com.github.andrewoma.dexx.collection
Class DerivedKeyHashMap<K,V>

java.lang.Object
  com.github.andrewoma.dexx.collection.internal.base.AbstractTraversable<E>
      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:

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.

Constructor Summary

DerivedKeyHashMap(KeyFunction<K,V> keyFunction)

Method Summary

boolean	containsKey(K key) Returns true if this map contains the specified key.
static <K,V> BuilderFactory<Pair<K,V>,DerivedKeyHashMap<K,V>>	factory(KeyFunction<K,V> keyFunction)
<U> void	forEach(Function<Pair<K,V>,U> f) All collection methods can be built upon this forEach definition.
V	get(K key) Returns the value associated with the key or null if the no value exists with the key specified.
Iterator<Pair<K,V>>	iterator()
DerivedKeyHashMap<K,V>	put(K key, V value) Returns a map with the value specified associated to the key specified.
DerivedKeyHashMap<K,V>	remove(K key) Returns a map with the value associated with the key removed if it exists.
int	size() Returns the size of the collection.

Methods inherited from class com.github.andrewoma.dexx.collection.internal.base.AbstractMap

asMap, equals, hashCode, keys, values

Methods inherited from class com.github.andrewoma.dexx.collection.internal.base.AbstractTraversable

isEmpty, makeString, makeString, to, toArray, toArray, toIndexedList, toSet, toSortedSet, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.github.andrewoma.dexx.collection.Traversable

isEmpty, makeString, makeString, to, toArray, toArray, toIndexedList, toSet, toSortedSet

Constructor Detail

DerivedKeyHashMap

public DerivedKeyHashMap(@NotNull
                         KeyFunction<K,V> keyFunction)

Method Detail

factory

@NotNull
public static <K,V> 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 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 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<Pair<K,V>>

Overrides:

size in class AbstractTraversable<Pair<K,V>>

forEach

public <U> void forEach(@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<Pair<K,V>>

Overrides:

forEach in class AbstractIterable<Pair<K,V>>

iterator

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