CODEWITHSUNDEEP
javaarraysarraylist
Helen
Helen

Reputation: 1

dynamicaly create arrayList in JAVA

I need to create 50 arraylists but rather than having to initialise them all individually. Is there a way in JAVA that I can do this dynamically??

i.e.

pseudo code:

for int i=1; i<51; i++
List<String> Counti = new ArrayList<String>();

So that in the loop it goes through and create 50 arraylists all called Count1, Count2, Count3 etc up until Count50.

I've tried creating a string and then naming the list by the string but it doesnt seem to recognise that teh name is a variable.

e.g.

for int i=1; i<51; i++
String Name="Count "+i
List<String> Name = new ArrayList<String>();

Instead it just creates a list called "Name"

Upvotes: 0

Views: 133

Answers (4)

Pier-Alexandre Bouchard
Pier-Alexandre Bouchard

Reputation: 5235

You need a List of ArrayList.

List<List<String>> lists = new ArrayList<>();

for (int i = 0; i < 50; i++){
    lists.add(new ArrayList<String>());
}

Upvotes: 1

ToYonos
ToYonos

Reputation: 16833

You should store them in a List and not create 50 variables

List<List<String>> lists = new ArrayList<ArrayList<String>>();
for (int i = 0; i < 50; i++)
{
    lists.add(new ArrayList<String>());
}

Upvotes: 1

nano_nano
nano_nano

Reputation: 12523

one another possible solution is to use a HashMap like this to name the ArrayLists:

Map<String, ArrayList<String>> mAllArrayListsByName = new HashMap<String, ArrayList<String>>();
for (int i = 0 ; i < 50 ; i++){
  mAllArrayListsByName.put("List"+String.valueOf(i), new ArrayList<String>());
}
ArrayList<String> lMyArrayList = mAllArrayListsByName.get("List0"); // get List 0

Upvotes: 0

wvdz
wvdz

Reputation: 16641

You can do this with reflection, but this is a pretty bad idea. What you probably want to do is create an arraylist of arraylists.

 ArrayList<ArrayList<String>> listOfLists = new ArrayList<ArrayList<String>>();
 for (int i = 0; i < 50; i++)
      listOfLists.add(new ArrayList<String>());

Upvotes: 3

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