Java Collections.sort return null when sorting list of strings -

i trying sort list of strings (that contain alphanumeric characters punctuation) via collections.sort:

public class sorterdriver {     public static void main(string[] args) {         list<string> tosort = new arraylist<string>();          tosort.add("fizzbuzz");         system.out.println("tosort size " + tosort.size());          list<string> sorted = collections.sort(tosort);         if(sorted == null) {             system.out.println("i null , sad.");         } else {             system.out.println("i not null.");         }     } } 

when run get:

tosort size 1 null , sad. 

why null?

collections.sort() returns void, new collection sorted never initialized.

list<string> sorted = collections.sort(tosort); 

is like

list<string> sorted = null; collections.sort(tosort);     //                 ^------------> tosort being sorted! 

to use correctly collections.sort() method must know you sorting same object put in method:

collections.sort(collectiontobesorted); 

in case:

public class sorterdriver {     public static void main(string[] args) {         list<string> tosort = new arraylist<string>();          tosort.add("fizzbuzz");         system.out.println("tosort size " + tosort.size());          collections.sort(tosort);         if(tosort == null) {             system.out.println("i null , sad.");         } else {             system.out.println("i not null.");         }     } }