Displaying JList elements without DefaultListModel

I DefaultListModel trying to output a JList without a DefaultListModel , using my own List and add method to add to the JList . I get a list of errors like

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at javax.swing.JList $ 4.getSize (Unknown Source)

The task is exactly in the output without DefaultListModel .

In the MyForm() constructor

  import laba2.ACrafts; import laba2.List; import javax.swing.*; public class MyForm extends JFrame{ JFrame formShow; private JList<ACrafts> list; public List li; private JButton btnAdd; public MyForm() { li = new List(); JPanel panelShow = new JPanel(); formShow = new JFrame("Aircrafts"); formShow.setBounds(100, 100, 700, 550); formShow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); formShow.add(panelShow); panelShow.setLayout(null); list = new JList<ACrafts>(); list.setLayoutOrientation(JList.VERTICAL); list.setBounds(20, 20, 640, 150); ACrafts[] arr; arr = li.toArray(); list.setListData(arr); panelShow.add(list); public void setData(ACrafts a) { li.add(a); } } 

Methods add in the List class

 class Element{ Element left; ACrafts data; Element right; } public class List implements ListImpl{ private Element first; private Element last; private int size; public List() { first = null; last = null; size = 0; } public void add(ACrafts e){ Element elem = new Element(); elem.data = e; if (size == 0) first = last = elem; else last.right = elem; elem.left = last; last = elem; size++; } } 

In Maine:

 public static void main(String[] args) { ACrafts[] aircraft = new ACrafts[5]; aircraft[0] = new ACrafts("Boeing 767-300F","США",7130,54000,13100,850); aircraft[1] = new ACrafts("Airbus 310-300F","Франция",39000,9600,12200,850); aircraft[2] = new ACrafts("Boeing 757-200F","США",7100,39780,12500,935); aircraft[3] = new ACrafts("IL-86","Украина",3300,15000,11000,950); aircraft[4] = new ACrafts("Avro RJ-100","Великобритания",2255,9500,10600,890); MyForm form = new MyForm(); form.setData(aircraft[0]); form.setData(aircraft[1]); form.setData(aircraft[2]); form.setData(aircraft[3]); form.setData(aircraft[4]); form.formShow.setVisible(true); } 

And if you make a list by pressing a button, then everything is displayed. And the previous version is not.

 btnAdd = new JButton("Просмотреть"); btnAdd.setBounds(30, 250, 100, 50); panelShow.add(btnAdd); btnAdd.addMouseListener(new MouseAdapter() { public void mouseClicked(MouseEvent event) { ACraft[] petsArr; petsArr = li.toArray(); z1.setListData(petsArr);} }); z1 = new JList(); z1.setLayoutOrientation(JList.VERTICAL); z1.setBounds(20, 20, 640, 150); panelShow.add(z1);