jsimple.util

Class HashMap<K,V>

java.lang.Object

jsimple.util.Map<K,V>

jsimple.util.HashMap<K,V>

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

HashMap is an implementation of Map. All optional operations (adding and removing) are supported. Keys and values can be any objects.

Changes from the java.util version:

Does not implement Serializable

Does not support clone; use HashMap constructor taking a Map argument instead (which is more flexible and type safe)

Does not support null keys. They are rarely used and removing support for them makes the implementation slightly simpler/faster and allows tighter nullable constraints. Null values, however, are still supported.

Constructor Summary

Constructors

Constructor and Description
HashMap() Constructs a new empty HashMap instance.
HashMap(int capacity) Constructs a new HashMap instance with the specified capacity.
HashMap(int capacity, float loadFactor) Constructs a new HashMap instance with the specified capacity and load factor.
HashMap(Map<K,V> map) Constructs a new HashMap instance containing the mappings from the specified map.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all mappings from this hash map, leaving it empty.
boolean	containsKey(K key) Returns whether this map contains the specified key.
boolean	containsValue(V value) Returns whether this map contains the specified value.
Set<MapEntry<K,V>>	entrySet() Returns a set containing all of the mappings in this map.
V	get(K key) Returns the value of the mapping with the specified key
boolean	isEmpty() Returns whether this map is empty.
Set<K>	keySet() Returns a set of the keys contained in this map.
V	put(K key, V value) Maps the specified key to the specified value.
void	putAll(Map<? extends K,? extends V> map) Copies all the mappings in the specified map to this map.
V	remove(K key) Removes the mapping with the specified key from this map.
int	size() Returns the number of elements in this map.
Collection<V>	values() Returns a collection of the values contained in this map.

Methods inherited from class jsimple.util.Map

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

HashMap

public HashMap()

Constructs a new empty HashMap instance.

HashMap

public HashMap(int capacity)

Constructs a new HashMap instance with the specified capacity.

Parameters:

capacity - the initial capacity of this hash map.

Throws:

ProgrammerError - when the capacity is less than zero.

HashMap

public HashMap(int capacity,
               float loadFactor)

Constructs a new HashMap instance with the specified capacity and load factor.

Parameters:

capacity - the initial capacity of this hash map.

loadFactor - the initial load factor.

Throws:

ProgrammerError - when the capacity is less than zero or the load factor is less or equal to zero

HashMap

public HashMap(Map<K,V> map)

Constructs a new HashMap instance containing the mappings from the specified map.

Changes from the java.util version: The constructor there supported covariance, taking a Map<? extends K, ? extends V> argument where the keys & values can be subclasses of E and V. This constructor only allows maps of exact type K and V, but you can call the putAll method instead if really need to copy a map with subtypes.

Parameters:

map - the mappings to add.

Method Detail

clear

public void clear()

Removes all mappings from this hash map, leaving it empty.

Specified by:

clear in class Map<K,V>

See Also:

isEmpty(), size()

containsKey

public boolean containsKey(K key)

Returns whether this map contains the specified key.

Specified by:

containsKey in class Map<K,V>

Parameters:

key - the key to search for.

Returns:

true if this map contains the specified key, false otherwise.

containsValue

public boolean containsValue(V value)

Returns whether this map contains the specified value.

Specified by:

containsValue in class Map<K,V>

Parameters:

value - the value to search for.

Returns:

true if this map contains the specified value, false otherwise.

entrySet

public Set<MapEntry<K,V>> entrySet()

Returns a set containing all of the mappings in this map. Each mapping is an instance of MapEntry. As the set is backed by this map, changes in one will be reflected in the other.

Specified by:

entrySet in class Map<K,V>

Returns:

a set of the mappings.

get

public V get(K key)

Returns the value of the mapping with the specified key

Specified by:

get in class Map<K,V>

Parameters:

key - the key.

Returns:

the value of the mapping with the specified key, or null / default value for non-nullable value type if no mapping for the specified key is found.

isEmpty

public boolean isEmpty()

Returns whether this map is empty.

Specified by:

isEmpty in class Map<K,V>

Returns:

true if this map has no elements, false otherwise.

See Also:

size()

keySet

public Set<K> keySet()

Returns a set of the keys contained in this map. The set is backed by this map so changes to one are reflected by the other. The set does not support adding.

Specified by:

keySet in class Map<K,V>

Returns:

a set of the keys.

put

public V put(K key,
             V value)

Maps the specified key to the specified value.

Specified by:

put in class Map<K,V>

Parameters:

key - the key.

value - the value.

Returns:

the value of any previous mapping with the specified key or null / default value for non-nullable value type if there was no such mapping

putAll

public void putAll(Map<? extends K,? extends V> map)

Copies all the mappings in the specified map to this map. These mappings will replace all mappings that this map had for any of the keys currently in the given map.}

Specified by:

putAll in class Map<K,V>

Parameters:

map - the map to copy mappings from.

Throws:

java.lang.NullPointerException - if map is null.

remove

public V remove(K key)

Removes the mapping with the specified key from this map.

Specified by:

remove in class Map<K,V>

Parameters:

key - the key of the mapping to remove.

Returns:

the value of the removed mapping or null / default value for non-nullable value type if no mapping for the specified key was found

size

public int size()

Returns the number of elements in this map.

Specified by:

size in class Map<K,V>

Returns:

the number of elements in this map.

values

public Collection<V> values()

Returns a collection of the values contained in this map. The collection is backed by this map so changes to one are reflected by the other. The collection supports remove, removeAll, retainAll and clear operations, and it does not support add or addAll operations.

This method returns a collection which is the subclass of AbstractCollection. The iterator method of this subclass returns a "wrapper object" over the iterator of map's entrySet(). The size method wraps the map's size method and the contains method wraps the map's containsValue method.

The collection is created when this method is called for the first time and returned in response to all subsequent calls. This method may return different collections when multiple concurrent calls occur, since no synchronization is performed.

Specified by:

values in class Map<K,V>

Returns:

a collection of the values contained in this map.