Submission A #6

Zabuzard · 2025-12-01T08:08:08Z

Submission by user A

Zabuzard · 2025-12-01T08:12:01Z

Contest/Assignment/test/SanityTest.java

-
-                ElevatorSnapshot currentElevatorSnapshot =
-                        currentSnapshot.getElevatorSnapshot(maybeElevatorId.orElseThrow());
-                assertEquals(human.getStartingFloor(), currentElevatorSnapshot.currentFloor(),
-                        ERROR_MESSAGE_PRE
-                                + "When a human enters an elevator, the elevator must be at the humans starting floor. But '%s' entered elevator with ID '%d' at a different floor.".formatted(
-                                human, maybeElevatorId.orElseThrow()));
            }

            boolean exitedElevator =
                    previousState != Human.State.ARRIVED && currentState == Human.State.ARRIVED;
            if (exitedElevator) {
                assertTrue(currentHumanSnapshot.currentElevatorId().isEmpty(), ERROR_MESSAGE_PRE
                        + "When a human exits an elevator, they must not have a current elevator id anymore. But '%s' has.".formatted(
                        human));

                // Only if the human actually travelled around
                if (human.getStartingFloor() != human.getDestinationFloor()) {
                    OptionalInt maybeElevatorId = previousHumanSnapshot.currentElevatorId();
                    assertTrue(maybeElevatorId.isPresent(), ERROR_MESSAGE_PRE
                            + "When a human exits an elevator, they must have had a current elevator id previously. But '%s' does not.".formatted(
                            human));

                    assertEquals(Human.State.TRAVELING_WITH_ELEVATOR, previousState,
                            "When a human exits an elevator, their previous state must be traveling. But '%s' was in state %s.".formatted(
                                    human, previousState));

                    ElevatorSnapshot currentElevatorSnapshot =
                            currentSnapshot.getElevatorSnapshot(maybeElevatorId.orElseThrow());
-                    assertEquals(human.getDestinationFloor(),
-                            currentElevatorSnapshot.currentFloor(), ERROR_MESSAGE_PRE
-                                    + "When a human exits an elevator, the elevator must be at the humans destination floor. But '%s' exited elevator with ID '%d' at a different floor.".formatted(
-                                    human, maybeElevatorId.orElseThrow()));


removed important sanity checks

Zabuzard · 2025-12-01T08:14:30Z

Contest/Assignment/src/org/togetherjava/event/elevator/simulation/Simulation.java

-        return humans.stream()
-                .map(Human::getCurrentState)
-                .allMatch(Human.State.ARRIVED::equals);
+        return humanTravelingCount == 0;


(prob an optimization to avoid big iterations)

Zabuzard · 2025-12-01T08:15:05Z

Contest/Assignment/src/org/togetherjava/event/elevator/simulation/Simulation.java

+
+    public void addHuman(Human human) {
+        if (isDone()) {
+            throw new SimulationFinishedException("Can't add new human after simulation is finished!");


okay, but a IllegalStateException might have been more appropriate. but shows they can use exceptions, neat

Zabuzard · 2025-12-01T08:15:47Z

Contest/Assignment/src/org/togetherjava/event/elevator/simulation/Simulation.java

+        if (human.getCurrentState() != Human.State.ARRIVED) {
+            humanTravelingCount++;
+        }


isnt the initial state always not-arrived by definition? smells a bit

Zabuzard · 2025-12-01T08:16:19Z

Contest/Assignment/src/org/togetherjava/event/elevator/simulation/Simulation.java

+    @Override
+    public synchronized void onHumanArrived(Human human) {
+        if (humanTravelingCount > 0) {
+            humanTravelingCount--; //We trust that the human hasnt notified us twice.


kek. but okay

Zabuzard · 2025-12-01T08:17:00Z

Contest/Assignment/src/org/togetherjava/event/elevator/simulation/Simulation.java

+
+    @Override
+    public synchronized void onHumanArrived(Human human) {
+        if (humanTravelingCount > 0) {


defensive behavior smells, why not an exception? does this actually happen?

Zabuzard · 2025-12-01T08:18:40Z

Contest/Assignment/src/org/togetherjava/event/elevator/humans/Human.java

     */
    private Integer currentEnteredElevatorId;
-
+    private final List<HumanArrivedListener> listeners = new ArrayList<>();


design-wise this is a bit weird. like, why would humans contact anyone when they arrived. more reasonable might be something like an elevator notifying the elevator system when a human leaves the elevator.
but even that is technically IRL not a thing - anyways, fair solution to the performance problem.

Zabuzard · 2025-12-01T08:19:59Z

Contest/Assignment/src/org/togetherjava/event/elevator/humans/Human.java

+        if (currentState == State.ARRIVED) {
+            return; //dont want to notify listeners again for our arrival
+        }
+        this.currentState = State.ARRIVED;
+        for (var listener : listeners) {
+            listener.onHumanArrived(this);
+        }


this logic is easy to accidentally miss by directly setting the state. if such a logic is used, all state-changes should flow through a setter, not just for ARRIVED

Zabuzard · 2025-12-01T08:22:05Z

Contest/Assignment/src/org/togetherjava/event/elevator/humans/Human.java

+        bestElevator = floorPanelSystem.bestElevator(destinationFloor, destinationFloor > startingFloor ? TravelDirection.UP : TravelDirection.DOWN);
+        if(bestElevator.getCurrentFloor() == startingFloor) {
+            this.currentEnteredElevatorId = bestElevator.getId();
+            this.currentState = State.TRAVELING_WITH_ELEVATOR;
+            return;
+        }
+        floorPanelSystem.requestElevator(bestElevator,startingFloor);


this works but with respect to real life thats not a thing. humans dont get told which elevator to use and wait for, they press a button and when the door opens they enter, regardless of elevator ID

Zabuzard · 2025-12-01T08:22:33Z

Contest/Assignment/src/org/togetherjava/event/elevator/humans/Human.java

+        if (destinationFloor == startingFloor) {
+            return;
+        }
+        bestElevator = floorPanelSystem.bestElevator(destinationFloor, destinationFloor > startingFloor ? TravelDirection.UP : TravelDirection.DOWN);


method naming could be improved. its also unclear that this is essentially a getter/compute method as its missing any verb

Zabuzard · 2025-12-01T08:24:00Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/FloorPanelSystem.java

+    void requestElevator(Elevator bestElevator, int atFloor);
+    Elevator bestElevator(int atFloor, TravelDirection desiredTravelDirection);


missing javadoc

Zabuzard · 2025-12-01T08:30:59Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/Elevator.java

    private final int floorsServed;
    private int currentFloor;

+    private final List<Integer> floorRequests = new ArrayList<>();


a queue would prob be more appropriate

Zabuzard · 2025-12-01T08:31:49Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/Elevator.java

+    public void incrementFloorByOne() {
+        if (currentFloor+1 > this.getTopFloor()) {
+            return;
+        }
+        currentFloor++;
+    }
+
+    public void decrementFloorByOne() {
+        if (currentFloor-1 < minFloor) {
+            return;
+        }
+        currentFloor--;


use of math.min/max would be more idiomatic but ok

Zabuzard · 2025-12-01T08:32:40Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/Elevator.java

+
+        //if we have arrived at our floor, or we already are there, we remove the request
+        if (currentFloor == floorRequests.getFirst()) {
+            synchronized (this) {


(the sync placement looks correct, neat)

Zabuzard · 2025-12-01T08:33:42Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/ElevatorSystem.java

+        elevatorListeners.parallelStream().forEach(listener -> listener.onElevatorSystemReady(this));
+    }
+
+    public static int floorAndElevatorDistance(int floor, Elevator elevator) {


method naming is confusing

Zabuzard · 2025-12-01T08:33:57Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/ElevatorSystem.java

+        return Math.abs(elevator.getCurrentFloor()-floor);
+    }
+    @Override
+    public Elevator bestElevator(int atFloor, TravelDirection desiredTravelDirection) {


method naming is confusing

Zabuzard · 2025-12-01T08:35:55Z

Contest/Assignment/src/org/togetherjava/event/elevator/elevators/ElevatorSystem.java

+        for (var elevator : elevators) {
+            if (floorAndElevatorDistance(atFloor, elevator) < floorAndElevatorDistance(atFloor, candidates.stream().findAny().get())) {
+                candidates.clear();
+                candidates.add(elevator);
+            } else if (floorAndElevatorDistance(atFloor, elevator) == floorAndElevatorDistance(atFloor, candidates.stream().findAny().get())) {
+                candidates.add(elevator);


this could benefit from some smaller improvements. for example saving the method call results in vars, using orElseThrow() instead of get() and some other smaller things maybe

Zabuzard

quite sophisticated implementation:

elevators serve humans with a request-queue (FIFO)
the elevator system picks the "best elevator" for each humans request based on which one is closest and then breaks ties by least amount of work per elevator (nice)
humans wait for their assigned elevator id (kinda unrealistic, but works)
extra mile: added multithreading/syncing, perf improvement by using "human arrived counter based on listener" instead of iterating every human every step
the code quality is ok. not very clean, method names, missing javadoc, ... but readable :)

Submission

0c6b9af

Zabuzard added submission event_november_2025 labels Dec 1, 2025

Zabuzard commented Dec 1, 2025

View reviewed changes

		void requestElevator(Elevator bestElevator, int atFloor);
		Elevator bestElevator(int atFloor, TravelDirection desiredTravelDirection);

Submission A #6

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Submission A #6

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Zabuzard Dec 1, 2025 •

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