不想每次都创建一个新的实例吗？

Question

我正在创建一个控制台库应用程序作为大学项目的一部分。我已经建立了两个对象，一个是书，另一个是期望ArrayList书的图书馆。添加到书籍的现有ArrayList时，我想将其添加到库。用户应该能够在不创建库的新实例的情况下添加新书，它应该添加到现有的书籍ArrayList而不是新的库实例。

下面是一些我一起工作的代码，代码的第一部分是刚刚从我的书类的构造函数，第二个是从图书馆类：

// Initialising variables 
private String title, author; 
private int bookID, timesLoaned; 
private boolean onLoan; 

// Setting up the constructor 
public Book(String title, String author, int bookID, int timesLoaned, boolean onLoan) { 
    this.title = title; 
    this.author = author; 
    this.bookID = bookID; 
    this.timesLoaned = timesLoaned; 
    this.onLoan = onLoan; 
} 

库类的构造函数：

// Initialising variables 
int ID; 
String name, address; 
String phoneNumber; 
ArrayList<Book> newBook = new ArrayList<Book>(); 

// Setting up the constructor 
public Library(int ID, String name, String address, String phoneNumber, ArrayList<Book> newBook) { 
    this.ID = ID; 
    this.name = name; 
    this.address = address; 
    this.phoneNumber = phoneNumber; 
    this.newBook = newBook; 
} 

以下代码是在一类称为HelperUtilities：

public static ArrayList<Book> createBook(){ 
    // Book needs title, author, category, bookID, times loaned, onLoan 
    String[] title = {"Harry Potter and the Goblet of Fire", "The Fault in Our Stars", 
      "Vampire Acadamy", "The Perks of Being a Wallflower", "Thirteen Reasons Why", 
      "The Maze Runner", "Looking for Alaska", "The Hunger Gamers"}; 

    String[] author = {"J.K. Rowling", "John Green", "Richelle Mead", "Stephen Chobsky", 
      "Jay Asher", "James Dashner", "John Green", "Suzanne Collins"}; 

    int[] bookID = new int[8]; 

    // Temporary values 
    String tName = "", tAuthor = ""; 
    int tID = 0; 

    ArrayList<Book> book = new ArrayList<Book>(); 
    for(int i = 0; i < 8; i++){ 
     tName = title[i]; 
     tAuthor = author[i]; 
     bookID[i] = (int) Math.round(Math.random() * 1000000); 
     tID = bookID[i]; 

     book.add(new Book(tName, tAuthor, tID, 0, false)); 
    } 

    return book; 
} 

public static ArrayList<Library> createLibrary(){ 
    String name = "Draperstown", address = "Magherafelt", phone = "000"; 
    int id = (int) Math.round(Math.random() * 1000000); 

    ArrayList<Library> library = new ArrayList<Library>(); 
    for(int i = 0; i < 1; i++) { 
     library.add(new Library(id, name, address, phone, createBook())); 
    } 

    return library; 
} 

的你将看到的下一个方法是addBook方法，该方法应该创建一本书的新实例并将其添加到书籍的ArrayList中，然后将其添加到现有的库中，这是我陷入困境的地方。

public static void addBook(Scanner sc){ 
    // Books 
    // Variables for use in addBook 
    int bookID = (int) Math.round(Math.random() * 1000000); // Generates random book ID 

    // User input 
    System.out.print("Enter a title for the book: "); 
    String title = sc.nextLine(); 

    System.out.print("Enter an author for the book: "); 
    String author = sc.nextLine(); 

    // ArrayList holds values of user input for new book 
    ArrayList<Book> newBook = new ArrayList<Book>(); 
    newBook.add(new Book(title, author, bookID, 0, false)); 

    // Takes existing ArrayList from HelperUtilities 
    ArrayList<Book> existBook = new ArrayList<Book>(); 
    existBook = HelperUtilities.createBook(); 

    // Joins both ArrayLists together 
    ArrayList<Book> addBook = new ArrayList<Book>(); 
    addBook.addAll(existBook); 
    addBook.addAll(newBook); 

    System.out.println("Book '" + title + "' has been added."); 
} 

我有一种感觉，我会被要求添加一个库的新实例，但这是我最终想避免的。如果需要其他代码，我将很乐意提供。

Answer 1

我认为你没有正确的思考这个问题。从你的描述中，你可能应该添加一个方法到Library类中，该类有一个书籍数组列表作为参数。然后，您应该使用一个循环遍历此数组列表，将此数组中的每本书添加到Library类已具有的数组列表中。通过你的HelperUlitlies课阅读，我不确定你为什么以这种方式使用这门课。图书馆应该有一种方法将书籍添加到书架上，你不应该为此使用外部类。这可能是一个好主意，有一个管理图书馆类的类，接受用户输入并实例化图书馆类的新图书列表添加。