FULL PRODUCT VERSION :
java version " 1.7.0_09 "
Java(TM) SE Runtime Environment (build 1.7.0_09-b05)
Java HotSpot(TM) Client VM (build 23.5-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
If you add youself as a NotificationListener on the GarbageCollectors in the ManagementFactory, the GarbageCollectionNotificationInfo you receive contains the same information for getMemoryUsageBeforeGc and getMemoryUsageAfterGc

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
This is the default garbage collector
{Tenured Gen=init = 11206656(10944K) used = 0(0K) committed = 11206656(10944K) max = 178978816(174784K), Eden Space=init = 4521984(4416K) used = 2014904(1967K) committed = 4521984(4416K) max = 71630848(69952K), Code Cache=init = 163840(160K) used = 662976(647K) committed = 688128(672K) max = 33554432(32768K), Survivor Space=init = 524288(512K) used = 0(0K) committed = 524288(512K) max = 8912896(8704K), Perm Gen=init = 12582912(12288K) used = 1649968(1611K) committed = 12582912(12288K) max = 67108864(65536K)}
{Tenured Gen=init = 11206656(10944K) used = 278024(271K) committed = 11206656(10944K) max = 178978816(174784K), Eden Space=init = 4521984(4416K) used = 0(0K) committed = 4521984(4416K) max = 71630848(69952K), Code Cache=init = 163840(160K) used = 662976(647K) committed = 688128(672K) max = 33554432(32768K), Survivor Space=init = 524288(512K) used = 0(0K) committed = 524288(512K) max = 8912896(8704K), Perm Gen=init = 12582912(12288K) used = 1649968(1611K) committed = 12582912(12288K) max = 67108864(65536K)}

ACTUAL -
This is with the G1 garbage collector
{G1 Eden Space=init = 8388608(8192K) used = 1048576(1024K) committed = 8388608(8192K) max = -1(-1K), G1 Old Gen=init = 8388608(8192K) used = 0(0K) committed = 8388608(8192K) max = 268435456(262144K), Code Cache=init = 163840(160K) used = 661696(646K) committed = 688128(672K) max = 33554432(32768K), G1 Perm Gen=init = 12582912(12288K) used = 1649968(1611K) committed = 12582912(12288K) max = 67108864(65536K), G1 Survivor Space=init = 0(0K) used = 0(0K) committed = 0(0K) max = -1(-1K)}
{G1 Eden Space=init = 8388608(8192K) used = 2097152(2048K) committed = 8388608(8192K) max = -1(-1K), G1 Old Gen=init = 8388608(8192K) used = 0(0K) committed = 8388608(8192K) max = 268435456(262144K), Code Cache=init = 163840(160K) used = 661696(646K) committed = 688128(672K) max = 33554432(32768K), G1 Perm Gen=init = 12582912(12288K) used = 1649968(1611K) committed = 12582912(12288K) max = 67108864(65536K), G1 Survivor Space=init = 0(0K) used = 0(0K) committed = 0(0K) max = -1(-1K)}


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.lang.management.PlatformManagedObject;
import java.util.ArrayList;
import java.util.List;

import javax.management.Notification;
import javax.management.NotificationEmitter;
import javax.management.NotificationListener;
import javax.management.openmbean.CompositeData;

import com.sun.management.GarbageCollectionNotificationInfo;

/**
 *
 */
public class NotificationTest {

  public static void main(String[] args) {
    for (GarbageCollectorMXBean bean : ManagementFactory.getGarbageCollectorMXBeans()) {
      addNotificationListener(bean);
    }

    List<String> strings = new ArrayList<String>();
    
    for(int i=0;i<10000;i++) {
      System.out.println(i);
    }
    
    System.gc();
    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
    }
  }
  
  public static void addNotificationListener(PlatformManagedObject mbs) {
    if (mbs instanceof NotificationEmitter) {
      NotificationEmitter emitter = (NotificationEmitter)mbs;
      emitter.addNotificationListener(new NotificationListener() {
        @Override
        public void handleNotification(Notification notification, Object handback) {
          String notifType = notification.getType();
          if (notifType.equals(GarbageCollectionNotificationInfo.GARBAGE_COLLECTION_NOTIFICATION)) {
            // retrieve the garbage collection notification information
            GarbageCollectionNotificationInfo info = GarbageCollectionNotificationInfo.from((CompositeData)notification
                    .getUserData());
            System.out.println(info.getGcInfo().getMemoryUsageBeforeGc());
            System.out.println(info.getGcInfo().getMemoryUsageAfterGc());
          }
        }
      }, null, null);
    }
  }

}

---------- END SOURCE ----------