General Java Questions III

You could add a delete() method if you don t need the instance anymore:

public class Single{

   private static Single single;

   private Single {}

   public static Single getInstance(){

      if(single==null)

          single = new Single();

      return single;

    }

   public static delete(){

      single = null;

   }

}

The garbage collector can now remove the single object after delete() is called if

memory is needed.

Rijk Jan van Haaften

Dept of Computer Science, Utrecht University, The Netherlands

P.S by John: 

Doing more deeper investigation of this question I found one very good article about

this topic. Everybody who are interested can read full article here:

http://developer.java.sun.com/developer/technicalArticles/Programming/singletons/ 

For the rest of our audience shortly:

A Singleton class can be garbage collected and when 

".. a Singleton class is garbage collected and then reloaded, a new Singleton

instance is created. Any class can be garbage collected when no other object holds

reference to the class or its instances. If no object holds a reference to the  

Singleton object, then the Singleton class may disappear, later to be reloaded when

the Singleton is again needed. In that case, a new Singleton object will be created.

Any static or instance 

fields saved for the object will be lost and reinitialized. 

This problems exists in older JavaTM Virtual Machines1. JDK 1.2 VMs, in particular,

conform to a newer class garbage collection model that forbids any class in a given

classloader to be collected until all are unreferenced"

And you "... can also set your VM to have no class garbage collection ( Xnoclassgc

on the JRE 1.3, or  noclassgc on the IBM JVM). Keep in mind that if you have a

long running program that frequently reloads classes (perhaps through special class 

loaders such as the remote class loaders), you have to consider whether that could

cause a problematic buildup of garbage classes in the VM."

Also some people asked what is a Singleton and what is relation has it to Java.

Shortly a Singleton is one of classical design patterns that are used in software

development. More please read in free book here: 

http://www.patterndepot.com/put/8/JavaPatterns.htm

 Q: I study patterns now and would be lost and forget everything very soon! Help!

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