For answer http://stackoverflow.com/questions/4587837/dynamic-fields-addition-in-java-swing-form

Entry.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package dynamicfields;

import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
 *
 * @author ndunn
 */
public class Entry extends JPanel {
    private JComboBox comboBox;
    private JTextField textField;
    private JButton plus;
    private JButton minus;
    private EntryList parent;

    public Entry(JComboBox comboBox, String textFieldText, EntryList list) {
        this.comboBox = comboBox;
        this.parent = list;
        this.plus = new JButton(new AddEntryAction());
        this.minus = new JButton(new RemoveEntryAction());
        this.textField = new JTextField(10);
        this.textField.setText(textFieldText);
        add(this.plus);
        add(this.minus);
        add(this.comboBox);
        add(this.textField);
    }

    public JComboBox getComboBox() {
        return comboBox;
    }

    public class AddEntryAction extends AbstractAction {

        public AddEntryAction() {
            super("+");
        }

        public void actionPerformed(ActionEvent e) {
            parent.cloneEntry(Entry.this);
        }

    }

    public class RemoveEntryAction extends AbstractAction {

        public RemoveEntryAction() {
            super("-");
        }

        public void actionPerformed(ActionEvent e) {
            parent.removeItem(Entry.this);
        }
    }

    public void enableAdd(boolean enabled) {
        this.plus.setEnabled(enabled);
    }
    public void enableMinus(boolean enabled) {
        this.minus.setEnabled(enabled);
    }
}

EntryList.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package dynamicfields;

import java.util.ArrayList;
import java.util.List;
import javax.swing.JComboBox;
import javax.swing.JPanel;

/**
 *
 * @author ndunn
 */
public class EntryList extends JPanel{
    private List<Entry> entries;
    // Replace with your database stuff
    private static final String[] comboBoxEntries = {"Test","Two","Three"};


    public EntryList() {
        this.entries = new ArrayList<Entry>();

        Entry initial = new Entry(new JComboBox(comboBoxEntries), "", this);
        addItem(initial);
    }

    public void cloneEntry(Entry entry) {
        Object selected = entry.getComboBox().getSelectedItem();
        JComboBox copy = new JComboBox(comboBoxEntries);
        copy.setSelectedItem(selected);
        Entry theClone = new Entry(copy, "", this);

        addItem(theClone);
    }

    private void addItem(Entry entry) {
        entries.add(entry);

        add(entry);
        refresh();
    }

    public void removeItem(Entry entry) {
        entries.remove(entry);
        remove(entry);
        refresh();
    }

    private void refresh() {
        revalidate();

        if (entries.size() == 1) {
            entries.get(0).enableMinus(false);
        }
        else {
            for (Entry e : entries) {
                e.enableMinus(true);
            }
        }
    }

}

Main.java

package dynamicfields;

import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 *
 * @author ndunn
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        EntryList panel = new EntryList();
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

}