【问题标题】:Java static array modificationsJava 静态数组修改
【发布时间】:2012-10-19 00:42:12
【问题描述】:

我有以下两个 java 类(如下所列) Class BookInfo 声明了静态数组块

         public class BookInfo {

        // Global arrays accessible by all methods

        private static String[] isbnInfo;
        private static String[] bookTitleInfo;
        private static String[] authorInfo;
        private static String[] publisherInfo;
        private static String[] dateAddedInfo;;
        private static int[] qtyOnHandInfo;
        private static double[] wholesaleInfo;
        private static double[] retailInfo;

        static {

            isbnInfo = new String[] {

                                    "978-0060014018",
                                    "978-0449221431",
                                    "978-0545132060",
                                    "978-0312474881",
                                    "978-0547745527"

                                    };

            bookTitleInfo = new String[] {

                                    "The Greatest Stories",
                                    "The Novel",
                                    "Smile",
                                    "The Bedford Introduction to Drama",
                                    "AWOL on the Appalachian Trail"

                                    };

            authorInfo = new String[]  {

                                     "Rick Beyer",
                                     "James A. Michener",
                                     "Raina Telgemeier",
                                     "Lee A. Jacobus",
                                     "David Miller"

                                    };

            publisherInfo = new String[] {

                                    "HerperResource",
                                    "Fawcett",
                                    "Graphix",
                                    "Bedford St. Martins",
                                    "Mariner Books"

                                    };

            dateAddedInfo = new String[] {

                "05/18/2003", 
                "07/07/1992", 
                "02/01/2010", 
                "09/05/2008", 
                "11/01/2011"

                };

            qtyOnHandInfo = new int[] {7, 5, 10, 2, 8};

            wholesaleInfo = new double[] {12.91, 7.99, 6.09, 54.99, 10.17};

            retailInfo = new double[] {18.99, 3.84, 4.90, 88.30, 14.95};

        }

        public static void BookInfo() {

            System.out.println("             Serendipity Booksellers");
            System.out.println("                Book Information\n");       


            for(int i = 0; i < isbnInfo.length; i++){

                System.out.println("ISBN: " + isbnInfo[i]);
                System.out.println("Title: " + bookTitleInfo[i]);
                System.out.println("Author: " + authorInfo[i]);
                System.out.println("Publisher: " + publisherInfo[i]);
                System.out.println("Date Added: " + dateAddedInfo[i]);
                System.out.println("Quantity-On-Hand: " + qtyOnHandInfo[i]);
                System.out.println("Wholesale Cost: $ " + wholesaleInfo[i]);
                System.out.println("Retail Price: $ " + retailInfo[i]);
                System.out.println();

            }
        }
        }

如何从这个类访问数组列表?到目前为止,只有以下内容有效,但我如何从这个类中修改(添加、删除、编辑等)(这个类中没有主要的主要内容) BookInfo bookinfo = new BookInfo(); bookinfo.BookInfo(); System.out.println(bookinfo.isbnInfo[0]);如何从主菜单修改(添加、删除、编辑等)

     import java.util.Scanner;

     public class InvMenu {
     public static void addBook(){

      System.out.println("\nYou selected Add a Book\n");
       BookInfo bookinfo = new BookInfo();
      bookinfo.BookInfo(); // only these two are working but I cannot modify arrays at all
      System.out.println(bookinfo.isbnInfo[0]);

        }

       public static void editBook(){

     System.out.println("\nYou selected Edit a Book's Record\n"); 

     }

     public static void deleteBook(){

      System.out.println("\nYou selected Delete a Book\n");

    }

    public static void printInvMenu(){

    String choice;
    int x = 0;
    boolean b;
    char letter;
    boolean menu = true;

    Scanner keyboard = new Scanner(System.in);

    System.out.println("Serendipity Booksellers");
    System.out.println("Inventory Database\n");
    System.out.println("       1. Look Up a Book");
    System.out.println("       2. Add a Book");
    System.out.println("       3. Edit a Book's Record");
    System.out.println("       4. Delete a Book");
    System.out.println("       5. Return to the Main Menu\n");

    do{

        System.out.print("Enter your choice: ");
        choice = keyboard.nextLine();
        b = true;

        try {
            x = Integer.parseInt(choice);
            System.out.println(x);

        }

        catch(NumberFormatException nFE) {

            b = false;
            System.out.println("You did not enter a valid choice. Try again!\n");

        }

           }while(b == false);

        do{

        else if(x == 1){

            addBook();

        }

        else if(x == 2){

            editBook();

        }

        else if(x == 3){

            deleteBook();

        }

        else if(x == 4){

            System.out.println("Returning to the Main Menu\n");
            break;

        }

        else{

            System.out.println("\nYou did not enter a valid choice. Try again!\n");

        }

        printInvMenu();

       }while(x == 5);

          }
         }

我可以从其他类主菜单轻松访问一些功能:BookInfo bookinfo = new BookInfo(); bookinfo.BookInfo(); System.out.println(bookinfo.isbnInfo[0]);如何从主菜单修改(添加、删除、编辑等)?任何想法,建议都非常感谢!

【问题讨论】:

  • 我看到您在 Stack Overflow 上也有一个帐户...您是不是不小心在这里发布了这个?
  • 您尝试过 BookInfo.isbnInfo[0] = "new value" 吗?这应该工作

标签: java static arrays project


【解决方案1】:

我认为您需要重新考虑一下您的设计。我提供了一个示例,说明如何使某些功能与您当前的代码一起使用,但这样做会产生一些非常讨厌的代码。

静态信息通常用于在实例之间共享信息,这些信息是唯一的。通常的例子是作为实例计数器。因此,每次创建实例时,它都会增加值,以便您可以跟踪唯一实例。

问题在于 bookInfo 不知道它的含义。它想成为一个数据存储,但也描述一个独特的对象。想想如果你想创建另一个 BookInfo 会发生什么。编辑一个实例的任何静态都会影响其他实例。

您可以轻松编辑静态 String[] 中的信息。

public int getBookLocation(String name){
    return bookTitleInfo.IndexOf(name)
}

然后您可以随意操作特定条目。

public void SetBookName(String oldname, String newname){
    int index = getBookLocation(oldname);
    if(index > 0){
        bookTitleInfo[index] = newname;
}

这对编辑来说还不错,但删除条目会很麻烦。这是一些伪代码

first have to find the bookindes. - getBookLocation(...)

For each entry in static string[]
    create a new one of size-1, 
        For each entry in String[]
            add existing entry to new string[].

您需要为每个数组执行此操作。即 isbnInfo, bookInfoName, ...., 这是很多不必要的迭代。


虽然不能解决您的问题,但以下是一种更好的设计方法,将关注点分离到类中。

  • 一个类应该代表您的图书对象。此类将提供存储/设置/检索单个书籍对象的所有数据的功能。

  • 另一个代表书店,它将存储书籍对象列表,用书籍初始化数据,提供从商店添加、删除、编辑书籍的功能。

    公共类 BookInfo {

     //Class variables
     private String isbnInfo;
     private String bookTitleInfo;
     //....
     private double wholesaleInfo;
     private double retailInfo;
    
     //Constructors
     BookInfo(){
         //put default behaviour here
     }
    
     BookInfo(String isbnInfo, String bookTitleInfo, .....){
         this.isbnInfo = isbnInfo;        
         this.bookTitleInfo = bookTitleInfo;
         this.authorInfo = authorInfo;
    
         //....
    
    
     //Setter Method
     public String getIsbnInfo(){
         return isbnInfo;
     }
    
     //Getter Method
     public void setBookTitleInfo(String isbnInfo){
         this.isbnInfo = isbnInfo;
     }
    
     //.....
    

所以现在您可以创建 Book info 并设置/获取其所有变量,以 OOP 方式封装。

接下来我们看看BookInfos的存储/访问类。

public class BookStore {
    private isbnInfo = new String[] {"978-0060014018", "978-0449221431", "978-0545132060",
                                "978-0312474881", "978-0547745527" };
    
    private bookTitleInfo = new String[] { "The Greatest Stories", "The Novel", "Smile",
                                "The Bedford Introduction to Drama", 
                                 "AWOL on the Appalachian Trail" };

    //...rest of strings

    //here is where we store our book objects
    //we will create methods to add, remove, edit, later
    private BookInfo booklist = new List<BookInfo>();
    private String storename;
    
    //Default Constructor initialises booklist based on stored values
    public BookStore(){
         for(int i = 0; i < isbnInfo.lenght; i++){
             AddBook(isbnInfo [i], bookTitleInfo[i],.....,retailInfo[i]);
         )
    }
    
    //overloaded constructors you probably want to read from external file, db, etc eventually.
    public BookStore(String filelocation){
         //Do stuff to read from a file and add books to booklist 
    }
    
    //Add a new book to the list by passing in all the info
    public void AddBook(String isbn, String title, 
         BookInfo newbook = new BookInfo(isbn, title, ....)
         booklist.add(newbook);
    
    //Add a new book by passing in a book object.
    public void AddBook(BookInfo newbook){
         booklist.add(newbook);
    }
       
    //Find Book
    public int getBook(String isbn){
        for(int i=0; i++; i < booklist.lenght){
            if(book.getIsbn() == isbn)
                return i;
        }
        return -1;
    
    //Remove Book from list
    public void removeBook(String isbn){
         int loc = getbook(isbn);
         if(loc > -1){
             booklist.remove(loc);
         }
         else{
             System.out.println(Could not find book);
         }
    }     
    
    public void DisplayBookList(){
    //.. print list
    }
}

所以现在 BookStore 需要的所有必需功能都位于它需要的位置。您现在可以根据需要添加任何其他功能。

您的主要驱动程序类也需要更改。您的驱动程序类需要创建 BookStore。

如果用户想要删除一本书,他们需要输入书名。然后你打电话

bookstore.removeBook(userstring);

添加一本书需要用户输入更多的值,但基本相同

String isbn = scanner.next();
String bookname = scanner.next();
.......
double wholesaleinfo = Double.ParseDouble(scanner.next());

然后您可以通过将信息作为参数传递来添加您的罐子

bookstore.addBook(isbn, bookname, ...., wholesaleinfo);

或书籍对象。

BookInfo newbook = new BookInfo(isbn, bookname, ...., wholesaleinfo)
bookstore.addBook(newbook);

我会将用户逻辑留给您想要的任何方式。希望这已经说明了一些事情。在我所做的工作上肯定有可以改进的地方。

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