What is the memory consumption of an object in Java?

Question

Is the memory space consumed by one object with 100 attributes the same as that of 100 objects, with one attribute each?

How much memory is allocated for an object?<

Answer 1

Is the memory space consumed by one object with 100 attributes the same as that of 100 objects, with one attribute each?

No.

How much memory is allocated for an object?

• The overhead is 8 bytes on 32-bit, 12 bytes on 64-bit; and then rounded up to a multiple of 4 bytes (32-bit) or 8 bytes (64-bit).

How much additional space is used when adding an attribute?

• Attributes range from 1 byte (byte) to 8 bytes (long/double), but references are either 4 bytes or 8 bytes depending not on whether it's 32bit or 64bit, but rather whether -Xmx is < 32Gb or >= 32Gb: typical 64-bit JVM's have an optimisation called "-UseCompressedOops" which compress references to 4 bytes if the heap is below 32Gb.