Question

当我运行此代码时，我得到一个空指针异常。

    try {
        String sql = "INSERT INTO viwa(name,tele,surname) VALUES(?,?,?)";
         pst = conn.prepareStatement(sql);

        pst.setString(1, jTextField_name.getText());
        pst.setString(2, jTextField_age.getText());
        pst.setString(3, jTextField_tele.getText());

        pst.execute();
        JOptionPane.showMessageDialog(null, "Saved");
    } catch (Exception e) {
        e.printStackTrace();
    }

* 这是完整的代码 *

`import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.Statement;进口 javax.swing.JOptionPane中;

public class go扩展javax.swing.JFrame {

Connection conn = null;
ResultSet rs = null;   PreparedStatement pst = null;


public go() {
    try {
        initComponents();
        connect.getMyConn();

    } catch (Exception e) {
        e.printStackTrace();
    }
}


@SuppressWarnings("unchecked")
 // <editor-fold defaultstate="collapsed" desc="Generated    Code">                          
private void initComponents() {

    jLabel1 = new javax.swing.JLabel();
    jLabel2 = new javax.swing.JLabel();
    jLabel3 = new javax.swing.JLabel();
    jTextField_Tele = new javax.swing.JTextField();
    jTextField_Surname = new javax.swing.JTextField();
    jTextField_Name = new javax.swing.JTextField();
    jButton_search = new javax.swing.JButton();
    jButton_Update = new javax.swing.JButton();
    jButton_Delete = new javax.swing.JButton();
    jButton_save = new javax.swing.JButton();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    getContentPane().setLayout(new org.netbeans.lib.awtextra.AbsoluteLayout());

    jLabel1.setText("Tele");
    getContentPane().add(jLabel1, new org.netbeans.lib.awtextra.AbsoluteConstraints(140, 140, -1, -1));

    jLabel2.setText("Surname");
    getContentPane().add(jLabel2, new org.netbeans.lib.awtextra.AbsoluteConstraints(140, 210, -1, -1));

    jLabel3.setText("Name");
    getContentPane().add(jLabel3, new org.netbeans.lib.awtextra.AbsoluteConstraints(140, 70, -1, -1));

    jTextField_Tele.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jTextField_TeleActionPerformed(evt);
        }
    });
    getContentPane().add(jTextField_Tele, new org.netbeans.lib.awtextra.AbsoluteConstraints(230, 140, 170, -1));
    getContentPane().add(jTextField_Surname, new org.netbeans.lib.awtextra.AbsoluteConstraints(230, 210, 170, -1));
    getContentPane().add(jTextField_Name, new org.netbeans.lib.awtextra.AbsoluteConstraints(230, 70, 170, -1));

    jButton_search.setText("Search");
    getContentPane().add(jButton_search, new org.netbeans.lib.awtextra.AbsoluteConstraints(230, 310, 120, -1));

    jButton_Update.setText("Update");
    getContentPane().add(jButton_Update, new org.netbeans.lib.awtextra.AbsoluteConstraints(390, 310, 120, -1));

    jButton_Delete.setText("Delete");
    getContentPane().add(jButton_Delete, new org.netbeans.lib.awtextra.AbsoluteConstraints(540, 310, 120, -1));

    jButton_save.setText("Save");
    jButton_save.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton_saveActionPerformed(evt);
        }
    });
    getContentPane().add(jButton_save, new org.netbeans.lib.awtextra.AbsoluteConstraints(90, 310, 120, -1));

    pack();
}// </editor-fold>                        

private void jTextField_TeleActionPerformed(java.awt.event.ActionEvent evt) {      

    // TODO add your handling code here:
}                                               

private void jButton_saveActionPerformed(java.awt.event.ActionEvent evt) {         

    try {

        String sql = "INSERT INTO viwa (name,tele,surname) VALUES(?,?,?)";
       pst =  conn.prepareStatement(sql);

        pst.setString(1, jTextField_Name.getText());
        pst.setString(2, jTextField_Tele.getText());
        pst.setString(3, jTextField_Surname.getText());

        pst.execute();

        JOptionPane.showMessageDialog(this, "Saved");
    } catch (Exception e) {
        e.printStackTrace();
    }

}      `

Answer 1

使用您的IDE，在此代码的开头放置一个断点，并逐步查看所有变量。您的一个变量包含意外的null值。您的代码中没有其他明显的NPE原因。

java INSERT查询不起作用（java.lang.NullPointerException）

1 个答案: