import java.util.*; interface LibraryVisitor { (1) : (2) : void printSum(); } class LibrarySumPrintVisitor implements LibraryVisitor { //打印总页数 private int sum = 0; public void visit(Book p_book) { sum = sum + p_book.getNumberOfPages(); public void visit(Article p_article) { sum = sum + p_article.getNumberOfPages0; } public void printSum(){ System.out.println("SUM = " + sum); } } interface LibraryItemInterface { (3) ; } class Article implements LibraryItemInterface{ private String m_title; //价仑文名 。 private String m_author; //仑文作者 private int m_start_page; private int m_end_page; public Article(String p_author, String p_title,int p_start_page,int p_end_page){ m_title=p_title; m_author= p_author; m_end_page=p_end_page; } public int getNumbelOfPages(){ rctum m_end_page - m_start_page; } public void acccpt(LibraryVisitor Visitor){ (4) : } } class Book implements LibraryItemInterface{ private String m_title; //书名 private String m_author; //书作者 private int m_pages; //页教 public Book(String p_author, String p_title,int p_ pages){ m_title= p_title; m_author= p_author; m_pages= p_pages; } public int getNumberOfPages(){ return m_pages; } public void accept(LibraryVisitor visitor){ (5)___; } }