public class SumOfMultiples {
    private final int sum;

    public SumOfMultiples(int number, int[] set) {
        sum = calculateSum(number, set);
    }

    public int getSum() {
        return sum;
    }

    private int calculateSum(int number, int[] set) {

        int sum = 0;
        int count = 0;

        for (int i = 1; i < number; i++) {

            for (int j = 0; j < set.length; j++) {
                if (i % set[j] == 0) {
                    count++;
                }
            }

            if (count > 0) {
                sum = sum + i;
                count = 0;
            }
        }

        return sum;
    }

}

import java.util.Arrays;
import java.util.stream.IntStream;

public class SumOfMultiples {
    private final int sum;

    public SumOfMultiples(int number, int[] set) {
        sum = calculateSum(number, set);
    }

    public int getSum() {
        return sum;
    }

    private int calculateSum(int number, int[] set) {

        int sum = IntStream.range(1,number)
                .filter(i -> Arrays.stream(set).filter(j -> i % j == 0).count() > 0)
                .sum();

        return sum;
    }

}

replace forloop