Learn about object overhead in JVM

Question

I am studying java, and I remember reading somewhere that java objects, had some overhead inside the JVM, which was used for administration reasons by the virtual machine. S

Answer 1

Here is a snippet for object header, object overhead, array header, object reference. Hope it helps someone, if not the OP as it is a quite old question.

    private static int OBJ_HEADER;
    private static int ARR_HEADER;
    private static int INT_FIELDS = 12;
    private static int OBJ_REF;
    private static int OBJ_OVERHEAD;
    private static boolean IS_64_BIT_JVM;

     static {
    String arch = System.getProperty("sun.arch.data.model");

    IS_64_BIT_JVM = (arch == null) || arch.contains("32");
    OBJ_HEADER = IS_64_BIT_JVM ? 16 : 8;
    ARR_HEADER = IS_64_BIT_JVM ? 24 : 12;
    OBJ_REF = IS_64_BIT_JVM ? 8 : 4;
    OBJ_OVERHEAD = OBJ_HEADER + INT_FIELDS + OBJ_REF + ARR_HEADER;
       }

I should say that I know only the solution, but I haven't yet figured out why this works. This is why people should leave comments in their code... Oh, well, when I do figure it out, I will share the logic behind it.