/**
 * Make a withdrawal from this account
 * @param withDrawAmount amount to withdraw in pennies
 */
public synchronized void withdraw( long withdrawAmount ) throws BankingException
   {
   if ( withdrawAmount < 0 )
      {
      throw new BankingException( "Negative withrawals should be handled as corrections or deposits" ):
      }
   if ( balance < withdrawAmount )
      {
      throw new BankingException( "Insufficient funds" );
      }
   this.balance -= withDrawAmount;
   }