#Java hashtab code

Returns the hash code value for this Map as per the definition in the Returns the value to which the specified key is mapped in this hashtable. Returns a Set view of the entries contained in this Hashtable.Ĭompares the specified Object with this Map for equality,

Returns an enumeration of the values in this hashtable. Returns true if this Hashtable maps one or more keys to this value. Tests if the specified object is a key in this hashtable. Tests if some key maps into the specified value in this hashtable. See also: equals(), hashCode(), rehash(), Collection, Map, HashMap, TreeMapĬonstructs a new, empty hashtable with a default capacity and loadĬonstructs a new hashtable with the same mappings as the givenĬonstructs a new, empty hashtable with the specified initial capacityĬonstructs a new, empty hashtable with the specified initialĬlears this hashtable so that it contains no keys The Enumerations returned by Hashtable's keys and values methods are Modification, the Iterator fails quickly and cleanly, rather than riskingĪrbitrary, non-deterministic behavior at an undetermined time in the future. Iterator's own remove or add methods, the Iterator will throw aĬoncurrentModificationException. Of the Collections returned by all of Hashtable's 'collection view methods'Īre fail-fast: if the Hashtable is structurally modifiedĪt any time after the Iterator is created, in any way except through the The Iterators returned by the iterator and listIterator methods The new collection implementations, Vector is synchronized. So that it becomes a part of Java's collection framework. To retrieve a number, use the following code:Īs of JDK1.2, this class has been retrofitted to implement Map, This example creates a hashtable of numbers. If many entries are to be made into a Hashtable,Ĭreating it with a sufficiently large capacity may allow theĮntries to be inserted more efficiently than letting it performĪutomatic rehashing as needed to grow the table. Memory more efficiently, at the expense of larger expected time Load factor and the current capacity, the capacity is increased byĬalling the rehash method. The number of entries in the hashtable exceeds the product of the The load factor should be between 0.0 and 1.0. Objects used as keys must implement the hashCodeĪn instance of Hashtable has two parameters thatĪffect its efficiency: its capacity and its loadįactor. To successfully store and retrieve objects from a hashtable, the Non- null object can be used as a key or as a value. This class implements a hashtable, which maps keys to values. In Java, the Hashtable responds to a collision by placing multiple values into the same bucket (other implementations may handle collisions differently).Implements Map, Cloneable, java.io.Serializable Sometimes, however, multiple objects may map to the same bucket, an event known as a collision.

The hashcode only tells the Hashtable into which bucket to drop the key/value. (This is a simplistic example the Hashtable will massage the hashcode first so the Hashtable doesn't try to insert the value outside the bucket.)īy using the hashcode this way, the Hashtable can also quickly determine in which bucket it has placed the value when you try to retrieve it. Likewise, if the hashcode is two, the Hashtable places the value into Bucket 2. So, for example, if the hashcode equals zero, the Hashtable places the value into Bucket 0. The Hashtable uses that code to determine the bucket in which to place the key/value. When you pass a key/value to the Hashtable, it queries the key's hashcode. The Hashtable uses the key's hashcode to determine to which bucket the key/value pair should map. A Hashtable internally contains buckets in which it stores the key/value pairs.