DAO Setter 在设置 BigDecimal 值时显示 NullPointerException 错误 - Java Swing

Question

设置十进制值时出现以下错误。请忽略命名约定，抱歉，它是从遗留应用程序复制的。

错误

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at com.shams.MainWindow.btnSaveActionPerformed(MainWindow.java:161)
    at com.shams.MainWindow.access0(MainWindow.java:25)
    at com.shams.MainWindow.actionPerformed(MainWindow.java:85)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
    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.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
    at java.awt.Component.processMouseEvent(Component.java:6525)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6290)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4881)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2739)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
    at java.awt.EventQueue.access0(EventQueue.java:97)
    at java.awt.EventQueue.run(EventQueue.java:697)
    at java.awt.EventQueue.run(EventQueue.java:691)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue.run(EventQueue.java:719)
    at java.awt.EventQueue.run(EventQueue.java:717)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
    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)

ExpenseDTO

import java.math.BigDecimal;
import java.util.Date;

//
public class Expense {
    BigDecimal fltAmt=BigDecimal.ZERO;
    Date dtDate;
    Category category;
    Long intExpenseId;

    public Category getCategory() {
        return category;
    }

    public void setCategory(Category category) {
        this.category = category;
    }

    public Long getIntExpenseId() {
        return intExpenseId;
    }

    public void setIntExpenseId(Long intExpenseId) {
        this.intExpenseId = intExpenseId;
    }

    public BigDecimal getFltAmt() {
        return fltAmt;
    }

    public void setFltAmt(BigDecimal fltAmt) {
        this.fltAmt = fltAmt;
    }

    public Date getDtDate() {
        return dtDate;
    }

    public void setDtDate(Date dtDate) {
        this.dtDate = dtDate;
    }
}

主窗口

.......

    private void btnSaveActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
        Date selectedDate = (Date) datePicker.getModel().getValue();
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        CBItem selected_item = (CBItem) txtCategory.getSelectedItem();

System.out.println(selected_item.getId());
System.out.println(selected_item.getName());

        lbl.setText(txtAmt.getText() + "," + txtCategory.getSelectedIndex() + ","+ dateFormat.format(selectedDate));
       /* AddNewPanel.add(lbl);
        AddNewPanel.revalidate();
        AddNewPanel.repaint();*/
        BigDecimal vl=new BigDecimal(txtAmt.getText());
        System.out.print(BigDecimal.ONE);
        expense.setFltAmt(BigDecimal.ONE);
        /*expense.setDtDate(new Date(dateFormat.format(selectedDate)));
        category.setIntCatId(selected_item.getId());
        expense.setCategory(category);*/
    }

我知道错误是设置 BigDecimal 的行，但无法确定导致问题的原因。当我评论这行时。我在这里只复制了必需的（我认为）代码。任何人都想要完整的代码，我也可以复制它。任何帮助都会很棒...!!

谢谢...

已编辑- 主窗口代码完全...

/*
 * 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 com.shams;

import com.shams.dto.Category;
import com.shams.dto.Expense;
import com.shams.utils.DBConnection;
import java.math.BigDecimal;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.JLabel;
import net.sourceforge.jdatepicker.impl.JDatePanelImpl;
import net.sourceforge.jdatepicker.impl.JDatePickerImpl;
import net.sourceforge.jdatepicker.impl.UtilDateModel;
/**
 *
 * @author Shamseer
 */
public class MainWindow extends javax.swing.JFrame {
    Expense expense;
    Category category;
    /**
     * Creates new form MainWindow
     */
    public MainWindow() {

        initComponents();
        initMyComponents();
        loadData();
    }

    /**
     * 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() {

        mainPanel = new javax.swing.JPanel();
        AddNewPanel = new javax.swing.JPanel();
        txtCategory = new javax.swing.JComboBox();
        txtAmt = new javax.swing.JTextField();
        btnSave = new javax.swing.JButton();
        ViewPanel = new javax.swing.JPanel();
        txtReportType = new javax.swing.JComboBox();
        menuBarETApp = new javax.swing.JMenuBar();
        fileMenu = new javax.swing.JMenu();
        menuAddNew = new javax.swing.JMenuItem();
        viewMenu = new javax.swing.JMenu();
        jMenuItem1 = new javax.swing.JMenuItem();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        mainPanel.setLayout(new java.awt.CardLayout());

        txtCategory.setEditable(true);
        txtCategory.setAutoscrolls(true);
        txtCategory.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                txtCategoryActionPerformed(evt);
            }
        });
        txtCategory.addKeyListener(new java.awt.event.KeyAdapter() {
            public void keyTyped(java.awt.event.KeyEvent evt) {
                txtCategoryKeyTyped(evt);
            }
        });
        AddNewPanel.add(txtCategory);

        txtAmt.setPreferredSize(new java.awt.Dimension(50, 25));
        AddNewPanel.add(txtAmt);

        btnSave.setText("Save");
        btnSave.setToolTipText("");
        btnSave.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnSaveActionPerformed(evt);
            }
        });
        AddNewPanel.add(btnSave);

        mainPanel.add(AddNewPanel, "cardAddNewPanel");

        txtReportType.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Item 1", "Item 2", "Item 3", "Item 4" }));

        javax.swing.GroupLayout ViewPanelLayout = new javax.swing.GroupLayout(ViewPanel);
        ViewPanel.setLayout(ViewPanelLayout);
        ViewPanelLayout.setHorizontalGroup(
            ViewPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(ViewPanelLayout.createSequentialGroup()
                .addGap(20, 20, 20)
                .addComponent(txtReportType, javax.swing.GroupLayout.PREFERRED_SIZE, 83, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(516, Short.MAX_VALUE))
        );
        ViewPanelLayout.setVerticalGroup(
            ViewPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(ViewPanelLayout.createSequentialGroup()
                .addGap(21, 21, 21)
                .addComponent(txtReportType, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(414, Short.MAX_VALUE))
        );

        mainPanel.add(ViewPanel, "cardViewPanel");

        getContentPane().add(mainPanel, java.awt.BorderLayout.CENTER);

        fileMenu.setText("File");

        menuAddNew.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_N, 0));
        menuAddNew.setText("Add New");
        fileMenu.add(menuAddNew);

        menuBarETApp.add(fileMenu);

        viewMenu.setText("View");

        jMenuItem1.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_V, 0));
        jMenuItem1.setText("View Transactions");
        jMenuItem1.setToolTipText("");
        viewMenu.add(jMenuItem1);

        menuBarETApp.add(viewMenu);

        setJMenuBar(menuBarETApp);

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

    private void txtCategoryActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
    }                                           

    private void txtCategoryKeyTyped(java.awt.event.KeyEvent evt) {                                     
        // TODO add your handling code here:

    }                                    

    private void btnSaveActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
        Date selectedDate = (Date) datePicker.getModel().getValue();
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        CBItem selected_item = (CBItem) txtCategory.getSelectedItem();

System.out.println(selected_item.getId());
System.out.println(selected_item.getName());

        lbl.setText(txtAmt.getText() + "," + txtCategory.getSelectedIndex() + ","+ dateFormat.format(selectedDate));
       /* AddNewPanel.add(lbl);
        AddNewPanel.revalidate();
        AddNewPanel.repaint();*/
        BigDecimal vl=new BigDecimal(txtAmt.getText());
        System.out.print(BigDecimal.ONE);
        expense.setFltAmt(BigDecimal.ONE);
        /*expense.setDtDate(new Date(dateFormat.format(selectedDate)));
        category.setIntCatId(selected_item.getId());
        expense.setCategory(category);*/
    }                                       

    /**
     * @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(MainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(MainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(MainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(MainWindow.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

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

    // Variables declaration - do not modify                     
    private javax.swing.JPanel AddNewPanel;
    private javax.swing.JPanel ViewPanel;
    private javax.swing.JButton btnSave;
    private javax.swing.JMenu fileMenu;
    private javax.swing.JMenuItem jMenuItem1;
    private javax.swing.JPanel mainPanel;
    private javax.swing.JMenuItem menuAddNew;
    private javax.swing.JMenuBar menuBarETApp;
    private javax.swing.JTextField txtAmt;
    private javax.swing.JComboBox txtCategory;
    private javax.swing.JComboBox txtReportType;
    private javax.swing.JMenu viewMenu;
    // End of variables declaration                   

    UtilDateModel model = new UtilDateModel();
    JDatePanelImpl datePanel = new JDatePanelImpl(model);
    JDatePickerImpl datePicker = new JDatePickerImpl(datePanel);

    JLabel lbl=new JLabel("");

    @SuppressWarnings("unchecked")
    private void loadData() {
        //JDatePickerUtil datPick = new JDatePickerUtil();
        //CBItem array=new CBItem[]{"test",9};
        //Vector vctItem = new Vector();
        //CBItem[] cbIt = null;//=new ArrayList<>();
        try{
            Connection conn = new DBConnection().createConnection();
            Statement stmt = conn.createStatement();
            String sql = "Select * from category";
            //List<String> catNames= new ArrayList<>();
            ResultSet rs = stmt.executeQuery(sql);
            //int size=0;
            while(rs.next()){
                //catNames.add(rs.getString("strCatName"));
                //cbIt=new CBItem[size+1];
                //cbIt[size]=new CBItem(rs.getInt("intCatId"), rs.getString("strCatName"));//.addElement( new CBItem(1, "car" ) );
                txtCategory.addItem(new CBItem(rs.getInt("intCatId"), rs.getString("strCatName")));
                //size++;
            }
            //txtCategory.addItem(cbIt);
        }
        catch(Exception e){
            e.printStackTrace();
        }

    }

    private void initMyComponents() {

        AddNewPanel.add(datePicker);
        AddNewPanel.revalidate();
        AddNewPanel.repaint();
    }
}
class CBItem{
    int id;
    String name;

    CBItem(int i, String car) {
        this.id=i;
        this.name=car;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString(){
        return name+" ("+id+")";
    }


}

Answer 1

你有：

Expense expense;

已定义变量，但从未设置。那就是您获得 NPE 的地方。你不应该至少初始化它吗？

Expense expense = new Expense();

DAO Setter 在设置 BigDecimal 值时显示 NullPointerException 错误 - Java Swing

DAO Setter shows NullPointerException error when setting the BigDecimal value - Java Swing

java

nullpointerexception

dto

bigdecimal