`class HashMap<KeyType, ValueType>`

This class implements an efficient association between keys and values. This class is identical to the Map class except for the fact that it uses a hash table as its underlying representation. Although the HashMap class operates in constant time, the iterator for HashMap returns the values in a seemingly random order.

Constructor
HashMap()	O(1)	Initializes a new empty map that associates keys and values of the specified types.
Methods
clear()	O(N)	Removes all entries from this map.
containsKey(`key`)	O(1)	Returns `true` if there is an entry for `key` in this map.
equals(`map`)	O(N log N)	Returns `true` if the two maps contain the same elements.
get(`key`)	O(1)	Returns the value associated with `key` in this map.
isEmpty()	O(1)	Returns `true` if this map contains no entries.
keys()	O(N)	Returns a `Vector` copy of all keys in this map.
mapAll(`fn`)	O(N)	Iterates through the map entries and calls `fn(key, value)` for each one.
put(`key`, `value`)	O(1)	Associates `key` with `value` in this map.
remove(`key`)	O(1)	Removes any entry for `key` from this map.
size()	O(1)	Returns the number of entries in this map.
toString()	O(N)	Converts the map to a printable string representation.
values()	O(N)	Returns a `Vector` copy of all values in this map.
Operators
`map`[`key`]	O(1)	Selects the value associated with `key`.
`map1` == `map1`	O(N)	Returns `true` if `map1` and `map2` contain the same elements.
`map1` != `map2`	O(N)	Returns `true` if `map1` and `map2` are different.
`ostream` << `map`	O(N)	Outputs the contents of the map to the given output stream.
`istream` >> `map`	O(N)	Reads the contents of the given input stream into the map.

Constructor detail

HashMap();

Initializes a new empty map that associates keys and values of the specified types. The type used for the key must define the == operator, and there must be a free function with the following signature:

    int hashCode(KeyType key);

that returns a positive integer determined by the key. This interface exports hashCode functions for string and the C++ primitive types.

Usage:

HashMap<KeyType, ValueType> map;

Method detail

void clear();

Removes all entries from this map.

Usage:

map.clear();

bool containsKey(KeyType key) const;

Returns true if there is an entry for key in this map.

Usage:

if (map.containsKey(key)) ...

bool equals(const HashMap& map) const;

Returns true if the two maps contain exactly the same set of key/value pairs. Identical in behavior to the == operator.

Usage:

if (map.equals(map2)) ...

ValueType get(KeyType key) const;

Returns the value associated with key in this map. If key is not found, get returns the default value for ValueType.

Usage:

ValueType value = map.get(key);

bool isEmpty() const;

Returns true if this map contains no entries.

Usage:

if (map.isEmpty()) ...

Vector<KeyType> keys() const;

Returns a Vector copy of all keys in this map. The elements will appear in the same order that a for-each loop over the map would produce them, though that order is seemingly random for hash maps. Because a map cannot contain duplicate keys, the elements of the vector will be unique.

Usage:

Vector<KeyType> keys = map.keys();

Available since: 2014/02/01 version of C++ library

void mapAll(void (*fn)(KeyType, ValueType)) const;
void mapAll(void (*fn)(const KeyType&, const ValueType&)) const;
void mapAll(FunctorType fn) const;

Iterates through the map entries and calls fn(key, value) for each one. The keys are processed in an undetermined order.

Usage:

map.mapAll(fn);

void put(KeyType key, ValueType value);

Associates key with value in this map. Any previous value associated with key is replaced by the new value.

Usage:

map.put(key, value);

void remove(KeyType key);

Removes any entry for key from this map.

Usage:

map.remove(key);

int size() const;

Returns the number of entries in this map.

Usage:

int nEntries = map.size();

string toString();

Converts the map to a printable string representation, such as "{k1:v1, k2:v2, k3:v3}". The key/value pairs appear in an unpredictable order.

Usage:

string str = map.toString();

Vector<ValueType> values() const;

Returns a Vector copy of all values in this map. The elements will appear in the same order that a for-each loop over the map would produce them, though that order is seemingly random for hash maps. A map can contain duplicate values, so the elements of the vector are not guaranteed to be unique.

Usage:

Vector<ValueType> values = map.values();

Available since: 2014/02/01 version of C++ library

Operator detail

ValueType& operator[](KeyType key);
ValueType operator[](KeyType key) const;

Selects the value associated with key. This syntax makes it easy to think of a map as an "associative array" indexed by the key type. If key is already present in the map, this function returns a reference to its associated value. If key is not present in the map, a new entry is created whose value is set to the default for the value type.

Usage:

map[key]