arrays - java.lang.NullPointerException in LinkedList[] add() method

I'm having problem when i'm adding node in Array of LinkedList.

int vertices = 100;
LinkedList[] AdjList = new LinkedList[vertices+1];


for (i = 1; i <= vertices; ++i) {         

    for (j = 1; j <= 6 && j + i <= vertices; ++j) {

        AdjList[i].add(j);    //Error occurs here.
    }
   }

Answer

You need to create the list before inserting into it. In your first for loop add this line, before the second for loop

AdjList[i] = new LinkedList();