de.caff.generics

Class SoftValueHashMap<K,V>

java.lang.Object

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

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

All Implemented Interfaces:

java.util.Map<K,V>

public class SoftValueHashMap<K,V>
extends RefValueHashMap<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 RefValueHashMap.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 RefValueHashMap.containsValue(Object) may return different results.
• When auto cleaning is switched on, the same is true for calls to RefValueHashMap.containsKey(Object).
• When auto cleaning is switched on, the entries in the returned set of RefValueHashMap.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 RefValueHashMap.put(Object, Object), RefValueHashMap.putAll(java.util.Map) and RefValueHashMap.get(Object) methods, when expecting a null return on the latter even if a value was added before.

Author:

Rammi

See Also:

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

Method Summary

Methods inherited from class de.caff.generics.RefValueHashMap

clear, containsKey, containsValue, entrySet, get, hasDeadValue, isEmpty, keySet, put, putAll, remove, removeDeadValues, size, values

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

SoftValueHashMap

public SoftValueHashMap()

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

SoftValueHashMap

public SoftValueHashMap(int initialCapacity)

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

Parameters:

initialCapacity - the initial capacity.

Throws:

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

SoftValueHashMap

public SoftValueHashMap(int initialCapacity,
                        float loadFactor)

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

Parameters:

initialCapacity - The initial capacity.

loadFactor - The load factor.

Throws:

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

SoftValueHashMap

public SoftValueHashMap(@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:

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

Throws:

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

SoftValueHashMap

public SoftValueHashMap(boolean autoClean)

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

Parameters:

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

SoftValueHashMap

public SoftValueHashMap(boolean autoClean,
                        int initialCapacity)

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

Parameters:

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

initialCapacity - the initial capacity.

Throws:

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

SoftValueHashMap

public SoftValueHashMap(boolean autoClean,
                        int initialCapacity,
                        float loadFactor)

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

Parameters:

autoClean - if true call RefValueHashMap.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.

SoftValueHashMap

public SoftValueHashMap(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:

autoClean - if true call RefValueHashMap.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.