Java 使用Nimbus外观时writeObject()期间出现NullPointerException
我有4个类:TestGUI、MainMenuBar、MainFrame和ProjectToAdd。 大型机和ProjectToAdd实现了可序列化。当我在MainMenuBar中单击New>Project时,我想创建一个新项目,为它创建一个新目录,并在该目录中编写一个可序列化的对象。当对象被写入时,我会得到NullPointerException(参见末尾的stacktrace)。若我删除了main方法中代码的Look-and-Feel部分,那个么我就不会再有错误了。。。我正在使用NetBeans IDE 8.0.2 TestGUI代码:Java 使用Nimbus外观时writeObject()期间出现NullPointerException,java,swing,nullpointerexception,serializable,nimbus,Java,Swing,Nullpointerexception,Serializable,Nimbus,我有4个类:TestGUI、MainMenuBar、MainFrame和ProjectToAdd。 大型机和ProjectToAdd实现了可序列化。当我在MainMenuBar中单击New>Project时,我想创建一个新项目,为它创建一个新目录,并在该目录中编写一个可序列化的对象。当对象被写入时,我会得到NullPointerException(参见末尾的stacktrace)。若我删除了main方法中代码的Look-and-Feel部分,那个么我就不会再有错误了。。。我正在使用NetBean
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);
}
});
}
}
主菜单栏代码:
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();
}
}
}
大型机代码:
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());
}
}
}
}
堆栈跟踪:
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)
抛出NPE是因为您试图序列化MainFrame,这个对象包含很多GUI碎片,包括Nimbus L&F信息,这些东西不应该序列化,看起来是不可序列化的。我怎么知道?标记该场瞬态并查看发生了什么:
class ProjectToAdd implements Serializable {
private static final long serialVersionUID = 1L;
private String nameOfProject;
private transient MainFrame mainFrame; // **********
private String projectPath;
如果需要序列化大型机中保存的信息,那么创建一个非GUI模型类,该类包含大型机中的关键业务数据,并序列化该数据,而不是视图,而不是GUI本身。通常,无论如何都不应该序列化视图,从视图代码中重构程序逻辑总是一个好主意
你是对的,这是:
objectOutputStream.writeObject(this);
与NPE有关。向您道歉。请发布stacktrace。@Tunaki,我知道什么是NullPointerException,但我不知道我在代码中哪里出错了。我已经经历了好几个小时,但我就是看不到。如果你乍一看,你比我更有经验,你可以在几分钟内帮助我。。。将问题标记为重复并指向NullPointerException一般解释对我来说不是建设性的,也没有帮助,作为一个java noob…你为什么认为,“
我在objectOutputStream.writeObject(this)上得到NullPointerException;在ProjectToAdd类中”
这就是引发NPE的地方?在stacktrace的任何地方都没有提到ProjectToAdd类。我必须问你是否要在EDT上启动GUI?我已经告诉过你一些必须做的事情,以确保Nimbus不会引发异常:启动GUI并在EDT上设置外观。考虑一下这一点。@ HoVrCRAFTFulfFeels:是的,似乎根本原因是成立的。主机上的变量是这样做的:谢谢你的提示!我计划构建一个非GUI模型。干杯
objectOutputStream.writeObject(this);