Ever Feel Like Life Is Just Scrolling By?

 
// Very simple example of implementing  
// something that acts like a
// scrolling cursor in JDBC.  Don't use this as 
// an example of good 
// program structure, rather use it as an example 
// for how to get the job done.


class OrderTable extends Object {

     public double   orderID;    // variables for my
                                 // column values
     public String   orderDate;  // " "
     public String   description;// " "

    public  Connection   // connection for executing
       theConnection;
                          // SQL
    public  Vector  keys;// Vector that will hold my
                          // primary key values

//
// Primary Constructor
//
// This constructor primes the "keys" Vector
// with all of my primary keys from the order
// table. This is what provides 
// the ability to reference rows at random, 
// via indexing into the vector of primary key 
// values. The memory overhead of 
// loading an array of primary keys is very 
// small when compared to the option of 
     // keeping the entire row in memory. 
     //
     public OrderTable ( Connection aConnection ) {
       ResultSet                       aResult;

       theConnection = aConnection;
       // assign the instance's
       // JDBC connection

       keys = new Vector();
       try {
       // Exceute the SQL that will select all
       // of the desired keys, then load all of
       // those key values into the "keys"
       // Vector so I can index them later

       aResult = theConnection.prepareStatement(
         "select order_id from order"
         ).executeQuery();
             while( aResultSet.next() )
                keys.addElement ( new 
                Double(aResultSet.getDouble(1)) );
           } catch ( SQLException e ) {
            System.out.println ( e.getMessage() );
             }
      }

     //
     // loadElementAt This is the method that does
     // the other half of the work, loading the
     // column values into the instance variables.
     // Note that I reference the primary key in the
     // "keys" Vector.
     //
       
     public void loadElementAt( int anIndex ){
       ResultSet  aResult;
       Statement  aStatement;

       try {
         // Execute the SQL (using variable
         // replacement )
         
         aStatement = aConnection.prepareStatement
           ( "select order_id,
           order_date, description
           from order where order_id = ?" );
         aStatement.setDouble ( 1,
           (keys.elementAt( anIndex ));
           // this replaces the "?" with
           // the key value
           aResult = aStatement.executeQuery();
           aResult.next();
           orderID = aResult.getDouble (
           "order_id");
           // load the values one by one
           orderDate = aResult.getString (
             "order_date");
           // ...
           description = aResult.getString (
             "description");
           // ...
          } catch ( SQLException e ) {
               System.out.println ( e.getMessage() );
            }
      }
}


//
// init()
//
// Here's an example of how to use this ...
//

init()
{
  theConnection = ...Connection to JDBC database ...
  OrderTable theOrderTable = 
    new OrderTable( theConnection );
  theOrderTable.loadElementAt( 2 ); // load the row
                                    // at index #2
  System.out.println ( theOrderTable.description );
}