Toy Robot in Java 7

robots.java

package com.mikerowecode.robot;

import java.util.Scanner;
import java.util.StringTokenizer;

public class Robots {
    public static void main(String[] args) {

        Robot robot = new Robot(-1, -1, Direction.WEST);

        Scanner in = new Scanner(System.in);
        while (in.hasNextLine()) {
            Command c = Command.fromString(in.nextLine());
            robot = c.go(robot);
        }
    }
}

enum Direction {
    NORTH, EAST, SOUTH, WEST;
    public Direction left() { return values()[((ordinal() + 3) % values().length)]; }
    public Direction right() { return values()[((ordinal() + 1) % values().length)]; }
}

class Robot {
    public static final int HEIGHT = 5;
    public static final int WIDTH = 5;

    public final int x;
    public final int y;
    public final Direction facing;

    public Robot(int x, int y, Direction facing) {
        this.x = x;
        this.y = y;
        this.facing = facing;
    }

    public boolean onTable() {
        return x >= 0 && x < WIDTH && y >= 0 && y < HEIGHT;
    }
}

abstract class Command {

    public abstract Robot go(Robot robot);

    public static Command fromString(String s) {
        StringTokenizer tokenizer = new StringTokenizer(s);
        String c = tokenizer.nextToken();
        if ("PLACE".equals(c)) {
            if (tokenizer.hasMoreTokens()) {
                String[] v = tokenizer.nextToken().split(",");
                try {
                    return new Place(Integer.valueOf(v[0]), Integer.valueOf(v[1]), Direction.valueOf(v[2]));
                } catch (Exception e) {
                    // fall through
                }
            }
        }

        if ("MOVE".equals(c)) return new Move();
        if ("LEFT".equals(c)) return new Left();
        if ("RIGHT".equals(c)) return new Right();
        if ("REPORT".equals(c)) return new Report();
        // default to noop
        return new Command() { public Robot go(Robot robot) { return robot; } };
    }
}

class Place extends Command {
    private final int x;
    private final int y;
    private final Direction dir;

    public Place(int x, int y, Direction dir) {
        this.x = x;
        this.y = y;
        this.dir = dir;
    }

    public Robot go(Robot robot) {
        return new Robot(x, y, dir);
    }
}

class Left extends Command {
    public Robot go(Robot robot) {
        return new Robot(robot.x, robot.y, robot.facing.left());
    }
}

class Right extends Command {
    public Robot go(Robot robot) {
        return new Robot(robot.x, robot.y, robot.facing.right());
    }
}

class Move extends Command {
    public Robot go(Robot robot) {
        if (robot.onTable()) {
            Robot schrodingerRobot = null;
            switch (robot.facing) {
                case NORTH:
                    schrodingerRobot = new Robot(robot.x, robot.y + 1, robot.facing);
                    break;
                case SOUTH:
                    schrodingerRobot = new Robot(robot.x, robot.y - 1, robot.facing);
                    break;
                case EAST:
                    schrodingerRobot = new Robot(robot.x + 1, robot.y, robot.facing);
                    break;
                case WEST:
                    schrodingerRobot = new Robot(robot.x + 1, robot.y, robot.facing);
                    break;
            }
            if (schrodingerRobot.onTable()) return schrodingerRobot;
        }
        return robot;
    }
}

class Report extends Command {
    public Robot go(Robot robot) {
        System.out.printf("%d,%d,%s\n", robot.x, robot.y, robot.facing);
        return robot;
    }
}