Package com.cedarsoftware.util

Class AbstractConcurrentNullSafeMap<K,V>

java.lang.Object

com.cedarsoftware.util.AbstractConcurrentNullSafeMap<K,V>

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Implemented Interfaces:

ConcurrentMap<K,V>, Map<K,V>

Direct Known Subclasses:

ConcurrentHashMapNullSafe, ConcurrentNavigableMapNullSafe

public abstract class AbstractConcurrentNullSafeMap<K,V>
extends Object
implements ConcurrentMap<K,V>

An abstract thread-safe implementation of the ConcurrentMap interface that allows null keys and null values. Internally, AbstractConcurrentNullSafeMap uses sentinel objects to represent null keys and values, enabling safe handling of null while maintaining compatibility with ConcurrentMap behavior.

Key Features

• Thread-Safe: Implements ConcurrentMap with thread-safe operations.
• Null Handling: Supports null keys and null values using sentinel objects (AbstractConcurrentNullSafeMap.NullSentinel).
• Customizable: Allows customization of the underlying ConcurrentMap through its constructor.
• Standard Map Behavior: Adheres to the Map and ConcurrentMap contract, supporting operations like putIfAbsent(K, V), computeIfAbsent(K, java.util.function.Function<? super K, ? extends V>), merge(K, V, java.util.function.BiFunction<? super V, ? super V, ? extends V>), and more.

Null Key and Value Handling

The AbstractConcurrentNullSafeMap uses internal sentinel objects (AbstractConcurrentNullSafeMap.NullSentinel) to distinguish null keys and values from actual entries. This ensures that null keys and values can coexist with regular entries without ambiguity.

Customization

This abstract class requires a concrete implementation of the backing ConcurrentMap. To customize the behavior, subclasses can provide a specific implementation of the internal map.

Usage Example

 // Example subclass using ConcurrentHashMap as the backing map
 public class MyConcurrentNullSafeMap<K, V> extends AbstractConcurrentNullSafeMap<K, V> {
     public MyConcurrentNullSafeMap() {
         super(new ConcurrentHashMap<>());
     }
 }

 // Using the map
 MyConcurrentNullSafeMap<String, String> map = new MyConcurrentNullSafeMap<>();
 map.put(null, "nullKey");
 map.put("key", null);
 System.out.println(map.get(null));  // Outputs: nullKey
 System.out.println(map.get("key")); // Outputs: null
 

Additional Notes

• Equality and HashCode: Ensures consistent behavior for equality and hash code computation in compliance with the Map contract.
• Thread Safety: The thread safety of this class is determined by the thread safety of the underlying ConcurrentMap implementation.
• Sentinel Objects: The AbstractConcurrentNullSafeMap.NullSentinel.NULL_KEY and AbstractConcurrentNullSafeMap.NullSentinel.NULL_VALUE are used internally to mask null keys and values.

Author:

John DeRegnaucourt ([email protected])
Copyright (c) Cedar Software LLC

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

License

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

See Also:

• ConcurrentMap
• ConcurrentHashMap

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected static enum	AbstractConcurrentNullSafeMap.NullSentinel

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

Map.Entry<K,V>

Field Summary

Fields

Modifier and Type	Field	Description
protected final ConcurrentMap<Object,Object>	internalMap

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AbstractConcurrentNullSafeMap(ConcurrentMap<Object,Object> internalMap)	Constructs a new AbstractConcurrentNullSafeMap with the provided internal map.

Method Summary

Modifier and Type	Method	Description
void	clear()
V	compute(K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
V	computeIfAbsent(K key, Function<? super K,? extends V> mappingFunction)
boolean	containsKey(Object key)
boolean	containsValue(Object value)
Set<Map.Entry<K,V>>	entrySet()
boolean	equals(Object o)	Overrides the equals method to ensure proper comparison between two maps.
V	get(Object key)
V	getOrDefault(Object key, V defaultValue)
int	hashCode()	Overrides the hashCode method to ensure consistency with equals.
boolean	isEmpty()
Set<K>	keySet()
protected Object	maskNullKey(K key)
protected Object	maskNullValue(V value)
V	merge(K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction)
V	put(K key, V value)
void	putAll(Map<? extends K,? extends V> m)
V	putIfAbsent(K key, V value)
V	remove(Object key)
boolean	remove(Object key, Object value)
V	replace(K key, V value)
boolean	replace(K key, V oldValue, V newValue)
int	size()
String	toString()	Overrides the toString method to provide a string representation of the map.
protected K	unmaskNullKey(Object key)
protected V	unmaskNullValue(Object value)
Collection<V>	values()

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.concurrent.ConcurrentMap

computeIfPresent, forEach, replaceAll

Field Details

internalMap

protected final ConcurrentMap<Object,Object> internalMap

Constructor Details

AbstractConcurrentNullSafeMap

protected AbstractConcurrentNullSafeMap(ConcurrentMap<Object,Object> internalMap)

Constructs a new AbstractConcurrentNullSafeMap with the provided internal map.

Parameters:

internalMap - the internal ConcurrentMap to use

Method Details

maskNullKey

protected Object maskNullKey(K key)

unmaskNullKey

protected K unmaskNullKey(Object key)

maskNullValue

protected Object maskNullValue(V value)

unmaskNullValue

protected V unmaskNullValue(Object value)

size

public int size()

Specified by:

size in interface Map<K,V>

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Map<K,V>

containsKey

public boolean containsKey(Object key)

Specified by:

containsKey in interface Map<K,V>

containsValue

public boolean containsValue(Object value)

Specified by:

containsValue in interface Map<K,V>

get

public V get(Object key)

Specified by:

get in interface Map<K,V>

put

public V put(K key,
 V value)

Specified by:

put in interface Map<K,V>

remove

public V remove(Object key)

Specified by:

remove in interface Map<K,V>

putAll

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

Specified by:

putAll in interface Map<K,V>

clear

public void clear()

Specified by:

clear in interface Map<K,V>

getOrDefault

public V getOrDefault(Object key,
 V defaultValue)

Specified by:

getOrDefault in interface ConcurrentMap<K,V>

Specified by:

getOrDefault in interface Map<K,V>

putIfAbsent

public V putIfAbsent(K key,
 V value)

Specified by:

putIfAbsent in interface ConcurrentMap<K,V>

Specified by:

putIfAbsent in interface Map<K,V>

remove

public boolean remove(Object key,
 Object value)

Specified by:

remove in interface ConcurrentMap<K,V>

Specified by:

remove in interface Map<K,V>

replace

public boolean replace(K key,
 V oldValue,
 V newValue)

Specified by:

replace in interface ConcurrentMap<K,V>

Specified by:

replace in interface Map<K,V>

replace

public V replace(K key,
 V value)

Specified by:

replace in interface ConcurrentMap<K,V>

Specified by:

replace in interface Map<K,V>

computeIfAbsent

public V computeIfAbsent(K key,
 Function<? super K,? extends V> mappingFunction)

Specified by:

computeIfAbsent in interface ConcurrentMap<K,V>

Specified by:

computeIfAbsent in interface Map<K,V>

compute

public V compute(K key,
 BiFunction<? super K,? super V,? extends V> remappingFunction)

Specified by:

compute in interface ConcurrentMap<K,V>

Specified by:

compute in interface Map<K,V>

merge

public V merge(K key,
 V value,
 BiFunction<? super V,? super V,? extends V> remappingFunction)

Specified by:

merge in interface ConcurrentMap<K,V>

Specified by:

merge in interface Map<K,V>

values

public Collection<V> values()

Specified by:

values in interface Map<K,V>

keySet

public Set<K> keySet()

Specified by:

keySet in interface Map<K,V>

entrySet

public Set<Map.Entry<K,V>> entrySet()

Specified by:

entrySet in interface Map<K,V>

equals

public boolean equals(Object o)

Overrides the equals method to ensure proper comparison between two maps. Two maps are considered equal if they contain the same key-value mappings.

Specified by:

equals in interface Map<K,V>

Overrides:

equals in class Object

Parameters:

o - the object to be compared for equality with this map

Returns:

true if the specified object is equal to this map

hashCode

public int hashCode()

Overrides the hashCode method to ensure consistency with equals. The hash code of a map is defined to be the sum of the hash codes of each entry in the map.

Specified by:

hashCode in interface Map<K,V>

Overrides:

hashCode in class Object

Returns:

the hash code value for this map

toString

public String toString()

Overrides the toString method to provide a string representation of the map. The string representation consists of a list of key-value mappings in the order returned by the map's entrySet view's iterator, enclosed in braces ("{}"). Adjacent mappings are separated by the characters ", " (comma and space).

Overrides:

toString in class Object

Returns:

a string representation of this map