Here is an example of login form in java swing. The code accepts the username and password from the user and check whether the user is valid. If the user is valid, the user will be moved to another page. Otherwise an error message will get displayed.

1)LoginDemo.java:

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

class LoginDemo extends JFrame{
 JButton SUBMIT;
 JLabel label1,label2;
 final JTextField  text1,text2;
  LoginDemo(){
    setTitle("Login Form");
    setLayout(null);
    label1 = new JLabel();
    label1.setText("Username:");
    text1 = new JTextField(15);

    label2 = new JLabel();
    label2.setText("Password:");
    text2 = new JPasswordField(15);

    SUBMIT=new JButton("SUBMIT");
    label1.setBounds(350,100,100,20);
    text1.setBounds(450,100,200,20);
    label2.setBounds(350,130,100,20);
    text2.setBounds(450,130,200,20);
    SUBMIT.setBounds(450,160,100,20);
   add(label1);
   add(text1);
   add(label2);
   add(text2);
   add(SUBMIT);

   setVisible(true);
   setSize(1024,768);

 SUBMIT.addActionListener(new ActionListener(){
   public void actionPerformed(ActionEvent ae){
    String value1=text1.getText();
    String value2=text2.getText();
    try{
 Class.forName("com.mysql.jdbc.Driver");
           Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root");
           Statement st=con.createStatement();
           ResultSet rs=st.executeQuery("select * from login where username='"+value1+"' and password='"+value2+"'");
           String uname="",pass="";
           if(rs.next()){
               uname=rs.getString("username");
               pass=rs.getString("password");
           }
 if(value1.equals("") && value2.equals("")) {
      JOptionPane.showMessageDialog(null,"Enter login name or password","Error",JOptionPane.ERROR_MESSAGE);
  }
 else if(value1.equals(uname) && value2.equals(pass)) {
    NextPage page=new NextPage(uname);
    page.setVisible(true);
    }
 else if (!value1.equals(uname) && !value2.equals(pass)) {
     text1.setText("");
     text2.setText("");
    }
    }
    catch(Exception e){}
}
 });
  }

  public static void main(String arg[]){
  new LoginDemo();
}
}

2)NextPage.java:

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

class NextPage extends JFrame
{
  NextPage(String st)
   {
      setLayout(null);
     setDefaultCloseOperation(javax.swing. WindowConstants.DISPOSE_ON_CLOSE);
     setTitle("Welcome");
     JLabel lab=new JLabel("Welcome  "+st);

     lab.setBounds(10,10,500,20);
     add(lab);

       setSize(1024, 768);
      }
 }