Ajuda tela de login

@augustocparaujo escreveu:

estou fazendo uma tela de login, quando o usuário max loga, ele apresenta a tela principal. Mas quando qualquer outro usuário tenta logar aparece "java.lang.NULLPointerException". Lembrando estou começando a programar.
segue codigo:

package br.com.sisclube.telas;

import java.sql.*;
import br.com.sisclube.dal.ModuloConexao;
import javax.swing.JOptionPane;

public class TelaLogin extends javax.swing.JFrame {
    Connection conexao = null;
    PreparedStatement pst = null;
    ResultSet rs = null;

    //metodo logar
    public void logar() {
	String sql = "select * from Usuarios where Nome=? and Senha=?";
	try {
	    pst = conexao.prepareStatement(sql);
	    pst.setString(1, txtUsuario.getText());
	    pst.setString(2, txtSenha.getText());
	    rs = pst.executeQuery();
	    if (rs.next()) {
		String Ativo = rs.getString(6);
		if (Ativo.equals("V")) {
		    TelaPrincipal principal = new TelaPrincipal();
		    principal.setVisible(true);
		    this.dispose();
		    conexao.close();
		} else {
		    JOptionPane.showMessageDialog(null, "Usuário inativo");
		    this.dispose();
		    conexao.close();
		}

	    } else {
		JOptionPane.showMessageDialog(null, "Usuário e/ou senha inválido");
	    }

	} catch (Exception e) {
	    JOptionPane.showMessageDialog(null, e);
	}
    }

    public TelaLogin() {
	initComponents();
	conexao = ModuloConexao.conector();
	if (conexao != null) {
	    lblStatus.setText("Conectado");
	} else {
	    lblStatus.setText("Desconectado");
	}
    }

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

        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        txtUsuario = new javax.swing.JTextField();
        txtSenha = new javax.swing.JPasswordField();
        lblStatus = new javax.swing.JLabel();
        btnLogar = new javax.swing.JButton();
        lblfundo = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Login");
        getContentPane().setLayout(null);

        jLabel1.setFont(new java.awt.Font("Tahoma", 1, 14)); // NOI18N
        jLabel1.setText("Login");
        getContentPane().add(jLabel1);
        jLabel1.setBounds(60, 70, 50, 17);

        jLabel2.setFont(new java.awt.Font("Tahoma", 1, 14)); // NOI18N
        jLabel2.setText("Senha");
        getContentPane().add(jLabel2);
        jLabel2.setBounds(60, 140, 43, 17);
        getContentPane().add(txtUsuario);
        txtUsuario.setBounds(130, 60, 160, 30);
        getContentPane().add(txtSenha);
        txtSenha.setBounds(130, 130, 160, 30);

        lblStatus.setText("...");
        getContentPane().add(lblStatus);
        lblStatus.setBounds(20, 280, 60, 14);

        btnLogar.setText("ENTRAR");
        btnLogar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnLogarActionPerformed(evt);
            }
        });
        getContentPane().add(btnLogar);
        btnLogar.setBounds(200, 180, 90, 30);

        lblfundo.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/sisclube/icones/fund_login.png"))); // NOI18N
        getContentPane().add(lblfundo);
        lblfundo.setBounds(0, 0, 400, 300);

        setSize(new java.awt.Dimension(416, 339));
        setLocationRelativeTo(null);
    }// </editor-fold>                        

    private void btnLogarActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
	logar();
    }                                        

    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(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
	} catch (InstantiationException ex) {
	    java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
	} catch (IllegalAccessException ex) {
	    java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
	} catch (javax.swing.UnsupportedLookAndFeelException ex) {
	    java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
	}
	//</editor-fold>

	/* Create and display the form */
	java.awt.EventQueue.invokeLater(new Runnable() {
	    public void run() {
		new TelaLogin().setVisible(true);
	    }
	});
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btnLogar;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel lblStatus;
    private javax.swing.JLabel lblfundo;
    private javax.swing.JPasswordField txtSenha;
    private javax.swing.JTextField txtUsuario;
                  
}

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