org.apache.commons.collections

Class SequencedHashMap

public class SequencedHashMap extends Object implements Map, Cloneable, Externalizable

Deprecated: Replaced by LinkedMap and ListOrderedMap in map subpackage. Due to be removed in v4.0.

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.

Since: Commons Collections 2.0

Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $

Author: Michael A. Smith Daniel Rall Henning P. Schmiedehausen Stephen Colebourne

See Also: LinkedMap ListOrderedMap

Constructor Summary
SequencedHashMap()
Construct a new sequenced hash map with default initial size and load factor.
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.
SequencedHashMap(Map m)
Construct a new sequenced hash map and add all the elements in the specified map.
Method Summary
voidclear()
Implements Map#clear().
Objectclone()
Creates a shallow copy of this object, preserving the internal structure by copying only references.
booleancontainsKey(Object key)
Implements Map#containsKey(Object).
booleancontainsValue(Object value)
Implements Map#containsValue(Object).
SetentrySet()
Implements Map#entrySet().
booleanequals(Object obj)
Implements Map#equals(Object).
Objectget(Object o)
Implements Map#get(Object).
Objectget(int index)
Gets the key at the specified index.
EntrygetFirst()
Return the entry for the "oldest" mapping.
ObjectgetFirstKey()
Return the key for the "oldest" mapping.
ObjectgetFirstValue()
Return the value for the "oldest" mapping.
EntrygetLast()
Return the entry for the "newest" mapping.
ObjectgetLastKey()
Return the key for the "newest" mapping.
ObjectgetLastValue()
Return the value for the "newest" mapping.
ObjectgetValue(int index)
Gets the value at the specified index.
inthashCode()
Implements Map#hashCode().
intindexOf(Object key)
Gets the index of the specified key.
booleanisEmpty()
Implements Map#isEmpty().
Iteratoriterator()
Gets an iterator over the keys.
SetkeySet()
Implements Map#keySet().
intlastIndexOf(Object key)
Gets the last index of the specified key.
Objectput(Object key, Object value)
Implements Map#put(Object, Object).
voidputAll(Map t)
Adds all the mappings in the specified map to this map, replacing any mappings that already exist (as per Map#putAll(Map)).
voidreadExternal(ObjectInput in)
Deserializes this map from the given stream.
Objectremove(Object key)
Implements Map#remove(Object).
Objectremove(int index)
Removes the element at the specified index.
Listsequence()
Returns a List view of the keys rather than a set view.
intsize()
Implements Map#size().
StringtoString()
Provides a string representation of the entries within the map.
Collectionvalues()
Implements Map#values().
voidwriteExternal(ObjectOutput out)
Serializes this map to the given stream.

Constructor Detail

SequencedHashMap

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

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)

SequencedHashMap

public SequencedHashMap(Map m)
Construct a new sequenced hash map and add all the elements in the specified map. The order in which the mappings in the specified map are added is defined by putAll.

Method Detail

clear

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

clone

public Object clone()
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.

Throws: CloneNotSupportedException if clone is not supported by a subclass.

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

Throws: ArrayIndexOutOfBoundsException if the index is < 0 or > the size of the map.

getFirst

public 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 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

Throws: ArrayIndexOutOfBoundsException if the index is < 0 or > the size of the map.

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.

Throws: NullPointerException if t is null

readExternal

public void readExternal(ObjectInput in)
Deserializes this map from the given stream.

Parameters: in the stream to deserialize from

Throws: IOException if the stream raises it ClassNotFoundException if the stream raises it

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.

Throws: ArrayIndexOutOfBoundsException if the index is < 0 or > the size of the map.

sequence

public List sequence()
Returns a List view of the keys rather than a set view. The returned list is unmodifiable. This is required because changes to the values of the list (using java.util.ListIterator#set(Object)) will effectively remove the value from the list and reinsert that value at the end of the list, which is an unexpected side effect of changing the value of a list. This occurs because changing the key, changes when the mapping is added to the map and thus where it appears in the list.

An alternative to this method is to use keySet

Returns: The ordered list of keys.

See Also: keySet

size

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

toString

public String toString()
Provides a string representation of the entries within the map. The format of the returned string may change with different releases, so this method is suitable for debugging purposes only. If a specific format is required, use entrySet.Set#iterator() iterator() and iterate over the entries in the map formatting them as appropriate.

values

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

writeExternal

public void writeExternal(ObjectOutput out)
Serializes this map to the given stream.

Parameters: out the stream to serialize to

Throws: IOException if the stream raises it

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