The Java Language Specification, Third Edition

8.3.2 Initialization of Fields CLASSES
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It is a compile-time error if the evaluation of a variable initializer for a static
field of a named class (or of an interface) can complete abruptly with a checked
exception (§11.2).
It is compile-time error if an instance variable initializer of a named class can
throw a checked exception unless that exception or one of its supertypes is explicitly
declared in the throws clause of each constructor of its class and the class has
at least one explicitly declared constructor. An instance variable initializer in an
anonymous class (§15.9.5) can throw any exceptions.
8.3.2.1 Initializers for Class Variables
If a reference by simple name to any instance variable occurs in an initialization
expression for a class variable, then a compile-time error occurs.
If the keyword this (§15.8.3) or the keyword super (§15.11.2, §15.12)
occurs in an initialization expression for a class variable, then a compile-time
error occurs.
One subtlety here is that, at run time, static variables that are final and that
are initialized with compile-time constant values are initialized first. This also
applies to such fields in interfaces (§9.3.1). These variables are “constants” that
will never be observed to have their default initial values (§4.12.5), even by devious
programs. See §12.4.2 and §13.4.9 for more discussion.
Use of class variables whose declarations appear textually after the use is
sometimes restricted, even though these class variables are in scope. See §8.3.2.3
for the precise rules governing forward reference to class variables.
8.3.2.2 Initializers for Instance Variables
Initialization expressions for instance variables may use the simple name of any
static variable declared in or inherited by the class, even one whose declaration
occurs textually later.
Thus the example:
class Test {
float f = j;
static int j = 1;
}
compiles without error; it initializes j to 1 when class Test is initialized, and initializes
f to the current value of j every time an instance of class Test is created.
Initialization expressions for instance variables are permitted to refer to the
current object this (§15.8.3) and to use the keyword super (§15.11.2, §15.12).
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