java - How can I convert List<List<String>> into String[][]? -

in project have list contains lists of strings (list<list<string>>) , have convert list array of string arrays (string[][]).

if had single list<string> (for example mylist) convert string[]:

string[] myarray = new string[mylist.size()]; myarray = mylist.toarray(myarray); 

but in case have lots of list of string inside list (of list of strings). how can this? i've spent lots of time didn't find solution..

i wrote generic utility method few days own usage, converts list<list<t>> t[][]. here's method. can use purpose:

public static <t> t[][] multilisttoarray(final list<list<t>> listoflist,                                           final class<t> classz) {     final t[][] array = (t[][]) array.newinstance(classz, listoflist.size(), 0);      (int = 0; < listoflist.size(); i++) {         array[i] = listoflist.get(i).toarray((t[]) array.newinstance(classz, listoflist.get(i).size()));     }      return array; } 

there i've created array using array#newinstance() method, since cannot create array of type parameter t directly.

since we're creating 2-d array, , don't yet know how many columns having, i've given column size 0 initially. anyways, code initializing each row new array inside loop. so, don't need worry that.

this line:

array[i] = listoflist.get(i).toarray((t[]) array.newinstance(classz, listoflist.get(i).size())); 

uses list#toarray(t[]) method convert inner list array, did. i'm passing array parameter method return value t[], can directly assign current row - array[i].

now can use method as:

string[][] arr = multilisttoarray(yourlist, string.class); 

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thanks @arshaji, can modify generic method pass uninitialized array 2^nd parameter, instead of class<t>:

public static <t> void multilisttoarray(final list<list<t>> listoflist,                                          final t[][] arr) {     (int = 0; < listoflist.size(); ++i) {         arr[i] = listoflist.get(i).toarray(arr[i]);     } } 

but then, have pass array method this:

list<list<string>> list = new arraylist<>(); // initialize list string[][] arr = new string[list.size()][0]; multilisttoarray(list, arr); 

note that, since passing array argument, no longer need return method. modification done in array reflected array in calling code.