code: public static synchronized void setDefault(Locale.Category category,
          Locale newLocale) {
          if (category == null)
              throw new NullPointerException("Category cannot be NULL");
          if (newLocale == null)
              throw new NullPointerException("Can't set default locale to NULL");
  
          /* J2ObjC removed.
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) sm.checkPermission(new PropertyPermission
                          ("user.language", "write"));*/
          switch (category) {
          case DISPLAY:
              defaultDisplayLocale = newLocale;
              break;
          case FORMAT:
              defaultFormatLocale = newLocale;
              break;
          default:
              assert false: "Unknown Category";
          }
      }
docs: Sets the default locale for the specified Category for this instance
  of the Java Virtual Machine. This does not affect the host locale.
  <p>
  If there is a security manager, its checkPermission method is called
  with a PropertyPermission("user.language", "write") permission before
  the default locale is changed.
  <p>
  The Java Virtual Machine sets the default locale during startup based
  on the host environment. It is used by many locale-sensitive methods
  if no locale is explicitly specified.
  <p>
  Since changing the default locale may affect many different areas of
  functionality, this method should only be used if the caller is
  prepared to reinitialize locale-sensitive code running within the
  same Java Virtual Machine.
  <p>
  
  @param category - the specified category to set the default locale
  @param newLocale - the new default locale
  @throws SecurityException - if a security manager exists and its
  checkPermission method doesn't allow the operation.
  @throws NullPointerException - if category and/or newLocale is null
  @see SecurityManager#checkPermission(java.security.Permission)
  @see PropertyPermission
  @see #getDefault(Locale.Category)
  @since 1.7