Problema com gerador de serial

Ai galera fiz o código abaixo, só que ao executar o update ele da erro, eu peguei o código que sai do strSQL e joguei no sql e deu certo, não sei pq nao está dando, alguem ajuda.
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class geraserial extends JanelaConf implements ActionListener{
	Connection Con;
	static Statement Stm;
	String strMsg = "";
int i2, i3, serial2, serial4, serial6, serial8,serial10,serial12,serial14,serial16;
double serial, serial3, serial5, serial7, serial9, serial11, serial13,serial15;
JTextField qtdcarro, serialg, sger;
JLabel qtdc, seriall;
String i;
JButton gser;
public geraserial(){
	super("Serial", new Dimension (280, 180));
	serial();
}
	public void serial(){
		
		qtdc = new JLabel("Quantidade de Carros:");
		add(qtdc);
		qtdc.setBounds(10,10,150,25);
		qtdcarro = new JTextField();
		add(qtdcarro);
		qtdcarro.setBounds(150,10,50,25);
		
		
		gser = new JButton("Gerar");
		add(gser);
		gser.setBounds(10,100,100,25);
		gser.addActionListener(this);
		
		sger = new JTextField();
		add(sger);
		sger.setBounds(0,0,0,0);
		
		serial = Math.random()*11;
		serial2 = (int) Math.round(serial);
		serial3 = Math.random()*22;
		serial4 = (int) Math.round(serial3);
		serial5 = Math.random()*33;
		serial6 = (int) Math.round(serial5);
		serial7 = Math.random()*44;
		serial8 = (int) Math.round(serial7);
		
		serial9 = Math.random()*55;
		serial10 = (int) Math.round(serial9);
		serial11 = Math.random()*66;
		serial12 = (int) Math.round(serial11);
		serial13 = Math.random()*77;
		serial14 = (int) Math.round(serial13);
		serial15 = Math.random()*88;
		serial16 = (int) Math.round(serial15);
		sger.setText(serial2+"-"+serial4+"-"+serial6+"-"+serial8+"-"+serial10+"-"+serial12+"-"+serial14+"-"+serial16);
	
}
    public void actionPerformed(ActionEvent e){
    	if(e.getSource() == gser){
    		cserial();
    	}
    }
    
    public void cserial(){
	String strSQL = "";
	strSQL = "INSERT INTO serial (serial,qtdcarros) VALUES ('"+sger.getText().trim()+"','"+qtdcarro.getText().trim()+"')";
	try{
		Stm.executeUpdate(strSQL);
	}
	catch(SQLException sqle){}
    }
public static void main(String[] args){
	new geraserial().show();
}
}
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