org.apache.commons.collections

Class SequencedHashMap

Implemented Interfaces:
Cloneable, Externalizable, Map
Known Direct Subclasses:
LRUMap

public class SequencedHashMap
extends java.lang.Object
implements Map, Cloneable, Externalizable

A map of objects whose mapping entries are sequenced based on the order in which they were added. This data structure has fast O(1) search time, deletion time, and insertion time.

Although this map is sequenced, it cannot implement java.util.List because of incompatible interface definitions. The remove methods in List and Map have different return values (see: java.util.List.remove(Object) and java.util.Map.remove(Object)).

This class is not thread safe. When a thread safe implementation is required, use java.util.Collections.synchronizedMap(Map) as it is documented, or use explicit synchronization controls.

Version:
$Revision: 1.28 $ $Date: 2004/02/18 01:15:42 $
Authors:
Michael A. Smith
Daniel Rall
Henning P. Schmiedehausen
Stephen Colebourne
Since:
Commons Collections 2.0
See Also:
LinkedMap, ListOrderedMap

Constructor Summary

SequencedHashMap()
Construct a new sequenced hash map with default initial size and load factor.
SequencedHashMap(Map m)
Construct a new sequenced hash map and add all the elements in the specified map.
SequencedHashMap(int initialSize)
Construct a new sequenced hash map with the specified initial size and default load factor.
SequencedHashMap(int initialSize, float loadFactor)
Construct a new sequenced hash map with the specified initial size and load factor.

Method Summary

void
clear()
Implements Map.clear().
Object
clone()
Creates a shallow copy of this object, preserving the internal structure by copying only references.
boolean
containsKey(Object key)
Implements Map.containsKey(Object).
boolean
containsValue(Object value)
Implements Map.containsValue(Object).
Set
entrySet()
Implements Map.entrySet().
boolean
equals(Object obj)
Implements Map.equals(Object).
Object
get(Object o)
Implements Map.get(Object).
Object
get(int index)
Gets the key at the specified index.
Map.Entry
getFirst()
Return the entry for the "oldest" mapping.
Object
getFirstKey()
Return the key for the "oldest" mapping.
Object
getFirstValue()
Return the value for the "oldest" mapping.
Map.Entry
getLast()
Return the entry for the "newest" mapping.
Object
getLastKey()
Return the key for the "newest" mapping.
Object
getLastValue()
Return the value for the "newest" mapping.
Object
getValue(int index)
Gets the value at the specified index.
int
hashCode()
Implements Map.hashCode().
int
indexOf(Object key)
Gets the index of the specified key.
boolean
isEmpty()
Implements Map.isEmpty().
Iterator
iterator()
Gets an iterator over the keys.
Set
keySet()
Implements Map.keySet().
int
lastIndexOf(Object key)
Gets the last index of the specified key.
Object
put(Object key, Object value)
Implements Map.put(Object, Object).
void
putAll(Map t)
Adds all the mappings in the specified map to this map, replacing any mappings that already exist (as per Map.putAll(Map)).
void
readExternal(ObjectInput in)
Deserializes this map from the given stream.
Object
remove(Object key)
Implements Map.remove(Object).
Object
remove(int index)
Removes the element at the specified index.
List
sequence()
Returns a List view of the keys rather than a set view.
int
size()
Implements Map.size().
String
toString()
Provides a string representation of the entries within the map.
Collection
values()
Implements Map.values().
void
writeExternal(ObjectOutput out)
Serializes this map to the given stream.

Constructor Details

SequencedHashMap

public SequencedHashMap()
Construct a new sequenced hash map with default initial size and load factor.

SequencedHashMap

public SequencedHashMap(Map m)

SequencedHashMap

public SequencedHashMap(int initialSize)
Construct a new sequenced hash map with the specified initial size and default load factor.
Parameters:
initialSize - the initial size for the hash table
See Also:
HashMap.HashMap(int)

SequencedHashMap

public SequencedHashMap(int initialSize,
                        float loadFactor)
Construct a new sequenced hash map with the specified initial size and load factor.
Parameters:
initialSize - the initial size for the hash table
loadFactor - the load factor for the hash table.
See Also:
HashMap.HashMap(int,float)

Method Details

clear

public void clear()
Implements Map.clear().

clone

public Object clone()
            throws CloneNotSupportedException
Creates a shallow copy of this object, preserving the internal structure by copying only references. The keys and values themselves are not clone()'d. The cloned object maintains the same sequence.
Returns:
A clone of this instance.

containsKey

public boolean containsKey(Object key)
Implements Map.containsKey(Object).

containsValue

public boolean containsValue(Object value)
Implements Map.containsValue(Object).

entrySet

public Set entrySet()
Implements Map.entrySet().

equals

public boolean equals(Object obj)
Implements Map.equals(Object).

get

public Object get(Object o)
Implements Map.get(Object).

get

public Object get(int index)
Gets the key at the specified index.
Parameters:
index - the index to retrieve
Returns:
the key at the specified index, or null

getFirst

public Map.Entry getFirst()
Return the entry for the "oldest" mapping. That is, return the Map.Entry for the key-value pair that was first put into the map when compared to all the other pairings in the map. This behavior is equivalent to using entrySet().iterator().next(), but this method provides an optimized implementation.
Returns:
The first entry in the sequence, or null if the map is empty.

getFirstKey

public Object getFirstKey()
Return the key for the "oldest" mapping. That is, return the key for the mapping that was first put into the map when compared to all the other objects in the map. This behavior is equivalent to using getFirst().getKey(), but this method provides a slightly optimized implementation.
Returns:
The first key in the sequence, or null if the map is empty.

getFirstValue

public Object getFirstValue()
Return the value for the "oldest" mapping. That is, return the value for the mapping that was first put into the map when compared to all the other objects in the map. This behavior is equivalent to using getFirst().getValue(), but this method provides a slightly optimized implementation.
Returns:
The first value in the sequence, or null if the map is empty.

getLast

public Map.Entry getLast()
Return the entry for the "newest" mapping. That is, return the Map.Entry for the key-value pair that was first put into the map when compared to all the other pairings in the map. The behavior is equivalent to:
    Object obj = null;
    Iterator iter = entrySet().iterator();
    while(iter.hasNext()) {
      obj = iter.next();
    }
    return (Map.Entry)obj;
  
However, the implementation of this method ensures an O(1) lookup of the last key rather than O(n).
Returns:
The last entry in the sequence, or null if the map is empty.

getLastKey

public Object getLastKey()
Return the key for the "newest" mapping. That is, return the key for the mapping that was last put into the map when compared to all the other objects in the map. This behavior is equivalent to using getLast().getKey(), but this method provides a slightly optimized implementation.
Returns:
The last key in the sequence, or null if the map is empty.

getLastValue

public Object getLastValue()
Return the value for the "newest" mapping. That is, return the value for the mapping that was last put into the map when compared to all the other objects in the map. This behavior is equivalent to using getLast().getValue(), but this method provides a slightly optimized implementation.
Returns:
The last value in the sequence, or null if the map is empty.

getValue

public Object getValue(int index)
Gets the value at the specified index.
Parameters:
index - the index to retrieve
Returns:
the value at the specified index, or null

hashCode

public int hashCode()
Implements Map.hashCode().

indexOf

public int indexOf(Object key)
Gets the index of the specified key.
Parameters:
key - the key to find the index of
Returns:
the index, or -1 if not found

isEmpty

public boolean isEmpty()
Implements Map.isEmpty().

iterator

public Iterator iterator()
Gets an iterator over the keys.
Returns:
an iterator over the keys

keySet

public Set keySet()
Implements Map.keySet().

lastIndexOf

public int lastIndexOf(Object key)
Gets the last index of the specified key.
Parameters:
key - the key to find the index of
Returns:
the index, or -1 if not found

put

public Object put(Object key,
                  Object value)
Implements Map.put(Object, Object).

putAll

public void putAll(Map t)
Adds all the mappings in the specified map to this map, replacing any mappings that already exist (as per Map.putAll(Map)). The order in which the entries are added is determined by the iterator returned from Map.entrySet() for the specified map.
Parameters:
t - the mappings that should be added to this map.

readExternal

public void readExternal(ObjectInput in)
            throws IOException,
                   ClassNotFoundException
Deserializes this map from the given stream.
Parameters:
in - the stream to deserialize from

remove

public Object remove(Object key)
Implements Map.remove(Object).

remove

public Object remove(int index)
Removes the element at the specified index.
Parameters:
index - The index of the object to remove.
Returns:
The previous value corresponding the key, or null if none existed.

sequence

public List sequence()
Returns:
The ordered list of keys.
See Also:
keySet()

size

public int size()
Implements Map.size().

toString

public String toString()

values

public Collection values()
Implements Map.values().

writeExternal

public void writeExternal(ObjectOutput out)
            throws IOException
Serializes this map to the given stream.
Parameters:
out - the stream to serialize to

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