Java 8 memory notes

gistfile1.txt

On 64-bit JVM all objects will require a multiple of 8 bytes: 8, 16, 24, 32, 48, 56, 64, etc.

Empty String: 24 bytes
  String itself:
    24 bytes = 8 bytes "headers" + (4 bytes "size" + 4 bytes "hash" - not anymore since Java 8) + 4 bytes "value reference" + 4 bytes "padding to make 20 to become multiple of 8".
  char[0]:
    0 bytes = does not cost any memory for this string, because it's shared empty char array, used by all empty strings.
String with 3 chars: 48 bytes
  String itself:
    24 bytes = 8 bytes "headers" + 4 bytes "size" + 4 bytes "hash" + 4 bytes "value reference" + 4 bytes "padding to make 20 to become multiple of 8".
  char[3]:
    24 bytes = 12 bytes "headers" + 4 bytes "size" + 6 bytes "3 chars" + 2 bytes "padding to make 22 to become multiple of 8"
String with 4 chars: 48 bytes
  String itself:
    24 bytes = 8 bytes "headers" + 4 bytes "size" + 4 bytes "hash" + 4 bytes "value reference" + 4 bytes "padding to make 20 to become multiple of 8".
  char[4]:
    24 bytes = 12 bytes "headers" + 4 bytes "size" + 8 bytes "4 chars"
String with 5 chars: 56 bytes
  String itself:
    24 bytes = 8 bytes "headers" + 4 bytes "size" + 4 bytes "hash" + 4 bytes "value reference" + 4 bytes "padding to make 20 to become multiple of 8".
  char[5]:
    32 bytes = 12 bytes "headers" + 4 bytes "size" + 10 bytes "5 chars" + 6 bytes "padding to make 50 to become multiple of 8"