// Satisfy the Java filename/class rules.  Ignore this class.
public class Subtype {}

class Point {
    protected int x;
    protected int y; 
    public Point(int x, int y) {
        this.x = y;
        this.y = y;
    }
    public int getX() { return x; }
    public int getY() { return y; }
}

class ColorPoint extends Point {
    protected String color;
    public ColorPoint(int x, int y, String color) {
        super(x, y);
        this.color = color;
    }
    public String getColor() { return color; }
}


/*
 * For which pairs (X,Y) in {A, B, C, D} does X <: Y hold?
 * (Assume we change the declaration of X to be include "X extends Y".)
 */

interface AI {
    Point shift(Point p);
}

interface BI {
    ColorPoint shift(ColorPoint cp);
}

interface CI {
    Point shift(ColorPoint cp);
}


interface DI {
    ColorPoint shift(Point p);
}

/*
 * Below are sample implementations of these interfaces to help reason
 * about subtyping rules.
 */
class A implements AI {
    Point shift(Point p) {
        return new Point(p.getX() - 10, p.getY() + 10);
    }
}

class B implements BI {
    ColorPoint shift(ColorPoint cp) {
        if (cp.getColor().equals("red")) {
            return new ColorPoint(cp.getX(), cp.getY() + 10, "blue");
        } else {
            return cp;
        }
    }
}

class C implements CI {
    Point shift(ColorPoint cp) {
        if (cp.getColor().equals("red")) {
            return new Point(cp.getX(), cp.getY() + 10);
        } else {
            return cp;
        }
    }
}


class D implements DI {
    ColorPoint shift(Point p) {
        return new ColorPoint(p.getX() - 10, p.getY(), "blue");
    }
}


Point p = new Point(1,2);

ColorPoint cp = new ColorPoint(3,4,"red");


Y shifter = new X();

// px = p or cp
YReturnType py = shifter.shift(px);
// Use all methods of YReturnType on py.