public Initialize() {
    setTitle("");
    setSize(400, 300);
    setLocationRelativeTo(null);
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(3, 2));
    typel = new JLabel("Animal Type:");
    typef = new JComboBox();
    typef.addItem("Cow");
    typef.addItem("Deer");
    typef.addItem("Horse");
    tot_popl = new JLabel("Initial population:");
    tot_pop = new JTextField(12);
    annuler = new JButton("Cancel");
    validate = new JButton("Create");

    annuler.addActionListener(this);
    validate.addActionListener(this);
    p.add(typel);
    p.add(typef);
    p.add(tot_popl);
    p.add(tot_pop);
    p.add(annuler);
    p.add(validate);
    setContentPane(p);
    this.pack(); // bien regrouper les éléments
  }
  @Override
  public void actionPerformed(ActionEvent e) {

    Object source = e.getSource();

    if (source == annuler) {
      this.setVisible(false);
    }

    if (source == validate) {

      // ***************here we test if the field is filled or not************
      if (tot_pop.getText().equals("")) {

        JOptionPane.showMessageDialog(errorMsg, "Fill the initial population");
      } else {

        total_popInt = Integer.parseInt(tot_pop.getText());
        // Animal a=new Animal(0,typef.getText(),total);
        int index = typef.getSelectedIndex();
        String typeAnim = (typef.getItemAt(index)).toString();
        // ****************here we test if what we insert exist with the function above********
        if (testingInit("cow")) {
          write = new fileWriting("init_pop", typeAnim + " " + total_popInt);
          anima = new AnimalType(total_popInt, typeAnim);
          this.setVisible(false);
          // JOptionPane.showMessageDialog(null, "The animal type is created successfully");
        } else {
          JOptionPane.showMessageDialog(errorMsg, "Information on this date already given");
        }

        switch (typeAnim) {
          case "Cow":
            AppFrame.totalPopulationCOW = AppFrame.totalPopulationCOW + total_popInt;
            initialPopCOW = total_popInt;
            break;
          case "Deer":
            AppFrame.totalPopulationDEER = AppFrame.totalPopulationDEER + total_popInt;
            initialPopDEER = total_popInt;
            break;
          case "Horse":
            AppFrame.totalPopulationHORSE = AppFrame.totalPopulationHORSE + total_popInt;
            initialPopHORSE = total_popInt;
            break;
          default:
            System.out.println("Switch in Initialize is not working");
            break;
        }
        Main.totalPopulation = Main.totalPopulation + total_popInt;
        new AnimalDetails(
            "2009", "01", CreateAnimal.animalTypeToEnum(typeAnim), total_popInt, 0, "Winter");
        new CreateAnimal(CreateAnimal.animalTypeToEnum(typeAnim), total_popInt);
      }
    }
  }