reduce in java 8 understanding example code

ReduceUnderstanding.java

package com.java8.streams;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

public class ReduceUnderstanding {

    public static void main(String[] args) {

        List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        // sum of numbers without reduce
        int sum = 0;
        for (int x : listOfNumbers) {
            sum += x;
        }
        System.out.println("sum of numbers without using reduce " + sum);

        // with using reduce
        //Integer sumOfNumbers = listOfNumbers.stream().reduce(0,(a,b) -> a+b);
        Integer sumOfNumbers = listOfNumbers.stream().reduce(0, Integer::sum);
        System.out.println("sum of numbers with reduce used : " + sumOfNumbers);

        // count no of dishes in stream using the map and reduce.
        Integer noOfDIshes = Dish.menu.stream()
                // map each dish in a stream as integer 1 if we have {Dish1.Dish2,Dish3} stream then it ll map to {1,1,1}
                .map(dish -> 1).reduce(0, (a, b) -> a + b);
        System.out.println("No of dishes using map and reduce : " + noOfDIshes);

        // OOTB count implementation below is using reduce internally
        System.out.println("No of dishes using count method on streams: " + Dish.menu.stream().count());

        //using reduce to find maximum integer in given integer values
        //Optional<Integer> maxNo = listOfNumbers.stream().reduce((var0, var1) -> var0 >= var1 ? var0 : var1);
        Optional<Integer> maxNo = listOfNumbers.stream().reduce(Integer::max);
        System.out.println("Find Max integer usnig reduce : " + (maxNo.isPresent() ? maxNo.get() : 0));

    }
}

Output :
sum of numbers without using reduce 55
sum of numbers with reduce used : 55
No of dishes using map and reduce : 9
No of dishes using count method on streams: 9
Find Max integer usnig reduce : 10