Where is array’s length property defined?

We can determine the length of an ArrayList<E> using its public method size(), like

ArrayList<Integer> arr = new ArrayList(10);
int size = arr.size();

Similarly we can determine the length of an Array object using the length property

String[] str = new String[10];
int size =  str.length;

Whereas the size() method of ArrayList is defined inside the ArrayList class, where is this length property of Array defined?