Dynamically define text to Jlabels according to text field validation

Question

I tried to add one label for each required component of my screen that is empty (field 01 and field 02), so I created a list of labels with the corresponding amount of fields/components. However, the attempts I made to have it "set" the corresponding messages of each label (with the names of each field) not working properly.

In the example I used only 3 fields of the type JTextField, however, the idea is that the amount of fields may vary.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class AdicionaCmp extends JFrame {

    private MeuJTextField jTextField1 = new MeuJTextField(true, "Campo 01");
    private MeuJTextField jTextField2 = new MeuJTextField(true, "Campo 02");
    private MeuJTextField jTextField3 = new MeuJTextField(false, "Campo 03");
    private JButton jButton = new JButton("Validar");
    //private JLabel labelInferior = new JLabel();
    private Font fonte = new Font("Arial", Font.PLAIN, 10);

    private List<JLabel> listLabel = new ArrayList<>();
    private List<JComponent> listComponentes = new ArrayList<>();

    public static void main(String[] args) {
        EventQueue.invokeLater(AdicionaCmp::new);
    }

    public AdicionaCmp() {
        add(montaTela());
        //setSize(600, 350);
        pack();

        setVisible(true);
        actionButton();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    private JComponent montaTela() {
        JPanel painelPrincipal = new JPanel();

        JPanel painel = new JPanel();
        painel.setLayout(new GridBagLayout());
        adicionaComponente(1, 1, 1, 1, painel, painelPrincipal);
        adicionaComponente(1, 1, 1, 2, jTextField1, painel);
        adicionaComponente(2, 1, 1, 2, jTextField2, painel);
        adicionaComponente(3, 1, 1, 2, jTextField3, painel);
        adicionaComponente(4, 1, 1, 1, jButton, painel);
        return painelPrincipal;
    }

    public void adicionaComponente(int linha, int coluna, int linhas, int colunas, JComponent componente, JPanel painel) {

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridy = linha;
        gbc.gridx = coluna;
        gbc.gridheight = 1;
        gbc.gridwidth = 1;
        gbc.anchor = GridBagConstraints.EAST;
        gbc.insets = new Insets(5, 5, 5, 5);

        JPanel painelInterno = new JPanel();
        painelInterno.setLayout(new GridBagLayout());
        JLabel rotulo = new JLabel();

        if (componente instanceof MeuJTextField) {
            rotulo = new JLabel(((MeuJTextField) componente).getNome());
        }

        GridBagConstraints gbc1 = new GridBagConstraints();
        gbc1.gridx = 1;
        gbc1.gridy = 1;
        gbc1.anchor = GridBagConstraints.WEST;
        gbc1.insets = new Insets(5, 5, 5, 5);
        painelInterno.add(rotulo, gbc1);

        GridBagConstraints gbc2 = (GridBagConstraints) gbc1.clone();
        gbc2.gridx = 2;
        gbc2.fill = GridBagConstraints.BOTH;
        gbc2.gridwidth = GridBagConstraints.REMAINDER; //Especifica que esse componente é o último componente em sua coluna ou linha.
        painelInterno.add(componente, gbc2);

        GridBagConstraints gbc3 = (GridBagConstraints) gbc1.clone();
        gbc3.gridx = 2;
        gbc3.gridy = 2;

        listComponentes.add(componente);

        if ((componente instanceof MeuJTextField) && (((MeuJTextField) componente).eObrigatorio())) {

            JLabel labelInferior = new JLabel();

            for (int i = 0; i < listComponentes.size(); i++) {
                labelInferior = new JLabel();
                painelInterno.add(labelInferior, gbc3);
                setMessage(listLabel, ((MeuJTextField) componente).getNome());
                //listLabel.add(labelInferior);
            }
            listLabel.add(labelInferior);
        }

        gbc.anchor = GridBagConstraints.WEST;
        gbc.gridx++;
        gbc.gridheight = linhas;
        gbc.gridwidth = colunas;
        painel.add(painelInterno, gbc);
    }

    private void actionButton() {
        jButton.addActionListener(e -> {
            validaComponentes();
        });
    }

    private void setMessage(List<JLabel> listLabel, String message) {
        for (JLabel labels : listLabel) {
            labels.setFont(fonte);
            labels.setForeground(new Color(255, 21, 8));
            labels.setText(message);
        }
        pack();
    }

    private boolean validaComponentes() {
        java.lang.reflect.Field[] allFields = this.getClass().getDeclaredFields();
        for (java.lang.reflect.Field field : allFields) {
            if (Modifier.isPrivate(field.getModifiers())) {
                try {
                    field.setAccessible(true);
                    Object fieldValue = field.get(this);
                    if (fieldValue instanceof MeuJTextField) {
                        if (((MeuJTextField) fieldValue).isEmpty()) {
                            setMessage(listLabel, "O " + ((MeuJTextField) fieldValue).getNome() + " não pode ser vazio !");
                            return false;
                        }
                    }
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
        return true;

    }

    class MeuJTextField extends JTextField implements MeuComponente {

        private boolean eObrigatorio;
        private String nome;

        public MeuJTextField(boolean eObrigatorio, String nome) {
            this.eObrigatorio = eObrigatorio;
            this.nome = nome;
            setPreferredSize(new Dimension(200, 25));
        }

        @Override
        public String getNome() {
            return nome;
        }

        public boolean isEmpty() {
            return getText().trim().isEmpty();
        }

        @Override
        public boolean eObrigatorio() {
            return eObrigatorio;
        }
    }

    public interface MeuComponente {

        public String getNome();

        public boolean eObrigatorio();
    }
}

Answer 1

As asked in the comments, this response is an alternative to what you have already done, which makes the code more organized and readable:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;


public class ValidarCamposComLabelTest  extends JFrame{

    private List<MeuJTextField> fields =  new ArrayList<>();
    private List<JLabel> labels = new ArrayList<>();
    private JButton jButton = new JButton("Validar");

    private Font fonte = new Font("Arial", Font.PLAIN, 10);

    public static void main(String[] args) {
        EventQueue.invokeLater(ValidarCamposComLabelTest::new);
    }

    public ValidarCamposComLabelTest() {

        JPanel painelPrincipal = new JPanel();

        JPanel painel = new JPanel();
        painel.setLayout(new GridBagLayout());

        fields.add(new MeuJTextField(true, "Campo 01"));
        fields.add(new MeuJTextField(true, "Campo 02"));
        fields.add(new MeuJTextField(true, "Campo 03"));

        int linhaAtual = 1;

        for(int i = 0; i < fields.size(); i++, linhaAtual++) {
            adicionaComponente(linhaAtual, 1, 1, 1, new JLabel(fields.get(i).getNome()), painel);
            adicionaComponente(linhaAtual, 2, 1, 2, fields.get(i), painel);

            if(fields.get(i).eObrigatorio()) {

                JLabel label = new JLabel("");
                label.setFont(fonte);
                label.setForeground(new Color(255, 21, 8));
                adicionaComponente(++linhaAtual, 2, 1, 1, label, painel);
                labels.add(label);
            } 
        }


        adicionaComponente(++linhaAtual, 1, 1, 1, jButton, painel);
        jButton.addActionListener(e -> validaComponentes());

        painelPrincipal.add(painel);
        add(painelPrincipal);
        pack();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
    }

    private boolean validaComponentes() {
        boolean retorno = true;

        for(int i = 0; i <fields.size(); i++) {
            if(fields.get(i).isEmpty()) {
                labels.get(i).setText(fields.get(i).getNome() +  " não pode ser vazio !");
                retorno = false;
            } else {
                labels.get(i).setText("");
            }
        }
        pack();
        return retorno;
    }

    private void adicionaComponente(int linha, int coluna, int linhas, int colunas, JComponent componente,
            JPanel painel) {

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridy = linha;
        gbc.gridx = coluna;
        gbc.gridheight = linhas;
        gbc.gridwidth = colunas;
        gbc.insets = new Insets(5, 5, 5, 5);        
        painel.add(componente, gbc);

    }

    class MeuJTextField extends JTextField implements MeuComponente {

        private boolean eObrigatorio;
        private String nome;

        public MeuJTextField(boolean eObrigatorio, String nome) {
            this.eObrigatorio = eObrigatorio;
            this.nome = nome;
            setPreferredSize(new Dimension(200, 25));
        }

        @Override
        public String getNome() {
            return nome;
        }

        public boolean isEmpty() {
            return getText().trim().isEmpty();
        }

        @Override
        public boolean eObrigatorio() {
            return eObrigatorio;
        }
    }

    public interface MeuComponente {

        public String getNome();

        public boolean eObrigatorio();
    }
}

Changes I’ve made:

• created field lists(fields) and another for their respective fields, and added these according to the amount of fields;

• the variable linhaAtual was created to be able to control the addition of the added components in the variable painel;

• when adding a label referring to the notice to fill in a text field, a preincrement in linhaAtual so that this component is added to the line below the text field;

• the method adicionaComponente() was abstracted so that it can now be used to add any component to any panel on your screen that has a GridBagLayout as its layout, respecting the values passed to the GridBagConstraints;

• the method validaComponentes() is leaner thanks to our lists of text fields and Abels, without the need for recursiveness to sweep the fields. With an additional, it now also cleans the Abels when the field passes the validation.

I reiterate that although functional, I particularly find this form of validation approach very bad, fill the screen of Abels to show message of each field does not improve the UX of your application, quite the contrary.

Using InputVerifier I think you’ll be more friendly, if you want an example, see at this link or in this answer what I did here on the site.