我正在尝试从我的数据库中删除一行，但我收到以下错误
线程中的异常“AWT-EventQueue-0”java.lang.NullPointerException
我还有"where ID = 1"
我是否可以使用getmethod来获取密钥（数字），而不必输入1,2或3等等。代码的副本在下面
package prototype4;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JTextField;
import java.awt.TextArea;
import java.awt.event.ActionEvent;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;
import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class DeleteSong extends JFrame implements ActionListener {
private Connection con;
private Statement stmt;
private ResultSet res;
JTextField songNo = new JTextField(7);
TextArea information = new TextArea(2, 50);
JButton delete = new JButton("Delete Song");
JButton update = new JButton("Update Table");
static String[] columnNames = {"trackNo", "Artist", "trackName"};
static Object[][] data = null;
static JTable table;
static DefaultTableModel modeltable = new DefaultTableModel(data, columnNames);
Font timeFont = new Font("Gill Sans MT", Font.BOLD, 15);
//object constructor which delcares the physical look of the frame including the title
public DeleteSong() {
setLayout(new BorderLayout());
setBounds(100, 100, 1000, 250); //set the size of the frame in pixels
setTitle("Delete Song"); //set the title of the frame
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
JPanel top = new JPanel();
top.add(new JLabel("Enter Song Number:"));
top.add(songNo);
top.add(delete);
delete.addActionListener(this);
top.add(update);
update.addActionListener(this);
add("North", top);
JPanel middle = new JPanel(); line
middle.add(information);
add("Center", middle);
JPanel panel2 = new JPanel();
table = new JTable(modeltable);
table.setPreferredScrollableViewportSize(new Dimension(500, 70));
table.setFillsViewportHeight(true);
JScrollPane scrollPane = new JScrollPane(table);
panel2.add(scrollPane);
add("West", panel2);
setResizable(false);
setVisible(true);
setLocationRelativeTo(null);
information.setFont(timeFont);
information.setForeground(Color.BLUE);
}
public void actionPerformed(ActionEvent e) {
try {
stmt = con.createStatement();
res = stmt.executeQuery("SELECT * FROM LibraryTable");
String key = songNo.getText(); //get the song number from the songNo text field
String name = LibraryData.getName(key); //get the name of the song from the LibraryData.java(another java class)
//conditions
if (name == null) {
information.setText("No such song");
} else {
int confirm = JOptionPane.showConfirmDialog(null, "Are you sure you want to delete " + key + " " + name.toUpperCase() + " ?");
if (confirm == 0) {
LibraryData.remove(key);
stmt = con.createStatement();
String sql = "DELETE FROM LibraryTable "
+ "WHERE ID = 1";
stmt.executeUpdate(sql);
information.setText(key + "-" + name + " has been deleted and database updated!");
}
}
} catch (SQLException ex) {
Logger.getLogger(DeleteSong.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
线程“AWT-EventQueue-0”中的异常java.lang.NullPointerException 在prototype4.DeleteSong.actionPerformed（DeleteSong.java:92）at javax.swing.AbstractButton.fireActionPerformed（AbstractButton.java:2018） 在 javax.swing.AbstractButton中的$ Handler.actionPerformed（AbstractButton.java:2341） 在 javax.swing.DefaultButtonModel.fireActionPerformed（DefaultButtonModel.java:402） 在 javax.swing.DefaultButtonModel.setPressed（DefaultButtonModel.java:259） 在 javax.swing.plaf.basic.BasicButtonListener.mouseReleased（BasicButtonListener.java:252） 在java.awt.Component.processMouseEvent（Component.java:6505）at javax.swing.JComponent.processMouseEvent（JComponent.java:3321）at java.awt.Component.processEvent（Component.java:6270）at java.awt.Container.processEvent（Container.java:2229）at java.awt.Component.dispatchEventImpl（Component.java:4861）at java.awt.Container.dispatchEventImpl（Container.java:2287）at java.awt.Component.dispatchEvent（Component.java:4687）at java.awt.LightweightDispatcher.retargetMouseEvent（Container.java:4832） 在 java.awt.LightweightDispatcher.processMouseEvent（Container.java:4492） at java.awt.LightweightDispatcher.dispatchEvent（Container.java:4422） 在java.awt.Container.dispatchEventImpl（Container.java:2273）at java.awt.Window.dispatchEventImpl（Window.java:2719）at java.awt.Component.dispatchEvent（Component.java:4687）at java.awt.EventQueue.dispatchEventImpl（EventQueue.java:735）at at java.awt.EventQueue.access $ 200（EventQueue.java:103）at java.awt.EventQueue $ 3.run（EventQueue.java:694）at java.awt.EventQueue $ 3.run（EventQueue.java:692）at java.security.AccessController.doPrivileged（Native Method）at java.security.ProtectionDomain $ 1.doIntersectionPrivilege（ProtectionDomain.java:76） 在 java.security.ProtectionDomain $ 1.doIntersectionPrivilege（ProtectionDomain.java:87） 在java.awt.EventQueue $ 4.run（EventQueue.java:708）at java.awt.EventQueue $ 4.run（EventQueue.java:706）at java.security.AccessController.doPrivileged（Native Method）at java.security.ProtectionDomain $ 1.doIntersectionPrivilege（ProtectionDomain.java:76） 在java.awt.EventQueue.dispatchEvent（EventQueue.java:705）at java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:242） 在 java.awt.EventDispatchThread.pumpEventsForFilter（EventDispatchThread.java:161） 在 java.awt.EventDispatchThread.pumpEventsForHierarchy（EventDispatchThread.java:150） 在 java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:146） 在 java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:138） at java.awt.EventDispatchThread.run（EventDispatchThread.java:91） 拿起JAVA_TOOL_OPTIONS：-Djava.vendor =“新甲骨文”