Why does Integer::max not work as a Comparator? [duplicate]

  • A+
Category:Languages

I have this exercise and I don't understand the last result:

import java.util.Arrays; import java.util.Comparator; import java.util.List; public class Test {     public static void main(String[] args) {         List<Integer> list = Arrays.asList(10, 20, 8);         System.out.println(list.stream().max(Comparator.comparing(a -> a)).get()); //Line 1         System.out.println(list.stream().max(Integer::compareTo).get()); //Line 2         System.out.println(list.stream().max(Integer::max).get()); //Line 3     } } 

The result is: 20 20 10

If Integer::max works like Math::max, it should return the largest value between two elements. So, the max element of list is 20.

Why is the result 10?

 


Integer.max returns the larger of the two integers.

As such, Integer.max(10, 20) returns 20. 20 is greater than zero, so by the contract of Comparator.compare (which is that compare(a, b) returns a number greater than zero if a > b), 10 is considered "greater than" 20.

Similarly, Integer.max(10, 8) returns 10, greater than zero, so 10 is "greater than" 8.

As such, the final "max" is 10.

Comment

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen: