java - linked list NullPointerException -

i getting nullpointerexception , don't know why.

linkedlist<character>[][] list = new linkedlist[n][n];  (int j = 0; j < n; ++j) {     (int m = 0; m < 1; m++)     {                 // here problem         list[j][m].add("" + (characterarray[j]));     } } 

i want add characters array list. when run it says nullpointerexception. don't know how initialize list.

the problem here created 2 dimensional array of linkedlist objects. remember default value objects in java null, when array first created have 2 dimensional array of nulls. in nested loops trying populate linkedlist objects think have don't (their value null). say

null.add("" + (characterarray[j])); 

obviously creates null pointer exception.

so solution make object (in case make new linkedlist object) before trying add it. either having separate 2 nested loops follows:

for(int j = 0; j < n; j++) {     for(int m = 0; m < n; m++)     {         list[j][m] = new linkedlist<charater>();     } } 

followed code nested loops.

or can declare object inside nested loops

for (int j = 0; j < n; ++j) {     (int m = 0; m < 1; m++)     {                 // here problem         list[j][m] = new linkedlist<charater>();         list[j][m].add("" + (characterarray[j]));     } }