Just seeing how painful it is to try to be functional in Java

Painful.java

class Painful {
    public static void main(String[] args) {
        int[] firstTenIntegers = {1,2,3,4,5,6,7,8,9,10};

        Functional squareFunction = new Functional() {
            public int apply(int x) {
                return x*x;
        }};
        
        Functional cubeFunction = new Functional() {
            public int apply(int x) {
                return x*x*x;
        }};
        
        System.out.println("Sum of squares of first ten numbers is: " + sum(firstTenIntegers, squareFunction));
        System.out.println("Sum of cubes of first ten numbers is: " + sum(firstTenIntegers, cubeFunction));
    }
    
    public static int sum(int[] list, Functional f) {
        int answer=0;
        for (int i=0; i<list.length; i++) {
            answer+=f.apply(list[i]);
        }
        return answer;
    }
}

interface Functional {
    public int apply(int x) ;
}