How to demo Garbage Collection, JConsole and VisualVM

First, create with JDK 7 this Java Project in Eclipse:

package com.pierre.gctests;

import java.lang.management.ManagementFactory;

import javax.management.InstanceAlreadyExistsException;
import javax.management.MBeanRegistrationException;
import javax.management.MBeanServer;
import javax.management.MalformedObjectNameException;
import javax.management.NotCompliantMBeanException;
import javax.management.ObjectName;

public class GCTestMain {

 private static void init() throws MalformedObjectNameException, InstanceAlreadyExistsException, MBeanRegistrationException, NotCompliantMBeanException {
  MBeanServer mbs = null;
  mbs = ManagementFactory.getPlatformMBeanServer();
  GCTestAgent agent = new GCTestAgent();
  ObjectName agentName;
  agentName = new ObjectName("PVTests:name=GCTestAgent");
  mbs.registerMBean(agent, agentName);
 }
 
 public static void main(String[] args) throws Exception {
  init();
  for (;;) {
   Thread.sleep(1000);
  }
 }
}

package com.pierre.gctests;

public interface GCTestAgentMBean {
 void newThread(String threadName);
 void newCollectableObject(int size);
 void newLeakedObject(int size);
 void clearLeaked();
 void cpuIntensiveOperation(int iterations);
}

package com.pierre.gctests;

import java.util.ArrayList;
import java.util.Date;

public class GCTestAgent implements GCTestAgentMBean, Runnable {
 ArrayList<Object> leakingMap = new ArrayList<Object>(); 
 volatile double val = 10;

 @Override
 public void newThread(String threadName) {
  Thread newThread = new Thread(this);
  newThread.setName(threadName);
  newThread.start();
 }

 @Override
 public void newCollectableObject(int size) {
  createObject(size);
 }

 private Object createObject(int size) {
  ArrayList<String> list = new ArrayList<String>();
  for (int i = 0; i < size; i++) {
   list.add( (new Date()).toString() + " " +  i);
  }
  return list;
 }

 @Override
 public void newLeakedObject(int size) {
  leakingMap.add(createObject(size));
 }

 @Override
 public void run() {
  for (;;) {
   System.out.println(Thread.currentThread().getName());
   try {
    Thread.sleep(10000);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }
 }

 @Override
 public void clearLeaked() {
  leakingMap.clear();
 }

 @Override
 public void cpuIntensiveOperation(int iterations) {
  int[] myArrayToBeSorted = new int[] {4,2,6,7,2,1,6};
  for (int i = 0; i < iterations; i++) {
   for (int j = 0; j < myArrayToBeSorted.length - 1; j++) {
    myArrayToBeSorted[j] = myArrayToBeSorted[j] + myArrayToBeSorted[j + 1];
   }
  }
 }

}

Then, install the VisualVM GC plugin. Run the GCTestMain main, using these JVM arguments: -verbose:gc -Xms256m -Xmx256m. THen connect with JConsole and with VisualVM (I downloaded the one from the main website.... beware that there can be issues on connection when running on Windows when the username has uppercase characters (Windows sucks, don't forget).