Memory usage of basic java types:
boolean 1 byte
byte 1 byte
char 2 bytes
int 4 bytes
float 4 bytes
long 8 bytes
double 8 bytes
object overhead 16 bytes
array overhead 24 bytes
Reference 8 bytes
Each object uses padding of a multiple of 8 bytes
Total memory usage of a data type value:
Primitive type: 1 byte for boolean or byte, 2 bytes for char, 4 bytes for int or float, 8 bytes for long or double.
Object reference: 8 bytes.
Array: 24 bytes + memory of each array entry.
Object: 16 bytes + memory for each instance variable + 8 if inner class (for pointer to enclosing class).
Padding: round up to multiple of 8 types.
Example
class example {
int[] a = new int[8];
String b = "abc";
long timestamp c = 0L;
boolean d = false;
}
For an object of class example, we calculate the total amount of memory usage as the following:
the memory usage = 16 bytes object overhead
+ 24 bytes array overhead + 4 bytes x 8
+ 8 bytes reference
+ 8 bytes long
+ 1 byte boolean
+ 7 bytes padding to round up to multiple of 8 bytes
------------------------------------------------------------------
96 bytes
