java.util
Class Hashtable

java.lang.Object
  java.util.Dictionary
      java.util.Hashtable

All Implemented Interfaces:

Cloneable, Map, Serializable

Direct Known Subclasses:

Properties

public class Hashtable

extends Dictionary

implements Map, Cloneable, Serializable

Hashtable associates keys with values. Keys and values cannot be null. The size of the Hashtable is the number of key/value pairs it contains. The capacity is the number of key/value pairs the Hashtable can hold. The load factor is a float value which determines how full the Hashtable gets before expanding the capacity. If the load factor of the Hashtable is exceeded, the capacity is doubled.

See Also:

Enumeration, Serializable, Object.equals(java.lang.Object), Object.hashCode(), Serialized Form

Constructor Summary

Hashtable()
Constructs a new Hashtable using the default capacity and load factor.

Hashtable(int capacity)
Constructs a new Hashtable using the specified capacity and the default load factor.

Hashtable(int capacity, float loadFactor)
Constructs a new Hashtable using the specified capacity and load factor.

Hashtable(Map map)
Constructs a new instance of Hashtable containing the mappings from the specified Map.

Method Summary

void	clear() Removes all key/value pairs from this Hashtable, leaving the size zero and the capacity unchanged.
Object	clone() Answers a new Hashtable with the same key/value pairs, capacity and load factor.
boolean	contains(Object value) Answers if this Hashtable contains the specified object as the value of at least one of the key/value pairs.
boolean	containsKey(Object key) Answers if this Hashtable contains the specified object as a key of one of the key/value pairs.
boolean	containsValue(Object value) Searches this Hashtable for the specified value.
Enumeration	elements() Answers an Enumeration on the values of this Hashtable.
Set	entrySet() Answers a Set of the mappings contained in this Hashtable.
boolean	equals(Object object) Compares the specified object to this Hashtable and answer if they are equal.
Object	get(Object key) Answers the value associated with the specified key in this Hashtable.
int	hashCode() Answers an integer hash code for the receiver.
boolean	isEmpty() Answers if this Hashtable has no key/value pairs, a size of zero.
Enumeration	keys() Answers an Enumeration on the keys of this Hashtable.
Set	keySet() Answers a Set of the keys contained in this Hashtable.
Object	put(Object key, Object value) Associate the specified value with the specified key in this Hashtable.
void	putAll(Map map) Copies every mapping in the specified Map to this Hashtable.
protected void	rehash() Increases the capacity of this Hashtable.
Object	remove(Object key) Remove the key/value pair with the specified key from this Hashtable.
int	size() Answers the number of key/value pairs in this Hashtable.
String	toString() Answers the string representation of this Hashtable.
Collection	values() Answers a Collection of the values contained in this Hashtable.

Methods inherited from class java.lang.Object

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

Constructor Detail

Hashtable

public Hashtable()

Constructs a new Hashtable using the default capacity and load factor.

Hashtable

public Hashtable(int capacity)

Constructs a new Hashtable using the specified capacity and the default load factor.

Parameters:

capacity - the initial capacity

Hashtable

public Hashtable(int capacity,
                 float loadFactor)

Constructs a new Hashtable using the specified capacity and load factor.

Parameters:

capacity - the initial capacity

loadFactor - the initial load factor

Hashtable

public Hashtable(Map map)

Constructs a new instance of Hashtable containing the mappings from the specified Map.

Parameters:

map - the mappings to add

Method Detail

clear

public void clear()

Removes all key/value pairs from this Hashtable, leaving the size zero and the capacity unchanged.

Specified by:

clear in interface Map

See Also:

isEmpty(), size()

clone

public Object clone()

Answers a new Hashtable with the same key/value pairs, capacity and load factor.

Overrides:

clone in class Object

Returns:

a shallow copy of this Hashtable

See Also:

Cloneable

contains

public boolean contains(Object value)

Answers if this Hashtable contains the specified object as the value of at least one of the key/value pairs.

Parameters:

value - the object to look for as a value in this Hashtable

Returns:

true if object is a value in this Hashtable, false otherwise

See Also:

containsKey(java.lang.Object), Object.equals(java.lang.Object)

containsKey

public boolean containsKey(Object key)

Answers if this Hashtable contains the specified object as a key of one of the key/value pairs.

Specified by:

containsKey in interface Map

Parameters:

key - the object to look for as a key in this Hashtable

Returns:

true if object is a key in this Hashtable, false otherwise

See Also:

contains(java.lang.Object), Object.equals(java.lang.Object)

containsValue

public boolean containsValue(Object value)

Searches this Hashtable for the specified value.

Specified by:

containsValue in interface Map

Parameters:

value - the object to search for

Returns:

true if value is a value of this Hashtable, false otherwise

elements

public Enumeration elements()

Answers an Enumeration on the values of this Hashtable. The results of the Enumeration may be affected if the contents of this Hashtable are modified.

Specified by:

elements in class Dictionary

Returns:

an Enumeration of the values of this Hashtable

See Also:

keys(), size(), Enumeration

entrySet

public Set entrySet()

Answers a Set of the mappings contained in this Hashtable. Each element in the set is a Map.Entry. The set is backed by this Hashtable so changes to one are relected by the other. The set does not support adding.

Specified by:

entrySet in interface Map

Returns:

a Set of the mappings

equals

public boolean equals(Object object)

Compares the specified object to this Hashtable and answer if they are equal. The object must be an instance of Map and contain the same key/value pairs.

Specified by:

equals in interface Map

Overrides:

equals in class Object

Parameters:

object - the object to compare with this object

Returns:

true if the specified object is equal to this Map, false otherwise

See Also:

hashCode()

get

public Object get(Object key)

Answers the value associated with the specified key in this Hashtable.

Specified by:

get in interface Map

Specified by:

get in class Dictionary

Parameters:

key - the key of the value returned

Returns:

the value associated with the specified key, null if the specified key does not exist

See Also:

put(java.lang.Object, java.lang.Object)

hashCode

public int hashCode()

Answers an integer hash code for the receiver. Objects which are equal answer the same value for this method.

Specified by:

hashCode in interface Map

Overrides:

hashCode in class Object

Returns:

the receiver's hash

See Also:

equals(java.lang.Object)

isEmpty

public boolean isEmpty()

Answers if this Hashtable has no key/value pairs, a size of zero.

Specified by:

isEmpty in interface Map

Specified by:

isEmpty in class Dictionary

Returns:

true if this Hashtable has no key/value pairs, false otherwise

See Also:

size()

keys

public Enumeration keys()

Answers an Enumeration on the keys of this Hashtable. The results of the Enumeration may be affected if the contents of this Hashtable are modified.

Specified by:

keys in class Dictionary

Returns:

an Enumeration of the keys of this Hashtable

See Also:

elements(), size(), Enumeration

keySet

public Set keySet()

Answers a Set of the keys contained in this Hashtable. The set is backed by this Hashtable so changes to one are relected by the other. The set does not support adding.

Specified by:

keySet in interface Map

Returns:

a Set of the keys

put

public Object put(Object key,
                  Object value)

Associate the specified value with the specified key in this Hashtable. If the key already exists, the old value is replaced. The key and value cannot be null.

Specified by:

put in interface Map

Specified by:

put in class Dictionary

Parameters:

key - the key to add

value - the value to add

Returns:

the old value associated with the specified key, null if the key did not exist

See Also:

elements(), get(java.lang.Object), keys(), Object.equals(java.lang.Object)

putAll

public void putAll(Map map)

Copies every mapping in the specified Map to this Hashtable.

Specified by:

putAll in interface Map

Parameters:

map - the Map to copy mappings from

rehash

protected void rehash()

Increases the capacity of this Hashtable. This method is sent when the size of this Hashtable exceeds the load factor.

remove

public Object remove(Object key)

Remove the key/value pair with the specified key from this Hashtable.

Specified by:

remove in interface Map

Specified by:

remove in class Dictionary

Parameters:

key - the key to remove

Returns:

the value associated with the specified key, null if the specified key did not exist

See Also:

get(java.lang.Object), put(java.lang.Object, java.lang.Object)

size

public int size()

Answers the number of key/value pairs in this Hashtable.

Specified by:

size in interface Map

Specified by:

size in class Dictionary

Returns:

the number of key/value pairs in this Hashtable

See Also:

elements(), keys()

toString

public String toString()

Answers the string representation of this Hashtable.

Overrides:

toString in class Object

Returns:

the string representation of this Hashtable

values

public Collection values()

Answers a Collection of the values contained in this Hashtable. The collection is backed by this Hashtable so changes to one are reflected by the other. The collection does not support adding.

Specified by:

values in interface Map

Returns:

a Collection of the values