Difference between implicit and explicit ArrayList size declarations?

Question

what is the difference between the following declarations:

List list1 = new ArrayList();

List list2 = new ArrayList(10);

By default is allocates it with 10. But is there any difference? Can I add an 11th element to list2 by list2.add("something")?

Answer 1

Here is the source code for you for first example

public  ArrayList() {
    this(10);
 }

So there is no difference. Since the initial capacity is 10, no matter you pass 10 or not, it gets initialised with capacity 10.

Can I add 11th element in the list2 by list2.add("something")?

Ofcourse, initial capacity is not final capacity. So as you keep on adding more than 10, the size of the list keeps increasing.

If you want to have a fixed size container, use Arrays.asList (or, for primitive arrays, the asList methods in Guava) and also consider java.util.Collections.unmodifiableList()

Worth reading about this change in Java 8 : In Java 8, why is the default capacity of ArrayList now zero?

In short, providing initial capacity wont really change anything interms of size.