class FunctionalComposition {

​

    public static void main(String[] args) {

        Function<Square, Integer> fun1 = s -> s.getArea();

        Function<Integer, Double> fun2 = area -> Math.sqrt(area);

        Function<Square, Double> getSide = fun2.compose(fun1);

        Square s = new Square();

        s.setArea(100);

        Double side = getSide.apply(s);

        System.out.println(side);

    }

​

}