Question

What I have is

public static LinkedList<Mp3> musicList;        
...
if (musicList == null) {
    musicList = new LinkedList<Mp3>();
}//create... this works

but if I have like 5 or more lists how can I do something like this:

Object[] ob = new Object[]{musicList,musicList2,...,musicList10};

for (int i = 0; i < ob.length; i++){
    if (ob[i] == null) ob[i] = new LinkedList<Mp3>();
}

If I put it in first way it’s working; how can I put it in like in second snippet?

Answer 1

Changing the references in the array will not change the original references used to create the array.

The references in the array are a copy of what was in the initialization.

What you should do is get rid of the musicListN variables and only have an array, or better yet use a List.

List<List<Mp3>> musicLists = new ArrayList<List<Mp3>>(LIST_COUNT);
for (int i = 0; i < LIST_COUNT; i++) {
  musicLists.add(new LinkedList<Mp3>());
}

Then use musicLists.get() to everywhere you would have used the older variables.