Case study · Advanced

Design an Elevator System

Multiple elevators, hall and cabin requests, and a scheduler that decides which car goes where — modelled with a direction State machine and a pluggable dispatch Strategy.

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step 1 / 8
1/2Model the system
elevators *dispatch
ElevatorSystem
+ request(floor, dir)
«interface»
Dispatcher
+ pick(req): Elevator
Request
- floor
- dir
Elevator
- floor
- dir
- stops
+ addStop(f)
Button
- floor
Model the system
 1class ElevatorSystem {
 2    List<Elevator> elevators;
 3    DispatchStrategy dispatch;
 4    void request(int floor, Dir dir) {
 5        Elevator e = dispatch.pick(new Request(floor, dir));
 6        e.addStop(floor);
 7    }
 8}
State
requirementroute requests to cars
✦

ElevatorSystem is the entry point. It receives hall requests and delegates the genuinely hard "which car?" decision rather than deciding inline.