java - 线程中出现异常 "AWT-EventQueue-0"java.lang.NullPointerException JInternalFrame 关闭方法

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 3 年前。

有人可以帮我解决这个错误吗？

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at oopw4.FormManager.searchForm(FormManager.java:51)
    at oopw4.FormManager.unregisterForm(FormManager.java:40)

FormManager.class

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package oopw4;

import java.util.ArrayList;
import javax.swing.JInternalFrame;

public class FormManager {

    private JInternalFrame openedForm = null;
    private ArrayList<JInternalFrame> frameList = new ArrayList<>();

    public boolean isFormOpened(String namaForm) {
        boolean isFound = false;
        JInternalFrame jif = searchForm(namaForm);
        if (jif != null) {
            isFound = true;
            openedForm = jif;
        }
        return isFound;
    }

    public JInternalFrame getOpenedForm() {
        return openedForm;
    }

    public void registerForm(JInternalFrame frame) {
        frameList.add(frame);
    }

    public void unregisterForm(JInternalFrame frame) {
        JInternalFrame jif = (JInternalFrame)searchForm(frame.getName());
        if (jif != null) {
            frameList.remove(frame);
        }
    }

    private JInternalFrame searchForm(String namaForm) {
        JInternalFrame frame = null;
        int idx = 0;

        while (idx < frameList.size()) {
            if (frameList.get(idx).getName().equals(namaForm)) {
                frame = frameList.get(idx);
                break;
            } else {
                idx++;
            }
        }
        return frame;
    }
}

UserCrud.class

private void closeButtonActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
        AppLib.formManager.unregisterForm(this);
    }

MainFormDemo.class

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package oopw4;

import javax.swing.*;
import simbengkel.AppLib;

public class MainFormDemo extends javax.swing.JFrame {

    /**
     * Creates new form Frame   
     */
    public MainFormDemo() {
        initComponents();
        setExtendedState(JFrame.MAXIMIZED_BOTH);
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        DesktopPane = new javax.swing.JDesktopPane();
        jMenuBar1 = new javax.swing.JMenuBar();
        jMenu1 = new javax.swing.JMenu();
        menuOpenedForm = new javax.swing.JMenuItem();
        openFormTableUser = new javax.swing.JMenuItem();
        menuClosedForm = new javax.swing.JMenuItem();
        jMenu2 = new javax.swing.JMenu();
        menuHelp = new javax.swing.JMenu();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setLocation(new java.awt.Point(0, 0));
        getContentPane().setLayout(new java.awt.GridLayout(1, 0));

        javax.swing.GroupLayout DesktopPaneLayout = new javax.swing.GroupLayout(DesktopPane);
        DesktopPane.setLayout(DesktopPaneLayout);
        DesktopPaneLayout.setHorizontalGroup(
            DesktopPaneLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 507, Short.MAX_VALUE)
        );
        DesktopPaneLayout.setVerticalGroup(
            DesktopPaneLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 319, Short.MAX_VALUE)
        );

        getContentPane().add(DesktopPane);

        jMenu1.setText("File");

        menuOpenedForm.setText("Tic Tac Toe");
        menuOpenedForm.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                menuOpenedFormActionPerformed(evt);
            }
        });
        jMenu1.add(menuOpenedForm);

        openFormTableUser.setText("Table User");
        openFormTableUser.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                openFormTableUserActionPerformed(evt);
            }
        });
        jMenu1.add(openFormTableUser);

        menuClosedForm.setText("Logout");
        menuClosedForm.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                menuClosedFormActionPerformed(evt);
            }
        });
        jMenu1.add(menuClosedForm);

        jMenuBar1.add(jMenu1);

        jMenu2.setText("Edit");

        menuHelp.setText("Help");
        jMenu2.add(menuHelp);

        jMenuBar1.add(jMenu2);

        setJMenuBar(jMenuBar1);

        pack();
        setLocationRelativeTo(null);
    }// </editor-fold>                        

    private void menuOpenedFormActionPerformed(java.awt.event.ActionEvent evt) {                                               
        // TODO add your handling code here:
        this.dispose();
        TicTacToe main = new TicTacToe();
        main.show();
    }                                              

    private void menuClosedFormActionPerformed(java.awt.event.ActionEvent evt) {                                               
        // TODO add your handling code here:
        this.dispose();
        LoginUser login = new LoginUser();
        login.show();
    }                                              

    private void openFormTableUserActionPerformed(java.awt.event.ActionEvent evt) {                                                  
        // TODO add your handling code here:
        if (AppLib.formManager.isFormOpened("UserCrud")) {
            JOptionPane.showMessageDialog(this, "Form Already Opened");
            JInternalFrame jif = AppLib.formManager.getOpenedForm();
            jif.setVisible(true);
        } else {
            UserCrud tableUser = new UserCrud();
            DesktopPane.add(tableUser);
            tableUser.setVisible(true);
            AppLib.formManager.registerForm(tableUser);
        }
    }                                                 

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(MainFormDemo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(MainFormDemo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(MainFormDemo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(MainFormDemo.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MainFormDemo().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JDesktopPane DesktopPane;
    private javax.swing.JMenu jMenu1;
    private javax.swing.JMenu jMenu2;
    private javax.swing.JMenuBar jMenuBar1;
    private javax.swing.JMenuItem menuClosedForm;
    private javax.swing.JMenu menuHelp;
    private javax.swing.JMenuItem menuOpenedForm;
    private javax.swing.JMenuItem openFormTableUser;
    // End of variables declaration                   
}

错误:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at oopw4.FormManager.searchForm(FormManager.java:51)
    at oopw4.FormManager.unregisterForm(FormManager.java:40)
    at oopw4.UserCrud.closeButtonActionPerformed(UserCrud.java:263)
    at oopw4.UserCrud.access$500(UserCrud.java:24)
    at oopw4.UserCrud$6.actionPerformed(UserCrud.java:187)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6533)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6298)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    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.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    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)

有人可以帮助我吗？

Answer 1

请记住 Swing UI 在其自己的线程上运行。而且 Swing 中的组件并非设计为线程安全的。那么，欢迎来到 Swing。您可能会发现您的搜索功能在此处发生故障 frameList.get(idx).getName().equals(namaForm) ...因为框架尚未创建。阅读“InvokeLater”并使用它来响应 UX 事件。这可以确保在您尝试对组件执行任何操作之前，执行窗口管理的 Swing 线程全部被捕获。