public class LinkedHashMap<K, V>
- Object
- AbstractMap<K, V>
- HashMap<K, V>
- LinkedHashMap
ImplementsMap<K, V>
LinkedHashMap is a variant of HashMap. Its entries are kept in a
doubly-linked list. The iteration order is, by default, the order in which
keys were inserted. Reinserting an already existing key doesn’t change the
order. A key is existing if a call to containsKey would return true.
If the three argument constructor is used, and order is specified as
true, the iteration will be in the order that entries were accessed.
The access order gets affected by put(), get(), putAll() operations, but not
by operations on the collection views.
Null elements are allowed, and all the optional map operations are supported.
Note: The implementation of LinkedHashMap is not synchronized.
If one thread of several threads accessing an instance modifies the map
structurally, access to the map needs to be synchronized. For
insertion-ordered instances a structural modification is an operation that
removes or adds an entry. Access-ordered instances also are structurally
modified by put(), get() and putAll() since these methods change the order of
the entries. Changes in the value of an entry are not structural changes.
The Iterator that can be created by calling the iterator method
throws a ConcurrentModificationException if the map is structurally
changed while an iterator is used to iterate over the elements. Only the
remove method that is provided by the iterator allows for removal of
elements during iteration. It is not possible to guarantee that this
mechanism works in all cases of unsynchronized concurrent modification. It
should only be used for debugging purposes.
Constructors
public LinkedHashMap() | Constructs a new empty LinkedHashMap instance. |
public LinkedHashMap(int s) | Constructs a new LinkedHashMap instance with the specified capacity. |
public LinkedHashMap(int s, float lf) | Constructs a new LinkedHashMap instance with the specified capacity and load factor. |
public LinkedHashMap(int s, float lf, boolean order) | Constructs a new LinkedHashMap instance with the specified capacity, load factor and a flag specifying the ordering behavior. |
public LinkedHashMap(Map<? extends K, ? extends V> m) | Constructs a new LinkedHashMap instance containing the mappings from the specified map. |
Methods
public boolean containsValue(Object value) | Returns whether this map contains the specified value. |
public V get(Object key) | Returns the value of the mapping with the specified key. |
public V put(K key, V value) | Maps the specified key to the specified value. |
public Set<Map.Entry<K, V>> entrySet() | Returns a set containing all of the mappings in this map. |
public Set<K> keySet() | Returns a set of the keys contained in this map. |
public Collection<V> values() | Returns a collection of the values contained in this map. |
public V remove(Object key) | Removes the mapping with the specified key from this map. |
protected boolean removeEldestEntry(Map.Entry<K, V> eldest) | This method is queried from the put and putAll methods to check if the eldest member of the map should be deleted before adding the new member. |
public void clear() | Removes all elements from this map, leaving it empty. |
Inherited nested types
Inherited methods
From HashMap
From AbstractMap
Constructor details
LinkedHashMap
public LinkedHashMap()LinkedHashMap instance.LinkedHashMap
public LinkedHashMap(int s)LinkedHashMap instance with the specified
capacity.Parameters
sint- the initial capacity of this map.
Throws
IllegalArgumentException- if the capacity is less than zero.
LinkedHashMap
public LinkedHashMap(int s, float lf)LinkedHashMap instance with the specified
capacity and load factor.Parameters
sint- the initial capacity of this map.
lffloat- the initial load factor.
Throws
IllegalArgumentException- when the capacity is less than zero or the load factor is less or equal to zero.
LinkedHashMap
public LinkedHashMap(int s, float lf, boolean order)LinkedHashMap instance with the specified
capacity, load factor and a flag specifying the ordering behavior.Parameters
sint- the initial capacity of this hash map.
lffloat- the initial load factor.
orderbooleantrueif the ordering should be done based on the last access (from least-recently accessed to most-recently accessed), andfalseif the ordering should be the order in which the entries were inserted.
Throws
IllegalArgumentException- when the capacity is less than zero or the load factor is less or equal to zero.
LinkedHashMap
public LinkedHashMap(Map<? extends K, ? extends V> m)LinkedHashMap instance containing the mappings
from the specified map. The order of the elements is preserved.Parameters
mMap<? extends K, ? extends V>- the mappings to add.
Method details
containsValue
public boolean containsValue(Object value)Parameters
valueObject- the value to search for.
Returns
true if this map contains the specified value,
false otherwise.get
public V get(Object key)Parameters
keyObject- the key.
Returns
null
if no mapping for the specified key is found.put
public V put(K key, V value)Parameters
keyK- the key.
valueV- the value.
Returns
null if there was no such mapping.entrySet
public Set<Map.Entry<K, V>> entrySet()Map.Entry. As the set is backed by this map,
changes in one will be reflected in the other.Returns
keySet
public Set<K> keySet()Returns
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.
Returns
remove
public V remove(Object key)Parameters
keyObject- the key of the mapping to remove.
Returns
null if no mapping
for the specified key was found.removeEldestEntry
protected boolean removeEldestEntry(Map.Entry<K, V> eldest)Parameters
eldestMap.Entry<K, V>- the entry to check if it should be removed.
Returns
true if the eldest member should be removed.clear
public void clear()Throws
UnsupportedOperationException- if removing from this map is not supported.