5.5

Casting Conversion

CONVERSIONS AND PROMOTIONS

If

S

 is a class type:

N

If

T

 is a class type, then

S

 and

T

 must be related classes that is,

S

 and

T

must be the same class, or

S

 a subclass of

T

,

 or

T

 a subclass of

S

; otherwise

a compile time error occurs.

N

If

T

 is an interface type:

O

If

S

 is not a

final

 class ( 8.1.2), then the cast is always correct at com 

pile time (because even if

S

 does not implement

T

, a subclass of

S

 might).

O

If

S

 is a

final

 class ( 8.1.2), then

S

 must implement

T

, or a compile 

time error occurs.

N

If

T

 is an array type, then

S

 must be the class

Object

, or a compile time

error occurs.

If

S

 is an interface type:

N

If

T

 is a class type that is not

final

 ( 8.1.2), then the cast is always correct

at compile time (because even if

T

 does not implement

S

, a subclass of

T

might).

N

If

T

 is a class type that is

final

 ( 8.1.2), then

T

 must implement

S

, or a

compile time error occurs.

N

If

T

 is an interface type and if

T

 and

S

 contain methods with the same signa 

ture ( 8.4.2) but different return types, then a compile time error occurs.

If

S

 is an array type

SC[]

, that is, an array of components of type

SC

:

N

If

T

 is a class type, then if

T

 is not

Object

, then a compile time error occurs

(because

Object

 is the only class type to which arrays can be assigned).

N

If

T

 is an interface type, then a compile time error occurs unless

T

 is the

interface type

Cloneable

, the only interface implemented by arrays.

N

If

T

 is an array type

TC[]

, that is, an array of components of type

TC

, then a

compile time error occurs unless one of the following is true:

O

TC

 and

SC

 are the same primitive type.

O

TC

 and

SC

 are reference types and type

SC

 can be cast to

TC

 by a recursive

application of these compile time rules for casting.

See  8 for the detailed specifications of classes,  9 for interfaces, and  10 for

arrays.

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