stateful batch apex in salesforce code example

Example: stateful batch apex in salesforce

global class SummarizeAccountTotal implements Database.Batchable<sObject>, Database.Stateful{
    global final String Query;
    global integer Summary;
    global SummarizeAccountTotal(String q){
        Query=q;
        Summary = 0;
    }
    global Database.QueryLocator start(Database.BatchableContext BC){
        return Database.getQueryLocator(query);
    }
    global void execute (
        Database.BatchableContext BC,
        List<sObject> scope){
            for(sObject s : scope){
                Summary = Integer.valueOf(s.get(‘total__c’))+Summary;
            }
        }
    global void finish(Database.BatchableContext BC){
    }
}