一段時間以來一直在嘗試解決這個 Firebase 加載數組列表問題，但不知道如何解決。項目等級public class Book {    private String title;    private String author;    private String ISBN;    private String photo;    private String ownerEmail;    private String ownerID;    private String BookID;    private Date returnDate;    private Status status;    private String borrowerID;    public Book(){}    public Book(String title, String author, String ISBN, String photo, String ownerEmail, String ownerID) {        this.title = title;        this.author = author;        this.ISBN = ISBN;        this.photo = photo;        this.ownerEmail = ownerEmail;        this.ownerID = ownerID;        this.status = Status.Available;        if(this.BookID == null || this.BookID.isEmpty())            this.BookID = UUID.randomUUID().toString();    }    public enum Status{        Available,        Requested,        Accepted,        Borrowed    }    這是我的 firebase 數據庫 firebase 數據庫 我不斷收到無法將類型對象轉換java.util.ArrayList為類型com.example.cmput301w19t15.Book在線錯誤Book book = dataSnapshot.getValue(Book.class); 我不確定為什么我收到轉換對象錯誤，我不想搜索單個變量并設置它們，這違背了對象類的目的我真的很想對此有所了解