A static initialization blocks allows more complex initialization, for example using conditionals:
static double a;
static {
if (SomeCondition) {
a = 0;
} else {
a = 1;
}
}
Or when more than just construction is required: when using a builder to create your instance, exception handling or work other than creating static fields is necessary.
A static initialization block also runs after the inline static initializers, so the following is valid:
static double a;
static double b = 1;
static {
a = b * 4; // Evaluates to 4
}