Question

As we all know that java uses the following data types

byte    Occupy 8 bits in memory
short   Occupy 16 bits in memory
int     Occupy 32 bits in memory
long    Occupy 64 bits in memory 

If I create a class like

class Demo{
    byte b;        
    int i;
    long l;
}

Demo obj = new Demo();

Now my question is obj size is < or > or = the size of b+i+l which is 104 bytes. Please give me the clarification with proper reason.

Thanks,
Anil Kumar C

Answer 1

The in-memory size of the object depends on the architecture, mainly on whether the VM is 32 or 64-bit. The actual VM implementation also matters.

For each object, you need space for its object header (typically 2*8 bytes on 64-bit VMs), its fields (extra space for alignment depending on the VM implementation). The final space is then rounded up to the nearest multiple of the word size.