Class DerivedKeyHashMap<K,V>

java.lang.Object
com.github.andrewoma.dexx.collection.internal.base.AbstractTraversable<Pair<K,V>>
com.github.andrewoma.dexx.collection.internal.base.AbstractIterable<Pair<K,V>>
com.github.andrewoma.dexx.collection.internal.base.AbstractMap<K,V>
com.github.andrewoma.dexx.collection.DerivedKeyHashMap<K,V>
All Implemented Interfaces:
Iterable<Pair<K,V>>, Map<K,V>, Traversable<Pair<K,V>>, 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.

  • Field Details

  • Constructor Details

  • Method Details

    • factory

      @NotNull public static <K,V> @NotNull BuilderFactory<Pair<K,V>, DerivedKeyHashMap<K,V>> factory(KeyFunction<K,V> keyFunction)

    • 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>>

    • forEach

      public <U> void forEach(@NotNull @NotNull Function<Pair<K,V>, U> f)
      Description copied from interface: Traversable
      All collection methods can be built upon this forEach definition.
      Specified by:
      forEach in interface Traversable<K>
      Overrides:
      forEach in class AbstractIterable<Pair<K,V>>

    • iterator

      @NotNull public @NotNull Iterator<Pair<K,V>> iterator()