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Class sun.server.util.Cache 

java.lang.Object
   |
   +----java.util.Dictionary
           |
           +----sun.server.util.Cache
public class Cache
extends Dictionary
The Cache class. Maps keys to values. Any object can be used as a key and/or value. This is very similar to the Hashtable class, except that after putting an object into the Cache, it is not guaranteed that a subsequent get will return it. The Cache will automatically remove entries if memory is getting tight and if the entry is not referenced from outside the Cache.

To sucessfully store and retrieve objects from a hash table the object used as the key must implement the hashCode() and equals() methods.

This example creates a Cache of numbers. It uses the names of the numbers as keys: 

	Cache numbers = new Cache();
	numbers.put("one", new Integer(1));
	numbers.put("two", new Integer(1));
	numbers.put("three", new Integer(1));
To retrieve a number use: 
	Integer n = (Integer)numbers.get("two");
	if (n != null) {
	    System.out.println("two = " + n);
	}

See Also:
hashCode, equals, Ref

Constructor Index

o Cache()
Constructs a new, empty Cache.
o Cache(int)
Constructs a new, empty Cache with the specified initial capacity.
o Cache(int, float)
Constructs a new, empty Cache with the specified initial capacity and the specified load factor.

Method Index

o clear()
Clears the cache so that it has no more entries in it.
o elements()
Returns an enumeration of the elements.
o get(Object)
Gets the object associated with the specified key in the Cache.
o isEmpty()
Returns true if the Cache contains no elements.
o keys()
Returns an enumeration of the Cache's keys.
o put(Object, Object)
Puts the specified element into the Cache, using the specified key.
o rehash()
Rehashes the contents of the table into a bigger table.
o remove(Object)
Removes the element corresponding to the key.
o size()
Returns the number of elements contained within the Cache.

Constructors

o Cache 
 public Cache(int initialCapacity,
              float loadFactor)
Constructs a new, empty Cache with the specified initial capacity and the specified load factor.

Parameters:
initialCapacity - the initial number of buckets
loadFactor - a number between 0.0 and 1.0, it defines the threshold for rehashing the Cache into a bigger one.
Throws: IllegalArgumentException
If the initial capacity is less than or equal to zero.
Throws: IllegalArgumentException
If the load factor is less than or equal to zero.
o Cache 
 public Cache(int initialCapacity)
Constructs a new, empty Cache with the specified initial capacity.

Parameters:
initialCapacity - the initial number of buckets
o Cache 
 public Cache()
Constructs a new, empty Cache. A default capacity and load factor is used. Note that the Cache will automatically grow when it gets full.

Methods

o size 
 public int size()
Returns the number of elements contained within the Cache.

Overrides:
size in class Dictionary
o isEmpty 
 public boolean isEmpty()
Returns true if the Cache contains no elements.

Overrides:
isEmpty in class Dictionary
o keys 
 public synchronized Enumeration keys()
Returns an enumeration of the Cache's keys.

Overrides:
keys in class Dictionary
See Also:
elements, Enumeration
o elements 
 public synchronized Enumeration elements()
Returns an enumeration of the elements. Use the Enumeration methods on the returned object to fetch the elements sequentially.

Overrides:
elements in class Dictionary
See Also:
keys, Enumeration
o get 
 public synchronized Object get(Object key)
Gets the object associated with the specified key in the Cache.

Parameters:
key - the key in the hash table
Returns:
s the element for the key or null if the key is not defined in the hash table.
Overrides:
get in class Dictionary
See Also:
put
o rehash 
 protected void rehash()
Rehashes the contents of the table into a bigger table. This is method is called automatically when the Cache's size exceeds the threshold.

o put 
 public synchronized Object put(Object key,
                                Object value)
Puts the specified element into the Cache, using the specified key. The element may be retrieved by doing a get() with the same key. The key and the element cannot be null.

Parameters:
key - the specified hashtable key
value - the specified element
Returns:
the old value of the key, or null if it did not have one.
Throws: NullPointerException
If the value of the specified element is null.
Overrides:
put in class Dictionary
See Also:
get
o remove 
 public synchronized Object remove(Object key)
Removes the element corresponding to the key. Does nothing if the key is not present.

Parameters:
key - the key that needs to be removed
Returns:
the value of key, or null if the key was not found.
Overrides:
remove in class Dictionary
o clear 
 public synchronized void clear()
Clears the cache so that it has no more entries in it. 

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