Hi Deepu sfdc,

Let's say you are tracking a State, County, and Country information on Lead object as a custom fields such as Custom_State__c, Custom_County__c, and Custom-Country__c. Also, you have additional custom field named Custom_Zip_Code__c (a number field).

Your requirment is that whenever user enters a lead record with a value on Custom_Zip_Code__c field, all other fields (Custom_State__c, Custom_County__c, and Custom-Country__c) should be automatically updated with a use of FUTURE METHOD. Why Future method and not trigger directly? It's because your business requirements says so, or you are not in hurry to update these fields, or you are looking for a greater sets of government limits etc.. The reason can be anything.

Now, imagine you have a seperate object in salesforce named Master Address (this object has nothing to do with Lead object means no relationship at all) which contains information about all zip codes in US with their appropriate State, County and Country info.

Something like below.
Zip Code         State                County                       Country
1000              New Jersey        Morris                        United States
2000               New York          Chester                      United States
45000              Vermont            Vermont County         United States
+++++             +++++++             ++++++++++++++         ++++++++++
+++++             +++++++             ++++++++++++++         ++++++++++
up to very last zip code in US :)
+++++             +++++++             ++++++++++++++         ++++++++++
+++++             +++++++             ++++++++++++++         ++++++++++

Scenario:
Example: If lead is entered with name Mark Hunt with zip code as 45000 then Custom State, Custom County, and Custom Country should be updated as VT, Vermont County, and United States. Just imagine that 45000 is a zip code for vermont even though.. its probably not :) ). Hope this is making sense so far..


Now here comes the trigger + Future method magic. Below trigger calls a Future method class.

Trigger Code:

Trigger LeadCustomAddress on Lead (After Insert, After UnDelete, Before Update) {
	 
    List<Id> flaggedLeadIds = New List<Id>();
    Set<String> zipCodes = New Set<String>(); 
    
    If(LeadCustomAddress_ProcessControl.visited == False)
    {
        If(Trigger.IsInsert || Trigger.IsUnDelete || Trigger.IsUpdate)
        {
            For(Lead Ld: Trigger.New)
            {
                If(Ld.Custom_Zip_Code__c != NULL && Ld.Custom_State__c == NULL
                                                 && Ld.Custom_County__c == NULL
                                                 && Ld.Custom_Country__c == NULL)
                {
                       flaggedLeadIds.add(Ld.Id); 
                       zipCodes.add(Ld.Custom_Zip_Code__c);
                }
            }
        }
        LeadCustomAddress_FutureClass.LeadCutomAddress_FutureMethod(flaggedLeadIds, zipCodes); 
    }
   
    
}

FUTURE METHOD:
 

Public class LeadCustomAddress_FutureClass {
	 
    @Future
    Public static Void LeadCutomAddress_FutureMethod(List<Id> leadIds, Set<String> leadZips){
        
        List<Lead> comingLeads = [Select Id, Custom_Zip_Code__c, Custom_State__c, Custom_County__c, Custom_Country__c
                                 		FROM Lead WHERE Id =: leadIds];
        
        List<Master_Address__c> allNeededMasterAddressInfo = [Select Id, Zip_Code__c, State__c, County__c, Country__c
                                                             		FROM Master_Address__c
                                                              			WHERE Zip_Code__c =: leadZips];
        
        //system.debug('*****The size of comingLeads is: ' + comingLeads.size());
        system.debug('*****The size of allNeededMasterAddressInfo is: ' + allNeededMasterAddressInfo.size());
        
        List<Lead> leadFinalListToUpdate = New List<Lead>();
        For(Lead EveryLead : comingLeads)
        {
            If(EveryLead.Custom_Zip_Code__c != NULL && EveryLead.Custom_State__c == NULL
              								 		&& EveryLead.Custom_County__c == NULL
                                             		&& EveryLead.Custom_Country__c == NULL)
            {
                For(Master_Address__c EveryMasterRecord : allNeededMasterAddressInfo)
                {
                    If(String.valueof(EveryMasterRecord.Zip_Code__c) == String.valueof(EveryLead.Custom_Zip_Code__c))
                    {
                    	EveryLead.Custom_State__c =  EveryMasterRecord.State__c;
                        EveryLead.Custom_County__c =  EveryMasterRecord.County__c;
                        EveryLead.Custom_Country__c =  EveryMasterRecord.Country__c;
                    }
                }    
            }
            leadFinalListToUpdate.add(EveryLead);
        }
        /*
        system.debug('Updating Leads Info: Zip Code Is: ' + leadFinalListToUpdate[0].Custom_Zip_Code__c
                    					   + 'State Is: ' + leadFinalListToUpdate[0].Custom_State__c
                    					   + 'County Is: ' + leadFinalListToUpdate[0].Custom_County__c
                    					   + 'Country Is: ' + leadFinalListToUpdate[0].Custom_Country__c);*/
        
        //update leadFinalListToUpdate;
        
        try{
            If(!leadFinalListToUpdate.isEmpty())
            {
                LeadCustomAddress_ProcessControl.visited = TRUE;
                update leadFinalListToUpdate;
            }
        }Catch(Exception e){
            system.debug('Thrown Exception For LeadCutomAddress_FutureMethod Is: ' + e.getmessage());
        }
        
    }
}

Hope this example helps and if this answers your question then kindly mark it as BEST ANSWER!