javac ShellPong.java && java -cp . ShellPong; rm ShellPong*.class

ShellPong.java

public class ShellPong {

    private static final int width = 80;
    private static final int height = 24;

    private static final char CORNER = '+';
    private static final char H_WALL = '-';
    private static final char V_WALL = '|';
    private static final char PADDLE = '#';
    private static final char BALL = 'O';
    private static final char BLANK = ' ';

    private static final int GOAL = 3;

    public static void main(String[] args) throws Exception {

        final char[][] buf = new char[height][width];

        Ball b = new Ball();
        b.x = width / 2;
        b.y = height / 2;

        Paddle p1 = new Paddle();
        p1.x = 4;
        p1.y = height / 2 - p1.height / 2;

        Paddle p2 = new Paddle();
        p2.x = -5;
        p2.y = height / 2 - p2.height / 2;

        int p1Score = 0;
        int p2Score = 0;

        boolean ballMissed = false;

        while (p1Score < GOAL && p2Score < GOAL) {

            if (ballMissed) {
                b.x = width / 2;
                b.y = height / 2;
                b.dx = Math.random() > .5 ? 1 : -1;
                b.dy = Math.random() > .5 ? 1 : -1;
            }

            int yp1 = 0;
            int yp2 = 0;
            toggleRawInput();
            while (System.in.available() > 0) {
                final int c = System.in.read();
                switch (c) {
                    case 'w':
                        yp1 = -1;
                        break;
                    case 's':
                        yp1 = 1;
                        break;
                    case 'o':
                        yp2 = -1;
                        break;
                    case 'l':
                        yp2 = 1;
                        break;
                    default:
                        System.out.println("" + c);
                }
            }
            toggleRawInput();
            System.out.println("Player 1: " + p1Score + " - Player 2: " + p2Score);
            clear(buf);
            drawFrame(buf);
            updatePaddle(p1, yp1);
            drawPaddle(p1, buf);
            updatePaddle(p2, yp2);
            drawPaddle(p2, buf);
            ballMissed = !updateBall(b, buf);
            drawBall(b, buf);
            draw(buf);
            sleep();


            if (ballMissed) {
                if (b.x < p1.x) {
                    p2Score++;
                } else {
                    p1Score++;
                }
            }
        }

        System.out.println("Player " + (p1Score == GOAL ? "1" : "2") + " won!");
    }

    private static void updatePaddle(Paddle p, int dy) {
        int ny = p.y + dy;

        if (ny == 0) {
            return;
        }
        if (ny + height == heightBound(-1)) {
            return;
        }

        p.y = ny;
    }

    private static void drawPaddle(Paddle p, char[][] buf) {
        drawVerticalLine(buf, PADDLE, p.x, p.y, p.y + p.height);
    }

    public static boolean updateBall(Ball b, char[][] buf) {
        int nx = b.x + b.dx;
        int ny = b.y + b.dy;
        if (nx == b.x && ny == b.y) {
            return true;
        }
        final char nc = get(buf, nx, ny);
        if (nc == V_WALL) {
            return false;
        }
        if (nc == H_WALL) {
            ny = b.y;
            b.dy *= -1;
            ny += b.dy;
        }
        if (nc == PADDLE) {
            nx = b.x;
            b.dx *= -1;
            nx += b.dx;
        }
        b.x = nx;
        b.y = ny;

        return true;
    }

    private static void drawBall(Ball b, char[][] buf) {
        drawDot(buf, BALL, b.x, b.y);
    }

    private static void drawFrame(char[][] buf) {
        drawDot(buf, CORNER, 0, 0);
        drawDot(buf, CORNER, -1, 0);
        drawDot(buf, CORNER, 0, -1);
        drawDot(buf, CORNER, -1, -1);
        drawHorizontalLine(buf, H_WALL, 1, 0, -2);
        drawHorizontalLine(buf, H_WALL, 1, -1, -2);
        drawVerticalLine(buf, V_WALL, 0, 1, -2);
        drawVerticalLine(buf, V_WALL, -1, 1, -2);
    }

    private static int widthBound(int x) {
        return mod(width + x, width);
    }

    private static int heightBound(int y) {
        return mod(height + y, height);
    }

    private static void clear(char[][] buf) {
        for (int x = 0; x < width; ++x) {
            for (int y = 0; y < height; ++y) {
                buf[y][x] = BLANK;
            }
        }
    }

    private static void draw(char[][] buf) {
        for (char[] chars : buf) {
            System.out.println(chars);
        }
    }

    private static void drawHorizontalLine(char[][] buf, char c, int x, int y, int x2) {
        final char[] line = buf[heightBound(y)];
        x = widthBound(x);
        x2 = widthBound(x2);
        final int min = Math.min(x, x2);
        final int max = Math.max(x, x2);

        for (int i = min; i <= max; ++i) {
            line[i] = c;
        }
    }

    private static void drawVerticalLine(char[][] buf, char c, int x, int y, int y2) {
        x = widthBound(x);
        y = heightBound(y);
        y2 = heightBound(y2);
        final int min = Math.min(y, y2);
        final int max = Math.max(y, y2);

        for (int i = min; i <= max; ++i) {
            buf[i][x] = c;
        }
    }

    private static void drawDot(char[][] buf, char c, int x, int y) {
        buf[heightBound(y)][widthBound(x)] = c;
    }

    private static char get(char[][] buf, int x, int y) {
        return buf[heightBound(y)][widthBound(x)];
    }

    private static int mod(int a, int b) {
        return ((a % b) + b) % b;
    }

    private static void sleep()
    {
        try {
            Thread.sleep(100);
        } catch (InterruptedException ignored) {}
    }

    private static boolean isRaw = false;
    private static final String[] RAW_INPUT_COMMAND = {"/bin/sh", "-c", ""};
    private static void toggleRawInput() throws Exception {
        RAW_INPUT_COMMAND[RAW_INPUT_COMMAND.length - 1] = "stty " + (isRaw ? "sane" : "raw") + " </dev/tty";
        isRaw = !isRaw;
        Runtime.getRuntime().exec(RAW_INPUT_COMMAND).waitFor();
    }

    private static class Ball {
        public int x = 0;
        public int y = 0;

        public int dx = 1;
        public int dy = 1;
    }

    private static class Paddle {
        public int x = 0;
        public int y = 0;
        public int height = 5;
    }
}