K- the type of keys maintained by this map.
V- the type of mapped values.
public class MultivaluedHashMap<K,V> extends AbstractMultivaluedMap<K,V> implements Serializable
This implementation provides all of the optional map operations. This class makes no guarantees as to the order of
the map; in particular, it does not guarantee that the order will remain constant over time. The implementation
null key. By default the implementation does also permit
null values, but ignores them. This
behavior can be customized by overriding the protected
This implementation provides constant-time performance for the basic operations (
assuming the hash function disperses the elements properly among the buckets. Iteration over collection views
requires time proportional to the "capacity" of the map instance (the number of buckets) plus its size (the number of
key-value mappings). Thus, it's very important not to set the initial capacity too high (or the load factor too low)
if iteration performance is important.
An instance of
MultivaluedHashMap has two parameters that affect its performance: initial capacity
and load factor. The capacity is the number of buckets in the hash table, and the initial capacity is
simply the capacity at the time the hash table is created. The load factor is a measure of how full the hash
table is allowed to get before its capacity is automatically increased. When the number of entries in the hash table
exceeds the product of the load factor and the current capacity, the hash table is rehashed (that is, internal
data structures are rebuilt) so that the hash table has approximately twice the number of buckets.
As a general rule, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values
decrease the space overhead but increase the lookup cost (reflected in most of the operations of the
put). The expected number of entries in the map and its load factor should
be taken into account when setting its initial capacity, so as to minimize the number of rehash operations. If the
initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operations will
If many mappings are to be stored in a
MultivaluedHashMap instance, creating it with a sufficiently large
capacity will allow the mappings to be stored more efficiently than letting it perform automatic rehashing as needed
to grow the table.
Note that this implementation is not guaranteed to be synchronized. If multiple threads access a hash map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with a key that an instance already contains is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map.
The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is
structurally modified at any time after the iterator is created, in any way except through the iterator's own
remove method, the iterator will throw a
ConcurrentModificationException. Thus, in the face of
concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic
behavior at an undetermined time in the future.
ConcurrentModificationExceptionon a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
|Constructor and Description|
Constructs an empty multivalued hash map with the default initial capacity (
Constructs an empty multivalued hash map with the specified initial capacity and the default load factor (
Constructs an empty multivalued hash map with the specified initial capacity and load factor.
Constructs a new multivalued hash map with the same mappings as the specified single-valued
Constructs a new multivalued hash map with the same mappings as the specified
add, addAll, addAll, addFirst, addFirstNull, addNull, clear, containsKey, containsValue, entrySet, equals, equalsIgnoreValueOrder, get, getFirst, getValues, hashCode, isEmpty, keySet, put, putAll, putSingle, remove, size, toString, values
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
16) and the default load factor (
public MultivaluedHashMap(int initialCapacity)
initialCapacity- the initial capacity.
IllegalArgumentException- if the initial capacity is negative.
public MultivaluedHashMap(int initialCapacity, float loadFactor)
initialCapacity- the initial capacity
loadFactor- the load factor
IllegalArgumentException- if the initial capacity is negative or the load factor is nonpositive
public MultivaluedHashMap(MultivaluedMap<? extends K,? extends V> map)
Listinstances holding the values of each key are created anew instead of being reused.
map- the multivalued map whose mappings are to be placed in this multivalued map.
NullPointerException- if the specified map is
map- the single-valued map whose mappings are to be placed in this multivalued map.
NullPointerException- if the specified map is
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