How to set index when inserting item in JComboBox?

André ,

If you are using model on your JComboBox that implements interface MutableComboBoxModel you will be able to do:

((MutableComboBoxModel) jComboBox.getModel()).insertElementAt(carlos, 0);
((MutableComboBoxModel) jComboBox.getModel()).insertElementAt(maria, 1);

But I strongly advise you to create the list of items before putting in your JComboBox , something like:

List<Pessoa> pessoas = new ArrayList<>();
pessoas.add(new Pessoa(12, "Carlos" , 0.0f));//adicionando o carlos na lista
pessoas.add(new Pessoa(23, "Maria" ,0.0f));

//com a lista pronta, altere o model no seu jComboBox
jComboBox.setModel(new DefaultComboBoxModel<>(pessoas.toArray()));

When you say you want the index to be 12 or 23, this is only possible if you have more than 23 items in your jComboBox . The index in the case is the position that the element is in its jComboBox , where 0 is the first position up to list size -1.

What you might want is to display these numbers next to the name in your jComboBox . For this you only need to override the toString() method in your Pessoa class.

public class Pessoa{

  private String nome;
  private int idade;

  @Override
  public String toString(){
    return idade + " - " + nome;
  }

}

So your jComboBox will display the items like this:

• 12 - Carlos
  
• 23 - Maria

Here's a working example of what you want. Basically the key is to implement the toString() method properly.

package testes;

import java.awt.EventQueue;
import java.awt.FlowLayout;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class TesteComboBox {
    public static void main(String[] args) {
        EventQueue.invokeLater(TesteComboBox::exemplo);
    }

    private static void exemplo() {
        JFrame jf = new JFrame("Exemplo");
        JComboBox<Pessoa> jComboBoxF = new JComboBox<>();
        jf.setLayout(new FlowLayout());
        jf.add(jComboBoxF);

        Pessoa carlos = new Pessoa(12, "Carlos", 0.0f);
        Pessoa maria = new Pessoa(23, "Maria", 0.0f);
        jComboBoxF.addItem(carlos);
        jComboBoxF.addItem(maria);

        JButton mensagem = new JButton("Mostrar");
        jf.add(mensagem);
        mensagem.addActionListener(e -> {
            int idx = jComboBoxF.getSelectedIndex();
            if (idx == -1) {
                JOptionPane.showMessageDialog(jf, "Você não escolheu ninguém.");
            } else {
                Pessoa escolha = jComboBoxF.getItemAt(jComboBoxF.getSelectedIndex());
                JOptionPane.showMessageDialog(jf, "Você escolheu " + escolha.getNome() + " de id " + escolha.getId());
            }
        });

        jf.pack();
        jf.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        jf.setVisible(true);
    }

    public static class Pessoa {
        private final int id;
        private final String nome;
        private final double outraCoisa;

        public Pessoa(int id, String nome, double outraCoisa) {
            this.id = id;
            this.nome = nome;
            this.outraCoisa = outraCoisa;
        }

        public int getId() {
            return id;
        }

        public String getNome() {
            return nome;
        }

        public double getOutraCoisa() {
            return outraCoisa;
        }

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

If the object you want to add in the combobox can not have an appropriate toString() method, then use an auxiliary class with toString() suitable:

public class MinhaClasseAuxiliar {
    private final Pessoa p;
    public MinhaClasseAuxiliar(Pessoa p) {
        this.p = p;
    }

    public Pessoa getPessoa() {
        return p;
    }

    @Override
    public String toString() {
        // Aqui você faz o que quiser.
    }
}

And then you add auxiliary class objects instead of adding Pessoa .

I understood your doubt! But I do not know if that's going to work for you after all this time, but it can suddenly work for someone else. This link has something that can serve you: link