Why am i getting java.sql.SQLException: ORA-01002: fetch out of sequence exception

I am running a simple update statement in my java code to an oracle database (JDBC call) and it updates when record is found but when record doesn't exist i get " java.sql.SQLException: ORA-01002: fetch out of sequence" exception. Here is my code, why exception? Where should I improve it. Code sample would be very helpful.

public String preformUpdate(String someValue){
    ResultSet rs;
    String result = "Update failed record not found.";
    StringBuffer sb = new StringBuffer();

    try{
        conn = DBConnect.getInstance().dbOracleConnect();   

        StringBuffer sbUpdate = new StringBuffer();
        sbUpdate = new StringBuffer("UPDATE sometable ");
        sbUpdate.append("SET value1 = ? ");
        sbUpdate.append("WHERE value2 = ?" );

        ps = conn.prepareStatement(sbUpdate.toString());  
        ps.setString(1, "0");
        ps.setString(2, someValue);

        rs = ps.executeQuery();

        if (rs.next()){
            result = "Value updated";               
        }

    }
    catch (Exception e){
        e.printStackTrace();
    }
    finally{
        JDBCHelper.close(cs);   
        JDBCHelper.close(conn);         
    }

    return result;
}