8.3.3

Examples of Field Declarations

CLASSES

If a reference by simple name to any instance variable occurs in an initializa 

tion expression for a class variable, then a compile time error occurs.

If the keyword

this

 ( 15.7.2) or the keyword

super

 ( 15.10.2,  15.11)

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 ( 4.5.4), even by devious

programs. See  12.4.2 and  13.4.8 for more discussion.)

8.3.2.2

Initializers for Instance Variables

A compile time error occurs if an initialization expression for an instance variable

contains a use by a simple name of that instance variable or of another instance

variable whose declaration occurs to its right (that is, textually later) in the same

class. Thus:

class Test {

float f = j;

int j = 1;

int k = k+1;

}

causes two compile time errors, because

j

 is referred to in the initialization of

f

before

j

 is declared and because the initialization of

k

 refers to

k

 itself.

Initialization expressions for instance variables may use the simple name of

any

static

 variable declared in or inherited by the class, even one whose declara 

tion 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 ini 

tializes

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

 ( 15.7.2) and to use the keyword

super

 ( 15.10.2,  15.11).

8.3.3   Examples of Field Declarations

The following examples illustrate some (possibly subtle) points about field decla 

rations.

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