This class implements a hashtable data structure, which maps key objects to value objects and allows the efficient lookup of the value associated with a given key. In Java 1.2 and later Hashtable has been modified to impement the Map interface. The HashMap class is typically preferred over this one, although the synchronized methods of this class are useful in multi-threaded applications. (But see java.util.concurrent.ConcurrentHashMap.) In Java 5.0 this class has been made generic along with the Map interface. The type variable K represents the type of the hashtable keys and the type variable V represents the type of the hashtable values.

put( ) associates a value with a key in a Hashtable. get( ) retrieves a value for a specified key. remove( ) deletes a key/value association. keys( ) and elements( ) return Enumeration objects that allow you to iterate through the complete set of keys and values stored in the table. Objects used as keys in a Hashtable must have valid equals( ) and hashCode( ) methods (the versions inherited from Object are okay). null is not legal as a key or value in a Hashtable.

Figure 16-26. java.util.Hashtable<K,V>

public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, 
        Cloneable, Serializable {
// Public Constructors
     public Hashtable( );  
1.2  public Hashtable(Map<? extends K,? extends V> t);  
     public Hashtable(int initialCapacity);  
     public Hashtable(int initialCapacity, float loadFactor);  
// Public Instance Methods
     public void clear( );         Implements:Map synchronized
     public boolean contains(Object value);         synchronized
     public boolean containsKey(Object key);        Implements:Map synchronized
     public V get(Object key);   Implements:Map synchronized
     public boolean isEmpty( );    Implements:Map synchronized default:true
     public V put(K key, V value);                  Implements:Map synchronized
     public V remove(Object key);                   Implements:Map synchronized
     public int size( );           Implements:Map synchronized
// Methods Implementing Map
     public void clear( );                           synchronized
     public boolean containsKey(Object key);                  synchronized
1.2  public boolean containsValue(Object value);  
1.2  public Set<Map.Entry<K,V>> entrySet( );  
1.2  public boolean equals(Object o);                         synchronized
     public V get(Object key);                           synchronized
1.2  public int hashCode( );                           synchronized
     public boolean isEmpty( );                      synchronized default:true
1.2  public Set<K> keySet( );  
     public V put(K key, V value);                       synchronized
1.2  public void putAll(Map<? extends K,? extends V> t);     synchronized
     public V remove(Object key);                        synchronized
     public int size( );                                   synchronized
1.2  public Collection<V> values( );  
// Public Methods Overriding Dictionary
     public Enumeration<V> elements( );                     synchronized
     public Enumeration<K> keys( );                         synchronized
// Public Methods Overriding Object
     public Object clone( );                               synchronized
     public String toString( );                            synchronized
// Protected Instance Methods
     protected void rehash( );  
}

Subclasses

Properties