Arraylist giving error

Question

I’m doing a little program with a database and I can’t seem to get my list to appear in one jtable. I created the method and at the time I call my method it error, someone can help me code this down?

Error:

Exception in thread "AWT-Eventqueue-0" java.lang.Nullpointerexception at presentcao.TelaCliente.formInternalFrameOpened(Telacliente . java:593)

List method

public List<cliente>preencherTabela(){
        String sql = "select * from cliente";
        cliente c=new cliente();

        List<cliente> lista = new ArrayList<>();

         try(PreparedStatement stmt = conexao.prepareStatement(sql)){

            ResultSet rs = stmt.executeQuery();
            while(rs.next()){
                c.setIdcodigo(rs.getInt("idcodigo"));
                c.setNome(rs.getString("nome"));
                c.setEndereco(rs.getString("endereco"));
                c.setEmail(rs.getString("email"));
                c.setCidade(rs.getString("cidade"));
                c.setBairro(rs.getString("bairro"));
                c.setTelefone(rs.getString("telefone"));
                c.setCelualr(rs.getString("celular"));
                c.setCep(rs.getString("cep"));
                c.setRg(rs.getString("rg"));
                c.setCpf(rs.getString("cpf"));
                c.setDatanascimento(rs.getString("datanascimento"));
                c.setUf(rs.getString("uf"));
                c.setSexo(rs.getString("sexo"));
            }
        }catch (SQLException ex) {
            JOptionPane.showMessageDialog(null,"Usuario nao encontrado" + ex);
        }
        return lista;
    }
}      

code to call the method

private void formInternalFrameOpened(javax.swing.event.InternalFrameEvent evt) {                                         
        cliente c = new cliente();
        List<cliente> lista = new ArrayList<>();
        Conexao con=null;
        lista=con.preencherTabela();

        for(int i=0;i<lista.size();i++){
            c=lista.get(i);
            jPcad.setValueAt(c.getIdcodigo(), i, 0);
            jPcad.setValueAt(c.getNome(), i, 1);
        }

    }          

Answer 1

There are several problems in this code. One of the problems is that you are returning an empty list because the method preencheTabela() creates objects from the bank, but are never added to the list. Add a lista.add(c)at the end of while:

public List<cliente> preencherTabela(){
        String sql = "select * from cliente";
        cliente c=new cliente();

        List<cliente> lista = new ArrayList<>();

         try(PreparedStatement stmt = conexao.prepareStatement(sql)){

            ResultSet rs = stmt.executeQuery();
            while(rs.next()){
                c.setIdcodigo(rs.getInt("idcodigo"));
                c.setNome(rs.getString("nome"));
                c.setEndereco(rs.getString("endereco"));
                c.setEmail(rs.getString("email"));
                c.setCidade(rs.getString("cidade"));
                c.setBairro(rs.getString("bairro"));
                c.setTelefone(rs.getString("telefone"));
                c.setCelualr(rs.getString("celular"));
                c.setCep(rs.getString("cep"));
                c.setRg(rs.getString("rg"));
                c.setCpf(rs.getString("cpf"));
                c.setDatanascimento(rs.getString("datanascimento"));
                c.setUf(rs.getString("uf"));
                c.setSexo(rs.getString("sexo"));
                lista.add(c);
            }
        }catch (SQLException ex) {
            JOptionPane.showMessageDialog(null,"Usuario nao encontrado" + ex);
        }
        return lista;
    }
}    

Another problem is that you assign null connection to the bank just before calling the above method:

private void formInternalFrameOpened(javax.swing.event.InternalFrameEvent evt) {                                         
        cliente c = new cliente();
        List<cliente> lista = new ArrayList<>();
        Conexao con=null;
        lista=con.preencherTabela();

        for(int i=0;i<lista.size();i++){
            c=lista.get(i);
            jPcad.setValueAt(c.getIdcodigo(), i, 0);
            jPcad.setValueAt(c.getNome(), i, 1);
        }

}   

Unconnected, con.preencherTabela(); will not work, will burst nullpointerexception. Start the connection so that the list can be returned.