ReduceFair.java

import java.util.HashMap;
import java.util.Map;

class Fair {
    private final int quantity;

    Fair(int quantity) {
        this.quantity = quantity;
    }

    int getQuantity() {
        return quantity;
    }
}

public class ReduceFair {
    public static void main(String args[]) {
        Map<String, Integer> products = new HashMap<>();
        products.put("Banana", 7);
        products.put("Apple", 2);
        products.put("Kiwi", 1);

        int totalInTheFair = products.keySet().stream()
                .reduce(
                        new Fair(0),
                        (accFair, productName) -> new Fair(accFair.getQuantity() + products.get(productName)),
                        (fair, fair2) -> new Fair(fair.getQuantity() + fair2.getQuantity()))
                .getQuantity();

        System.out.println(totalInTheFair);
    }
}