count mismatch in sql browser and java JDBC, due to high transaction

As im using sql server 2005 r2. There is more concurrent access on this table1 . when i execute the following query in sql browser im getting 2000 records, but when the same query is executed with java, no of records r varied.

EX: 1st execution --> 2000 records,
    2nd execution --> 2005 records, 
    3rd execution --> 1990 records


 select REGISTRATION_NO as TOTAL_ASSETS_COUNT from Contable1 a 
 inner join table2 b on a.REGISTRATION_NO = b.Registration_no and a.System_id=b.System_id 
 inner join table3 c on b.Registration_no=c.VehicleNo and b.System_id=c.System_id 
 where a.CLIENTID = ? and a.System_id = ? and b.User_id=?

im using isolation level as READ COMMITTED.

Due to high transaction on table1 the count is varied. please help to resolve why the count is varied in java.

thanks in advance.