gistfile1.cls

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

}


public class OpportunityRecordType() {
    //Lets add an instance property here
    public static OpportunityRecord instance = null;

    //public property
    public String id {
        get;
        private set;
    }

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

    public static OpportunityRecordType getInstance() {
        if (instance == null) {
            instance = new OpportunityRecordType();
        }
        return instance;

    }

}

}