我有2个表：employee和job_history。包含ID的属性的数据类型是CHAR（5）。当我测试调用ResultSet getEmID = con.excuteQuery("SELECT MAX(RIGHT(Employee_ID,4)) FROM employee");上的聚合函数时，它可以工作。但是现在当我尝试输入完整的数据时，它会出错。有人可以解释一下吗？
这是我的代码：`
package mainProgram;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import javax.swing.*;
public class newEmployee extends JFrame implements ActionListener,KeyListener{
String check = "";
Connect con = new Connect();
JPanel mainPanel,bottomPanel,panel;
JLabel lblName,lblEmail,lblPhone,lblSallary,lblJob,lblDepartment;
JTextField txtName,txtEmail,txtPhone,txtSallary,txtJob,txtDepartment;
JButton insBtn,rstBtn;
void init(){
mainPanel = new JPanel(new GridLayout(6,2));
bottomPanel = new JPanel(new GridLayout(1,2));
panel = new JPanel(new GridLayout(2,1));
lblName = new JLabel("Name");
lblEmail = new JLabel("Email");
lblPhone = new JLabel("Phone");
lblSallary = new JLabel("Sallary");
lblJob = new JLabel("Job");
lblDepartment = new JLabel("Department");
txtName = new JTextField();
txtEmail = new JTextField();
txtPhone = new JTextField();
txtSallary = new JTextField();
txtJob = new JTextField();
txtDepartment = new JTextField();
insBtn = new JButton("Next");
rstBtn = new JButton("Reset");
mainPanel.add(lblName);
mainPanel.add(txtName);
mainPanel.add(lblEmail);
mainPanel.add(txtEmail);
mainPanel.add(lblPhone);
mainPanel.add(txtPhone);
mainPanel.add(lblSallary);
mainPanel.add(txtSallary);
mainPanel.add(lblDepartment);
mainPanel.add(txtDepartment);
mainPanel.add(lblJob);
mainPanel.add(txtJob);
bottomPanel.add(insBtn);
bottomPanel.add(rstBtn);
panel.add(mainPanel);
panel.add(bottomPanel);
add(panel);
}
public newEmployee() {
setSize(650,450);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
init();
setVisible(true);
insBtn.addActionListener(this);
rstBtn.addActionListener(this);
}
@Override
public void actionPerformed(ActionEvent e) {
if(e.getSource()==insBtn){
String departmentName = txtDepartment.getText();
String jobName = txtJob.getText();
ResultSet getEmID = con.excuteQuery("SELECT MAX(RIGHT(Employee_ID,4)) FROM employee");
ResultSet getDepID = con.excuteQuery("SELECT Department_ID FROM departments WHERE Department_Name = '"+departmentName+"'");
ResultSet getJobID = con.excuteQuery("SELECT Job_ID FROM jobs WHERE Job_Name = '"+jobName+"'");
ResultSet getManID = con.excuteQuery("SELECT Manager_ID FROM departments WHERE Department_Name = '"+departmentName+"'");
//convert hasil query ke string
String employeeId = "";
String departmentId = "";
String jobId = "";
String managerId = "";
try {
employeeId = getEmID.getString("MAX(RIGHT(Employee_ID,4))");
departmentId = getDepID.getString("Department_ID");
jobId = getJobID.getString("Job_ID");
managerId = getManID.getString("Manager_ID");
} catch (SQLException e1) {
e1.printStackTrace();
}
Integer employeeID = Integer.parseInt(employeeId)+1;
String newID = "E"+employeeID;
String name = txtName.getText();
String email = txtEmail.getText();
String phone = txtPhone.getText();
String sallary = txtSallary.getText();
//get current date
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy/MM/dd");
LocalDate locale = LocalDate.now();
String date = dtf.format(locale);
con.executeUpdate("INSERT INTO employee(Employee_ID,Employee_Name,Email,Phone_Number,Job_ID,Hire_Date,Sallary,Manager_ID,Department_ID)VALUES('"+newID+"','"+name+"','"+email+"','"+phone+"','"+jobId+"','"+date+"','"+sallary+"','"+managerId+"','"+departmentId+"')");
con.executeUpdate("INSERT INTO job_history(Employee_ID,Job_ID,Department_ID)VALUES('"+newID+"','"+jobId+"','"+departmentId+"')");
JOptionPane.showMessageDialog(this, "Insert Success!");
dispose();
new newEmployeeDetail(newID);
}
}
@Override
public void keyPressed(KeyEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void keyReleased(KeyEvent arg0) {
// TODO Auto-generated method stub
}
public void keyTyped(KeyEvent e) {
if(e.getSource()==txtEmail){
check = txtEmail.getText();
if(check.contains("@")&&check.contains(".com")){
JOptionPane.showMessageDialog(this, "Invalid email name!");
}
}
if(e.getSource()==txtJob){
check = txtJob.getText();
if(!check.equals("Product Technician")&&!check.equals("System Analyst")&&!check.equals("Programmer")&&!check.equals("Junior Manager")){
JOptionPane.showMessageDialog(this, "Job must \"Product Technician\" or \"System Analyst\" or \"Programmer\" or \"Junior Manager\"");
}
}
}
}
` 这是我得到的错误
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.mysql.jdbc.ResultSet.buildIndexMapping(ResultSet.java:607)
at com.mysql.jdbc.ResultSet.findColumn(ResultSet.java:963)
at com.mysql.jdbc.ResultSet.getString(ResultSet.java:5584)
at mainProgram.newEmployee.actionPerformed(newEmployee.java:86)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)