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java.lang.Object
 java.util.Dictionary<K,V>
java.util.Hashtable<K,V>
- All Implemented Interfaces:
- Serializable, Cloneable, Map<K,V>
- Direct Known Subclasses:
- Properties, UIDefaults
- See Also:
- Top Examples, Source Code,
Object.equals(java.lang.Object),
Object.hashCode(),
rehash(),
Collection,
HashMap,
TreeMap
public void clear() - See Also:
- V, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
[634]Create object pool
By Anonymous on 2004/02/03 10:41:35 Rate
//Create object pool
import java.util.*;
public class Pool
{
private static Pool instance = null;
private int capacity;
private Hashtable locked, unlocked;
private Pool ( )
{
capacity = 10;
locked = new Hashtable ( ) ;
unlocked = new Hashtable ( ) ;
}
public synchronized Pool getInstance ( ) {
if ( instance == null ) {
instance = new Pool ( ) ;
}
return instance;
}
public synchronized Object checkOut ( )
{
Object o;
if ( unlocked.size ( ) > 0 )
{
Enumeration e = unlocked.keys ( ) ;
return unlocked.get ( e.nextElement ( ) ) ;
}
if ( capacity < locked.size ( ) + unlocked.size ( ) )
{
o = new Object ( ) ;
locked.put ( o, new Long (
System.currentTimeMillis ( ) ) ) ;
return ( o ) ;
} else {
//Handle error condition
}
}
public synchronized void checkIn ( Object o )
{
locked.remove ( o ) ;
unlocked.put ( o, new Long (
System.currentTimeMillis ( ) ) ) ;
}
}
//clear[1144]Understand the operation of hashtable completely
By mk_rauf { at } yahoo { dot } com on 2005/09/15 01:06:23 Rate
//IF USE READ THIS CODE U WILL UNDERSTAND THE OPERATION OF HASHTABLE COMPLETELY
import java.util.*;
public class UseHashTable {
public static void main ( String [ ] args ) {
//How to use HashTable
//Begin
String aa= "INDIA";
String bb="three";
Hashtable hashtable = new Hashtable ( ) ;
//To add Key and Value for Hashtable
hashtable.put ( "one",new Integer ( 1 ) ) ;
//hashtable.put ( "two",null ) ;
//HashTable will Not Take NULL values, where as we can add NULL values to HashMap
//HashTable is synchronized where as HashMap is Unsynchronized
hashtable.put ( bb,"THREE" ) ;
hashtable.put ( "four",aa ) ;
//To see the size and to check whether Hashtable is empty or not
System.out.println ( "The size of hashtable = "+hashtable.size ( ) ) ;
System.out.println ( "If hashtable empty = "+hashtable.isEmpty ( ) ) ;
//The elements of hashtable are ( by using iterator )
System.out.println ( "The elements of hashtable are ( by using iterator ) " ) ;
Set set= hashtable.keySet ( ) ;
Iterator iter = set.iterator ( ) ;
int i=1;
while ( iter.hasNext ( ) ) {
System.out.println ( " "+i+" ) "+hashtable.get ( iter.next ( ) ) ) ;
i++;
}
//The elements of hashtable are ( by using Enumeration )
System.out.println ( "The elements of hashtable are ( by using Enumeration ) " ) ;
Enumeration enum = hashtable.keys ( ) ;
i=1;
while ( enum.hasMoreElements ( ) )
{
String values = ( String ) enum.nextElement ( ) ;
System.out.println ( " "+i+" ) key ="+values+", value ="+hashtable.get ( values ) ) ;
i++;
}
// Checks whether this key/value is present in the hashtable or not
System.out.println ( "Contains this \"one\" Key ="+hashtable.containsKey ( "one" ) ) ;
System.out.println ( "Contains this \"five\" Key ="+hashtable.containsKey ( "five" ) ) ;
System.out.println ( "Contains this \"aa\" Value ="+hashtable.containsValue ( aa ) ) ;
System.out.println ( "Contains this \"new Integer ( 6 ) \" Value ="+hashtable.containsValue ( new Integer ( 6 ) ) ) ;
//The value for the key specified
System.out.println ( "The value for the \"three\" key ="+hashtable.get ( "three" ) ) ;
//Remove the value for the sepcified key
hashtable.remove ( bb ) ;
System.out.println ( "The size of HashMap has reduced by one" ) ;
System.out.println ( "The size of HashMap = "+hashtable.size ( ) ) ;
System.out.println ( "The values of HashMap are ="+hashtable.values ( ) ) ;
//The HashCode for this HashTable
System.out.println ( "The HashCode for this HashTable ="+hashtable.hashCode ( ) ) ;
//Remove all the elements from the hashtable
hashtable.clear ( ) ;
System.out.println ( "If hashmap empty = "+hashtable.isEmpty ( ) ) ;
//End of HashTable
}
}
public Object clone() - See Also:
Cloneable
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
[635]Simple cache
By Anonymous on 2004/04/21 06:02:31 Rate
//simple cache
import java.util.*;
public class Cache
{
private static Cache instance = null;
private Hashtable cache;
private Cache ( )
{
cache = new Hashtable ( ) ;
}
public synchronized Cache getInstance ( ) {
if ( instance == null ) {
instance = new Cache ( ) ;
}
return instance;
}
public synchronized void addObject ( Object key, Object value )
{
cache.put ( key, value ) ;
}
public Object getObject ( Object key )
{
return cache.get ( key ) ;
}
public void expire ( )
{
cache.clear ( ) ;
}
public synchronized void expire ( Object key )
{
cache.remove ( key ) ;
}
}
//clone
public boolean contains(Object value) - See Also:
Map, containsValue(Object), containsKey(Object), NullPointerException
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public boolean containsKey(Object key) - See Also:
contains(Object), NullPointerException, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public boolean containsValue(Object value) - See Also:
Map, NullPointerException, V
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Enumeration<V> elements() - See Also:
Map, values(), keys(), Dictionary
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Set<Map.Entry<K,V>> entrySet() - See Also:
- Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public boolean equals(Object o) - See Also:
- V, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public V get(Object key) - See Also:
put(Object, Object), NullPointerException, Dictionary, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public int hashCode() - See Also:
- Object, V, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Hashtable() - Geek's Notes:
- Description Add your codes or notes Search More Java Examples
[1546]New ways to synchronize hashmap
By Anonymous on 2005/09/25 18:26:44 Rate
//You should use ConcurrentHashMap in 1.5, no more Hashtable
Map myMap = new ConcurrentHashMap ( ) ;[1571]_
By Anonymous on 2005/10/14 16:51:09 Rate
you can also use
Collections.synchronizedMap
public Hashtable(int initialCapacity) - See Also:
- IllegalArgumentException
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
[1675]Difference between HashMap and Hashtable
By Anonymous on 2005/11/04 20:23:08 Rate
The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. ( HashMap allows null values as key and value whereas Hashtable doesnt allow ) . HashMap does not guarantee that the order of the map will remain constant over time. HashMap is non-synchronized and Hashtable is synchronized.
public Hashtable(int initialCapacity,
float loadFactor)- See Also:
- IllegalArgumentException
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Hashtable(Map<? extends K,? extends V> t) - See Also:
- NullPointerException
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public boolean isEmpty() - See Also:
- V, Dictionary, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Enumeration<K> keys() - See Also:
Map, keySet(), elements(), Dictionary
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Set<K> keySet() - See Also:
- Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Object put(Object key,
Object value)- See Also:
get(Object), Object.equals(Object), NullPointerException, Dictionary, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
[550]Sort Hashtable
By Ashok Das on 2003/12/01 07:38:06 Rate
import java.util.Hashtable;
import java.util.Vector;
import java.util.Collections;
import java.util.Enumeration;
public class SortHashtable {
public static void main ( String [ ] args ) {
// Create and populate hashtable
Hashtable ht = new Hashtable ( ) ;
ht.put ( "ABC", "abc" ) ;
ht.put ( "XYZ", "xyz" ) ;
ht.put ( "MNO", "mno" ) ;
// Sort hashtable.
Vector v = new Vector ( ht.keySet ( ) ) ;
Collections.sort ( v ) ;
// Display ( sorted ) hashtable.
for ( Enumeration e = v.elements ( ) ; e.hasMoreElements ( ) ; ) {
String key = ( String ) e.nextElement ( ) ;
String val = ( String ) ht.get ( key ) ;
System.out.println ( "Key: " + key + " Val: " + val ) ;
}
}
}
public V put(K key,
V value)- See Also:
get(Object), Object.equals(Object), NullPointerException, Dictionary, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public void putAll(Map<? extends K,? extends V> t) - See Also:
- NullPointerException
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
protected void rehash() - Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public V remove(Object key) - See Also:
- NullPointerException, Dictionary, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public int size() - See Also:
- V, Dictionary, Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public String toString() - See Also:
- Object
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
public Collection<V> values() - See Also:
- Map
- Geek's Notes:
- Description Add your codes or notes Search More Java Examples
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