Exception: No primary keys?

pgsql-jdbc

A simplest test failed when I use postgresql and pgsql-jdbc driver which were build from postgresql7.3b5 source code.
The test code is:
..
14 try{
15 Class.forName(strDrv);
16 conn = DriverManager.getConnection(strUrl, "postgl", "");
17 stmt = conn.createStatement();
18 rs = stmt.executeQuery(strSql);
19 while (rs.next())
20 {
21 System.out.println(rs.getString(1));
22 }
23 //rs.beforeFirst();
24 while (rs.previous())
25 {
26 System.out.println(rs.getString(1));
27 }
28 rs.moveToInsertRow();
29 rs.updateInt("a", 100);
30 rs.insertRow();
31 } catch(Exception e){
32 System.out.println(e.toString());
33 }

The table "test" has only two columns(a int, b varchar) and no primary keys.
The error message is: No primary keys.
It's all right with line 28,29 and 30 commented out.
It will also succedd when the table "test" has a primary key.
Can you tell me why?
My environment is:
redhat 7.3
j2sdk1.4.1_01
ant1.5.1

Thanks and regards,
　　　　　　　　

　　　　　　　　Han
　　　　　　　　zhouhanok(at)vip(dot)sina(dot)com
　　　　　　　　　　2002-12-02