13.4

Evolution of Classes

BINARY COMPATIBILITY

within the package in which they are declared. Such types may be deleted or oth 

erwise changed, even if incompatibilities are otherwise described here, provided

that the affected binaries of that package are updated together.

13.4   Evolution of Classes

This section describes the effects of changes to the declaration of a class and its

members and constructors on pre existing binaries.

13.4.1

abstract

 Classes

If a class that was not

abstract

 is changed to be declared

abstract

, then pre 

existing binaries that attempt to create new instances of that class will throw either

an

InstantiationError

 at link time, or an

InstantiationException

 at run

time (if the method

newInstance

 ( 20.3.6) of class

Class

 is used); such a change

is therefore not recommended for widely distributed classes.

Changing a class that was declared

abstract

 to no longer be declared

abstract

 does not break compatibility with pre existing binaries.

13.4.2

final

Classes

If a class that was not declared

final

 is changed to be declared

final

, then a

VerifyError

 is thrown if a binary of a pre existing subclass of this class is

loaded, because

final

 classes can have no subclasses; such a change is not rec 

ommended for widely distributed classes.

Changing a class that was declared

final

 to no longer be declared

final

does not break compatibility with pre existing binaries.

13.4.3

public

Classes

Changing a class that was not declared

public

 to be declared

public

 does not

break compatibility with pre existing binaries.

If a class that was declared

public

 is changed to not be declared

public

,

then an

IllegalAccessError

 is thrown if a pre existing binary is linked that

needs but no longer has access to the class type; such a change is not recom 

mended for widely distributed classes.

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