Creating multiple lists inside a loop

Maybe this is what you are looking for.

ArrayList<myItem>[] d = (ArrayList<myItem>[]) new ArrayList[3];

for (int i = 0; i < 3; i++) {
    d[i] = new ArrayList<myItems>();
}

No: variable names are merely a convenience for the programmer and are not kept track of after your code is compiled, so that kind of "dynamic variable naming" is not allowed. You will have to find another way to keep track of your lists, such as a Map<String, List<Item>> that maps string identifiers to lists:

Map<String, List<Item>> map = new HashMap<String, List<Item>>()
map.put("d1", new ArrayList<Item>());
...

To then access the list corresponding to "d1", for example you can just use map.get("d1").

Have a List<List<MyItem>> instead and fill it in the loop

If you do this:

for(i=0;i<3;i++){
  List<myItems> d = new ArrayList<myItems>();
}

You will create a new array list three times. But each time you will store it to a newly created reference d and once you leave the scope of the for loop, that reference will vanish.

What you may be looking for is this:

List<List<myItems>> d = new ArrayList<List<myItems)>();
for(i=0;i<3;i++){
  d.add(new ArrayList<myItems>());
}

This creates a nested list:

someListOfListsOfMyItems
  subListOfMyItems
    someMyItem
    anotherMyItem
  subListOfMyItems
    someOtherMyItem
    anotherOtherMyItem
  subListOfMyItems
    yetSomeOtherMyItem
    yetAnotherMyItem

Each sublist can be accessed like so:

d.get(indexOfSublist);