java - Random Tour Generation Issues -

i trying generate random tour graph. using adjacency-list method.

there problem vertices. when add vertex particular list, vertex gets added lists in graph. not understand why! here's code:

public static void main(string[] args) {     defaultdata(6); }  public static void defaultdata(int n) {     integer costs[] = { 26, 95, 38, 74, 80, 73, 73, 92, 22, 97, 13, 81, 41,       17, 4, 2, 47, 54, 21, 68, 78, 4, 77, 3, 66, 55, 99, 42, 62, 39, 8, 36,       53, 74, 26, 8, 42, 66, 30, 58, 69, 14, 49, 39, 85, 98, 72, 3, 18, 99,       96, 66, 64, 36, 17, 44, 70, 0, 8, 14, 62, 41, 84, 59, 94, 27, 5, 27,       96, 10, 15, 52, 43, 20, 2, 86, 45, 43, 32, 17, 49, 92, 9, 15, 6, 49,       72, 7, 51, 21, 2, 26, 63, 82, 98, 48, 21, 96, 16 };      arraylist<arraylist<integer>> costgraph = new arraylist<>();     arraylist<arraylist<integer>> completegraph = new arraylist<>();      random rand = new random(system.currenttimemillis());      int costindex = 0;     (int = 0; <= n; i++) {         arraylist<integer> cost = new arraylist<>();         arraylist<integer> edge = new arraylist<>();          (int j = 0; j <= n; j++) {             if (i == j) {                 continue;             }              edge.add(j);             cost.add(costs[costindex]);             costindex++;         }          completegraph.add(edge);         costgraph.add(cost);     }      system.out.println(completegraph);      arraylist<arraylist<integer>> dummygraph =       (arraylist<arraylist<integer>>)completegraph.clone();     arraylist<arraylist<integer>> randomtour = new arraylist<>();     arraylist<integer> dummylist = new arraylist<>();      (int = 0; <= n; i++) {         randomtour.add(dummylist);     }      system.out.println(dummygraph);      int edgecount = 0;     integer row = rand.nextint(n);     integer start = row;      while(edgecount <= n-1){         //dummylist = dummygraph.get(row);          // keep bounds of random equal         // new reduced size of lists in graph          integer col = dummygraph.get(row).get(rand.nextint(n-edgecount));          randomtour.get(row).add(col);          system.out.println(row);         system.out.println(randomtour);          edgecount++;         for(int k = 0; k < n; k++)             dummygraph.get(k).remove(row);         row = col;     }      randomtour.get(row).add(start);     system.out.println(randomtour); } 

i grateful timely response. in advance!

you don't want this:

for (int = 0; <= n; i++) {     randomtour.add(dummylist); } 

it keeps adding same reference lots of times, arraylists in arraylist same object.

instead want this:

for (int = 0; <= n; i++) {     randomtour.add(new arraylist<integer>()); } 

that way arraylist instances in arraylist different.

i hope answer timely enough!