java - Arraylist and Arrays

Question

What is the difference between

ArrayList<Object> al = new ArrayList<Object>(100);

and

Object[] ar = new Object[100];

Is there any difference in the internal implementation i.e. the allocation in the memory? Do both internally reserve 100 slots in the memory?

Answer 1

An ArrayList<Object> holds a backing Object[]. The backing Array will be "resized" (a new array will be created and the old data will be copied over) if you would possibly overflow the size and additions are possible.

List implementations also provide additional methods to work on them.

Another thing is that you may use Generics(1.5) with Lists.