void changeFocus(ISceptreFocus focus, ItemStack stack) { ISceptreFocus oldFocus = getFocus(stack); if (oldFocus != null) oldFocus.onDeactivated(stack); if (focus != null) { stack.stackTagCompound.setString("focus", focus.getFocusIdentifier()); focus.onActivated(stack); } else stack.stackTagCompound.removeTag("focus"); }