Java Maps
Common implementations: HashMap, LinkedHashMap, TreeMap
An object that maps keys to maps.
Basic methods
put(K key, V value) : V
Associates specified key with specified value in this map.
get(K key) : V
Returns the value to which the key is mapped, or null if there is no mapping.
remove(K key) : V
Removes the mapping from this map if it is present. Returns the value or null if it wasn't present.
remove(K key, V value) : boolean
Removes the mapping from this map only if it is mapped to the specified value.
replace(K key, V value) : V
Replaces the mapping at the key if it is mapped to some value (including a null value).
Returns the previously assigned value, or null if it does not exist.
replace(K key, V oldValue, V newValue) : boolean
Replaces the mapping at the key with newValue if it is currently mapped to oldValue.
Returns true if the value was replaced.
clear() : void
Removes all mappings from the map.
containsKey(K key) : boolean
Returns true if map contains specified key.
containsValue(K value) : boolean
Returns true if map maps one or more keys to the specified value.
entrySet() : Set<Map.Entry<K,V>>
Returns a Set of mappings.
keySet() : Set<K>
Returns a set of the key values.
values() : Collection<V>
Returns a Collection of the values contained in the map.
isEmpty() : boolean
Returns true if the map contains no key-value mappings.
Useful methods
getOrDefault(K key, V defaultValue) : V
Returns the value to which the key is mapped, or defaultValue if there is no mapping.
compute(K key, Function(K key, V value) : V) : V
Computes mapping for specified key and its currently mapped value. If there is no mapping, value is mapped to null.
Returns the computed value.
computeIfAbsent(K key, Function(K key) : V) : V
If the specified key is not associated with a value (or is null) it will compute value using mapping function and enter into the map.
Returns the computed value.
computeIfPresent(K key, Function(K key, V value) : V) : V
If the specified key is present and non-null, it will compute the new value using the mapping function (unless the mapping function returns null).
Returns the computed value;