WeekThreeHomeWork

WeekThreeHomeWorkClass

public with sharing class WeekThreeHomeworkHandler {
  //it is public static condition and not returning anything
  public static void leadHandler(List<Lead> lstLeads) {
    List<Task> listTask = new List<Task>(); // intiating a task list

    //writing an if condition where it will create a new task when productInterest picklist has one of the values
    //if(l.ProductInterest__c == 'Cookbook Authorship'
    //|| l.ProductInterest__c =='Cookbook Editing'
    //||l. ProductInterest__c =='Cookbook Distribution')
    for (Lead l : lstLeads) {
      if (l.ProductInterest__c != null) {
        Task task = new Task();
        task.subject = 'New Task' + l.ProductInterest__c; //assigning subject name as
        task.whoId = l.OwnerId;
        task.Status = 'Not Started';
        task.priority = 'Normal';

        listTask.add(task);
      }
    }
    insert listTask;
  }
  public static void leadHandlerUpdate(List<Lead> newLeads, Map<Id, Lead>oldLeads){
    List<Task> tasksToCreate = new List<Task>();
    for (Lead newLead : newLeads) {
        Lead oldLead = oldLeadsMap.get(newLead.Id);
        if (newLead.Product_Interest__c != null && 
            (oldLead == null || newLead.Product_Interest__c != oldLead.Product_Interest__c)) {
            Task tasks = new Task();
            tasks.Subject = 'New Task' + l.ProductInterest__c;
            tasks.Priority = 'Normal';
            tasks.Status = 'Not Started';
            tasks.WhoId = newLead.ownerId;
            tasksToCreate.add(tasks);
        }
    }
    insert tasksToCreate;
}
}

WeekThreeHomeWorkTrigger

trigger LeadTrigger on Lead (after insert, after update) {
    WeekThreeHomeworkHandler lhandler = new WeekThreeHomeworkHandler();
        if(Trigger.isInsert){ 
            lhandler.leadHandler(Trigger.new);
            
     }else if (Trigger.isupdate) {
       lhandler.leadHandlerUpdate(Trigger.new, Trigger.Old)
    }
}