Question

Why would I use a static block:

static {
   B = 10;
}

over:

Integer B = 10;

What is the advantages/disadvantages of one over the other?

Answer 1

You should only use a static initializer block, when it is necessary. For example, sometimes you need to do several steps to calculate the final value of the field. In this case you have two opportunities: write a method that calculates the value and declare your field as static final Integer B = calculateB(), or use an initializer block:

static final Integer B;
static {
  int temp = ...;
  ...
  B = temp;
}

In this case I prefer the static block, because a method might be confusing (other developers might try to call it, although it is only meant to be called once during initialization).

The same applies for instance fields as well, although normally one would avoid the unusual initialization block and simply write the initialization logic for fields into the constructor (which is of course not possible for static fields).