java在JFrame中调用整数和双精度。JTextField（）。setText（）；

Question

我刚刚用MVC学习了ORM。我上课

public bookController {

private static final Connection Connection = null;
    JFramebookstore frameBookstore;
    Bookimpl bookimpl;
    List<book> listbook;

// and i just add a function to show a books that choose from JTableBooks

public void showfield(int row) {
   frameBookstore.JtextBookid().setText(listbook().get(row).getBookId().toString());
frameBookstore.JtextSellingprice().setText(listbook().get(row).getsellprice().toString());
  }
}

调用getBookid（）和getbooksellprice（）时出错

这是我的构造函数类

public class book {

private int bookid;
private double booksellprice;

public final int getBookid() {
        return bookid;
    }
    public final void setBookid(int bookid) {
        this.bookid = bookid;
    }

public final double getBooksellprice() {
        return booksellprice;
    }
    public final void setBooksellprice(int booksellprice) {
        this.booksellprice= bookselprice;
    }

public book(int bookid, double booksellprice){

   super();
   this.bookid = bookid;
   this.booksellprice = booksellprice;
  }

    @Override
    public String toString() {
        return "book [bookid=" + bookid + ", booksellprice=" +booksellprice+"]
 }
}

我读过tutorial String但仍然无法解决我自己的问题

这是我的bookTable模型扩展AbstractTableModel

 public class bookTableModel extends AbstractTableModel {

 list<book> books;

public bookTableModel(List<book> books) {
    this.books = books;


@Override
public int getRowCount() {
    // TODO Auto-generated method stub
    return books.size();
}

@Override
public int getColumnCount() {
    // TODO Auto-generated method stub
    return 2;
}

public String getColumnName(int column) {
    switch (column) {
    case 0:
        return "bookid";
    case 1:
        return "booksellprice";
    default :
        return null;

    }

}

@Override
public Object getValueAt(int row, int column) {
    switch (column) {
    case 0:
        return books.get(row).getbookid();
    case 1:
        return books.get(row).getbooksellprice();
    default:
        return null;
    }
}
 }
}

这是我的bookDAO类实现bookimpl

'@Override
public class BookDAO implements bookimpl {
private final String select = "SELECT * FROM DSCM.BookData ";

public List<book> getByAll() t{
    List<book> books = null;


    try {
        books = new ArrayList<book>();
        Statement statement =  connection.createStatement();
        ResultSet result = statement.executeQuery(select);


        while (result.next()) {
            book b = new book();

            b.setbookid(result.getInt("bookid"));
            b.setbookid(result.getDouble("booksellprice"));


            books.add(book);
        }


    } catch (SQLException ex) {
        ex.printStackTrace();
    }
    return books;  

 }
}'

这是我的bookimpl课程

public interface bookimpl {

public void insertbook(Book b) throws Dascomerror;

public void updatebook(book b) throws Dascomerror;

public void deletebook(int bookid) throws Dascomerror;

public List<book> getByAll() throws Dascomerror;

'

错误是这样说的

java.lang.NullPointerException
at com.dascom.dao.bookDAO.getByAll(bookDAO.java:138)
at com.dascom.controller.bookController.<init>(bookController.java:38)
at com.dascom.view.JFramebook.<init>(JFramebook.java:136)

Answer 1

你似乎对变量和函数感到困惑。访问变量时不需要()

frameBookstore.JtextBookid().setText(listbook().get(row).getBookId().toString());//wrong

frameBookstore.JtextBookid.setText(listbook.get(row).getBookId().toString());//right way

您不能取消对int和double的引用，我的意思是.toString()对于int，double之类的基元类型不可用

跟着String.valueOf()

frameBookstore.JtextBookid.setText(String.valueOf(listbook.get(row).getBookId()));

这些函数名在getBookId()和getBookid()中是不同的，看起来像是打字错误 getsellprice()和getBooksellprice()