#Elevator Design Exercise

Author: Joe Tippetts

This is in response to Kuali's request to design an elevator system.

##Initial Thinking

A building has one or more Elevators that need to operate in unison. Each elevator has controls for its own actions, triggered by passengers pushing buttons. In addition a central Dispatcher needs to coordinate system level requests by passengers who haven't yet boarded an elevator.

Note: The numbers indicated in the code (e.g. Req#1) correspond to your requirements doc.

##Design Elements of the system.

###Classes

####Elevator An elevator.

#####Attributes

• floor - tells which floor the elevator is currently on [1..n]. If moving, this is the destination it's moving toward.
• door - state of the elevator door [open | opening | closed | closing].
• isWorking - is the elevator working [true] or in maintenance mode [false]?
• isOccupied - does the elevator have passengers? You know this if a request hasn't been completed.
• isMoving - is the elevator moving?
• dispatcher - reference to containing dispatcher to which elevator reports.
• tripCount - total count of trips (handled requests) made by elevator.
• floorCount - total count of floors passed.

#####Methods

• dispatch(request) - request from dispatcher.
• close() - close the elevator door if it's open.
• open() - opens the elevator door if it's stopped and not in maintenance.
• move(floor) - based on request sent to dispatcher, tells the elevator to move to the specified floor. Reports to dispatcher at each floor. If trip count is divisible by 100 when a request is re
• report() - how elevators tell dispatcher about their current state. Saved in

####Dispatcher Coordinates movements between working elevators to choose the fastest option for passengers. Singleton to ensure all reports from elevators and requests from passengers are handled in order.

#####Attributes

• elevators[] - Composed collection of elevator objects.
• elevatorCount - number of elevators in the building.
• floorCount - number of floors in building.
• openRequests[] - array of elevator requests in the order they're made should be processed first-in, first-out (FIFO).

#####Methods

• constructor(numElevators, numFloors) - initialize dispatcher with number of elevators and floors in the building.
• chooseElevator(request) - choose best elevator based on request. Returns elevator.

####Request Requests made from passengers to the Dispatcher. These happen in each floor's lobby [up | down] and inside each elevator [floor number | close | open].

#####Attributes

• created - timestamp request was made.
• started - timestamp when elevator was dispatched to fulfill request.
• completed - timestamp when request was finished.
• floor - the floor the request is made from.
• action - the action associated with the request [up | down | floor | open | close].