Field layout code starts laying out the instance fields block at super-klass instance boundary. This quirk makes the classes like this:

    public static class A {
        private boolean b;
    }

    public static class B extends A {
        private boolean b;
    }

    public static class C extends B {
        private boolean b;
    }

...to be laid out like this:

 C object internals:
   OFFSET SIZE TYPE DESCRIPTION VALUE
        0 12 (object header)
       12 1 boolean A.b N/A
       13 3 (alignment/padding gap)
       16 1 boolean B.b N/A
       17 3 (alignment/padding gap)
       20 1 boolean C.b N/A
       21 3 (loss due to the next object alignment)
  Space losses: 6 bytes internal + 3 bytes external = 9 bytes total

It seems legal to lay out the fields like this instead:

  C object internals:
   OFFSET SIZE TYPE DESCRIPTION VALUE
        0 12 (object header)
       12 1 boolean A.b N/A
       13 1 boolean B.b N/A
       14 1 boolean C.b N/A
       15 1 (loss due to the next object alignment)
  Space losses: 0 bytes internal + 1 bytes external = 1 bytes total

Which saves us 8 bytes per instance. This is layout change is OK, since we don't need booleans to be aligned by 4 (in fact, if we put all three booleans in the same class, they will be laid out exactly like this, side-to-side). The only reason we've got alignment is because the superclass instance size was the multiple of 4.