Where is array's length property defined?

Question

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

ArrayList arr = new ArrayL         


        

Answer 1

To answer it as it-is, where is this length property of array defined? In a special Object header.

Easy to see via JOL

 int [] ints = new int[23];
 System.out.println(ClassLayout.parseInstance(ints).toPrintable());

One of the lines from this output is going to be:

OFFSET  SIZE      TYPE DESCRIPTION
16       4        (object header)   17 00 00 00 (00010111 00000000 00000000 00000000) (23)

Usually Objects have two headers (mark and klass), arrays have one more that always occupy 4 bytes in length, as size is an int.