Class DerivedKeyHashMap<K,​V>

  • All Implemented Interfaces:
    Iterable<Pair<K,​V>>, Map<K,​V>, Traversable<Pair<K,​V>>, java.lang.Iterable<Pair<K,​V>>

    public class DerivedKeyHashMap<K,​V>
    extends AbstractMap<K,​V>
    DerivedKeyHashMap is a HashMap variant where the key for the Map is derived from the value stored.

    By deriving the key it is possible to reduce the memory overhead per node in the map (assuming the key is a primitive field in the value object). e.g.

     
     static class Value {
         int key;
         int value;
     }
    
     DerivedKeyHashMap<Integer, Value> map = new DerivedKeyHashMap<Integer, Value>(
         new KeyFunction<Integer, Value>() {
             public Integer key(Value value) {
                 return value.key;
             }
     });
    
     Value value = new Value();
     value.key = 1;
     value.value = 100;
     map = map.put(value.key, value);
     

    The underlying implementation is a port of Scala's HashMap which is an implementation of a hash array mapped trie.

    It uses significantly less memory than Scala's implementation as the leaf nodes are the values themselves (not objects containing keys, values and hashes).

    As the key is derived from the value, DerivedKeyHashMap does not support null values.

    • Constructor Detail

      • DerivedKeyHashMap

        public DerivedKeyHashMap​(@NotNull
                                 @NotNull KeyFunction<K,​V> keyFunction)
    • Method Detail

      • containsKey

        public boolean containsKey​(@NotNull
                                   K key)
        Description copied from interface: Map
        Returns true if this map contains the specified key.
      • put

        @NotNull
        public @NotNull DerivedKeyHashMap<K,​V> put​(@NotNull
                                                         K key,
                                                         V value)
        Description copied from interface: Map
        Returns a map with the value specified associated to the key specified.

        If value already exists for the key, it will be replaced.

      • get

        @Nullable
        public V get​(@NotNull
                     K key)
        Description copied from interface: Map
        Returns the value associated with the key or null if the no value exists with the key specified.
      • remove

        @NotNull
        public @NotNull DerivedKeyHashMap<K,​V> remove​(@NotNull
                                                            K key)
        Description copied from interface: Map
        Returns a map with the value associated with the key removed if it exists.
      • size

        public int size()
        Description copied from interface: Traversable
        Returns the size of the collection.

        Warning: infinite collections are possible, as are collections that require traversal to calculate the size.

        Specified by:
        size in interface Traversable<K>
        Overrides:
        size in class AbstractTraversable<Pair<K,​V>>
      • iterator

        @NotNull
        public @NotNull java.util.Iterator<Pair<K,​V>> iterator()