Java program to connect to a database Contd.

In my last post related with JDBC I mentioned only about creating tables and inserting new values to a database file using SQL statements. According to comments left by visitors today I am going to post on updating and deleting a particular record. For update or deletion of a record you will have tobe sure that the particular record actually exists in database. If this condition is not checked and you try to modify a non-existing record then you will get a run-time exception. So to avoid this first search for this record using an id(which must be unique) as below written code :
Statement stmt=con.createStatement(); //con is Connection object
ResultSet rs=stmt.executeQuery("SELECT Roll FROM Records"); //Roll is the unique id
         int an=0; 
         boolean found=false;        
         while(rs.next() && found==false){
            an=rs.getInt(0);  //0 as Roll. is the first column
            if(an==Integer.parseInt(enter_id))  //enter_id is input id
                    found=true;  //if id is found in database
            }
 Now you can modify or delete using id if found is true like below shown code :
if(found)  //then do anyone of below

  stmt.execute("UPDATE Records SET Sname="+n+" WHERE Roll="+enter_id); //for changing a value

  stmt.execute("DELETE Records WHERE Roll="+enter_id); //for deleting a record

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