Scheduler class example for batch apex.

Assume that our ORG has a custom object API named as "Product_Complaint__c".
Our aim is to schedule a batch apex which will responsible for make a select query on Product_Complaint__c object.

/**
 * This is a batch class.
 * https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_batch_interface.htm
 **/
global class BatchClassExample implements Database.Batchable<sObject>{
  global String query;

  global Database.QueryLocator start(Database.BatchableContext BC){
      return Database.getQueryLocator(query);
    }

    global void execute(Database.BatchableContext BC, List<sObject> scope){
       List<Product_Complaint__c> lstOfPC = (List<Product_Complaint__c>)scope;

       // Call any helper calss to do the logic.
       System.debug('Test PC Size ::::::::::::: ');
       System.debug('PC Size ::::::::::::: '+ lstOfPC.size());
   }


    global void finish(Database.BatchableContext BC){
    }
}

/**
 * This is a scheduler class example for batch apex.
 * This class implements the Schedulable interface for a class called AffectedScheculeClassExample.
 * 
 * Link: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_scheduler.htm
 **/
global class ScheduledBatchClassExample implements Schedulable {
  //This is implemented method and it must be declared as global or public.
  global void execute(SchedulableContext sc) {
    BatchClassExample batchInst = new BatchClassExample();
    batchInst.query = 'SELECT Id FROM Product_Complaint__c';
    database.executebatch(batchInst, 1);
  }
}

/**
 * This class is responsible for calling ScheduledBatchClassExample class to run the scheduler.
 * Call this class constractor from anonymous window.
 *
 **/
public class CallScheduledBatchClassExample
{
  //Constructor need to be call from annonymous window to run the schedule job.
  public CallScheduledBatchClassExample(){
    ScheduledBatchClassExample schBatchClsExmpl = new ScheduledBatchClassExample();
    /**
      *  Schedule structure:
      *  <Seconds> <Minutes> <Hours> <Day_of_month> <Month> <Day_of_week> <Optional_year>
      *
      * For below example it will schedulw the job @ 08:23 AM every day.
    */
    String sch = '0 23 8 * * ?';
    String schJobID = system.schedule('Scheduler Batch Example', sch, schBatchClsExmpl);
  }
}

To test this example instantiate CallScheduledBatchClassExample() 
from anonymous window as,
CallScheduledBatchClassExample inst = new CallScheduledBatchClassExample
();