de.caff.generics

Class RefValueHashMap<K,V>

java.lang.Object

de.caff.generics.RefValueHashMap<K,V>

All Implemented Interfaces:

java.util.Map<K,V>

Direct Known Subclasses:

SoftValueHashMap, WeakValueHashMap

public class RefValueHashMap<K,V>
extends java.lang.Object
implements java.util.Map<K,V>

A hashmap with strong keys and soft referenced values. According to the Java specification the references to the weak values are removed on garbage collection if there is no more memory available. See also WeakValueHashMap for a hash map with weak referenced values.

The behavior of this hashmap is that it is possible that a value is null because of garbage collection although containsKey(Object) says that the associated key is defined. It is able to handle null keys and null values.

The default constructors enable auto cleaning, which will automatically remove all dead values each time a dead value is detected, but there are also constructors accepting a boolean autoClean parameter which allow to switch this feature off.

Some invariances usually true for maps hold not here:

• Even when the map is not changed in between, subsequent calls to containsValue(Object) may return different results.
• When auto cleaning is switched on, the same is true for calls to containsKey(Object).
• When auto cleaning is switched on, the entries in the returned set of keySet() may no longer be keys when used.

With these restriction the best usage of this map is as a cache for values which can easily be reconstructed. The only methods which should be used without any problems are the put(Object, Object), putAll(java.util.Map) and get(Object) methods, when expecting a null return on the latter even if a value was added before.

Author:

Rammi

See Also:

SoftValueHashMap, WeakValueHashMap

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Constructor Summary

Constructors

Constructor and Description
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator) Constructs an empty SoftValueHashMap with the default initial capacity (16) and the default load factor (0.75).
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, boolean autoClean) Constructs an empty SoftValueHashMap with the default initial capacity (16) and the default load factor (0.75).
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, boolean autoClean, int initialCapacity) Constructs an empty SoftValueHashMap with the specified initial capacity and the default load factor (0.75).
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, boolean autoClean, int initialCapacity, float loadFactor) Constructs an empty HashMap with the specified initial capacity and load factor.
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, boolean autoClean, java.util.Map<? extends K,? extends V> m) Constructs a new HashMap with the same mappings as the specified Map.
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, int initialCapacity) Constructs an empty SoftValueHashMap with the specified initial capacity and the default load factor (0.75).
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, int initialCapacity, float loadFactor) Constructs an empty HashMap with the specified initial capacity and load factor.
RefValueHashMap(ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator, java.util.Map<? extends K,? extends V> m) Constructs a new HashMap with the same mappings as the specified Map.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all mappings from this map (optional operation).
boolean	containsKey(java.lang.Object key) Returns true if this map contains a mapping for the specified key.
boolean	containsValue(java.lang.Object value) Returns true if this map maps one or more keys to the specified value.
java.util.Set<java.util.Map.Entry<K,V>>	entrySet() Returns a set view of the mappings contained in this map.
V	get(java.lang.Object key) Returns the value to which this map maps the specified key.
boolean	hasDeadValue(K key) Return whether the value for a given key was garbage collected.
boolean	isEmpty() Returns true if this map contains no key-value mappings.
java.util.Set<K>	keySet() Returns a set view of the keys contained in this map.
V	put(K key, V value) Associates the specified value with the specified key in this map (optional operation).
void	putAll(java.util.Map<? extends K,? extends V> t) Copies all of the mappings from the specified map to this map (optional operation).
V	remove(java.lang.Object key) Removes the mapping for this key from this map if it is present (optional operation).
void	removeDeadValues() Remove all entries from this map which have dead values.
int	size() Returns the number of key-value mappings in this map.
java.util.Collection<V>	values() Returns a collection view of the values contained in this map.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, equals, forEach, getOrDefault, hashCode, merge, putIfAbsent, remove, replace, replace, replaceAll

Constructor Detail

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator)

Constructs an empty SoftValueHashMap with the default initial capacity (16) and the default load factor (0.75).

Parameters:

creator - reference creator

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       int initialCapacity)

Constructs an empty SoftValueHashMap with the specified initial capacity and the default load factor (0.75).

Parameters:

creator - reference creator

initialCapacity - the initial capacity.

Throws:

java.lang.IllegalArgumentException - if the initial capacity is negative.

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       int initialCapacity,
                       float loadFactor)

Constructs an empty HashMap with the specified initial capacity and load factor.

Parameters:

creator - reference creator

initialCapacity - The initial capacity.

loadFactor - The load factor.

Throws:

java.lang.IllegalArgumentException - if the initial capacity is negative or the load factor is nonpositive.

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       @NotNull
                       java.util.Map<? extends K,? extends V> m)

Constructs a new HashMap with the same mappings as the specified Map. The HashMap is created with default load factor (0.75) and an initial capacity sufficient to hold the mappings in the specified Map.

Parameters:

creator - reference creator

m - the map whose mappings are to be placed in this map.

Throws:

java.lang.NullPointerException - if the specified map is null.

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       boolean autoClean)

Constructs an empty SoftValueHashMap with the default initial capacity (16) and the default load factor (0.75).

Parameters:

creator - reference creator

autoClean - if true call removeDeadValues() when finding a dead value

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       boolean autoClean,
                       int initialCapacity)

Constructs an empty SoftValueHashMap with the specified initial capacity and the default load factor (0.75).

Parameters:

creator - reference creator

autoClean - if true call removeDeadValues() when finding a dead value

initialCapacity - the initial capacity.

Throws:

java.lang.IllegalArgumentException - if the initial capacity is negative.

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       boolean autoClean,
                       int initialCapacity,
                       float loadFactor)

Constructs an empty HashMap with the specified initial capacity and load factor.

Parameters:

creator - reference creator

autoClean - if true call removeDeadValues() when finding a dead value

initialCapacity - The initial capacity.

loadFactor - The load factor.

Throws:

java.lang.IllegalArgumentException - if the initial capacity is negative or the load factor is nonpositive.

RefValueHashMap

public RefValueHashMap(@NotNull
                       ReferenceCreator<? extends java.lang.ref.Reference<V>,V> creator,
                       boolean autoClean,
                       @NotNull
                       java.util.Map<? extends K,? extends V> m)

Constructs a new HashMap with the same mappings as the specified Map. The HashMap is created with default load factor (0.75) and an initial capacity sufficient to hold the mappings in the specified Map.

Parameters:

creator - reference creator

autoClean - if true call removeDeadValues() when finding a dead value

m - the map whose mappings are to be placed in this map.

Throws:

java.lang.NullPointerException - if the specified map is null.

Method Detail

size

public int size()

Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:

size in interface java.util.Map<K,V>

Returns:

the number of key-value mappings in this map.

isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings.

Specified by:

isEmpty in interface java.util.Map<K,V>

Returns:

true if this map contains no key-value mappings.

containsKey

public boolean containsKey(java.lang.Object key)

Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Specified by:

containsKey in interface java.util.Map<K,V>

Parameters:

key - key whose presence in this map is to be tested.

Returns:

true if this map contains a mapping for the specified key.

Throws:

java.lang.ClassCastException - if the key is of an inappropriate type for this map (optional).

java.lang.NullPointerException - if the key is null and this map does not permit null keys (optional).

containsValue

public boolean containsValue(java.lang.Object value)

Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.

Specified by:

containsValue in interface java.util.Map<K,V>

Parameters:

value - value whose presence in this map is to be tested.

Returns:

true if this map maps one or more keys to the specified value.

Throws:

java.lang.ClassCastException - if the value is of an inappropriate type for this map (optional).

java.lang.NullPointerException - if the value is null and this map does not permit null values (optional).

get

public V get(java.lang.Object key)

Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

Specified by:

get in interface java.util.Map<K,V>

Parameters:

key - key whose associated value is to be returned.

Returns:

the value to which this map maps the specified key, or null if the map contains no mapping for this key.

Throws:

java.lang.ClassCastException - if the key is of an inappropriate type for this map (optional).

java.lang.NullPointerException - if the key is null and this map does not permit null keys (optional).

See Also:

containsKey(Object)

put

public V put(K key,
             V value)

Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for this key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.))

Specified by:

put in interface java.util.Map<K,V>

Parameters:

key - key with which the specified value is to be associated.

value - value to be associated with the specified key.

Returns:

previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.

Throws:

java.lang.UnsupportedOperationException - if the put operation is not supported by this map.

java.lang.ClassCastException - if the class of the specified key or value prevents it from being stored in this map.

java.lang.IllegalArgumentException - if some aspect of this key or value prevents it from being stored in this map.

java.lang.NullPointerException - if this map does not permit null keys or values, and the specified key or value is null.

remove

public V remove(java.lang.Object key)

Removes the mapping for this key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

Specified by:

remove in interface java.util.Map<K,V>

Parameters:

key - key whose mapping is to be removed from the map.

Returns:

previous value associated with specified key, or null if there was no mapping for key.

Throws:

java.lang.ClassCastException - if the key is of an inappropriate type for this map (optional).

java.lang.NullPointerException - if the key is null and this map does not permit null keys (optional).

java.lang.UnsupportedOperationException - if the remove method is not supported by this map.

putAll

public void putAll(@NotNull
                   java.util.Map<? extends K,? extends V> t)

Copies all of the mappings from the specified map to this map (optional operation). The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is unspecified if the specified map is modified while the operation is in progress.

Specified by:

putAll in interface java.util.Map<K,V>

Parameters:

t - Mappings to be stored in this map.

Throws:

java.lang.UnsupportedOperationException - if the putAll method is not supported by this map.

java.lang.ClassCastException - if the class of a key or value in the specified map prevents it from being stored in this map.

java.lang.IllegalArgumentException - some aspect of a key or value in the specified map prevents it from being stored in this map.

java.lang.NullPointerException - if the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values.

clear

public void clear()

Removes all mappings from this map (optional operation).

Specified by:

clear in interface java.util.Map<K,V>

Throws:

java.lang.UnsupportedOperationException - clear is not supported by this map.

keySet

@NotNull
public java.util.Set<K> keySet()

Returns a set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

Specified by:

keySet in interface java.util.Map<K,V>

Returns:

a set view of the keys contained in this map.

values

@NotNull
public java.util.Collection<V> values()

Returns a collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

values in interface java.util.Map<K,V>

Returns:

a collection view of the values contained in this map.

entrySet

@NotNull
public java.util.Set<java.util.Map.Entry<K,V>> entrySet()

Returns a set view of the mappings contained in this map. Each element in the returned set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

entrySet in interface java.util.Map<K,V>

Returns:

a set view of the mappings contained in this map.

hasDeadValue

public boolean hasDeadValue(@NotNull
                            K key)

Return whether the value for a given key was garbage collected.

Parameters:

key - key to look for

Returns:

true the value was garbage collected and is no longer available,
false the value is still available (but may be gone soon)

removeDeadValues

public void removeDeadValues()

Remove all entries from this map which have dead values.