/**
 * Implementation of the terrain.
 */
class Terrain {

    /**
     * Can be used to set up a display list.
     */
    public Terrain() {
        // code goes here ...
    }

    /**
     * Draws the terrain.
     */
    public void draw() {
        // code goes here ...
    }

    /**
     * Computes the elevation of the terrain at ({@code x}, {@code y}).
     */
    public float heightAt(float x, float y) {
        return 0; // <- code goes here
    }
}