java - 登录系统并有权 Access

Question

大家好，我是 java 新手，我正在尝试运行此 java 代码，但由于某种原因，它没有在 Eclipse 控制台中显示错误。它确实在这一行有一个语法错误:

b.addActionListener (new ActionListener() {

我已经尝试了所有建议，但没有取得任何进展..我知道这很简单，但我以前从未让控制台不显示任何错误。感谢您的帮助!

import javax.swing.*;
import java.awt.event.*;
import java.sql.*;

public class Loging {
Connection con;
Statement st;
ResultSet rs;

JFrame f = new JFrame("User Login");
JLabel l = new JLabel("Username");
JLabel l1 = new JLabel("password");
JTextField t = new JTextField(10);
JTextField t1 = new JTextField(10);
JButton b = new JButton("Login");

public static void main(String[] args) {
    // TODO Auto-generated method stub
}

public void Loging1() {
    connect();
    frame();
}

public void connect() {
    try {
        String driver = "sun.jdbc.odbc.JdbcOdbcDriver";// Driver needed for
                                                        // connection
        Class.forName(driver);// Class.forName(driver);

        String db = "jdbc:odbc:db1";
        con = DriverManager.getConnection(db);
        st = con.createStatement();

    } catch (Exception ex) {

    }

}

public void frame()
        {
            f.setSize (600,400);
            f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            f.setVisible(true);

            JPanel p = new JPanel();
            p.add(l);
            p.add(t);
            p.add(l1);
            p.add(t1);
            p.add(b);

            f.add(p);
            b.addActionListener (new ActionListener() {


            }

public void actionPerformed(ActionEvent e) {
    try {
        String user = t.getText().trim();
        String pass = t1.getText().trim();

        String sql = "select user, pass from Table1 where user = '" + user
                + "'and pass = '" + pass + "'";// for sql query
        // String sql =
        // "select user, pass from Table1 where user = '"+user+"'pass = '"+pass+"'";
        // Getting the fields user and pass checks tthat both are equal to
        // each orther
        rs = st.executeQuery(sql);// executes query

        int count = 0;// cont the rows for the query
        while (rs.next()) {
            count = count + 1;// if no rows are returned then no user exist,
                                // if count is = to 1 then user exist }
        }

        if (count == 1)// if = to 1 user exist
        {
            JOptionPane.showMessageDialog(null, "Logged in!");
        } else if (count > 1)// if more that one
        {
            JOptionPane.showMessageDialog(null, "Duplicate user, DENIED!");
        }

        else {
            JOptionPane.showMessageDialog(null, "user not found");
        }

    } catch (Exception ex) {

    }
    // public static void main(String[] args) {

}
// New Loging1 ();
}

Answer 1

这个...

b.addActionListener (new ActionListener() {

}

将会给您一个编译器错误，因为您未能满足 ActionListener 接口(interface)的要求，即实现 actionPerformed 方法。

更像是......

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Loging {

    Connection con;
    Statement st;
    ResultSet rs;

    JFrame f = new JFrame("User Login");
    JLabel l = new JLabel("Username");
    JLabel l1 = new JLabel("password");
    JTextField t = new JTextField(10);
    JTextField t1 = new JTextField(10);
    JButton b = new JButton("Login");

    public static void main(String[] args) {
        // TODO Auto-generated method stub
    }

    public void Loging1() {
        connect();
        frame();
    }

    public void connect() {
        try {
            String driver = "sun.jdbc.odbc.JdbcOdbcDriver";//Driver needed for connection
            Class.forName(driver);//    Class.forName(driver);

            String db = "jdbc:odbc:db1";
            con = DriverManager.getConnection(db);
            st = con.createStatement();

        } catch (Exception ex) {

        }

    }

    public void frame() {
        f.setSize(600, 400);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);

        JPanel p = new JPanel();
        p.add(l);
        p.add(t);
        p.add(l1);
        p.add(t1);
        p.add(b);

        f.add(p);
        b.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {
                try {
                    String user = t.getText().trim();
                    String pass = t1.getText().trim();

                    String sql = "select user, pass from Table1 where user = '" + user + "'and pass = '" + pass + "'";//for sql query
                    //String sql = "select user, pass from Table1 where user = '"+user+"'pass = '"+pass+"'";
                    //Getting the fields user and pass checks tthat both are equal to each orther
                    rs = st.executeQuery(sql);//executes query  

                    int count = 0;//cont the rows for the query
                    while (rs.next()) {
                        count = count + 1;//if no rows are returned then no user exist, if count is = to 1 then user exist              }
                    }

                    if (count == 1)//if = to 1 user exist
                    {
                        JOptionPane.showMessageDialog(null, "Logged in!");
                    } else if (count > 1)//if more that one
                    {
                        JOptionPane.showMessageDialog(null, "Duplicate user, DENIED!");
                    } else {
                        JOptionPane.showMessageDialog(null, "user not found");
                    }

                } catch (Exception ex) {

                }
                //public static void main(String[] args) {

            }
            //  New Loging1 ();
        });
    }
}

至少会编译(抱歉，还有一些其他格式问题我不想讨论)

您还应该学习如何使用 PreparedStatements 请参阅 Using Prepared Statements更多详情，它们通常更灵活、更安全。

JdbcOdbcDriver 已折旧，您不应使用它。类似于 UCanAccess可能是一个更合适的解决方案，但您需要做一些研究

您可能还想查看How to Write an Action Listeners和 Nested Classes