java - java.sql.PreparedStatement 无法转换为 com.mysql.jdbc.PreparedStatement

Question

我试图使用 mysql 数据库连接创建一个 GUI 应用程序，但出现错误。这是我的代码。

package demo;

import java.awt.HeadlessException;
import java.sql.Statement;
import com.mysql.jdbc.Connection;
import com.mysql.jdbc.PreparedStatement;
import java.sql.DriverManager;
import java.sql.ResultSet;
import javax.swing.JOptionPane;
import java.sql.SQLException; 

public class NewJFrame extends javax.swing.JFrame {

    Connection con;
    PreparedStatement pst;
    ResultSet rs;
    
    public NewJFrame() {
        initComponents();
    }

    @SuppressWarnings("unchecked")                         
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jLabel3 = new javax.swing.JLabel();
        jLabel4 = new javax.swing.JLabel();
        jTextField1 = new javax.swing.JTextField();
        jComboBox1 = new javax.swing.JComboBox<>();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jPasswordField1 = new javax.swing.JPasswordField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jLabel1.setBackground(new java.awt.Color(51, 204, 0));
        jLabel1.setFont(new java.awt.Font("Times New Roman", 2, 24)); // NOI18N
        jLabel1.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
        jLabel1.setText("LOGIN PAGE");

        jLabel2.setFont(new java.awt.Font("Trebuchet MS", 1, 14)); // NOI18N
        jLabel2.setText("Username");

        jLabel3.setFont(new java.awt.Font("Trebuchet MS", 1, 14)); // NOI18N
        jLabel3.setText("Password");

        jLabel4.setFont(new java.awt.Font("Trebuchet MS", 1, 14)); // NOI18N
        jLabel4.setText("Select User");

        jComboBox1.setModel(new javax.swing.DefaultComboBoxModel<>(new String[] { "Select", "Admin", "User" }));

        jButton1.setFont(new java.awt.Font("Times New Roman", 1, 18)); // NOI18N
        jButton1.setText("LOGIN");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        jButton2.setFont(new java.awt.Font("Times New Roman", 1, 18)); // NOI18N
        jButton2.setText("CANCEL");
        jButton2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton2ActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGap(54, 54, 54)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                    .addComponent(jLabel3, javax.swing.GroupLayout.DEFAULT_SIZE, 174, Short.MAX_VALUE)
                    .addComponent(jLabel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(jLabel4, javax.swing.GroupLayout.DEFAULT_SIZE, 174, Short.MAX_VALUE)
                    .addComponent(jButton1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
                .addGap(70, 70, 70)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                    .addComponent(jTextField1)
                    .addComponent(jComboBox1, 0, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(jButton2, javax.swing.GroupLayout.DEFAULT_SIZE, 180, Short.MAX_VALUE)
                    .addComponent(jPasswordField1))
                .addContainerGap(149, Short.MAX_VALUE))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(42, 42, 42)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 30, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addGap(6, 6, 6)
                        .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE)))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, 30, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jPasswordField1, javax.swing.GroupLayout.PREFERRED_SIZE, 38, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(24, 24, 24)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                    .addComponent(jLabel4, javax.swing.GroupLayout.DEFAULT_SIZE, 30, Short.MAX_VALUE)
                    .addComponent(jComboBox1))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 31, Short.MAX_VALUE)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 47, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 47, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(29, 29, 29))
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();                  

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
System.exit(0);
    }                                        

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {  
        String uname=jTextField1.getText();
        String pword=jPasswordField1.getText();
        String option=jComboBox1.getSelectedItem().toString();
        if(uname.equals("")||pword.equals("")||option.equals("")){
            JOptionPane.showMessageDialog(rootPane,"Some fiels are Empty!!","Error",1);}
        else{
            try{
                con=Connections.getConnection();
                pst=con.prepareStatement("select * from `login` where username=? and passwor=?");
                pst.setString(1, unmae);
                pst.setString(2, pword);
                rs=pst.executeQuery();
                if(rs.next()){
                    String s1=rs.getString("option");
                    if(option.equalsIgnoreCase("Admin")&&s1.equalsIgnoreCase("admin"))
                    {
                        AdminPage ad=new AdminPage(uname);
                        ad.setVisible(true);
                        setVisible(false);
                    }
                    if(option.equalsIgnoreCase("User")&&s1.equalsIgnoreCase("admin"))
                    {
                        UserPage ad=new UserPage(uname);
                        ad.setVisible(true);
                        setVisible(false);
                    }
                }
                else{
                    JOptionPane.showMessageDialog(rootPane, "Username orr passswoord not mached","Login Error", 1);
                }
                    
            }
            catch(Excepton ex){
                System.out.println(""+ex);}
        }
    }                                        

    public static void main(String args[]) {
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }

    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JComboBox<String> jComboBox1;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabel4;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JPasswordField jPasswordField1;
    private javax.swing.JTextField jTextField1;   
}

在行

con=Connections.getConnection();
pst=con.prepareStatement("select * from `login` where username=? and passwor=?");
pst.setString(1, unmae);

它正在出错。它说找不到符号变量连接。不兼容的类型：java.sql.PreparedStatement 无法转换为 com.mysql.jdbc.PreparedStatement

请帮我。

标签： javamysql

Answer 1

您的导入有问题，您必须导入Connection,PreparedStatement和ResultSetfromjava.sql而不是 from com.mysql.jdbc，所以使用：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

而不是这个：

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.PreparedStatement;