How to save a record in PostgreSQL?

This error occurs when I try to save a record in the PostgreSQL database, I'm using java

mai 15, 2018 11:09:18 AM bibliotecapesca.CadastroLeitor BtnSalvarActionPerformed
GRAVE: null
org.postgresql.util.PSQLException: ResultSet não está posicionado corretamente, talvez você precise chamar next.
    at org.postgresql.jdbc.PgResultSet.checkResultSet(PgResultSet.java:2770)
    at org.postgresql.jdbc.PgResultSet.getString(PgResultSet.java:1893)
    at org.postgresql.jdbc.PgResultSet.getString(PgResultSet.java:2478)
    at bibliotecapesca.CadastroLeitor.BtnSalvarActionPerformed(CadastroLeitor.java:306)
    at bibliotecapesca.CadastroLeitor.access$100(CadastroLeitor.java:18)
    at bibliotecapesca.CadastroLeitor$2.actionPerformed(CadastroLeitor.java:108)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6533)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6298)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Insertion code:

private void BtnSalvarActionPerformed(java.awt.event.ActionEvent evt) {                                          

        if (Alterar = false){       
        try {

        PreparedStatement inclusao = Banco.Conn.prepareStatement("INSERT INTO leitor (nome_leitor, endereco_leitor, cpf, telefone_leitor, celular_leitor) VALUES (?,?,?,?,?)");


        inclusao.setString(1, TxtNome.getText());
        inclusao.setString(2, TxtEndereco.getText());
        inclusao.setString(3, TxtCpf.getText());
        inclusao.setString(4, TxtTelefone.getText());
        inclusao.setString(5, TxtCelular.getText());

        inclusao.executeUpdate();

        JOptionPane.showMessageDialog(null, "Cadastro Realizado com sucesso!!");

        //Limpa Campos
        TxtNome.setText(null);
        TxtEndereco.setText(null);
        TxtCpf.setText(null);
        TxtTelefone.setText(null);
        TxtCelular.setText(null);

        //Atualiza o banco de dados
        Banco.executaSQL("SELECT * From leitor");



         //Desabilita botões e campos

        BtnSalvar.setEnabled(false);
        BtnNovo.setEnabled(true);
        BtnAnterior.setEnabled(true);
        BtnPosterior.setEnabled(true);

        TxtNome.setEnabled(false);
        TxtEndereco.setEnabled(false);
        TxtCpf.setEnabled(false);
        TxtTelefone.setEnabled(false);
        TxtCelular.setEnabled(false);

        } catch (SQLException ex) {
            Logger.getLogger(CadastroLeitor.class.getName()).log(Level.SEVERE, null, ex);
            JOptionPane.showMessageDialog(null, "Ocorreu um erro na execução, contate o administrador!!");

        }//catch

        }//if
         //Salvar alteração
        else if (Alterar = true){
            try {
                PreparedStatement alteracao;
                alteracao = Banco.Conn.prepareStatement("UPDATE leitor SET nome_leitor=?, endereco_leitor=?, cpf=?, telefone_leitor=?, celular_leitor=? WHERE id_leitor=?");


                int id;
                id = Integer.parseInt(Banco.Rs.getString("id_leitor"));

                alteracao.setString(1, TxtNome.getText());
                alteracao.setString(2, TxtEndereco.getText());
                alteracao.setString(3, TxtCpf.getText());
                alteracao.setString(4, TxtTelefone.getText());
                alteracao.setString(5, TxtCelular.getText());
                alteracao.setInt(6, id);

                alteracao.executeUpdate();

                JOptionPane.showMessageDialog(null, "Dados alterados com sucesso!!");


                //Atualiza consulta
                Banco.executaSQL("SELECT * FROM leitor");    

                //Desabilita / Ativa botões e campos

                BtnSalvar.setEnabled(false);
                BtnNovo.setEnabled(true);
                BtnAnterior.setEnabled(true);
                BtnPosterior.setEnabled(true);

                TxtNome.setEnabled(false);
                TxtEndereco.setEnabled(false);
                TxtCpf.setEnabled(false);
                TxtTelefone.setEnabled(false);
                TxtCelular.setEnabled(false);

                TxtNome.setText(null);
                TxtEndereco.setText(null);
                TxtCpf.setText(null);
                TxtTelefone.setText(null);
                TxtCelular.setText(null);

                Alterar=false;


            } catch (SQLException ex) {
                Logger.getLogger(CadastroLeitor.class.getName()).log(Level.SEVERE, null, ex);
            }

        }
    }  

Bank Connection

public class ConnectionBank {     public Statement Stm; // Change, Exclude, Add     public ResultSet Rs; // Search

private String Driver = "org.postgresql.Driver";
private String Caminho = "jdbc:postgresql://localhost:5432/biblioteca";
private String Usuario = "postgres";
private String Senha = "0000";

public Connection Conn;



public void conexao()
{

    try {
        System.setProperty("jdbc.Drivers", Driver);
        Conn = DriverManager.getConnection(Caminho, Usuario, Senha);
        JOptionPane.showMessageDialog(null, "Conectado!!");
    } catch (SQLException ex) {
        Logger.getLogger(ConexaoBanco.class.getName()).log(Level.SEVERE, null, ex);
    }
}

public void executaSQL (String sql){
    try {
        Stm = Conn.createStatement(Rs.TYPE_SCROLL_INSENSITIVE, Rs.CONCUR_READ_ONLY);

        Rs = Stm.executeQuery(sql);

    } catch (SQLException ex) {
        Logger.getLogger(ConexaoBanco.class.getName()).log(Level.SEVERE, null, ex);
    }

}


public void desconecta()
{
    try{
        Conn.close();

    }catch (SQLException ex){
        Logger.getLogger(ConexaoBanco.class.getName()).log(Level.SEVERE, null, ex);
    }
}