[Java] HashSet Object 중복체크

eqauls, hashCode 메소드 override 해줘야 함.

private static class Cann {
    int x;
    int y;

    public Cann(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public boolean equals(Object o) {
        if (o instanceof Cann) {
            return x == ((Cann) o).x && y == ((Cann) o).y;
        } else {
            return false;
        }
    }

    @Override
    public int hashCode() {
        return Objects.hash(x, y);
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "(" + x + ", " + y + ")";
    }

}