with values in the map. If false, uses Object.equals(Object).
      • ensureCapacity

        public void ensureCapacity​(int additionalCapacity)
        Increases the size of the backing array to acommodate the specified number of additional items. Useful before adding many items to avoid multiple backing array resizes.
      • resize

        private void resize​(int newSize)
      • hash2

        private int hash2​(int h)
      • hash3

        private int hash3​(int h)
      • hash4

        private int hash4​(int h)
      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object
      • entries

        public IdentityMap.Entries<K,​V> entries()
        Returns an iterator for the entries in the map. Remove is supported. Note that the same iterator instance is returned each time this method is called. Use the IdentityMap.Entries constructor for nested or multithreaded iteration.
      • values

        public IdentityMap.Values<V> values()
        Returns an iterator for the values in the map. Remove is supported. Note that the same iterator instance is returned each time this method is called. Use the IdentityMap.Entries constructor for nested or multithreaded iteration.
      • keys

        public IdentityMap.Keys<K> keys()
        Returns an iterator for the keys in the map. Remove is supported. Note that the same iterator instance is returned each time this method is called. Use the IdentityMap.Entries constructor for nested or multithreaded iteration.