diff -r 0ed0960af27d agent/src/share/classes/sun/jvm/hotspot/oops/ObjectHistogram.java
--- a/agent/src/share/classes/sun/jvm/hotspot/oops/ObjectHistogram.java	Thu Feb 23 12:03:08 2012 -0800
+++ b/agent/src/share/classes/sun/jvm/hotspot/oops/ObjectHistogram.java	Wed Mar 14 14:03:02 2012 +0900
@@ -72,7 +72,7 @@
       num++;
       totalCount+=el.getCount();
       totalSize+=el.getSize();
-      tty.print(num + ":" + "\t\t");
+      tty.print(num + ":" + "\t"+ Long.toHexString(el.getId()) + "\t");
       el.printOn(tty);
     }
     tty.println("Total : " + "\t" + totalCount + "\t" + totalSize);
diff -r 0ed0960af27d agent/src/share/classes/sun/jvm/hotspot/oops/ObjectHistogramElement.java
--- a/agent/src/share/classes/sun/jvm/hotspot/oops/ObjectHistogramElement.java	Thu Feb 23 12:03:08 2012 -0800
+++ b/agent/src/share/classes/sun/jvm/hotspot/oops/ObjectHistogramElement.java	Wed Mar 14 14:03:02 2012 +0900
@@ -55,6 +55,11 @@
     return klass;
   }
 
+  /** Identifier of klass */
+  public long getId() {
+     return klass.hashCode();
+  }
+  
   /** Number of instances of klass */
   public long getCount() {
     return count;
@@ -110,7 +115,7 @@
   public static void titleOn(PrintStream tty) {
     tty.println("Object Histogram:");
     tty.println();
-    tty.println("num " + "\t" + "  #instances" + "\t" + "#bytes" + "\t" + "Class description");
+    tty.println("num " + "\t" + "hash code" + "\t" + "  #instances" + "\t" + "#bytes" + "\t" + "Class description");
     tty.println("--------------------------------------------------------------------------");
   }