java - Comparator.comparing(...) throwing non-static reference exception while taking String::compareTo -


below 2 lines of code snippet:

list<string> listdevs = arrays.aslist("alvin", "alchemist", "brutus", "larsen", "jason", "kevin");  listdevs.sort(comparator.comparing(string::length)); //this works fine listdevs.sort(string::comparetoignorecase); //this works fine

but (out of expermient) when try write 

listdevs.sort(comparator.comparing(string::comparetoignorecase));

the compiler throws error

cannot make static reference non-static method comparetoignorecase(string) type string

similar happens below code

listdevs.sort(comparator.comparing(string::compareto));

i understand error , works fine if remove comparator.comparing (as shown above).

but point is, how line works?

listdevs.sort(comparator.comparing(string::length));

i believe missing something. have read this thread. same scenario?

comparator.comparing expects function describes comparable property of elements. string::length sufficient length() property of string evaluating string int (that’s why comparingint preferable here).

in contrast, string.comparetoignorecase , string.compareto comparison methods. compare 2 string objects. references them sufficient comparator expected, not property function expected.

it’s have factory saying “gimme engine, , build car you” , trying give them complete car. while existing car valid car expected, there no sense in passing factory built car.

unfortunately, current compiler implementation bad @ reporting error functional signatures. see messages “cannot make static reference non-static method …” when signatures mismatch.


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