BINARY COMPATIBILITY

final

Fields and Constants

13.4.8

early implementations of Java this example would run without error, because of a

flaw in the implementation.)

We call a field that is

static

,

final

, and initialized with a compile time con 

stant expression a

primitive constant

. Note that all fields in interfaces are implic 

itly

static

 and

final

, and they are often, but not always, constants.

If a field is not a primitive constant, then deleting the keyword

final

 or

changing the value to which the field is initialized does not break compatibility

with existing binaries.

If a field is a primitive constant, then deleting the keyword

final

 or changing

its value will not break compatibility with pre existing binaries by causing them

not to run, but they will not see any new value for the constant unless they are

recompiled. If the example:

class Flags { final static boolean debug = true; }

class Test {

public static void main(String[] args) {

if (Flags.debug)

System.out.println("debug is true");

}

}

is compiled and executed, it produces the output:

debug is true

Suppose that a new version of class

Flags

 is produced:

class Flags { final static boolean debug = false; }

If

Flags

 is recompiled but not

Test

, then running the new binary with the exist 

ing binary of

Test

 produces the output:

debug is true

because the value of

debug

 was a compile time primitive constant, and could have

been used in compiling

Test

 without making a reference to the class

Flags

.

This result is a side effect of the decision to support conditional compilation,

as discussed at the end of  14.19.

This behavior would not change if

Flags

 were changed to be an interface, as

in the modified example:

interface Flags { boolean debug = true; }

class Test {

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