gistfile1.java

import java.lang.reflect.*;
import sun.misc.Unsafe;

public class Print {

   static Unsafe u = getUnsafe();

   public static void main(String... args) {
      try {
         long addr = u.staticFieldOffset(System.class.getDeclaredField("err")) +4;
         System.out.println("Java says sm is " + System.getSecurityManager());
         System.out.println("we say it is: " + (SecurityManager) u.getObject(System.class, addr));

         System.out.println("creating new sm in the normal way");
         System.setSecurityManager(new SecurityManager());
         System.out.println("Java says sm is " + System.getSecurityManager());
         System.out.println("we say it is: " + (SecurityManager) u.getObject(System.class, addr));

         System.out.println("Setting sm to null manually");
         u.putObject(System.class, addr, null);

         System.out.println("Java says sm is " + System.getSecurityManager());
         System.out.println("we say it is: " + (SecurityManager) u.getObject(System.class, addr));

      } catch (Exception e) {
         System.out.println(e);
      }
   }

   public static Unsafe getUnsafe() {
      try {
         Field f = Unsafe.class.getDeclaredField("theUnsafe");
         f.setAccessible(true);
         return (Unsafe) f.get(null);
      } catch (Exception e) {
         throw new RuntimeException("", e);
      }
   }

   public static long addressOf(Object o) throws Exception {
      Object[] array = new Object[] { o };

      long baseOffset = u.arrayBaseOffset(Object[].class);
      int addressSize = u.addressSize();
      long objectAddress;
      switch (addressSize) {
      case 4:
         objectAddress = u.getInt(array, baseOffset);
         break;
      case 8:
         objectAddress = u.getLong(array, baseOffset);
         break;
      default:
         throw new Error("unsupported address size: " + addressSize);
      }

      return (objectAddress);
   }
}