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com.tangosol.util
Class NullImplementation.NullMap

java.lang.Object
java.util.AbstractMap
com.tangosol.util.NullImplementation.NullMap

All Implemented Interfaces:

ExternalizableLite, PortableObject, Serializable, Map

Direct Known Subclasses:

NullImplementation.NullObservableMap

Enclosing class:

NullImplementation

public static class NullImplementation.NullMap

extends AbstractMap

implements Map, Serializable, ExternalizableLite, PortableObject

A Map that contains nothing and does nothing.

Nested Class Summary

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

Map.Entry

Field Summary

static Map

INSTANCE Since the Map contains no information, only one ever has to exist.

Constructor Summary

NullImplementation.NullMap()
Default constructor (for ExternalizableLite and PortableObject).

Method Summary

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 this value.
Set	entrySet() Returns a set view of the mappings contained in this map.
boolean	equals(Object o) Compares the specified object with this map for equality.
Object	get(Object key) Returns the value to which this map maps the specified key.
int	hashCode() Returns the hash code value for this map.
Set	keySet() Returns a Set view of the keys contained in this map.
Object	put(Object key, Object value) Associates the specified value with the specified key in this map (optional operation).
void	putAll(Map map) Copies all of the mappings from the specified map to this map (optional operation).
void	readExternal(DataInput in) Restore the contents of this object by loading the object's state from the passed DataInput object.
void	readExternal(PofReader in) Restore the contents of a user type instance by reading its state using the specified PofReader object.
Object	remove(Object key) Removes the mapping for this key from this map if present (optional operation).
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.
void	writeExternal(DataOutput out) Save the contents of this object by storing the object's state into the passed DataOutput object.
void	writeExternal(PofWriter out) Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Methods inherited from class java.util.AbstractMap

clear, clone, isEmpty, toString

Methods inherited from interface java.util.Map

clear, isEmpty

Field Detail

INSTANCE

public static final Map INSTANCE

Since the Map contains no information, only one ever has to exist.

Constructor Detail

NullImplementation.NullMap

public NullImplementation.NullMap()

Default constructor (for ExternalizableLite and PortableObject).

Method Detail

size

public int size()

Description copied from class: java.util.AbstractMap

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

This implementation returns entrySet().size().

Specified by:

size in interface Map

Overrides:

size in class AbstractMap

Returns:

the number of key-value mappings in this map.

get

public Object get(Object key)

Description copied from class: java.util.AbstractMap

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.

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, the entry's value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Specified by:

get in interface Map

Overrides:

get in class AbstractMap

Parameters:

key - key whose associated value is to be returned.

Returns:

the value to which this map maps the specified key.

See Also:

AbstractMap.containsKey(Object)

put

public Object put(Object key,
                  Object value)

Description copied from class: java.util.AbstractMap

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.

This implementation always throws an UnsupportedOperationException.

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 map previously associated null with the specified key, if the implementation supports null values.)

putAll

public void putAll(Map map)

Description copied from class: java.util.AbstractMap

Copies all of the mappings from the specified map to this map (optional operation). These mappings will replace any mappings that this map had for any of the keys currently in the specified map.

This implementation iterates over the specified map's entrySet() collection, and calls this map's put operation once for each entry returned by the iteration.

Note that this implementation throws an UnsupportedOperationException if this map does not support the put operation and the specified map is nonempty.

Specified by:

putAll in interface Map

Overrides:

putAll in class AbstractMap

Parameters:

map - mappings to be stored in this map.

remove

public Object remove(Object key)

Description copied from class: java.util.AbstractMap

Removes the mapping for this key from this map if present (optional operation).

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, its value is obtained with its getValue operation, the entry is removed from the Collection (and the backing map) with the iterator's remove operation, and the saved value is returned. If the iteration terminates without finding such an entry, null is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Note that this implementation throws an UnsupportedOperationException if the entrySet iterator does not support the remove method and this map contains a mapping for the specified key.

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 entry for key. (A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.)

containsKey

public boolean containsKey(Object key)

Description copied from class: java.util.AbstractMap

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

This implementation iterates over entrySet() searching for an entry with the specified key. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.

Specified by:

containsKey in interface Map

Overrides:

containsKey in class AbstractMap

Parameters:

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

Returns:

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

containsValue

public boolean containsValue(Object value)

Description copied from class: java.util.AbstractMap

Returns true if this map maps one or more keys to this 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 map.

This implementation iterates over entrySet() searching for an entry with the specified value. If such an entry is found, true is returned. If the iteration terminates without finding such an entry, false is returned. Note that this implementation requires linear time in the size of the map.

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 this value.

entrySet

public Set entrySet()

Description copied from class: java.util.AbstractMap

Returns a set view of the mappings contained in this map. Each element in this 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, the results of the iteration are undefined.) The set supports element removal, which removes the corresponding entry 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 Map

Specified by:

entrySet in class AbstractMap

Returns:

a set view of the mappings contained in this map.

keySet

public Set keySet()

Description copied from class: java.util.AbstractMap

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, the results of the iteration are undefined.) The Set supports element removal, which removes the corresponding entry from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

This implementation returns a Set that subclasses AbstractSet. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsKey method.

The Set is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same Set.

Specified by:

keySet in interface Map

Overrides:

keySet in class AbstractMap

Returns:

a Set view of the keys contained in this map.

values

public Collection values()

Description copied from class: java.util.AbstractMap

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, the results of the iteration are undefined.) The collection supports element removal, which removes the corresponding entry from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

This implementation returns a collection that subclasses abstract collection. The subclass's iterator method returns a "wrapper object" over this map's entrySet() iterator. The size method delegates to this map's size method and the contains method delegates to this map's containsValue method.

The collection is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same Collection.

Specified by:

values in interface Map

Overrides:

values in class AbstractMap

Returns:

a collection view of the values contained in this map.

equals

public boolean equals(Object o)

Description copied from class: java.util.AbstractMap

Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.keySet().equals(t2.keySet()) and for every key k in t1.keySet(), (t1.get(k)==null ? t2.get(k)==null : t1.get(k).equals(t2.get(k))) . This ensures that the equals method works properly across different implementations of the map interface.

This implementation first checks if the specified object is this map; if so it returns true. Then, it checks if the specified object is a map whose size is identical to the size of this set; if not, it returns false. If so, it iterates over this map's entrySet collection, and checks that the specified map contains each mapping that this map contains. If the specified map fails to contain such a mapping, false is returned. If the iteration completes, true is returned.

Specified by:

equals in interface Map

Overrides:

equals in class AbstractMap

Parameters:

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

Returns:

true if the specified object is equal to this map.

hashCode

public int hashCode()

Description copied from class: java.util.AbstractMap

Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's entrySet() view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.

This implementation iterates over entrySet(), calling hashCode on each element (entry) in the Collection, and adding up the results.

Specified by:

hashCode in interface Map

Overrides:

hashCode in class AbstractMap

Returns:

the hash code value for this map.

See Also:

Map.Entry.hashCode(), Object.hashCode(), Object.equals(Object), Set.equals(Object)

readExternal

public void readExternal(DataInput in)
                  throws IOException

Restore the contents of this object by loading the object's state from the passed DataInput object.

Specified by:

readExternal in interface ExternalizableLite

Parameters:

in - the DataInput stream to read data from in order to restore the state of this object

Throws:

IOException - if an I/O exception occurs

NotActiveException - if the object is not in its initial state, and therefore cannot be deserialized into

writeExternal

public void writeExternal(DataOutput out)
                   throws IOException

Save the contents of this object by storing the object's state into the passed DataOutput object.

Specified by:

writeExternal in interface ExternalizableLite

Parameters:

out - the DataOutput stream to write the state of this object to

Throws:

IOException - if an I/O exception occurs

readExternal

public void readExternal(PofReader in)
                  throws IOException

Restore the contents of a user type instance by reading its state using the specified PofReader object.

Specified by:

readExternal in interface PortableObject

Parameters:

in - the PofReader from which to read the object's state

Throws:

IOException - if an I/O error occurs

writeExternal

public void writeExternal(PofWriter out)
                   throws IOException

Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Specified by:

writeExternal in interface PortableObject

Parameters:

out - the PofWriter to which to write the object's state

Throws:

IOException - if an I/O error occurs

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