Question

我尝试过类似的东西：但错误出现了：

严重：空空值 com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：列'MYUSER'不能为空

虽然不应该？另外我想问一下我的程序中是否存在一些不良做法。任何提示？

/*
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 * and open the template in the editor.
 */



public class Main extends JFrame  {


   String text;

  public Main() throws HeadlessException {

    //opis
    JLabel opis = new JLabel("Opis: ");
    JTextField opisTextField = new JTextField();
    opisTextField.setPreferredSize(new Dimension(100, 20));
    add(opis);
    add(opisTextField);



//jak klikniemy w przycisk program doda wartosci wpisane do bazy danych.
    Button z = new Button("Dodaj do bazy danych"); 

     add(z);
    z.addMouseListener(new MouseAdapter() {

      @Override
      public void mouseClicked(MouseEvent e){}
      @Override
            public void mouseEntered(MouseEvent e){}
      @Override
            public void mouseExited(MouseEvent e){}
      @Override
            public void mouseReleased(MouseEvent e){}
      @Override
     public void mousePressed(MouseEvent e) {


        Main m = new Main();
        m.text = opisTextField.getText();






    });

  }

public void  readDataBase()  throws Exception {
    try {
      // this will load the MySQL driver, each DB has its own driver
      Class.forName("com.mysql.jdbc.Driver");
      // setup the connection with the DB.
      connect = DriverManager
          .getConnection("jdbc:mysql://localhost/feedback?"
              + "user=sqluser&password=sqluserpw");

      // statements allow to issue SQL queries to the database
      statement = connect.createStatement();
      // resultSet gets the result of the SQL query


      // preparedStatements can use variables and are more efficient
      preparedStatement = connect
          .prepareStatement("insert into  FEEDBACK.COMMENTS values (default, ?, ?, ?, ? , ?, ?)");
        // "myuser, webpage, datum, summary, COMMENTS from FEEDBACK.COMMENTS");
        // parameters start with 1

     preparedStatement.setString(1, text);

      preparedStatement.executeUpdate();



      // remove again the insert comment


    } catch (ClassNotFoundException | SQLException e) {
      throw e;
    } finally {
     // close();
    }

  }

  public static void main(String[] args) throws Exception {

    new Main().setVisible(true);

  }

}

Answer 1

很抱歉无法浏览所有代码，但看起来您已声明String text;并且您从未向其提供过值，并且您将此值传递给用户名preparedStatement.setString(1, text);，根据错误，该值不能为null。

java如何在另一个方法中使用方法中的变量

1 个答案: