You could use something along the lines of:
public BillatoDialog extends JDialog(){
private Delivery selectedDelivery; // Declare selectedDelivery variable
String selectedDate = comboBox.getSelectedItem(); // Returns the current selected item.
for (Delivery currentDelivery: deliveryList){ // Loop over a list with all the deliverys.
if (currentDelivery.toString()==selectedDate;){ // and break the for when match found.
selectedDelivery = currentDelivery; // assign it to selectedDelivery
break;
}
}
public Delivery getSelectedDelivery(){
return selectedDelivery;
}
}
And then in your JPanel
public BillatoPanel extends JPanel(){
openBillatoDialog();
getSelectedDelivery();
}