Class - Hashtable

Hashtable

Hashtable was part of the original java.util and is a concrete implementation of a Dictionary.

Hash table stores key/value pairs in a has table. In Hash table object is used as a key, and the value is that which want linked to that key. The key is then hashed, and the resulting hash code is used as the index at which the value is stored within the table.

A Hash table can only store objects that override the hashcode(). This method must compute and return the hash code for the object. The equals() method is also override which compares two objects. These method defined by object.

Constructors:

  Hashtable()

  Hashtable(int size)

  Hashtable(int size,float fillRatio)

  Hashtable(Map m)

The first version is default constructor.

The second version creates a hash table that has an initial size specified by size.

The third version creates a hash table that has an initial size specified by size and a fill ratio specified by fillRatio.

The fourth version creates a hash table that is initialized with the

elements is m.

Method:

void clear()

  Resets and empties the hash table

boolean contains(Object value)

Returns true if some value equal to value exists within the hash table. Returns false if the value isn’t found.

boolean containsKey(Object key)

Returns true if some key equal to key exists within the hash table. Returns false if the key isn’t found.

boolean containsValue(Object value)

Returns true if some value equal to value exists within the hash table. Returns false if the value isn’t found.

Enumeration elements( )

Returns an enumeration of the values contained in the hash table.

Object get(Object key)

Returns the object that contains the value associated with key. If key is not in the hash table, a null object is returned.

boolean isEmpty( )

Returns true if the hash table is empty;returns false if it contains at least one key.

Enumeration keys( )

Returns an enumeration of the keys contained in the hash table.

object get(object key)

Returns the object that contains the value associated with key. If key is not in the hash table, a null object is returned.

object Put(object key,object value)

Inserts a key and a value into the hash table. Returns null if key isn't allready in the hash table; returns the previous value associated with key. If key is allready in the hash table.

void rehash()

Increases the size of the hash table and rehashes all of its keys.

Object remove(object key)

            Removes key and its value. returns the value associated with key. If key is not in the hash table, a null object is returned.

Posted By : Ruchita Pandya