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edu.emory.mathcs.util
Class HashIntMap  

java.lang.Object
  edu.emory.mathcs.util.AbstractIntMap
      edu.emory.mathcs.util.HashIntMap

All Implemented Interfaces:

java.lang.Cloneable, IntMap, java.io.Serializable

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public class HashIntMap

extends AbstractIntMap

implements IntMap, java.lang.Cloneable, java.io.Serializable

Hash table based implementation of the IntMap interface. This implementation provides all of the optional map operations, and permixts null values. This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

This implementation provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets. Iteration over collection views requires time proportional to the "capacity" of the HashMap instance (the number of buckets) plus its size (the number of key-value mappings). Thus, it's very important not to set the intial capacity too high (or the load factor too low) if iteration performance is important.

An instance of HashIntMap has two parameters that affect its performance: initial capacity and load factor. The capacity is the number of buckets in the hash table, and the initial capacity is simply the capacity at the time the hash table is created. The load factor is a measure of how full the hash table is allowed to get before its capacity is automatically increased. When the number of entries in the hash table exceeds the product of the load factor and the current capacity, the capacity is roughly doubled by calling the rehash method.

As a general rule, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values decrease the space overhead but increase the lookup cost (reflected in most of the operations of the HashMap class, including get and put). The expected number of entries in the map and its load factor should be taken into account when setting its initial capacity, so as to minimize the number of rehash operations. If the initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operations will ever occur.

If many mappings are to be stored in a HashIntMap instance, creating it with a sufficiently large capacity will allow the mappings to be stored more efficiently than letting it perform automatic rehashing as needed to grow the table.

Note that this implementation is not synchronized. If multiple threads access this map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with a key that an instance already contains is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map:

 Map m = Collections.synchronizedMap(new HashMap(...));
 

The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-determixnistic behavior at an undetermined time in the future.

Since:

1.2

Version:

1.0

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Nested Class Summary
private static class	HashIntMap.EmptyHashIterator
private static class	HashIntMap.Entry           HashMap collision list entry.
private  class	HashIntMap.HashIterator

 

Field Summary
private  int	count           The total number of mappings in the hash table.
private static HashIntMap.EmptyHashIterator	emptyHashIterator
private static int	ENTRIES
private  java.util.Set	entrySet
private  float	loadFactor           The load factor for the hashtable.
private  int	modCount           The number of times this HashMap has been structurally modified Structural modifications are those that change the number of mappings in the HashMap or otherwise modify its internal structure (e.g., rehash).
private  HashIntMap.Entry[]	table           The hash table data.
private  int	threshold           The table is rehashed when its size exceeds this threshold.
private  java.util.Collection	values
private static int	VALUES

 

Constructor Summary

HashIntMap()           Constructs a new, empty map with a default capacity and load factor, which is 0.75.

HashIntMap(int initialCapacity)           Constructs a new, empty map with the specified initial capacity and default load factor, which is 0.75.

HashIntMap(int initialCapacity, float loadFactor)           Constructs a new, empty map with the specified initial capacity and the specified load factor.

HashIntMap(java.util.Map t)           Constructs a new map with the same mappings as the given map.

 

Method Summary
(package private)  int	capacity()
void	clear()           Removes all mappings from this map.
java.lang.Object	clone()           Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
boolean	containsKey(int key)           Returns true if this map contains a mapping for the specified key.
boolean	containsValue(java.lang.Object value)           Returns true if this map maps one or more keys to the specified value.
java.util.Set	entrySet()           Returns a collection view of the mappings contained in this map.
java.lang.Object	get(int key)           Returns the value to which this map maps the specified key.
private  java.util.Iterator	getHashIterator(int type)
boolean	isEmpty()           Returns true if this map contains no key-value mappings.
(package private)  float	loadFactor()
java.lang.Object	put(int key, java.lang.Object value)           Associates the specified value with the specified key in this map.
void	putAll(IntMap t)           Copies all of the mappings from the specified map to this one.
private  void	readObject(java.io.ObjectInputStream s)           Reconstitute the HashMap instance from a stream (i.e., deserialize it).
private  void	rehash()           Rehashes the contents of this map into a new HashMap instance with a larger capacity.
java.lang.Object	remove(int key)           Removes the mapping for this key from this map if present.
int	size()           Returns the number of key-value mappings in this map.
java.util.Collection	values()           Returns a collection view of the values contained in this map.
private  void	writeObject(java.io.ObjectOutputStream s)           Save the state of the HashIntMap instance to a stream (i.e., serialize it).

 

Methods inherited from class edu.emory.mathcs.util.AbstractIntMap

equals, hashCode, putAll, toString

 

Methods inherited from class java.lang.Object

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

 

Methods inherited from interface edu.emory.mathcs.util.IntMap

equals, hashCode

 

Field Detail

table

private transient HashIntMap.Entry[] table

The hash table data.

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count

private transient int count

The total number of mappings in the hash table.

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threshold

private int threshold

The table is rehashed when its size exceeds this threshold. (The value of this field is (int)(capacity * loadFactor).)

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loadFactor

private float loadFactor

The load factor for the hashtable.

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modCount

private transient int modCount

The number of times this HashMap has been structurally modified Structural modifications are those that change the number of mappings in the HashMap or otherwise modify its internal structure (e.g., rehash). This field is used to make iterators on Collection-views of the HashMap fail-fast. (See ConcurrentModificationException).

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entrySet

private transient java.util.Set entrySet

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values

private transient java.util.Collection values

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VALUES

private static final int VALUES

See Also:

Constant Field Values

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ENTRIES

private static final int ENTRIES

See Also:

Constant Field Values

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emptyHashIterator

private static HashIntMap.EmptyHashIterator emptyHashIterator

Constructor Detail

HashIntMap

public HashIntMap(int initialCapacity,
                  float loadFactor)

Constructs a new, empty map with the specified initial capacity and the specified load factor.

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HashIntMap

public HashIntMap(int initialCapacity)

Constructs a new, empty map with the specified initial capacity and default load factor, which is 0.75.

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HashIntMap

public HashIntMap()

Constructs a new, empty map with a default capacity and load factor, which is 0.75.

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HashIntMap

public HashIntMap(java.util.Map t)

Constructs a new map with the same mappings as the given map. The map is created with a capacity of twice the number of mappings in the given map or 11 (whichever is greater), and a default load factor, which is 0.75.

Method Detail

size

public int size()

Returns the number of key-value mappings in this map.

Specified by:

size in interface IntMap

Overrides:

size in class AbstractIntMap

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isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings.

Specified by:

isEmpty in interface IntMap

Overrides:

isEmpty in class AbstractIntMap

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containsValue

public boolean containsValue(java.lang.Object value)

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

Specified by:

containsValue in interface IntMap

Overrides:

containsValue in class AbstractIntMap

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containsKey

public boolean containsKey(int key)

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

Specified by:

containsKey in interface IntMap

Overrides:

containsKey in class AbstractIntMap

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get

public java.lang.Object get(int key)

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.

Specified by:

get in interface IntMap

Overrides:

get in class AbstractIntMap

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rehash

private void rehash()

Rehashes the contents of this map into a new HashMap instance with a larger capacity. This method is called automatically when the number of keys in this map exceeds its capacity and load factor.

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put

public java.lang.Object put(int key,
                            java.lang.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 IntMap

Overrides:

put in class AbstractIntMap

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remove

public java.lang.Object remove(int key)

Removes the mapping for this key from this map if present.

Specified by:

remove in interface IntMap

Overrides:

remove in class AbstractIntMap

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putAll

public void putAll(IntMap t)

Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified Map.

Specified by:

putAll in interface IntMap

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clear

public void clear()

Removes all mappings from this map.

Specified by:

clear in interface IntMap

Overrides:

clear in class AbstractIntMap

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clone

public java.lang.Object clone()

Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.

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values

public java.util.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 IntMap

Overrides:

values in class AbstractIntMap

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entrySet

public java.util.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 IntMap

Specified by:

entrySet in class AbstractIntMap

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getHashIterator

private java.util.Iterator getHashIterator(int type)

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writeObject

private void writeObject(java.io.ObjectOutputStream s)
                  throws java.io.IOException

Save the state of the HashIntMap instance to a stream (i.e., serialize it).

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readObject

private void readObject(java.io.ObjectInputStream s)
                 throws java.io.IOException,
                        java.lang.ClassNotFoundException

Reconstitute the HashMap instance from a stream (i.e., deserialize it).

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capacity

int capacity()

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loadFactor

float loadFactor()

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> edu >> emory >> mathcs >> [ util overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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