Hashtable in Java
Hashtable in Java
- Java Hashtable class implements a Map Interface and extends Dictionary class
- It is dual value pair collection in Java which stores <key,Value> pair in collection
The important points about Java Hashtable class are:
- A Hashtable is an array of list. Each list is known as a bucket. The position of the bucket is identified by calling the hashcode() method.
- A Hashtable contains values based on the key.
- It contains only unique elements.
- Value and key should not be NULL.
- It is synchronized. (Thread safe, can be used in multi-threading environment).
Syntax
Hashtable<Integer,String> hm=new Hashtable<Integer,String>();
Example
package Mypkg;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class MAPex {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("***********************************");
Hashtable<Integer,String> hm=new Hashtable<Integer,String>();
hm.put(100,"Besant");
hm.put(600,"Chennai");
hm.put(200,"Technology");
hm.put(103,"Bangalore");
for(Map.Entry m:hm.entrySet()){
System.out.println(m.getKey()+"-> "+m.getValue());
}
System.out.println("***********************************");
}
}
Output
*********************************
600-> Chennai
103-> Bangalore
200-> Technology
100-> Besant
***********************************
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Methods of Hashtable
| Method name | Description |
| void clear() | Removes all the key-value pairs. |
| boolean containsKey(Object key) | Returns true, if the Hashtable contains a value for the specified key. |
| boolean contains value(Object value) | Returns true, if the Hashtable maps a value for the specified key. |
| Enumeration<V> elements() | Iterates the values in the Hashtable. |
| Object get(Object key) | Returns the value to which the specified key is mapped, or null if the map contains no mapping for the key. |
| Set entrySet() | Returns a Sets which contains the key-value pairs of the map. |
| int hashCode() | Returns the hash code value for the Hashtable |
| boolean isEmpty() | Tests if this Hashtable maps no key value pairs. |
| Enumeration<K> keys() | Returns the keys mapped in the Hashtable with the type Enumeration. |
| Set<K> keySet() | Returns the keys mapped in the Hashtable as the type Set. |
| Value put(K key, V value) | Maps the specified key with the specified value in the Hashtable. |
| void rehash() | Increases the size of the Hashtable and re-maps the key values according to the new size. |
| V replace(K key, V value) | Replaces the value of the specified key with the value specified. |
| int size() | Returns the number of key-value pairs in the map. |
| Value remove(Object key) | Removes the key value pair for the specified key from the map if it is present. |
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