IntStream

import java.util.stream.IntStream;

class DifferenceOfSquaresCalculator {

    int computeSquareOfSumTo(int input) {
        int sum = IntStream.rangeClosed(1, input).sum();
        return sum * sum;
    }
    
    int computeSumOfSquaresTo(int input) {
        return IntStream.rangeClosed(1, input)
            .map(num -> num * num)
            .sum();
    }
    
    int computeDifferenceOfSquares(int input) {
        return computeSquareOfSumTo(input) - computeSumOfSquaresTo(input);
    }
}

This solution iterates using the rangeClosed() method of the IntStream class.

In computeSquareOfSumTo, the numbers are added with the sum() method. The sum of the numbers is then multiplied by itself to get the square of the summed numbers. Note it avoids using Math.pow() here, since multiplying a value by itself is usually more efficient than type-casting from intto double back to int.

In computeSumOfSquaresTo, each number is squared by multiplying it by itself inside the map() method. Again, the number is multiplied by itself instead of using pow() and converting the double result back into an int. All of the squared numbers are added using the sum() method.