（），而使用Nimbus外觀

我有4類：TestGUI，MainMenuBar，大型機和ProjectToAdd。 MainFrame和ProjectToAdd實現了Serializable。當我點擊MainMenuBar中的New> Project時，我想創建一個新項目，爲它創建新目錄，並在該目錄中編寫一個可序列化的對象。當對象被寫入時，我得到NullPointerException（見最後的stacktrace）。如果我在主方法中刪除了外觀和感覺代碼的一部分，我不會再收到錯誤...我正在使用NetBeans IDE 8.0.2。（），而使用Nimbus外觀

TestGUI代碼：

package testgui; 

import javax.swing.UIManager; 
import javax.swing.UIManager.LookAndFeelInfo; 

public class RiskManagerGUI { 

    public static void main(String[] args) { 

     java.awt.EventQueue.invokeLater(new Runnable() { 
      public void run() { 

       try { 
        for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) { 
         if ("Nimbus".equals(info.getName())) { 
          UIManager.setLookAndFeel(info.getClassName()); 
          break; 
         } 
        } 
       } catch (Exception e) { 
        // If Nimbus is not available, fall back to cross-platform 
        try { 
         UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName()); 
        } catch (Exception ex) { 
         // not worth my time 
        } 
       } 

       new MainFrame().setVisible(true); 

      } 
     }); 
    } 

}

MainMenuBar代碼：

package menu_package; 

import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import javax.swing.*; 
import testgui.MainFrame; 

public class MainMenuBar extends JMenuBar{ 

    private MainFrame mainFrame; 

    public MainMenuBar(MainFrame mainFrame){ 

     this.mainFrame = mainFrame; 

     JMenu fileMenu = new JMenu("File"); 
     JMenu newMenu = new JMenu("New"); 

     JMenuItem projectMenuItem = new JMenuItem("Project"); 
     projectMenuItem.addActionListener(new AddNewProject()); 

     newMenu.add(projectMenuItem); 

     fileMenu.add(newMenu); 

     add(fileMenu); 
    } 

    class AddNewProject implements ActionListener { 
    public void actionPerformed(ActionEvent event) { 

      mainFrame.addNewProject(); 

    } 
    } 
}

大型機代碼：

package testgui; 

import java.awt.*; 
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.ObjectOutputStream; 
import java.io.Serializable; 
import java.util.ArrayList; 
import javax.swing.*; 
import javax.swing.border.*; 
import left_panel_package.ProjectsJTree; 
import menu_package.MainMenuBar; 

public class MainFrame extends JFrame implements Serializable{ 

    private String instalationLocation; 
    private ArrayList <ProjectToAdd> listOfProjects; 

    public MainFrame(){ 
     initComponents(); 
    } 

    public void initComponents() { 


     setInstalationLocation("C:\\Users\\Pera\\Desktop\\RiskManagerGUI"); 
     listOfProjects = new ArrayList<ProjectToAdd>(); 

     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 
     setTitle("TEST"); 
     setName("mainFrame"); 

     JPanel mainPanel = new JPanel(); 

     setContentPane(mainPanel); 
     setJMenuBar(new MainMenuBar(this)); 

     GraphicsDevice gd = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice(); 
     int width = gd.getDisplayMode().getWidth(); 
     int height = gd.getDisplayMode().getHeight(); 
     setSize(width, height); 
     setLocationRelativeTo(null); 
    } 

    public String getInstalationLocation() { 
     return instalationLocation; 
    } 

    private void setInstalationLocation(String instalationLocation) { 
     this.instalationLocation = instalationLocation; 
    } 

    public void addNewProject(){ 
     String nameOfProject = JOptionPane.showInputDialog(null, "Enter the name of new project: ", "Add new project",JOptionPane.OK_CANCEL_OPTION); 
     if ((nameOfProject != null) && (nameOfProject.length() > 0)) { 
      try { 
       ProjectToAdd newProject = new ProjectToAdd(this, nameOfProject); 
       listOfProjects.add(newProject); 

       File theDir = new File(newProject.getProjectPath()); 
       theDir.mkdirs(); 

       newProject.writeToFile(); 

      } catch (IOException ex) { 
       System.out.println(ex.getMessage()); 
      } 

     } 
    } 
}

ProjectToAdd代碼：

package testgui; 


import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.ObjectOutputStream; 
import java.io.Serializable; 

public class ProjectToAdd implements Serializable{ 

    private String nameOfProject; 
    private MainFrame mainFrame; 
    private String projectPath; 

    public ProjectToAdd (MainFrame mainFrame, String nameOfProject) { 

      this.mainFrame = mainFrame; 
      setNameOfProject(nameOfProject); 
      setProjectPath(mainFrame.getInstalationLocation()+"\\Projects\\"+nameOfProject); 

    } 

    public String getNameOfProject() { 
     return nameOfProject; 
    } 

    public void setNameOfProject(String nameOfProject) { 
     this.nameOfProject = nameOfProject; 
    } 

    public void writeToFile() throws IOException{ 
     ObjectOutputStream objectOutputStream = 
      new ObjectOutputStream(new FileOutputStream(projectPath+ 
        "\\"+nameOfProject+".bin")); 
     objectOutputStream.writeObject(this); 
    } 
    public void readFromFile(){ 

    } 

    public String getProjectPath() { 
     return projectPath; 
    } 

    public void setProjectPath(String projectPath) { 
     this.projectPath = projectPath; 
    } 
}

堆棧跟蹤：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at javax.swing.plaf.synth.SynthLookAndFeel.paintRegion(SynthLookAndFeel.java:371) 
    at javax.swing.plaf.synth.SynthLookAndFeel.update(SynthLookAndFeel.java:335) 
    at javax.swing.plaf.synth.SynthRootPaneUI.update(SynthRootPaneUI.java:119) 
    at javax.swing.JComponent.paintComponent(JComponent.java:780) 
    at javax.swing.JComponent.paint(JComponent.java:1056) 
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5210) 
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1579) 
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1502) 
    at javax.swing.RepaintManager.paint(RepaintManager.java:1272) 
    at javax.swing.JComponent._paintImmediately(JComponent.java:5158) 
    at javax.swing.JComponent.paintImmediately(JComponent.java:4969) 
    at javax.swing.RepaintManager$4.run(RepaintManager.java:831) 
    at javax.swing.RepaintManager$4.run(RepaintManager.java:814) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814) 
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789) 
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738) 
    at javax.swing.RepaintManager.access$1200(RepaintManager.java:64) 
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732) 
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311) 
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756) 
    at java.awt.EventQueue.access$500(EventQueue.java:97) 
    at java.awt.EventQueue$3.run(EventQueue.java:709) 
    at java.awt.EventQueue$3.run(EventQueue.java:703) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) 
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

來源

2015-11-01 Dusan Cankovic

請發佈堆棧跟蹤。 – hotzst

added stacktrace –

@Tunaki，我知道什麼是NullPointerException，但我只是沒有看到它，我在代碼中犯了什麼錯誤。我已經度過了好幾個小時，而我卻沒有看到它。如果你第一眼看到它，比你更有經驗，而且你可以在短短几分鐘內幫助我...... 將問題標記爲重複並指向NullPointerException一般性解釋對我來說並不具有建設性，對我沒有幫助，作爲一個Java noob ... –

因爲你試圖序列大型機拋出的NPE，對象包含很多GUI碎屑，包括Nimbus的大號& F資料，東西，不應該是序列化和看起來是不可序列化的。我怎麼知道？馬克那場短暫的，看看會發生什麼：

class ProjectToAdd implements Serializable { 
    private static final long serialVersionUID = 1L; 
    private String nameOfProject; 
    private transient MainFrame mainFrame; // ********** 
    private String projectPath;

如果您需要序列化得舉辦的大型機內的信息，然後創建一個包含從大型機的關鍵業務數據的非GUI模型類和序列化，而不是視圖 - 而不是GUI本身。不管怎樣，你應該幾乎不會序列化視圖，並且從視圖代碼中重構程序邏輯總是一個好主意。

，你是對的，這一點：

objectOutputStream.writeObject(this);

被相關NPE。向你道歉。

來源

2015-11-01 18:28:19

mainFrame變量上的瞬態做到了:)感謝提示！我正在制定一個非GUI模型。乾杯m8 :) –

（），而使用Nimbus外觀

回答

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