org.guavaberry.collections

Class DefaultHashMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

java.util.HashMap<K,V>

org.guavaberry.collections.DefaultHashMap<K,V>

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>

public class DefaultHashMap<K,V>
extends HashMap<K,V>

This is the Java implementation of the Python defaultdict. DefaultHashMap is a subclass of HashMap that overrides only the method HashMap.get(Object). This class accepts as argument an instance factory. If a certain key is missing in the map, the class produces a default instance and returns it as a value.

The remaining functionality is the same as for the HashMap class and is not documented here.

An example on how to use DefaultHashMap:

 
     DefaultHashMap<Integer, List<String>> map = new DefaultHashMap(() -> new ArrayList<>());
     map.get(11).add("first");
 
 

Since:

0.1.0

Author:

Filippo Squillace

See Also:

HashMap, Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Constructor Summary

Constructors

Constructor and Description
DefaultHashMap(NullaryOperator<V> operator) Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).
DefaultHashMap(NullaryOperator<V> operator, int initialCapacity) Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).
DefaultHashMap(NullaryOperator<V> operator, int initialCapacity, float loadFactor) Constructs an empty HashMap with the specified initial capacity and load factor.
DefaultHashMap(NullaryOperator<V> operator, Map<? extends K,? extends V> otherMap) Constructs a new HashMap with the same mappings as the specified Map.

Method Summary

Modifier and Type	Method and Description
V	get(Object key) Returns the value to which the specified key is mapped, or a default value generated by the instance factory if this map contains no mapping for the key.

Methods inherited from class java.util.HashMap

clear, clone, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, forEach, getOrDefault, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Constructor Detail

DefaultHashMap

public DefaultHashMap(NullaryOperator<V> operator,
                      int initialCapacity,
                      float loadFactor)

Constructs an empty HashMap with the specified initial capacity and load factor.

Parameters:

operator - the instance factory

initialCapacity - the initial capacity

loadFactor - the load factor

Throws:

IllegalArgumentException - if the initial capacity is negative or the load factor is nonpositive

DefaultHashMap

public DefaultHashMap(NullaryOperator<V> operator,
                      int initialCapacity)

Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).

Parameters:

operator - the instance factory

initialCapacity - the initial capacity.

Throws:

IllegalArgumentException - if the initial capacity is negative.

DefaultHashMap

public DefaultHashMap(NullaryOperator<V> operator)

Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).

Parameters:

operator - the instance factory

DefaultHashMap

public DefaultHashMap(NullaryOperator<V> operator,
                      Map<? extends K,? extends V> otherMap)

Constructs a new HashMap with the same mappings as the specified Map. The HashMap is created with default load factor (0.75) and an initial capacity sufficient to hold the mappings in the specified Map.

Parameters:

operator - the instance factory

otherMap - the map whose mappings are to be placed in this map

Throws:

NullPointerException - if the specified map is null

Method Detail

get

public final V get(Object key)

Returns the value to which the specified key is mapped, or a default value generated by the instance factory if this map contains no mapping for the key.

By calling this method multiple times passing the same key, the method will return the same value (idempotent).

Specified by:

get in interface Map<K,V>

Overrides:

get in class HashMap<K,V>

Parameters:

key - the key for the lookup

Returns:

the mapped value or a default default if key does not exist in the map

See Also:

HashMap.put(Object, Object)