Light memory singleton object.

Question

Let's say you wanna build singleton but you want it to be kept in memory as long as someone is using it. This is possible if the instance static object is maintained via Soft or Weak reference. Here is how it is done:
class MySingleton
  private static Object objLock = new Object();
  private static WeakReference instance = null;
   * Gets the instance of this class.
   * @return MySingleton
  public static MySingleton getInstance()
    synchronized (objLock)
      if (instance == null || instance.get() == null)
        instance = new WeakReference(new MySingleton());
    return (MySingleton)instance.get();
}

Answer 1

Once you create the instance of the Sibgleton the GC
CANNOT clear it because of the static refernec to it.
If you don't know that fact first read more. I do understand what you want to do. I have been programming in Java for 10 years and have never heard about a person who has needed what you are trying to do, and I don't think that it is a good idea.
I can of course be 100% wrong on this since there are many different environments.
With the
weak or soft reference the GC can clear it anytime it
goes or needs memory (depending whether is weak or
soft). I know what weak a soft references do, but I don't understand why you want to use them. Your singleton will not be a singleton since instances will be created and destroyed. Creating your "heavy" object many times is worse than creating it one time.
That's the usefulness. It isn't useful. It's a singleton which isn't a singleton, and it's only good for read only data.
Let's say you have a
module that operates with huge objects and that
module is singleton. Once the application gets the
singleton it's created and never destroyed until the
app goes away. This way you ensure that this memory
is released after you don't use the singleton. Haven't you considered that you might create that huge object many many times with your design?
Kaj