Question

每次我将一个对象传递给我的数组时，它都会覆盖前一个条目。任何人都能发现为什么会这样吗？

addbook（） - 当我输入名称时，作者会分配一个值，但是当输入另一个标题和作者时，它会覆盖上一个条目。

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

我的借阅手册

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

您可能想要count static。我假设你每次创建一本新书时都想让计数上升。如果没有静态，计数值将不会在创建书籍时持续存在，因此每本书的bookID始终为0。那个可能就是你认为“它被覆盖”的原因。我不完全确定，因为你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，只需避开count变量即可。您可以使用count执行相同的操作。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;计划什么，但每次在循环中使用它，所以我可以看到这是可能的“它被覆盖” 问题。假设fiction和nonfiction延长loanbook

此外，我认为库类中不需要count。你可以摆脱它。

更新：

假设你想要fiction或nonfiction本书（他们都延伸loanbook) in your loanArray`你可能想要这样的东西

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

我的输入数组继续写自己

1 个答案: