跟着b站up主做的但到这发现一直报错 java.lang.NullPointerException
```package view;
import java.awt.EventQueue;
import java.sql.Connection;
import java.sql.ResultSet;
import java.util.Vector;
import javax.swing.JInternalFrame;
import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;
import dao.BookTypeDao;
import model.BookType;
import my.DbUtil;
import java.awt.Color;
import javax.swing.JScrollPane;
import javax.swing.LayoutStyle.ComponentPlacement;
public class BookTypeManageInterFrm extends JInternalFrame {
private JTable bookTypetable;
private DbUtil dbUtil =new DbUtil();
private BookTypeDao bookTypeDao = new BookTypeDao();
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
BookTypeManageInterFrm frame = new BookTypeManageInterFrm();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public BookTypeManageInterFrm() {
setClosable(true);
setBounds(100, 100, 863, 568);
JScrollPane scrollPane_1 = new JScrollPane();
GroupLayout groupLayout = new GroupLayout(getContentPane());
groupLayout.setHorizontalGroup(
groupLayout.createParallelGroup(Alignment.LEADING)
.addGroup(groupLayout.createSequentialGroup()
.addGap(152)
.addComponent(scrollPane_1, GroupLayout.PREFERRED_SIZE, 596, GroupLayout.PREFERRED_SIZE)
.addContainerGap(103, Short.MAX_VALUE))
);
groupLayout.setVerticalGroup(
groupLayout.createParallelGroup(Alignment.LEADING)
.addGroup(groupLayout.createSequentialGroup()
.addGap(85)
.addComponent(scrollPane_1, GroupLayout.PREFERRED_SIZE, 345, GroupLayout.PREFERRED_SIZE)
.addContainerGap(109, Short.MAX_VALUE))
);
bookTypetable = new JTable();
bookTypetable.setModel(new DefaultTableModel(
new Object[][] {
},
new String[] {
"\u7F16\u53F7", "\u56FE\u4E66\u7C7B\u522B\u540D\u79F0", "\u56FE\u4E66\u7C7B\u522B\u63CF\u8FF0"
}
) {
boolean[] columnEditables = new boolean[] {
false, false, false
};
public boolean isCellEditable(int row, int column) {
return columnEditables[column];
}
});
bookTypetable.getColumnModel().getColumn(0).setPreferredWidth(194);
bookTypetable.getColumnModel().getColumn(1).setPreferredWidth(200);
bookTypetable.getColumnModel().getColumn(2).setPreferredWidth(178);
scrollPane_1.setViewportView(bookTypetable);
getContentPane().setLayout(groupLayout);
this.fillTable(new BookType());
}
private void fillTable(BookType bookType)
{
DefaultTableModel dtm = (DefaultTableModel) bookTypetable.getModel();
dtm.setRowCount(0);
Connection con = null;
try {
con=dbUtil.getCon();
ResultSet rs =bookTypeDao.list(con, bookType);
while(rs.next()) {
@SuppressWarnings("rawtypes")
Vector v=new Vector();
v.add(rs.getString("id"));
v.add(rs.getString("bookTypeName"));
v.add(rs.getString("bookTypeDesc"));
dtm.addRow(v);
}
}catch(Exception e) {
e.printStackTrace();
}finally {
try {
dbUtil.closeCon(con);
} catch (Exception e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
}
}
报错信息：
java.lang.NullPointerException
at JDBC/my.StringUtil.isNotEmpty(StringUtil.java:15)
at JDBC/dao.BookTypeDao.list(BookTypeDao.java:22)
at JDBC/view.BookTypeManageInterFrm.fillTable(BookTypeManageInterFrm.java:140)
at JDBC/view.BookTypeManageInterFrm.<init>(BookTypeManageInterFrm.java:122)
at JDBC/view.MainFrm$3.actionPerformed(MainFrm.java:70)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.AbstractButton.doClick(AbstractButton.java:369)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1020)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1064)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6632)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
at java.desktop/java.awt.Component.processEvent(Component.java:6397)
at java.desktop/java.awt.Container.processEvent(Container.java:2263)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5008)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4840)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4918)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4547)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4488)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2772)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4840)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
java.lang.NullPointerException
空指针异常，具体哪一行代码？
swing有点过时了，可以考虑使用JavaFX
把详细的报错信息贴出来看看
代码有点不全呢，只能看看你这边具体的错误信息呢
ResultSet rs =bookTypeDao.list(con, bookType);
考虑以上这一行代码的参数可能为空