/** * The interface Appender,just as the 'Observe' interface in the observer pattern. */package cn.edu.nju.software.sd.cll; public interface Appender {/** * setLayout ,which will  be realized next. * @param layout */    public void setLayout(Layout layout)  ; /** * update,which likes the update method in the observer pattern. */    public void update(Logger logger,String message);}