java - 我的输入数组不断地 self 写入

Question

每次我将一个对象传递给数组时，它都会覆盖前一个条目。有人能找出为什么会发生这种情况吗？

addbook() - 当我输入名称和作者时，它会分配一个值，但是当输入另一个标题和作者时，它会覆盖以前的条目。

public class library {
    static Scanner keyboard = new Scanner(System.in);
    static int count = 0;
    public static void main(String [] args){
         addBook();
    }   // Main end
    static void addBook(){
        loanbook [] loanArray = new loanbook[5];

        String title,author;
        int choice;
        boolean onLoan;
        loanbook book1; // TESTING ONLY
        for(int x = 0; x < 5; x++){
            System.out.print("Press 1 for Fiction or 2 for Non Fiction: ");  // sub menu for fiction and non fiction
            choice = keyboard.nextInt();
            if (choice == 1){

                System.out.println("Please enter book title: ");
                title = keyboard.nextLine();
                title = keyboard.nextLine();
                System.out.println("Please enter book author: ");
                author = keyboard.nextLine();
                onLoan = false; // not used yet
                book1 = new fiction(title,author);
                System.out.println(book1.toString());
                loanArray[x] = new loanbook(title,author);

            }
            else if (choice == 2) {
                System.out.println("Please enter book title: ");
                title = keyboard.nextLine();
                title = keyboard.nextLine();
                System.out.println("Please enter book author: ");
                author = keyboard.nextLine();
                onLoan = false; // not used yet
                book1 = new nonfiction(title,author);
                System.out.println(book1.toString());
                loanArray[x] = new loanbook(title,author);
            }
        }
    }
} // Library end

我的贷款簿类(class)

public class loanbook {
    private String title,author;
    private int bookID, count = 0;

    public loanbook(String pTitle,String pAuthor){
        bookID = count;
        title = pTitle;
        author = pAuthor;
        count++;
    }  // Constructor
    public void setTitle(String pTitle){
        title = pTitle;
    } // setTitle
    protected String getTitle(){
        return title;
    }   // getTitle
    protected String getAuthor(){
        return author;
    }   // getAuthor
    public String toString(){
        return " BookID: "+ bookID+"\n" + " Title: "+ getTitle()+"\n" +" Author : "+ getAuthor()+ "\n";
    }
}  // loanbook

Answer 1

您可能希望将计数设为静态。我假设您希望每次创建新书时计数都会增加。如果没有静态，计数值将不会在每次创建图书时持续存在，因此每本书的 bookID 将始终为 0。这可能就是您认为“它正在被覆盖”的原因。我不太确定，因为你还没有真正解释这意味着什么。

private int bookID; 
public static int count = 0;           <-- static 

public loanbook(String pTitle,String pAuthor){
    bookID = count;
    title = pTitle;
    author = pAuthor;
    count++;
}

或者更好的是，避免使用 count 变量。您的操作与使用 count 相同。所以 count 是不必要的。

public static int bookID 0;

public loanbook(String pTitle,String pAuthor){
    title = pTitle;
    author = pAuthor;
    bookId++;
}

另外，我不知道你打算用 loanbook book1; 做什么，但它每次都会在循环中使用，所以我可以看到这是可能的”它正在被覆盖”问题。假设 fiction 和 nonfiction 扩展 loanbook

此外，我认为库类中不需要 count 。你可以摆脱它。

更新:

假设您想要在您的 loanArray` 中添加 fiction 或 nonfiction 书(它们都扩展了 loanbook)，您可能需要这样的

loanbook book = new fiction(title,author);
System.out.println(book1.toString());
loanArray[x] = book;