Responsible for creating the instances of JobRunShell to be used within the QuartzScheduler instance. 

JobRunShell instances are responsible for providing the 'safe' environment for Job s to run in, and for performing all of the work of executing the Job, catching ANY thrown exceptions, updating the Trigger with the Job's completion code, etc. 

This is the heart of Quartz, an indirect implementation of the org.quartz.Scheduler interface, containing methods to schedule org.quartz.Job s, register org.quartz.JobListener instances, etc. 

Contains all of the resources (JobStore,ThreadPool, etc.) necessary to create a QuartzScheduler instance. 

The thread responsible for performing the work of firing Trigger s that are registered with the QuartzScheduler . 

An object used to pass information about the 'client' to the QuartzScheduler.