Difference between static modifier and static block

In this example, there's one subtle difference - in your first example, foo isn't determined to be a compile-time constant, so it can't be used as a case in switch blocks (and wouldn't be inlined into other code); in your second example it, is. So for example:

switch (args[0]) {
    case foo:
        System.out.println("Yes");
        break;
}

That's valid when foo is deemed to be a constant expression, but not when it's "just" a static final variable.

However, static initializer blocks are usually used when you have more complicated initialization code - such as populating a collection.

The timing for initialization is described in JLS 12.4.2; any static final fields which are considered as compile-time constants are initialized first (step 6) and initializers are run later (step 9); all initializers (whether they're field initializers or static initializers) are run in textual order.