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

public class Common {

    public static void main(String[] args) {

        List<Integer> ls = Arrays.asList(3, 4, 6, 9, 2, 5, 7);
        System.out.println(ls.stream().reduce(Integer.MIN_VALUE, (a, b) -> a > b ? a : b));
        System.out.println(ls.stream().max(Integer::max).get());
        System.out.println(ls.stream().max(Integer::compare).get());
        System.out.println(ls.stream().max((a, b) -> a > b ? a : b));

        System.out.println();

        System.out.println("USING Integer.max()");
        System.out.println(ls.stream().max((o1, o2) -> {System.out.print(o1);
            System.out.print(o2);
            int max = Integer.max(o1, o2);
            System.out.print(max);
            System.out.print("\t");
            return max;})
                .get());

        /*
            Integer.max() returns the greater of two int values

            This is Comparator definition:
            A negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
            first argument x
            second argument y
            x<y RETURN negative integer
            x=y RETURN zero
            x>y RETURN positive integer

            This fake "Comparator"'s return statement "return max" always returns positive integers,
            meaning max() thinks that first argument which is 3 is always bigger than whatever argument we are comparing it to,
            it can be smaller or larger than 3.

            So the stream().max() method always thinks that 3 is bigger than whatever is being compared to because the function within max() always returns
            positive integers.

            In the end 3 was maximum because comparing it to other numbers always yielded positive integer.
        */


        System.out.println("USING Integer.compare()");
        System.out.println(ls.stream().max((o1, o2) -> {System.out.print(o1);
            System.out.print(o2);
            int max = Integer.compare(o1, o2);
            System.out.print(max);
            System.out.print("\t");
            return max;})
                .get());

        /*
            Integer.compare() works like this:
                (x < y) ? -1 : ((x == y) ? 0 : 1);

            This is how stream().max() works here:
            1) 3 compared to 4 means Integer.compare() returns -1 so stream().max() gets negative integer meaning that it has not found a max yet so max() moves to next numbers 4 and 6
            2) 4 compared to 6 means Integer.compare() returns -1 so stream().max() gets negative integer meaning that it has not found a max yet so max() moves to next numbers 6 and 9
            3) 6 compared to 9 means Integer.compare() returns -1 so stream().max() gets negative integer meaning that it has not found a max yet so max() moves to next numbers 9 and 2
            4) 9 compared to 2 means Integer.compare() returns 1 so stream().max() gets positive integer meaning it has found the max now as 9 and it keeps the max() to compare to next number 5
            5) 4 compared to 6 means Integer.compare() returns 1 so stream().max() gets positive integer meaning it has found the max now as 9 and it keeps the max() to compare to next number 7
            6) Now the stream().max() has found the max as 9 and returns it. get() is necessary to get it out of Optional
    }
        */


    }
}