ConcurrentHashMap (OpenJPA Parent POM 3.1.0 API)

java.lang.Object
- java.util.AbstractMap
- - org.apache.openjpa.lib.util.concurrent.ConcurrentHashMap

All Implemented Interfaces:

Serializable, Cloneable, Map, ConcurrentMap, SizedMap
```
public class ConcurrentHashMap
extends AbstractMap
implements ConcurrentMap, SizedMap, Cloneable, Serializable
```
This class implements a HashMap which has limited synchronization. In particular mutators are generally synchronized while accessors are generally not. Additionally the Iterators returned by this class are not "fail-fast", but instead try to continue to iterate over the data structure after changes have been made. The synchronization semantics are built right in to the implementation rather than using a delegating wrapper like the other collection classes do because it wasn't clear to me that the how the two should be seperated or that it would be useful to do so. This can probably be a topic for further debate in the future. This class is based heavily on the HashMap class in the Java collections package.

See Also:

Serialized Form

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

protected static class ConcurrentHashMap.Entry
- Nested classes/interfaces inherited from class java.util.AbstractMap
  AbstractMap.SimpleEntry<K,V>, AbstractMap.SimpleImmutableEntry<K,V>

Nested Classes
Modifier and Type	Class and Description
`protected static class`	`ConcurrentHashMap.Entry`

Constructor Summary

Constructors
Constructor and Description
`ConcurrentHashMap()` Constructs an empty `ConcurrentHashMap` with the default initial capacity(16) and the default load factor(0.75).
`ConcurrentHashMap(int initialCapacity)` Constructs an empty `ConcurrentHashMap` with the specified initial capacity and the default load factor(0.75).
`ConcurrentHashMap(int initialCapacity, float loadFactor)` Constructs an empty `ConcurrentHashMap` with the specified initial capacity and load factor.
`ConcurrentHashMap(Map m)` Constructs a new `ConcurrentHashMap` with the same mappings as the specified `Map`.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`int`	`capacity()` Returns the current capacity of backing table in this map.
`void`	`clear()` Removes all mappings from this map.
`Object`	`clone()` Returns a shallow copy of this `ConcurrentHashMap` instance: the keys and values themselves are not cloned.
`boolean`	`containsKey(Object key)` Returns `true` if this map contains a mapping for the specified key.
`boolean`	`containsValue(Object value)` Returns `true` if this map maps one or more keys to the specified value.
`protected ConcurrentHashMap.Entry`	`createEntry(int h, Object k, Object v, ConcurrentHashMap.Entry n)`
`Set`	`entrySet()` Returns a collection view of the mappings contained in this map.
`Object`	`get(Object key)` Returns the value to which the specified key is mapped in this identity hash map, or `null` if the map contains no mapping for this key.
`protected ConcurrentHashMap.Entry`	`getEntry(Object key)` Returns the entry associated with the specified key in the ConcurrentHashMap.
`int`	`getMaxSize()` The maximum number of entries, or Integer.MAX_VALUE for no limit.
`boolean`	`isEmpty()` Returns `true` if this map contains no key-value mappings.
`boolean`	`isFull()` Whether the map is full.
`Set`	`keySet()` Returns a set view of the keys contained in this map.
`float`	`loadFactor()` Returns the load factor for this map.
`void`	`overflowRemoved(Object key, Object value)` Overridable callback for when an overflow entry is automatically removed.
`Object`	`put(Object key, Object value)` Associates the specified value with the specified key in this map.
`void`	`putAll(Map t)` Copies all of the mappings from the specified map to this map These mappings will replace any mappings that this map had for any of the keys currently in the specified map.
`Object`	`putIfAbsent(Object key, Object value)`
`Iterator`	`randomEntryIterator()` Iterate over map entries, beginning at an arbitrary (not strictly random) entry.
`Object`	`remove(Object key)` Removes the mapping for this key from this map if present.
`Map.Entry`	`removeRandom()` Remove an arbitrary(not strictly random) entry from the map.
`void`	`setMaxSize(int maxSize)` The maximum number of entries, or Integer.MAX_VALUE for no limit.
`int`	`size()` Returns the number of key-value mappings in this map.
`Collection`	`values()` Returns a collection view of the values contained in this map.

Methods inherited from class java.util.AbstractMap
equals, hashCode, toString

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, equals, forEach, getOrDefault, hashCode, merge, remove, replace, replace, replaceAll

- Constructor Detail
  - ConcurrentHashMap
```
public ConcurrentHashMap(int initialCapacity,
                         float loadFactor)
```
    Constructs an empty ConcurrentHashMap with the specified initial capacity and load factor.
    
    Parameters:
    
    initialCapacity - The initial capacity.
    
    loadFactor - The load factor.
    
    Throws:
    
    IllegalArgumentException - if the initial capacity is negative or the load factor is nonpositive.
  - ConcurrentHashMap
```
public ConcurrentHashMap(int initialCapacity)
```
    Constructs an empty ConcurrentHashMap with the specified initial capacity and the default load factor(0.75).
    
    Parameters:
    
    initialCapacity - the initial capacity.
    
    Throws:
    
    IllegalArgumentException - if the initial capacity is negative.
  - ConcurrentHashMap
```
public ConcurrentHashMap()
```
    Constructs an empty ConcurrentHashMap with the default initial capacity(16) and the default load factor(0.75).
  - ConcurrentHashMap
```
public ConcurrentHashMap(Map m)
```
    Constructs a new ConcurrentHashMap with the same mappings as the specified Map. The ConcurrentHashMap 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:
    
    NullPointerException - if the specified map is null.
- Method Detail
  - capacity
```
public final int capacity()
```
    Returns the current capacity of backing table in this map.
    
    Returns:
    
    the current capacity of backing table in this map.
  - loadFactor
```
public final float loadFactor()
```
    Returns the load factor for this map.
    
    Returns:
    
    the load factor for this map.
  - getMaxSize
```
public int getMaxSize()
```
    Description copied from interface: SizedMap
    
    The maximum number of entries, or Integer.MAX_VALUE for no limit.
    
    Specified by:
    
    getMaxSize in interface SizedMap
  - setMaxSize
```
public void setMaxSize(int maxSize)
```
    Description copied from interface: SizedMap
    
    The maximum number of entries, or Integer.MAX_VALUE for no limit.
    
    Specified by:
    
    setMaxSize in interface SizedMap
  - isFull
```
public boolean isFull()
```
    Description copied from interface: SizedMap
    
    Whether the map is full.
    
    Specified by:
    
    isFull in interface SizedMap
  - overflowRemoved
```
public void overflowRemoved(Object key,
                            Object value)
```
    Description copied from interface: SizedMap
    
    Overridable callback for when an overflow entry is automatically removed.
    
    Specified by:
    
    overflowRemoved in interface SizedMap
  - size
```
public final int size()
```
    Returns the number of key-value mappings in this map.
    
    Specified by:
    
    size in interface Map
    
    Overrides:
    
    size in class AbstractMap
    
    Returns:
    
    the number of key-value mappings in this map.
  - isEmpty
```
public final boolean isEmpty()
```
    Returns true if this map contains no key-value mappings.
    
    Specified by:
    
    isEmpty in interface Map
    
    Overrides:
    
    isEmpty in class AbstractMap
    
    Returns:
    
    true if this map contains no key-value mappings.
  - get
```
public Object get(Object key)
```
    Returns the value to which the specified key is mapped in this identity hash map, or 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 is also possible that the map explicitly maps the key to null. The containsKey method may be used to distinguish these two cases.
    
    Specified by:
    
    get in interface Map
    
    Overrides:
    
    get in class AbstractMap
    
    Parameters:
    
    key - the 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.
    
    See Also:
    
    put(Object, Object)
  - containsKey
```
public final boolean containsKey(Object key)
```
    Returns true if this map contains a mapping for the specified key.
    
    Specified by:
    
    containsKey in interface Map
    
    Overrides:
    
    containsKey in class AbstractMap
    
    Parameters:
    
    key - The key whose presence in this map is to be tested
    
    Returns:
    
    true if this map contains a mapping for the specified key.
  - getEntry
```
protected ConcurrentHashMap.Entry getEntry(Object key)
```
    Returns the entry associated with the specified key in the ConcurrentHashMap. Returns null if the ConcurrentHashMap contains no mapping for this key.
  - put
```
public Object put(Object key,
                  Object value)
```
    Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced.
    
    Specified by:
    
    put in interface Map
    
    Overrides:
    
    put in class AbstractMap
    
    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 ConcurrentHashMap previously associated null with the specified key.
  - putIfAbsent
```
public Object putIfAbsent(Object key,
                          Object value)
```
    Specified by:
    
    putIfAbsent in interface Map
  - putAll
```
public final void putAll(Map t)
```
    Copies all of the mappings from the specified map to this map These mappings will replace any mappings that this map had for any of the keys currently in the specified map.
    
    Specified by:
    
    putAll in interface Map
    
    Overrides:
    
    putAll in class AbstractMap
    
    Parameters:
    
    t - mappings to be stored in this map.
    
    Throws:
    
    NullPointerException - if the specified map is null.
  - remove
```
public Object remove(Object key)
```
    Removes the mapping for this key from this map if present.
    
    Specified by:
    
    remove in interface Map
    
    Overrides:
    
    remove in class AbstractMap
    
    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. A null return can also indicate that the map previously associated null with the specified key.
  - clear
```
public void clear()
```
    Removes all mappings from this map.
    
    Specified by:
    
    clear in interface Map
    
    Overrides:
    
    clear in class AbstractMap
  - removeRandom
```
public Map.Entry removeRandom()
```
    Description copied from interface: ConcurrentMap
    
    Remove an arbitrary(not strictly random) entry from the map. This allows implementation of concurrent caches with size ceilings.
    
    Specified by:
    
    removeRandom in interface ConcurrentMap
    
    Returns:
    
    the removed entry, or null if map is empty
  - randomEntryIterator
```
public Iterator randomEntryIterator()
```
    Description copied from interface: ConcurrentMap
    
    Iterate over map entries, beginning at an arbitrary (not strictly random) entry.
    
    Specified by:
    
    randomEntryIterator in interface ConcurrentMap
  - containsValue
```
public final boolean containsValue(Object value)
```
    Returns true if this map maps one or more keys to the specified value.
    
    Specified by:
    
    containsValue in interface Map
    
    Overrides:
    
    containsValue in class AbstractMap
    
    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.
  - clone
```
public final Object clone()
```
    Returns a shallow copy of this ConcurrentHashMap instance: the keys and values themselves are not cloned.
    
    Overrides:
    
    clone in class AbstractMap
    
    Returns:
    
    a shallow copy of this map.
  - createEntry
```
protected ConcurrentHashMap.Entry createEntry(int h,
                                              Object k,
                                              Object v,
                                              ConcurrentHashMap.Entry n)
```
  - keySet
```
public final Set 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. The set supports element removal, which removes the corresponding mapping from this 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 Map
    
    Overrides:
    
    keySet in class AbstractMap
    
    Returns:
    
    a set view of the keys contained in this map.
  - values
```
public final Collection 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. The collection supports element removal, which removes the corresponding mapping from this 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 Map
    
    Overrides:
    
    values in class AbstractMap
    
    Returns:
    
    a collection view of the values contained in this map.
  - entrySet
```
public final Set entrySet()
```
    Returns a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. 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:
    
    entrySet in interface Map
    
    Specified by:
    
    entrySet in class AbstractMap
    
    Returns:
    
    a collection view of the mappings contained in this map.
    
    See Also:
    
    Map.Entry

Class ConcurrentHashMap

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractMap

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Map

Constructor Detail

ConcurrentHashMap

ConcurrentHashMap

ConcurrentHashMap

ConcurrentHashMap

Method Detail

capacity

loadFactor

getMaxSize

setMaxSize

isFull

overflowRemoved

size

isEmpty

get

containsKey

getEntry

put

putIfAbsent

putAll

remove

clear

removeRandom

randomEntryIterator

containsValue

clone

createEntry

keySet

values

entrySet