java报错java.lang.NumberFormatException: For input string 求助

package KS;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class JFQRUI extends JFrame implements ActionListener {

// 开始定义窗口组件：
JLabel JFQRje = new JLabel("缴费金额：");
JTextField JFQRKB = new JTextField();
// JLabel JFQRjeqr = new JLabel("金额确认：");
// JTextField JFQRKB2 = new JTextField();
JButton JFQRQR = new JButton("确认");
JButton JFQRQX = new JButton("取消");

// 开始添加窗口组件：
public JFQRUI() {
this.setTitle("确认缴费");
this.setLayout(null);
JFQRje.setBounds(20, 30, 100, 20);
this.add(JFQRje);
JFQRKB.setBounds(80, 30, 100, 20);
this.add(JFQRKB);
// JFQRjeqr.setBounds(20, 60, 100, 20);
// this.add(JFQRjeqr);
// JFQRKB2.setBounds(80, 60, 100, 20);
// this.add(JFQRKB2);
JFQRQR.setBounds(35, 100, 100, 20);
this.add(JFQRQR);
JFQRQX.setBounds(150, 100, 100, 20);
this.add(JFQRQX);
JFQRQR.addActionListener(this);
JFQRQX.addActionListener(this);
this.setVisible(true);
this.setBounds(10, 10, 300, 180);
setLocationRelativeTo(null);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}

public void actionPerformed(ActionEvent e) {
if (e.getSource() == JFQRQR) {
Connection conn = null;
try {
String name = MAINUI.getna();
String jfa = JFQRje.getText();
double jfje = Double.parseDouble(jfa);
// 开始加载驱动程序：
Class.forName("com.mysql.jdbc.Driver");

// 开始连接数据库：
String url = "jdbc:mysql://LocalHost:3306/dataSYSTEM?useSSL=true";
String user = "root";
String password = "ljj8135399";
conn = DriverManager.getConnection(url, user, password);

// 定义修改功能：
Statement stat = conn.createStatement();
ResultSet gx = stat
.executeQuery("update DATA set 当前余额=当前余额+jfje where 宿舍号=name");
gx.next();
dispose();
new JFUI();

} catch (Exception e1) {
e1.printStackTrace();
}
}
if (e.getSource() == JFQRQX) {
dispose();
new JFUI();
}
}
}

java.lang.NumberFormatException: For input string: " "
这个异常是说，在将字符串转换为number的时候格式化错误
“”空的字符串有对应的数值吗，显然没有

数字格式异常,看你是把什么东西转化成string的时候出现问题

你输入的时候加try..catch代码块，出现异常会有提示