stage 0: add arrays + interfaces and lists lessons

examples/stage0/snippets/src/Arrays.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+void main() {
+    // [motorSpeedsLiteral]
+    double[] motorSpeeds = {0.5, 0.5, 0.5, 0.5};
+    // [/motorSpeedsLiteral]
+
+    // [motorSpeedsEmpty]
+    double[] emptyMotorSpeeds = new double[4];
+    // [/motorSpeedsEmpty]
+
+    // [setSpeed]
+    motorSpeeds[0] = 0.7;
+    System.out.println(motorSpeeds[0]); // 0.7
+    // [/setSpeed]
+
+    // [speedsLength]
+    System.out.println(motorSpeeds.length); // 4
+    // [/speedsLength]
+
+    // [pathArray]
+    Point[] path = {
+        new Point(0, 0),
+        new Point(1, 2),
+        new Point(3, 3),
+    };
+    // [/pathArray]
+
+    // [pathArrayEmpty]
+    Point[] emptyPath = new Point[3];
+    // [/pathArrayEmpty]
+
+    try {
+        // [pathArrayNull]
+        emptyPath[0].norm(); // error: emptyPath[0] is null
+        // [/pathArrayNull]
+    } catch (NullPointerException e) {
+        // for demo purposes we don't care about the exception'
+    }
+
+    // [indexLoopSpeeds]
+    double total = 0;
+    for (int i = 0; i < motorSpeeds.length; i++) {
+        total += motorSpeeds[i];
+    }
+    System.out.println(total); // 2.2
+    // [/indexLoopSpeeds]
+
+    // [forEachPath]
+    for (Point waypoint : path) {
+        System.out.println(waypoint.getX() + ", " + waypoint.getY());
+    }
+    // [/forEachPath]
+
+    // [pathLength]
+    double pathLength = 0;
+    for (int i = 1; i < path.length; i++) {
+        Point segment = path[i].minus(path[i - 1]);
+        pathLength += segment.norm();
+    }
+    System.out.println(pathLength); // 4.47213595499958
+    // [/pathLength]
+}

examples/stage0/snippets/src/Loops.java

@@ -54,7 +54,7 @@ void main() {
 
     // [ForExample2]
     for (int i = 0; i < 6; i++) {
-    System.out.println("Hi!");
+        System.out.println("Hi!");
     }
     //[/ForExample2]
 
@@ -63,8 +63,4 @@ void main() {
         System.out.println(i); // prints 0, 1, 2, 3, 4
     }
     // [/forExample]
-
-
-
-
-}
+}

examples/stage0/snippets/src/interfaces-lists/DistanceSensor.java

@@ -0,0 +1,11 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+// [distanceSensorInterface]
+interface DistanceSensor {
+    double getDistanceMeters();
+}
+// [/distanceSensorInterface]

examples/stage0/snippets/src/interfaces-lists/InterfacesListsUsage.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+// [importList]
+import java.util.ArrayList;
+import java.util.List;
+// [/importList]
+
+// [isTooClose]
+boolean isTooClose(DistanceSensor sensor) {
+    return sensor.getDistanceMeters() < 1.0;
+}
+// [/isTooClose]
+
+// [genericLast]
+<T> T last(T[] items) {
+    return items[items.length - 1];
+}
+// [/genericLast]
+
+void main() {
+    // [distanceSensorCall]
+    DistanceSensor ultrasonic = new UltrasonicSensor();
+    DistanceSensor lidar = new LidarSensor();
+    System.out.println(isTooClose(ultrasonic)); // false
+    System.out.println(isTooClose(lidar));      // false
+    // [/distanceSensorCall]
+
+    // [genericLastCall]
+    Point[] path = {new Point(0, 0), new Point(1, 2), new Point(3, 3)};
+    DistanceSensor[] sensors = {ultrasonic, lidar};
+
+    System.out.println(last(path).getX());       // 3.0
+    System.out.println(last(sensors).getClass()); // class LidarSensor
+    // [/genericLastCall]
+
+    // [pairCall]
+    Pair<String, Integer> pair = new Pair<>("foo", 42);
+    String foo = pair.getFirst();
+    Pair<Point, Point> pointPair = new Pair<>(new Point(0, 0), new Point(1, 2));
+    Point secondPoint = pointPair.getSecond();
+    // [/pairCall]
+
+    // [historyList]
+    List<Point> waypoints = new ArrayList<>();
+    // [/historyList]
+
+    // [historyAdd]
+    waypoints.add(new Point(0, 0));
+    waypoints.add(new Point(1, 2));
+    System.out.println(waypoints.size()); // 2
+    // [/historyAdd]
+
+    // [forEachHistory]
+    RobotHistoryTracker tracker = new RobotHistoryTracker(Point.ORIGIN);
+    tracker.move(new Point(3, 0));
+    tracker.move(new Point(0, 4));
+
+    for (Point visited : tracker.getHistory()) {
+        System.out.println(visited.getX() + ", " + visited.getY());
+    }
+    // [/forEachHistory]
+}

examples/stage0/snippets/src/interfaces-lists/LidarSensor.java

@@ -0,0 +1,15 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+// [lidarSensorClass]
+class LidarSensor implements DistanceSensor {
+    @Override
+    public double getDistanceMeters() {
+        // In real life, this would actually interact with hardware
+        return 1.2;
+    }
+}
+// [/lidarSensorClass]

examples/stage0/snippets/src/interfaces-lists/Pair.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+
+// [pairClass]
+public class Pair<A, B> {
+  private final A first;
+  private final B second;
+
+  Pair(A first, B second) {
+    this.first = first;
+    this.second = second;
+  }
+
+  public A getFirst() {
+    return first;
+  }
+
+  public B getSecond() {
+    return second;
+  }
+}
+// [/pairClass]

examples/stage0/snippets/src/interfaces-lists/RobotHistoryTracker.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+import java.util.ArrayList;
+import java.util.List;
+
+// [robotHistoryTrackerClass]
+class RobotHistoryTracker {
+    private Point position;
+    private final List<Point> history = new ArrayList<>();
+
+    public RobotHistoryTracker(Point startPosition) {
+        this.position = startPosition;
+        this.history.add(startPosition);
+    }
+
+    public void move(Point delta) {
+        this.position = this.position.plus(delta);
+        this.history.add(this.position);
+    }
+
+    public Point getPosition() {
+        return this.position;
+    }
+
+    public List<Point> getHistory() {
+        return this.history;
+    }
+}
+// [/robotHistoryTrackerClass]

examples/stage0/snippets/src/interfaces-lists/UltrasonicSensor.java

@@ -0,0 +1,15 @@
+/*
+ * Copyright 2026 FRCSoftware
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+// [ultrasonicSensorClass]
+class UltrasonicSensor implements DistanceSensor {
+    @Override
+    public double getDistanceMeters() {
+        // In real life, this would actually interact with hardware
+        return 1.5;
+    }
+}
+// [/ultrasonicSensorClass]

src/config/sidebarConfig.ts

@@ -81,6 +81,14 @@ export const sidebarSections: Record<string, SidebarSection[]> = {
                         //     label: 'Methods',
                         //     slug: 'learning-course/stage0/methods',
                         // },
+                        {
+                            label: 'Arrays and For-Each Loops',
+                            slug: 'learning-course/stage0/arrays',
+                        },
+                        {
+                            label: 'Interfaces, Generics, and Lists',
+                            slug: 'learning-course/stage0/interfaces-lists',
+                        },
                     ],
                 },
                 {