How are class attributes/fields stored

Question

I know that an instance of this C++ class :

class A {
   char c;
   int iiii;
   short ss;   
};

would look kind of like this in memory : c| | | |i|i|i|i|s|s| | |

This 4/2 letter annotation has no sense (But I think that my point is clear)

1 byte for char, 3 bytes of padding, 4 bytes of int, 2 bytes for the short, and 2 bytes of tail padding (platform dependant, but it won't change the logic)

From C++ standards (Compilers wouldn't change the order of the fields in my example):

Nonstatic data members of a (non-union) class with the same access control (Clause 11) are allocated so that later members have higher addresses within a class object. The order of allocation of non-static data members with different access control is unspecified (Clause 11). Implementation alignment requirements might cause two adjacent members not to be allocated immediately after each other; so might requirements for space for managing virtual functions (10.3) and virtual base classes (10.1).

so, I would like to know if it is the same for Java classes, Can the compiler change the order to reduce the padding ?

Answer 1

First have a look at What do Java objects look like in memory during run-time? and Know Thy Java Object Memory Layout .

But I guess Java Objects Memory Structure answers your question.

In order to save some memory, the Sun VM doesn't lay out object's attributes in the same order they are declared. Instead, the attributes are organized in memory in the following order:

doubles and longs
ints and floats
shorts and chars
booleans and bytes
references