collections - How can I initialize an ArrayList with all zeroes in Java?

Question

It looks like arraylist is not doing its job for presizing:

// presizing 

ArrayList<Integer> list = new ArrayList<Integer>(60);

Afterwards when I try to access it:

list.get(5) 

Instead of returning 0 it throws IndexOutOfBoundsException: Index 5 out of bounds for length 0.

Is there a way to initialize all elements to 0 of an exact size like what C++ does?

Answer 1

The integer passed to the constructor represents its initial capacity, i.e., the number of elements it can hold before it needs to resize its internal array (and has nothing to do with the initial number of elements in the list).

To initialize an list with 60 zeros you do:

List<Integer> list = new ArrayList<Integer>(Collections.nCopies(60, 0));

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If you want to create a list with 60 different objects, you could use the Stream API with a Supplier as follows:

List<Person> persons = Stream.generate(Person::new)
                             .limit(60)
                             .collect(Collectors.toList());