JCombobox를 업데이트 할 때 Nullpointer

Question

나는 한동안이 문제에 시달렸습니다. 안 나는 그것이 버튼 클릭에 의해 생성 된 즉시로, 소유자의 객체와 빈 JComboBox에 업데이트하기 위해 노력하고있어,하지만 난이 고정 NullPointerException이

 package gui; 

    import java.awt.BorderLayout; 
    import java.awt.EventQueue; 

    import javax.swing.JFrame; 
    import javax.swing.JPanel; 
    import javax.swing.border.EmptyBorder; 
    import javax.swing.JMenuBar; 
    import javax.swing.JToolBar; 
    import javax.swing.JTabbedPane; 
    import javax.swing.JDesktopPane; 
    import javax.swing.border.TitledBorder; 
    import javax.swing.border.LineBorder; 
    import java.awt.Color; 
    import javax.swing.JLabel; 
    import javax.swing.JTextField; 
    import javax.swing.JButton; 
    import java.awt.Insets; 
    import java.awt.Button; 
    import java.awt.Component; 
    import javax.swing.JLayeredPane; 
    import javax.swing.JTable; 
    import javax.swing.Box; 
    import javax.swing.JSplitPane; 
    import javax.swing.AbstractAction; 
    import java.awt.event.ActionEvent; 
    import javax.swing.Action; 
    import javax.swing.JInternalFrame; 
    import java.awt.event.*; 
    import controller.ForestOwnerCtr; 


    import model.OwnerCon; 
    import model.Owner; 
    import model.Tree; 

    import java.awt.event.ActionListener; 
    import java.util.ArrayList; 
    import javax.swing.JList; 
    import javax.swing.JComboBox; 
    import java.awt.Choice; 
    import java.awt.Label; 
    import javax.swing.DefaultComboBoxModel; 

    public class ForestGui extends JFrame { 

     private static ForestOwnerCtr FOCtr; 
     private JPanel contentPane; 
     private JTextField txtOwnerName; 
     private JTextField txtOwnerAdress; 
     private JTextField txtOwnerPhone; 
     private JTextField txtName; 
     private JTextField txtLocation; 
     private JTextField txtArea; 
     private JTextField textField; 
     private JTextField textField_3; 
     private JTextField textField_4; 
     private JTextField txtAge; 
     private JComboBox<Owner> owner_select; 
     private ArrayList<Owner> test; 

     /** 
     * Launch the application. 
     */ 
     public static void main(String[] args) { 
      EventQueue.invokeLater(new Runnable() { 
       public void run() { 
        try { 
         ForestGui frame = new ForestGui(); 
         frame.setVisible(true); 
        } catch (Exception e) { 
         e.printStackTrace(); 
        } 
       } 
      }); 
      FOCtr = new ForestOwnerCtr(); 
     } 

     /** 
     * Create the frame. 
     */ 
     public ForestGui() { 
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
      setBounds(100, 100, 946, 509); 

      JMenuBar menuBar = new JMenuBar(); 
      setJMenuBar(menuBar); 

      JButton btnCreate = new JButton("Create"); 
      menuBar.add(btnCreate); 

      JButton btnSearch_1 = new JButton("Search"); 
      menuBar.add(btnSearch_1); 
      contentPane = new JPanel(); 
      contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
      setContentPane(contentPane); 
      contentPane.setLayout(null); 

      JPanel panel_search_forest = new JPanel(); 
      panel_search_forest.setBorder(new TitledBorder(new LineBorder(new Color(130, 135, 144)), "Seach forest", TitledBorder.LEADING, TitledBorder.TOP, null, null)); 
      panel_search_forest.setToolTipText("tst"); 
      panel_search_forest.setBounds(15, 11, 238, 238); 
      contentPane.add(panel_search_forest); 
      panel_search_forest.setLayout(null); 

      JLabel lblName_1 = new JLabel("Name"); 
      lblName_1.setBounds(10, 28, 46, 14); 
      panel_search_forest.add(lblName_1); 

      txtName = new JTextField(); 
      txtName.setColumns(10); 
      txtName.setBounds(92, 26, 119, 19); 
      panel_search_forest.add(txtName); 

      JLabel lblLocation = new JLabel("Location"); 
      lblLocation.setBounds(10, 56, 58, 14); 
      panel_search_forest.add(lblLocation); 

      JLabel lblArea = new JLabel("Area"); 
      lblArea.setBounds(10, 81, 46, 14); 
      panel_search_forest.add(lblArea); 

      txtLocation = new JTextField(); 
      txtLocation.setColumns(10); 
      txtLocation.setBounds(92, 54, 119, 19); 
      panel_search_forest.add(txtLocation); 

      txtArea = new JTextField(); 
      txtArea.setColumns(10); 
      txtArea.setBounds(92, 79, 119, 19); 
      panel_search_forest.add(txtArea); 

      JLabel lblAge = new JLabel("Age"); 
      lblAge.setBounds(10, 106, 46, 14); 
      panel_search_forest.add(lblAge); 

      txtAge = new JTextField(); 
      txtAge.setColumns(10); 
      txtAge.setBounds(92, 107, 119, 19); 
      panel_search_forest.add(txtAge); 

      JButton CreateForest = new JButton("New forest"); 
      CreateForest.addActionListener(new ActionListener() { 
       public void actionPerformed(ActionEvent arg0) { 
        createForest(); 
       } 
      }); 
      CreateForest.setBounds(109, 204, 119, 23); 
      panel_search_forest.add(CreateForest); 

      JLabel lblOwner = new JLabel("Owner"); 
      lblOwner.setBounds(10, 131, 46, 14); 
      panel_search_forest.add(lblOwner); 

      Choice choice = new Choice(); 
      choice.setBounds(92, 163, 119, 19); 
      panel_search_forest.add(choice); 

      JLabel lblTreeSorts = new JLabel("Tree sorts"); 
      lblTreeSorts.setBounds(10, 163, 76, 20); 
      panel_search_forest.add(lblTreeSorts); 


      JComboBox<Owner> owner_select = new JComboBox<Owner>(); 
      owner_select.setModel(new DefaultComboBoxModel(FOCtr.getOwners().toArray())); 
      owner_select.setBounds(90, 137, 121, 20); 

      panel_search_forest.add(owner_select); 




      JPanel searc_owner = new JPanel(); 
      searc_owner.setToolTipText("tst"); 
      searc_owner.setBorder(new TitledBorder(new LineBorder(new Color(130, 135, 144)), "Seach owner", TitledBorder.LEADING, TitledBorder.TOP, null, null)); 
      searc_owner.setBounds(263, 11, 250, 196); 
      contentPane.add(searc_owner); 
      searc_owner.setLayout(null); 

      JLabel lblName = new JLabel("Name"); 
      lblName.setBounds(10, 22, 46, 14); 
      searc_owner.add(lblName); 

      JLabel lblAdress = new JLabel("Adress"); 
      lblAdress.setBounds(10, 47, 46, 14); 
      searc_owner.add(lblAdress); 

      JLabel lblPhoneNumber = new JLabel("Phone number"); 
      lblPhoneNumber.setBounds(10, 77, 83, 14); 
      searc_owner.add(lblPhoneNumber); 

      txtOwnerName = new JTextField(); 
      txtOwnerName.setBounds(111, 20, 119, 17); 
      searc_owner.add(txtOwnerName); 
      txtOwnerName.setColumns(10); 

      txtOwnerAdress = new JTextField(); 
      txtOwnerAdress.setColumns(10); 
      txtOwnerAdress.setBounds(111, 45, 119, 17); 
      searc_owner.add(txtOwnerAdress); 

      txtOwnerPhone = new JTextField(); 
      txtOwnerPhone.setColumns(10); 
      txtOwnerPhone.setBounds(111, 75, 119, 17); 
      searc_owner.add(txtOwnerPhone); 

      JButton btnSearch = new JButton("New Owner"); 
      btnSearch.addActionListener(new ActionListener() { 
       public void actionPerformed(ActionEvent E) { 
        createOwner(); 
       } 
      }); 



      btnSearch.setBounds(141, 162, 89, 23); 
      searc_owner.add(btnSearch); 



      JPanel panel = new JPanel(); 
      panel.setLayout(null); 
      panel.setToolTipText("tst"); 
      panel.setBorder(new TitledBorder(new LineBorder(new Color(130, 135, 144)), "Seach forest", TitledBorder.LEADING, TitledBorder.TOP, null, null)); 
      panel.setBounds(585, 171, 238, 196); 
      contentPane.add(panel); 

      JLabel label = new JLabel("Name"); 
      label.setBounds(10, 28, 46, 14); 
      panel.add(label); 

      textField = new JTextField(); 
      textField.setColumns(10); 
      textField.setBounds(78, 25, 119, 17); 
      panel.add(textField); 

      JLabel label_1 = new JLabel("Location"); 
      label_1.setBounds(10, 56, 58, 14); 
      panel.add(label_1); 

      JLabel label_2 = new JLabel("Area"); 
      label_2.setBounds(10, 81, 46, 14); 
      panel.add(label_2); 

      textField_3 = new JTextField(); 
      textField_3.setColumns(10); 
      textField_3.setBounds(78, 53, 119, 17); 
      panel.add(textField_3); 

      textField_4 = new JTextField(); 
      textField_4.setColumns(10); 
      textField_4.setBounds(78, 78, 119, 17); 
      panel.add(textField_4); 

      JButton button_1 = new JButton("Search"); 
      button_1.setBounds(139, 162, 89, 23); 
      panel.add(button_1); 


      } 






    private void createForest(){ 

     String name = txtName.getText(); 
     String location = txtLocation.getText(); 
     int totalArea = Integer.parseInt(txtArea.getText()); 
     int age = Integer.parseInt(txtAge.getText()); 
     //Owner owner = 
     FOCtr.createForest(name, location, totalArea, age); 
     } 

    private void createOwner(){ 


     String newName = txtOwnerName.getText(); 
     String newAdress = txtOwnerAdress.getText(); 
     String newPhone = txtOwnerPhone.getText(); 
     Owner o = new Owner(newName, newAdress, newPhone); 
     test.add(o); 
     owner_select.addItem(o); 
     } 

    } 

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at gui.ForestGui.createOwner(ForestGui.java:285) 
    at gui.ForestGui.access$1(ForestGui.java:278) 
    at gui.ForestGui$3.actionPerformed(ForestGui.java:211) 
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source) 
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) 
    at java.awt.Component.processMouseEvent(Unknown Source) 
    at javax.swing.JComponent.processMouseEvent(Unknown Source) 
    at java.awt.Component.processEvent(Unknown Source) 
    at java.awt.Container.processEvent(Unknown Source) 
    at java.awt.Component.dispatchEventImpl(Unknown Source) 
    at java.awt.Container.dispatchEventImpl(Unknown Source) 
    at java.awt.Component.dispatchEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) 
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) 
    at java.awt.Container.dispatchEventImpl(Unknown Source) 
    at java.awt.Window.dispatchEventImpl(Unknown Source) 
    at java.awt.Component.dispatchEvent(Unknown Source) 
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
    at java.awt.EventQueue.access$200(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
    at java.awt.EventQueue.dispatchEvent(Unknown Source) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
    at java.awt.EventDispatchThread.run(Unknown Source) 

Answer 1

I have been struggling with this for a time 

가 계속 5 분 이상 걸리십시오.

NPE는 모두 해결해야 할 가장 쉬운 문제입니다. 스택 추적을 인쇄하고 발생하는 클래스와 행 번호를 기록한 다음 초기화되지 않은 참조가 널이 아닌 참조로 설정하여 해당 행을 스캔하십시오. 명확하지 않은 경우 디버거와 함께 IDE를 사용하십시오.

동일한 동작을 반복하고 다른 결과가 발생할 것으로 예상하지 마십시오. 그것이 당신의 문제를 일으키는 경쟁 조건이 아니라면 그것은 광기의 신호입니다.

FWIW, 너무 많은 코드를 작성 중입니다. 그것이 Swing을 싫어하는 이유 중 하나입니다. 너무 많은 코드! 약간의 생각과 분해가 먼 길을 갈 것입니다.

예를 들어 지구상에 수업을 연장 할 이유가 없습니다. JFrame. JPanel이 더 나은 선택이 될 것입니다. JFrame에 수업을 퍼갈 수 있습니다.

textField_4? 그게 뭐야? 그게 무엇인지 사람들이 어떻게 말할 수 있습니까? 신비화 된 개인은 심지어 3 주 후에 나올 수도 있습니다.

JComboBox<Owner> owner_select = new JComboBox<Owner>(); 

당신의 createOwner의 코드() 메소드 할 수 있습니다

이

private JComboBox<Owner> owner_select; 

그런 다음 당신은 당신의 생성자 null가 아닌 지역 변수를 만들 :

Answer 2

당신은 null 인 클래스 변수를 정의 클래스 변수에만 액세스하십시오. 생성자의 코드가 다음과 같아야하므로 로컬 변수를 만들고 싶지 않습니다.

owner_select = new JComboBox<Owner>();