In Java 8 (until Java 11) there is a method 'getObjectSize' in 'jdk.nashorn.internal.ir.debug.ObjectSizeCalculator' class.
This method lets us measure any Object size, containing any other elements or Objects inside it (that's called deep Object size)

'getObjectSize' was added in Java 8 as a part of 'Nashorn JavaScript engine' and depricated in Java 11.

This code is an example, showing how to get exact byte size of a single Integer in any Collections Framework class (or deep size size of any other object in Java)

(a single +1 Integer element costs):

Vector, Stack, ArrayList: 16 byte
(one link 8 byte + one Integer 8 byte)

LinkedList: 40 byte
(node 8 byte, prev\next\current link 8 byte each, Integer 8 byte)

ArrayDeque, PriorityQueue: 16 byte
(one link 8 byte + one Integer 8 byte)

HashSet: 48 byte
(node 8 byte, key\value links 8 byte each, key\value Integers 8 byte each, next element in bucket link 8 byte)

LinkedHashSet: 56 byte
(HashSet size + one link 8 byte)

TreeSet: 56 byte
(node 8 byte, key\value links 8 byte each, key\value Integers 8 byte each, two child elements 8 byte each)

HashMap: 48 byte
(same as HashSet)

LinkedHashMap: 56 byte
(same as HashMap)

TreeMap: 56 byte
(same as TreeSet)