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

Collections.max(list)

List<Integer> list = new ArrayList<>(); // Creating List

   list.add(3); //add elements

   list.add(6);

   list.add(9);

int maxNum = Collections.max(list); //save the biggest element in variable

System.out.println(max); //print 9

The theoretical limit for ArrayList capacity is Integer. MAX_VALUE, a.k.a. 2^31 - 1, a.k.a. 2,147,483,647. But you'll probably get an OutOfMemoryError long before that time because, well, you run out of memory