Class java.util.Hashtable

java.lang.Object
   |
   +----java.util.Dictionary
           |
           +----java.util.Hashtable



  
 public class Hashtable
  
 extends Dictionary
  
 implements Cloneable, Serializable

This class implements a hashtable, which maps keys to values. Any 
 non-null object can be used as a key or as a value. 
 

 To successfully store and retrieve objects from a hashtable, the 
 objects used as keys must implement the hashCode 
 method and the equals method. 
 

 An instance of Hashtable has two parameters that 
 affect its efficiency: its capacity and its load 
 factor. The load factor should be between 0.0 and 1.0. When 
 the number of entries in the hashtable exceeds the product of the 
 load factor and the current capacity, the capacity is increased by 
 calling the rehash method. Larger load factors use 
 memory more efficiently, at the expense of larger expected time 
 per lookup. 
 

 If many entries are to be made into a Hashtable, 
 creating it with a sufficiently large capacity may allow the 
 entries to be inserted more efficiently than letting it perform 
 automatic rehashing as needed to grow the table. 
 

 This example creates a hashtable of numbers. It uses the names of 
 the numbers as keys: 
 
     Hashtable numbers = new Hashtable();
     numbers.put("one", new Integer(1));
     numbers.put("two", new Integer(2));
     numbers.put("three", new Integer(3));
 
 

 To retrieve a number, use the following code: 
 
     Integer n = (Integer)numbers.get("two");
     if (n != null) {
         System.out.println("two = " + n);
     }
 




  Constructor Index


  
 Hashtable()
  
  Constructs a new, empty hashtable with a default capacity and load
 factor.
  
 Hashtable(int)
  
  Constructs a new, empty hashtable with the specified initial capacity
 and default load factor.
  
 Hashtable(int, float)
  
  Constructs a new, empty hashtable with the specified initial 
 capacity and the specified load factor.


  Method Index


  
 clear()
  
  Clears this hashtable so that it contains no keys.
  
 clone()
  
  Creates a shallow copy of this hashtable.
  
 contains(Object)
  
  Tests if some key maps into the specified value in this hashtable.
  
 containsKey(Object)
  
  Tests if the specified object is a key in this hashtable.
  
 elements()
  
  Returns an enumeration of the values in this hashtable.
  
 get(Object)
  
  Returns the value to which the specified key is mapped in this hashtable.
  
 isEmpty()
  
  Tests if this hashtable maps no keys to values.
  
 keys()
  
  Returns an enumeration of the keys in this hashtable.
  
 put(Object, Object)
  
  Maps the specified key to the specified 
 value in this hashtable.
  
 rehash()
  
  Rehashes the contents of the hashtable into a hashtable with a 
 larger capacity.
  
 remove(Object)
  
  Removes the key (and its corresponding value) from this 
 hashtable.
  
 size()
  
  Returns the number of keys in this hashtable.
  
 toString()
  
  Returns a rather long string representation of this hashtable.

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