«

To retrieve your entry, you have to use as key an object that equals the
original key.
Two answers :
1 - I think that what you are triying to build is already there. It is a
WeakHashMap in jsdk 1.2 and later. (Source code is available)
------------------------------------
A hashtable-based Map implementation with weak keys. An entry in a
WeakHashMap will automatically be removed when its key is no longer in
ordinary use. More precisely, the presence of a mapping for a given key will
not prevent the key from being discarded by the garbage collector, that is,
made finalizable, finalized, and then reclaimed. When a key has been
discarded its entry is effectively removed from the map, so this class
behaves somewhat differently than other Map implementations
------------------------------------

2 - if you persist, you should derive WeakReference to overload equals()
and hash() for your key object. When you use a key (say getkey) ou will get
the right object it if for this entry (entrykey), getkey.hash() ==
entrykey.hash() and (getkey == entrykey || getkey.equals(entrykey)).

"Jacob" <> a écrit dans le message de
news:...
> I have a caching system keepeing properties for
> objects in a HashMap. The objects may go away and
> I dont want the cache to block garbage collection.
>
> A natural choice whould be to use WeakReference as
> keys:
>
> HashMap map = new HashMap();
> String key = "KEY";
> map.put (new WeakReference (key), "VALUE");
>
> But neither of these approaches will return me
> the value:
>
> h.get ("KEY"); // returns null
> h.get (new WeakReference ("KEY")); // returns null
>
> Any ideas?
>
> Thanks!
>

I have a caching system keepeing properties for
objects in a HashMap. The objects may go away and
I dont want the cache to block garbage collection.

A natural choice whould be to use WeakReference as
keys:

HashMap map = new HashMap();
String key = "KEY";
map.put (new WeakReference (key), "VALUE");

But neither of these approaches will return me
the value:

h.get ("KEY"); // returns null
h.get (new WeakReference ("KEY")); // returns null

Any ideas?

Thanks!

Jacob wrote:

> I have a caching system keepeing properties for
> objects in a HashMap. The objects may go away and
> I dont want the cache to block garbage collection.
>
> A natural choice whould be to use WeakReference as
> keys:
>
> HashMap map = new HashMap();
> String key = "KEY";
> map.put (new WeakReference (key), "VALUE");
>
> But neither of these approaches will return me
> the value:
>
> h.get ("KEY"); // returns null
> h.get (new WeakReference ("KEY")); // returns null
>
> Any ideas?
>
> Thanks!

Use the WeakHashMap that comes with the JDK:

http://java.sun.com/j2se/1.4.2/docs/...akHashMap.html

--
Kind regards,
Christophe Vanfleteren

"Jacob" <> wrote in message
news:...
> I have a caching system keepeing properties for
> objects in a HashMap. The objects may go away and
> I dont want the cache to block garbage collection.
>
> A natural choice whould be to use WeakReference as
> keys:
>
> HashMap map = new HashMap();
> String key = "KEY";
> map.put (new WeakReference (key), "VALUE");
>
> But neither of these approaches will return me
> the value:
>
> h.get ("KEY"); // returns null
> h.get (new WeakReference ("KEY")); // returns null

If it's for a memory sensitive cache, ie you want the cache to hold objects
while they have references elsewhere, but once the other strong references
have been cleared you want the cache objects to be eligable for GC if memory
becomes an issue, then you should use a SoftReference for the value.

Object obj = new Object();//object to be cached
String key = "KEY";
map.put(key, new SoftReference(obj));

SoftReference ref = (SoftReference) map.get(key);
obj = ref.get();

!tested
!compiled

If you want to use weak references for the keys, then the objects will be
discarded once the keys are no longer in use elsewhere, which isn't much use
for a cache. This is what you've described above, and you can use
java.util.WeakHashMap to do exactly what you were trying to do with your
code.

Christophe Vanfleteren wrote:

> Use the WeakHashMap that comes with the JDK:

Thanks Christophe.

WeakHashMap is it.

Jacob wrote:
> A natural choice whould be to use WeakReference as
> keys:
>
> HashMap map = new HashMap();
> String key = "KEY";
> map.put (new WeakReference (key), "VALUE");
>
> But neither of these approaches will return me
> the value:
>
> h.get ("KEY"); // returns null
> h.get (new WeakReference ("KEY")); // returns null
>
> Any ideas?

Use java.util.WeakHashMap. In fact, this is one of the rare cases where
you actually *want* to use WeakHashMap. Most people who try to use the
class are misunderstanding its functionality. (Specifically, note that
is uses weak keys rather than weak values, which meets your needs just
fine but is counterintuitive to most everyone else.)

--
www.designacourse.com
The Easiest Way to Train Anyone... Anywhere.

Chris Smith - Lead Software Developer/Technical Trainer
MindIQ Corporation