private void btnAddActionPerformed(java.awt.event.ActionEvent evt) {
Connection conn = null;
PreparedStatement psm = null;
String cod = txtCod.getText();
String sql = "SELECT * FROM produtos WHERE cod = "+cod;
String nome = null;
float valor = 0;
String desc = null;
try{
    conn = DatabaseConnection.MysqlConnection();
    psm = conn.prepareStatement(sql);
    psm.execute();

    ResultSet result = psm.executeQuery(sql);

    while(result.next()){
        nome = result.getString("nome");
        valor = result.getFloat("valor_m2");
        desc = result.getString("descricao");
    }
    if(txtHeight.getText().equals("") && txtWidth.getText().equals("")){
        float a2 = Float.parseFloat(JOptionPane.showInputDialog(rootPane, "Por favor insira a área da peça", "Área", HEIGHT));

        float valorm = a2 * valor;

        MainForm mf = new MainForm();
        mf.addInTable(cod, nome, a2, valor, valorm);

        this.setVisible(false);
        psm.close();
        conn.close();
    }
    else{
        float alt = Float.parseFloat(txtHeight.getText());
        float lag = Float.parseFloat(txtWidth.getText());

        float area = alt * lag;
        float valorm = area * valor;

        MainForm mf = new MainForm();
        mf.addInTable(cod, nome, area, valor, valorm);

        this.setVisible(false);
        psm.close();
        conn.close();
    }
}
catch(Exception ex){
    System.out.println(ex);;
}

public void addInTable(String cod, String prod, float area, float prec, float precTot){
String nom = prod;
String con = cod;
String are = Float.toString(area);
String pre = Float.toString(prec);
String tot = Float.toString(precTot);

DefaultTableModel model = (DefaultTableModel) tblMain.getModel();
model.addRow(new Object[]{con, nom, are, pre, tot});

float total = 0;
total = total + precTot;


lblTrue.setText(Float.toString(total));

public List<EssaClasseVolta> findAll(){
}