What types of problems stem from high number of loaded classes?

Question

Currently we are in the process of testing our code for long-ish periods of time, between 4 hours and 24 hours+ non stop. The code is not interactive/user based. I first noticed that our garbage collection times were very high (about 15-25% of our total processing time). I then looked at loaded classes and there is a pretty steady rise over team of loaded classes. At the time of start up it is around 6-7k. After appproximately 4 hours its up around 25k loaded classes. Only 35 or so classes have been unloaded over this time. I'm wondering if the high number of loaded classes occurs because objects aren't fully dereferenced but then when a new object is created it reloads the class. My knowledge of class loading is fairly limited. Any help would be appreciated. Also, if you need more info let me know.
Heap Size: ~2GB
CMSPermGenSweepingEnabled
CMSClassUnloadingEnabled

Answer 1

Take a look at this example and the output:
public class Example {
      * @param args
     public static void main(String[] args) {
          StaticBlocks a = new StaticBlocks();
          StaticBlocks b = new StaticBlocks();
          a = new StaticBlocks();
class StaticBlocks {
     static {
          System.out.println("A static init block. Only happens when class is first loaded.");
          System.out.println("\tInstance init block. Happens every time a class is instantiated.");
     StaticBlocks(){
          System.out.println("\tYou instantiated a class!");
}Output:
A static init block. Only happens when class is first loaded.
     Instance init block. Happens every time a class is instantiated.
     You instantiated a class!
     Instance init block. Happens every time a class is instantiated.
     You instantiated a class!
     Instance init block. Happens every time a class is instantiated.
     You instantiated a class!I'm really not sure where to go from here... hopefully someone else that knows the JVM better can provide some insight.
Take a look at this link. It gives some details on class loading... might help you out a little.
[http://onjava.com/pub/a/onjava/2005/01/26/classloading.html?page=1|http://onjava.com/pub/a/onjava/2005/01/26/classloading.html?page=1]
Edited by: mikeyfreake on Jul 29, 2009 9:40 AM