how do get the array of size 152 how do i know it is 1240 and the padding why is it 3 ?

public class MysteryBox { private final int xo, x1, x2; private final boolean yo; private final double zo, 21, 22, 23; private final long[] a = new long[152]; 16 (object overhead) // 12 (3 int) // 1 (1 boolean) // 32 (4 double) // 8 (reference to array) // 1240 (long array of size 152) 3 (padding to round up to a multiple of 8) } 1312