Finding Max with Lambda Expression in Java -

Finding Max with Lambda Expression in Java -

this code

list<integer> ints = stream.of(1,2,4,3,5).collect(collectors.tolist()); integer maxint = ints.stream() .max(comparator.comparing(i -> i)) .get(); system.out.println("maximum number in set " + maxint);

output:

maximum number in set 5

i cannot create distingues between 2 in bellow section of code

comparator.comparing(i -> i)

can kind , explain difference between 2 i?

the method comparator.comparing(…) intended create comparator uses order based on property of objects compare. when using lambda look i -> i, short writing (int i) -> { homecoming i; } here, property provider function, resulting comparator compare values itself. works when objects compare have natural order integer has.

so

stream.of(1,2,4,3,5).max(comparator.comparing(i -> i)) .ifpresent(maxint->system.out.println("maximum number in set " + maxint));

does same as

stream.of(1,2,4,3,5).max(comparator.naturalorder()) .ifpresent(maxint->system.out.println("maximum number in set " + maxint));

though latter more efficient implemented singleton types have natural order (and implement comparable).

the reason why max requires comparator @ all, because using generic class stream might contain arbitrary objects.

this allows, e.g. utilize streamofpoints.max(comparator.comparing(p->p.x)) find point largest x value while point not have natural order. or streamofpersons.sorted(comparator.comparing(person::getage)).

when using specialized intstream can utilize natural order straight more efficient:

intstream.of(1,2,4,3,5).max() .ifpresent(maxint->system.out.println("maximum number in set " + maxint));

to illustrate difference between “natural order” , property based order:

stream.of("a","bb","aaa","z","b").max(comparator.naturalorder()) .ifpresent(max->system.out.println("maximum string in set " + max));

this print

maximum string in set z

as natural order of strings lexicographical order z greater b greater a

on other hand

stream.of("a","bb","aaa","z","b").max(comparator.comparing(s->s.length())) .ifpresent(max->system.out.println("maximum string in set " + max));

will print

maximum string in set aaa

as aaa has maximum length of strings in stream. intended utilize case comparator.comparing can made more readable when using method references, i.e. comparator.comparing(string::length) speaks itself…

java lambda max java-8