Came across this blog post by Daniel Lemire. It’s not his most interesting or informative post, but made me remember a little utility I wrote many years ago. MemoryEstimator is a tool to estimate the memory footprint of any Java type. (It’s part of ojAlgo.) Just had to verify if its estimates are aligned with the numbers presented in that blog post. In that post there is a table of estimated memory usage for byte arrays of different sizes. These are the numbers:
| size of the array | estimated memory usage |
|---|---|
| 0 | 16 bytes |
| 1 | 24 bytes |
| 2 | 24 bytes |
| 3 | 24 bytes |
| 4 | 24 bytes |
| 5 | 24 bytes |
| 6 | 24 bytes |
| 7 | 24 bytes |
| 8 | 24 bytes |
| 9 | 32 bytes |
Now, let’s see if MemoryEstimator produces the same estimates.
Example/Test Code
Console Output
class TheMemoryEstimator ojAlgo 2022-12-01 Size of byte[] of different lengths =================================== byte[0] == 16 bytes byte[1] == 24 bytes byte[2] == 24 bytes byte[3] == 24 bytes byte[4] == 24 bytes byte[5] == 24 bytes byte[6] == 24 bytes byte[7] == 24 bytes byte[8] == 24 bytes byte[9] == 32 bytes Memory footprint of Java's basic types ====================================== boolean 1 bytes 16 bytes when wrapped/boxed in a class byte 1 bytes 16 bytes when wrapped/boxed in a class char 2 bytes 16 bytes when wrapped/boxed in a class double 8 bytes 24 bytes when wrapped/boxed in a class float 4 bytes 16 bytes when wrapped/boxed in a class int 4 bytes 16 bytes when wrapped/boxed in a class long 8 bytes 24 bytes when wrapped/boxed in a class Object 4 bytes 16 bytes when wrapped/boxed in a class short 2 bytes 16 bytes when wrapped/boxed in a class Memory footprint of some specific types ======================================= BigDecimal == 40 bytes LocalDate == 24 bytes Instant == 24 bytes OptionalDouble == 24 bytes