Question

完全不熟悉Java，我需要一些帮助来创建这个BookList程序:)我已经阅读了我的书，我完全糊涂了。我需要创建一个名为BookList的arraylist，我需要显示一个带有案例开关的菜单，它将添加一本书，编辑一本书，删除一本书并显示书籍。我的程序已启动，但它不能完全工作它应该显示一个菜单供用户选择，它将执行以下功能，但我收到所有Book构造函数的错误消息。我希望你们中的一些Java大师可以帮助一个新手！这是我目前在BookList类

中的内容

import java.util.Scanner;
import java.util.ArrayList;

public class BookList {

public static void main (String[] args){





System.out.println(" =======================================");
    System.out.println("|       1. Add a book                   |");
    System.out.println("|       2. Edit a book                  |");
    System.out.println("|       3. Delete a book                |");
    System.out.println("|       4. Display all books            |");
    System.out.println("|       5. Exit the program             |");
    System.out.println("|  *Type a number to make a selection*  |");
    System.out.println(" =======================================");
    System.out.println("");
    System.out.print("Selection: ");

    public static Book()

    {
    int title;
    }
    Book a = new Book();

    a.setTitle("Stranger");


    Book b = new Book();

    b.setTitle("SQL");


    Book c = new Book();

    c.setTitle("HTML");


    ArrayList<Book> BookList = new ArrayList<Book>();
    BookList.add(a);
    BookList.add(b);
    BookList.add(c);





Scanner SC = new Scanner(System.in);

int Choice1;

   Choice1 = SC.nextInt();

   SC.close();


    switch (Choice1) {

    case 1:

        Scanner JK = new Scanner(System.in);

      System.out.println("'Add a book' selected");
      System.out.println(" ");


      break;

    case 2:
        System.out.println("'Edit a book's details' selected");
        System.out.println("Which Book would you like to edit?");
        System.out.println("");
        break;

    case 3:
        System.out.println("'Delete a book' selected");
        break;

    case 4:
          System.out.println("Display all books");
          break;



    case 5:
          System.out.println("Goodbye!");
          System.exit(0);

          break;


    default:
      System.out.println("Invalid selection. Try again");


    }
  }
  }

Answer 1

以下代码似乎试图在main方法中定义构造函数。

public static void main (String[] args){

    [...]

    public static Book()

    {
    int title;
    }
    Book a = new Book();

构造函数需要直接在类中。它也不应该有static修饰符。看起来title local应该是String类型的字段（在任何方法之外）。

private String title;

public Book() {
}

public static void main(String[] args) {
    [...]

    Book a = new Book();

Answer 2

Book类未正确声明。尝试将声明放在BookList类块之外。

public class BookList{
  [...]
}

public class Book{  

    public void setTitle(String newTitle){
      title = newTitle;
    }

    private int title;
}

请注意，Book的默认构造函数是隐含的，如果您想稍后使用它，则必须为标题添加getter。

Answer 3

考虑到你提出的问题，我试图尽我所能。

import java.util.Scanner;
import java.util.ArrayList;

public class BookList {

    public static void main (String[] args){
        Scanner SC = new Scanner(System.in);
        Book a = new Book();

        a.setTitle("Stranger");

        Book b = new Book();
        b.setTitle("SQL");

        Book c = new Book();

        c.setTitle("HTML");

        ArrayList<Book> BookList = new ArrayList<Book>();
        BookList.add(a);
        BookList.add(b);
        BookList.add(c);

        int Choice1=1;

        while(Choice1!=5)
        {
            System.out.println(" =======================================");
            System.out.println("|       1. Add a book                   |");
            System.out.println("|       2. Edit a book                  |");
            System.out.println("|       3. Delete a book                |");
            System.out.println("|       4. Display all books            |");
            System.out.println("|       5. Exit the program             |");
            System.out.println("|  *Type a number to make a selection*  |");
            System.out.println(" =======================================");
            System.out.println("");
            System.out.print("Selection: ");

            Choice1 = SC.nextInt();

            switch (Choice1) {

                case 1:

                System.out.println("'Add a book' ");
                System.out.println("Enter the name ");
                Book holder = new Book(SC.next());

                break;
                case 2:
                System.out.println("'Edit a book's details' selected");
                System.out.println("Which Book would you like to edit?");
                System.out.println("");

                // I do not understand what you want me to do here

                break;

                case 3:
                for(int i=0;i<BookList.size();i++){
                    System.out.println(i+1+") "+BookList.get(i));
                }
                System.out.println("Choose a book to delete: ");
                BookList.remove(SC.nextInt()-1);
                break;

                case 4:
                System.out.println("Display all books");
                for(Book x:BookList)
                    System.out.println(x);
                break;


                case 5:
                System.out.println("Goodbye!");
                System.exit(0);

                break;

                default:
                System.out.println("Invalid selection. Try again");

            }
        }
    }
}











public class Book{

    String Title;


    public Book()
    {
        Title="";
    }

    public Book(String bookTitle)
    {
        Title=bookTitle;
    }

    public void setTitle(String bookTitle)
    {
        Title=bookTitle;
    }

    public String toString(){
        return "Book Name "+Title;
    }
}

Java ArrayList和Case / Switch？

3 个答案: