Inheritable instance counter variable

Question

Here's a problem that's been bugging me for a while, and i'm sure there's a simple solution to it that is just escaping me.
I'm developing a pluggable module based system, so i have my base class module with a reference counter counter += 1 in the constructor
My problem is that subclasses of this module don't inherite their own counters (as in counters of the instances of that particular module), instead they just increment the base class's counter.
public abstract class Module {
    //... other stuff
    public static long instanceCount = 0;
    /** Creates a new instance of Module */
    public Module() {
        init();
    public void uninit(){
        Module.instanceCount -= 1;
    public void init(){
        Module.instanceCount += 1;
    //... more stuff
public class TestModule extends Module {
    //... more stuff
    public TestModule() {
        MenuItem = "Test/TestModule";
        ModuleID = "TESTMODULE";
    //... more stuff
public class TestModule1 extends Module {
    //... more stuff
    public TestModule1() {
        MenuItem = "Test/TestModule1";
        ModuleID = "TESTMODULE1";
    //... more stuff
}so, say i created 4 TestModules and 2 TestModule1s
I'm trying to get something like:
Module.instanceCount will equal 6
TestModule.instanceCount == 4
TestModule1.instanceCount == 2
thanks
-Mythagel

Answer 1

Here is an idea. Use the following class to keep track of instances of specific classes:
public class InstanceCounter {
  private static final Integer ONE = new Integer(1);
  private final Map counts = new HashMap();
  public void registerInstance(Class clazz) {
    final Integer oc = (Integer)counts.get(clazz);
    counts.put(clazz, oc == null ? ONE : new Integer(oc.intValue() + 1));
  public int getInstanceCount(Class clazz) {
    final Integer oc = (Integer)counts.get(clazz);
    return oc == null ? 0 : oc.intValue();
}You can then change your Module class to this:
public class Module {
  static final InstanceCounter instanceCount = new InstanceCounter();
  public Module() {
    instanceCount.registerInstance(getClass());