array of objects proper way of use?

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?

MByD · Accepted Answer · 2012-03-13 21:50:44Z

4

Avoid mixing arrays and generics.

Instead, consider this:

List<List<Mp3>> listsList = new ArrayList<List<Mp3>>();
listsList.add(new LinkedList<Mp3>());

answered Mar 13, 2012 at 21:50

MByD

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2 Comments

Hia Over a year ago

thanks for answer! I will try this way.. but it seems instead of shortening my code I will make it longer :D

MByD Over a year ago

I ignored the part of how to initialize to make the concept of using only generic collections clearer, it might make it a bit longer, but it will make it better IMHO.

Michael Krussel · Accepted Answer · 2012-03-13 21:57:57Z

2

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.

answered Mar 13, 2012 at 21:57

Michael Krussel

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2 Comments

Hia Over a year ago

I implemented it in my code, but have 1 more question.. when i init LIST_COUNT = 5, it creates list of 10? so when i look at musicLists.size() it is = 2xLIST_COUNT

Michael Krussel Over a year ago

@Hia Is the for loop running more then once. You might need to add checks that the list is empty before initializing it.

Community · Accepted Answer · 2017-05-23 10:24:24Z

0

If you really want to do one line object list initialization, look at this Q. Initialization of an ArrayList in one line

edited May 23, 2017 at 10:24

CommunityBot

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answered Mar 13, 2012 at 21:53

Michael Rice

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