Error :Exception in thread "AWT-Eventqueue-0" java.lang.Nullpointerexception

Question

Well, I’m trying to make a login screen, in which the data are in the database, and if you have the right data as in the bd appears a message to the user, but is giving error.

The Login page:

import java.awt.BorderLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

import Banco.Manipula;
import Logica.Usuario;

import java.awt.Color;
import javax.swing.JTextField;
import javax.swing.JPasswordField;
import java.awt.SystemColor;
import javax.swing.JLabel;
import javax.swing.JOptionPane;

import java.awt.Font;
import javax.swing.ImageIcon;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.SwingConstants;

public class Login extends JFrame {

    private JPanel contentPane;
    private JTextField txtUsuario;
    private JPasswordField txtSenha;
    private Manipula mani ;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            private JTextField txtUsuario;

            public void run() {
                try {
                    Login frame = new Login();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public Login() throws Exception {
        Manipula mani = new Manipula();
        
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 429, 414);
        contentPane = new JPanel();
        contentPane.setBackground(new Color(204, 0, 0));
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        setUndecorated(true);
        setLocationRelativeTo(null);
        
        mani=new Manipula();

        
        
        JLabel lblNewLabel_1 = new JLabel("X");
        lblNewLabel_1.setBounds(407, 10, 12, 13);
        lblNewLabel_1.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if(JOptionPane.showConfirmDialog(null, "Deseja realmente fechar? ", "Confirmação", JOptionPane.YES_NO_OPTION)==0) {
                    Login.this.dispose();
                }
            }
        });
        contentPane.setLayout(null);
        lblNewLabel_1.setFont(new Font("Arial", Font.BOLD, 11));
        lblNewLabel_1.setForeground(new Color(255, 255, 255));
        contentPane.add(lblNewLabel_1);
        
        JLabel lblNewLabel_5 = new JLabel("-");
        lblNewLabel_5.setBounds(385, 10, 12, 13);
        lblNewLabel_5.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                setExtendedState(ICONIFIED);
            }
        });
        lblNewLabel_5.setFont(new Font("Arial", Font.BOLD, 14));
        lblNewLabel_5.setForeground(Color.WHITE);
        contentPane.add(lblNewLabel_5);
        
        JPanel panel = new JPanel();
        panel.setBackground(Color.WHITE);
        panel.setBounds(101, 173, 225, 51);
        contentPane.add(panel);
        panel.setLayout(null);
        
        txtUsuario = new JTextField();
        txtUsuario.setBounds(12, 13, 162, 22);
        panel.add(txtUsuario);
        txtUsuario.setColumns(10);
        txtUsuario.setBorder(null);
        
        JLabel label = new JLabel("");
        label.setHorizontalAlignment(SwingConstants.CENTER);
        label.setIcon(new ImageIcon(Login.class.getResource("/imagens/e-mail_login.png")));
        label.setBounds(171, 0, 54, 51);
        panel.add(label);
        
        JPanel panel_1 = new JPanel();
        panel_1.setBackground(Color.WHITE);
        panel_1.setBounds(101, 250, 225, 51);
        contentPane.add(panel_1);
        panel_1.setLayout(null);
        
        txtSenha = new JPasswordField();
        txtSenha.setBounds(12, 13, 159, 19);
        panel_1.add(txtSenha);
        txtSenha.setBorder(null);
        
        JLabel label_1 = new JLabel("");
        label_1.setIcon(new ImageIcon(Login.class.getResource("/imagens/senha_login.png")));
        label_1.setHorizontalAlignment(SwingConstants.CENTER);
        label_1.setBounds(171, 0, 54, 51);
        panel_1.add(label_1);
        
        JPanel panel_2 = new JPanel();          
        panel_2.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                Usuario user = new Usuario();
                user.setEmail(txtUsuario.getText());
                user.setSenha(new String(txtSenha.getPassword()));

                if(VerificarUsuario(user.getEmail(),user.getSenha())) {
                JOptionPane.showMessageDialog(null,"Usuário e senha corretos"+user.getEmail()+user.getSenha());

                }else {
                JOptionPane.showMessageDialog(null,"Usuário ou senha incorretos");
                }

                
            }
        });
        panel_2.setBackground(Color.BLUE);
        panel_2.setBounds(137, 331, 146, 19);
        contentPane.add(panel_2);
        panel_2.setLayout(null);
        
        JLabel lblLogin = new JLabel("LOGIN");
        lblLogin.setHorizontalAlignment(SwingConstants.CENTER);
        lblLogin.setForeground(Color.WHITE);
        lblLogin.setFont(new Font("Arial", Font.BOLD, 16));
        lblLogin.setBounds(48, 0, 56, 16);
        panel_2.add(lblLogin);
        
        JLabel label_2 = new JLabel("");
        label_2.setIcon(new ImageIcon(Login.class.getResource("/imagens/user_login.png")));
        label_2.setBounds(185, 52, 64, 94);
        contentPane.add(label_2);
        
        JLabel lblCadastrarse = new JLabel("CADASTRAR-SE");
        lblCadastrarse.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent arg0) {
                Cadastrar cad;
                try {
                    cad = new Cadastrar();
                    Login.this.dispose();//fecha a janela do Login
                    cad.setVisible(true);//Abrindo o formulário principal
                } catch (Exception e) {
                    
                    e.printStackTrace();
                }

                

                
            }
        });
        lblCadastrarse.setFont(new Font("Arial", Font.BOLD, 13));
        lblCadastrarse.setForeground(Color.WHITE);
        lblCadastrarse.setBounds(40, 13, 111, 16);
        contentPane.add(lblCadastrarse);
    }
    public boolean VerificarUsuario(String email, String senha) {
        return(mani.Logar(email,senha));

    }

}

The connection:

import java.sql.*;

public class Conexao {

    public Connection connection = null;
    
    private final String DRIVER = "com.mysql.jdbc.Driver";
    private final String DBNAME = "sys_bible";
    private final String URL = "jdbc:mysql://localhost/"+DBNAME+"?autoReconnect=true&useSSL=false";
    private final String LOGIN = "root";
    private final String SENHA = "";

    
    public Connection getConnection(){
        try{
            Class.forName(DRIVER);
            connection = DriverManager.getConnection(URL, LOGIN, SENHA);
            System.out.println("Conectou"); 
            return connection;
        }
        catch(ClassNotFoundException erro){
            System.out.println("Driver nao encontrado " +erro.toString());
            return connection;
        }
        catch(SQLException erro){
            System.out.println("Falha ao conectar "+ erro.toString());
            return connection;
        }
    }
    
    public void close(){
        try{
            connection.close();
            System.out.println("Desconectou");
        }catch(SQLException erro){  
        }
    }

    
}

Manipulative class:

import java.sql.*;

import javax.swing.JOptionPane;

public class Manipula {
    
    private Connection minhaConexao;
    
    public Manipula() throws Exception{
        this.minhaConexao = new Conexao().getConnection();
    }
    
    public void inserir(String nome, String email, int rg, String senha){
        try{
            String sql ="insert into usuario (nome,email,rg,senha) values('"+nome+"','"+email+"',"+rg+",'"+senha+"')";                   
            PreparedStatement stmt = minhaConexao.prepareStatement(sql);
            stmt.executeUpdate();
            JOptionPane.showMessageDialog(null,"Inserido com Sucesso!");
         }catch(SQLException erro){
         JOptionPane.showMessageDialog(null,"Erro ao inserir");
         }            
       
}
    public boolean Logar(String email, String senha) {
           
          try {
                   String sql = "Select * from usuario where email = '"+ email+"' and senha='"+senha+"'";
                   PreparedStatement stmt = minhaConexao.prepareStatement(sql);
                   ResultSet rs = stmt.executeQuery(sql);

                   while(rs.next()) {
                       String nomebanco = rs.getString("email");
                       String senhabanco = rs.getString("senha");
                    

                       if(email.equals(nomebanco) && senhabanco.equals(senha)){
                           JOptionPane.showMessageDialog(null,"Seja bem vindo: ");
                           return true;
                           
                       }else{
                           JOptionPane.showMessageDialog(null,"Login ou Senha inválidos.");
                          return true;
                       }
                   }
               }catch(SQLException e){
                   e.printStackTrace(); 
                   JOptionPane.showMessageDialog(null,"Erro na conexão, com o banco de dados!","Título",JOptionPane.WARNING_MESSAGE);
                   return false;
               }
        return false;
           }


   
}

And the User class

public class Usuario {
private String email;
private String senha;

public Usuario() {


}


public void setEmail(String n) {
this.email=n;
}

public String getEmail() {
return this.email;
}

public void setSenha(String s) {
this.senha=s;
}

public String getSenha() {
return this.senha;
}

}

Answer 1

Whoa, good afternoon! What’s up? It would be easier if you put the whole mistake here, but come on! From what I noticed, when you call the method Verificausuario(), in it we have the Mani. Login(). The Mani object has not been initialized, hence the error. If I am right, the Nullpointerexception error appears to you, correct? I see two ways to fix this:

• Initialize it before it is called. It can be there on main;
• When calling it inside the Verify user() method, change the line of the Return and include the new before class, thus creating a local instance. Then I’d take her statement upstairs.

Since it’s just a method that returns a Boolean, I don’t think it’s necessary to declare the class up there to only use it down there once. Follow my suggestion for the Verifiuser method():

public boolean VerificarUsuario(String email, String senha) throws Exception {
    return (new Manipula().Logar(email, senha));
}