singleton.cls

trigger OpportunityTrigger on Opportunity (before Update, after Update)
{
  //Poor Design
  for (Account acc : Trigger.New)
    {
      //Creating instance of class for each trigger call
      OpportunityRecordType art = new OpportunityRecordType() 
      ......
    }
 
}


public class OpportunityRecordType()
{
  
  //public property
  public String id {get; private set;}

  //public constructor 
  id = Opportunity.sObjectType.getDescribe().getRecordTypeInforByName().get('Opp').getRecordTypeId();
}

}