Item in JComboBox instance of an object

Hello I have the following code to see if an item in the JComboBox is instance of a class(Persoon).

    public class ItemChangeListener implements ItemListener {

        Persoon selectedPerson;
        RekeningApp app;
        PersoonView view;

        public ItemChangeListener(PersoonView view) {

            this.view = view;

        }

        public void itemStateChanged(ItemEvent event) {
            if (event.getStateChange() == ItemEvent.SELECTED) {
                Object item = event.getItem();
                System.out.println("Itemchangelistener " + item);
                // do something with object
                if(item instanceof Persoon) {
                    System.out.println("Instance");
                    this.selectedPerson = (Persoon) item;
                    view.setOverzicht(this.selectedPerson);
                } else {
                    this.selectedPerson = null;
                }
            }
        }

    }

The output of item is the value of persoon.name variable. so the items in the JComboBox are actually strings.

this is how the JComboBox list is set.

personenList.addItem(persoon.getNaam());

My question is.. how can I check If this Persoon object excists and is the same as in the JComboBox?

You should add to the JComboBox the Person objects, not just the name, so when you call Object item = event.getItem(); this will return the Person, not an String. If you want to display the person's name in the JComboBox, override the toString method in Person class to something like this:

public String toString()
    return this.naam;
}

And you should add the items to the list.

personenList.addItem(persoon);

Edit

If you don't want (or can) override the toString method you should use a custom renderer. This is a link to and example:

http://docs.oracle.com/javase/tutorial/uiswing/components/combobox.html#renderer

Override toString method just for display purposes isn't a good practice. Also it's a potential bottleneck. Lets say for example you need to show two different JComboBox with persons: in one of them you need to show only the name and in the other one you need to show fullname. You can override Person#toString() method only one time.

The way to go through is using a ListCellRenderer. Example:

public class Person {
    private String _name;
    private String _surname;

    public Person(String name, String surname){
        _name = name;
        _surname = surname;
    }

    public String getName() {
        return _name;
    }

    public String getSurname() {
        return _surname;
    }    
}

And here is the GUI:

import java.awt.Component;
import java.awt.GridLayout;
import javax.swing.DefaultComboBoxModel;
import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Demo {

    private void initGUI(){
        Person person1 = new Person("First", "Person");
        Person person2 = new Person("Second", "Person");
        Person[] persons = new Person[]{person1, person2};

        /* 
         * This combo box will show only the person's name
         */
        JComboBox comboBox1 = new JComboBox(new DefaultComboBoxModel(persons));
        comboBox1.setRenderer(new DefaultListCellRenderer() {
            @Override
            public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if(value instanceof Person){
                    Person person = (Person) value;
                    setText(person.getName());
                }
                return this;
            }
        } );

        /* 
         * This combo box will show person's full name
         */
        JComboBox comboBox2 = new JComboBox(new DefaultComboBoxModel(persons));
        comboBox2.setRenderer(new DefaultListCellRenderer() {
            @Override
            public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if(value instanceof Person){
                    Person person = (Person) value;
                    StringBuilder sb = new StringBuilder();
                    sb.append(person.getSurname()).append(", ").append(person.getName());
                    setText(sb.toString());
                }
                return this;
            }
        } );

        JPanel content = new JPanel(new GridLayout(2, 2));
        content.add(new JLabel("Name:"));
        content.add(comboBox1);
        content.add(new JLabel("Surname, Name:"));
        content.add(comboBox2);

        JFrame frame = new JFrame("Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(content);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new Demo().initGUI();
            }
        });

    }
}

If you run this example you'll see something like this: