global class batchClass implements Database.batchable<SObject>{ 
   
   global Iterable<Sobject> start(Database.batchableContext info){ 
       Iterable<SObject> iterator = (Iterable<SObject>) new CustomIterator();
       return iterator; 
   }     
   
   global void execute(Database.batchableContext info, List<SObject> scope){ 
       for(Sobject s : scope)
       {
          if(s.getSObjectType() == 'Account')
          // account processing
          if(s.getSObjectType() == 'Contact')
             // contact processing

       }
   }     
   global void finish(Database.batchableContext info){     
   } 
}

global class CustomIterator implements Iterator<SObject>{ 
   
   List<SObject> soList {get; set;} 
   Integer i {get; Set;}
   public CustomIterator(){ 
       List<Account> a = [Select Id,name from Account Limit 2];
       soList= new List<SObject>();
       soList.addAll((List<SObject>)a);
       List<Contact> b = [Select Id,name from Contact limit 2];
       soList.addAll((List<SObject>)b);
       System.debug('soList'+soList);
       i=0;
   }   
    
     global boolean hasNext(){ 
      if(i >= soList.size()) { return false; }
       else { return true; } }
      global SObject next()
       {  if(i == soList.Size())
           {return null;}
            i++;
            return soList[i-1]; }
 }