java find the error3

public String studentDel(StudentBean studObj) throws ClassNotFoundException, SQLException
    {
        Connection conObj=DBConnections.setConnection();

        PreparedStatement ps= conObj.prepareStatement("DELETE FROM balastudent WHERE studentid=?");
        ps.setString(1, studObj.getStudentId());
        System.out.println(studObj.getStudentId());
        ps.executeUpdate();


        return "Success";

    }

public String studentIns(StudentBean studObj) throws ClassNotFoundException, SQLException
{
    Connection conObj=DBConnections.setConnection();
    Statement sObj = conObj.createStatement();
    ResultSet rObj=sObj.executeQuery("select studentId.nextval from dual");
    rObj.next();
    String studentId=rObj.getString(1);
    PreparedStatement ps= conObj.prepareStatement("insert into balastudent values (?,?,?,?)");
    ps.setString(1, studentId);
    ps.setString(2, studObj.getStudentName());
    ps.setString(3, studObj.getStudentAge());
    ps.setString(4, studObj.getStudentCollege());
    ps.executeUpdate();


    return "Success";

}



public ResultSet studentSearch(StudentBean studObj) throws ClassNotFoundException, SQLException
    {
        Connection conObj=DBConnections.setConnection();
        PreparedStatement ps= conObj.prepareStatement("select * from balastudent where studentId=?");
        ps.setString(1,studObj.getStudentId());
        ResultSet rs = ps.executeQuery();   

        return rs;

    }

public String studentUpd(StudentBean studObj) throws ClassNotFoundException, SQLException
    {
        Connection conObj=DBConnections.setConnection();

        PreparedStatement ps= conObj.prepareStatement("update balastudent set studentname=?,studentage=?,studentcollege=? where studentid=?");

        ps.setString(1, studObj.getStudentName());
        ps.setString(2, studObj.getStudentAge());
        ps.setString(3, studObj.getStudentCollege());
        ps.setString(4, studObj.getStudentId());
        ps.executeUpdate();


        return "Success";

    }