class UFOobservation {
    private final double tid, x, y;
    public UFOobservation(double tid, double x, double y) {
        this.tid = tid;
        this.x = x;
        this.y = y;
    }
    public boolean equals(Object o) {
        if (!(o instanceof UFOobservation))
            return false;
        UFOobservation u = (UFOobservation)o;
        return this.tid == u.tid &&
            this.x == u.x &&
            this.y == u.y;
    } // equals
    static boolean liknande(UFOobservation o1, UFOobservation o2) {
        return Math.abs(o1.tid - o2.tid) < 1 &&
            Math.abs(o1.x - o2.x) < 1 &&
            Math.abs(o1.y - o2.y) < 1;
    }
} // class UFOobservation

class OmöjligUFOobservationException
    extends Exception { }

class UFOobservation2 {
    private final double tid, x, y;
    public UFOobservation2(double tid, double x, double y)
      throws OmöjligUFOobservationException {
        if (tid < 0 || x < 0 || y < 0)
            throw new OmöjligUFOobservationException();
        this.tid = tid;
        this.x = x;
        this.y = y;
    }
    public boolean equals(Object o) {
        if (!(o instanceof UFOobservation))
            return false;
        UFOobservation2 u = (UFOobservation2)o;
        return this.tid == u.tid &&
            this.x == u.x &&
            this.y == u.y;
    } // equals
    static boolean liknande(UFOobservation2 o1, UFOobservation2 o2) {
        return Math.abs(o1.tid - o2.tid) < 1 &&
            Math.abs(o1.x - o2.x) < 1 &&
            Math.abs(o1.y - o2.y) < 1;
    }
} // class UFOobservation2

class AvanceradUFOobservation extends UFOobservation {
    private final double höjd;
    public AvanceradUFOobservation(double tid, double x, double y, double höjd) {
        super(tid, x, y);
        this.höjd = höjd;
    }

    public boolean equals(Object o) {
        if (o instanceof AvanceradUFOobservation) {
	    AvanceradUFOobservation u = (AvanceradUFOobservation)o;
	    return super.equals(o) && this.höjd == u.höjd;
	}
        else if (o instanceof UFOobservation)
            return super.equals(o);
	else
            return false;
    } // equals
} // class AvanceradUFOobservation

/*
    public boolean equals(Object o) {
        if (!(o instanceof AvanceradUFOobservation))
            return false;
        AvanceradUFOobservation u = (AvanceradUFOobservation)o;
        return super.equals(o) && this.höjd == u.höjd;
    } // equals
*/

class UFOtest {
    public static void main(String[] arg) {
        UFOobservation o1 = new UFOobservation(1, 2, 3);
        UFOobservation o2 = new UFOobservation(1, 2, 3);
        UFOobservation o3 = new UFOobservation(1.5, 2.9, 2.1);

        System.out.println("o1.equals(o2): " + o1.equals(o2));
        System.out.println("o1.equals(o3): " + o1.equals(o3));

        System.out.println("liknande(o1, o2)): " + UFOobservation.liknande(o1, o2));
        System.out.println("liknande(o1, o3)): " + UFOobservation.liknande(o1, o3));

        try {
            UFOobservation2 o4 = new UFOobservation2(1, 2, 3);
            UFOobservation2 o5 = new UFOobservation2(1, 2, -3);
            UFOobservation2 o6 = new UFOobservation2(1.5, 2.9, 2.1);
        }
        catch (OmöjligUFOobservationException e) {
            System.out.println("Fångat: " + e);
        }

	AvanceradUFOobservation ao1 = new AvanceradUFOobservation(1, 2, 3, 4);
	AvanceradUFOobservation ao2 = new AvanceradUFOobservation(1, 2, 3, 5);

        System.out.println("o1.equals(ao1): " + o1.equals(ao1));
        System.out.println("ao1.equals(o1): " + ao1.equals(o1));
        System.out.println("o1.equals(ao2): " + o1.equals(ao2));
        System.out.println("ao2.equals(o1): " + ao2.equals(o1));

        System.out.println("ao1.equals(ao2): " + ao1.equals(ao2));
        System.out.println("ao2.equals(ao1): " + ao2.equals(ao1));





    } // main
} // class UFOtest