JAVA连接MySQL数据库，删除和修改就会出现异常

public class Jdbc { private static final boolean NULL = false; Connection con = null; Statement statement = null; ResultSet res = null; String driver = "com.mysql.jdbc.Driver"; String url = "jdbc:mysql://127.0.0.1:3306/user"; String name = "root"; String passwd = "root";public Jdbc(){ try{ Class.forName(driver).newInstance(); con = DriverManager.getConnection(url,name,passwd); con.setAutoCommit(false); statement = con.createStatement(); }catch(ClassNotFoundException e){ System.out.println("对不起，找不到这个Driver"); e.printStackTrace(); }catch(SQLException e){ e.printStackTrace(); }catch(Exception e){ e.printStackTrace(); } }
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)