8.4.6

Inheritance, Overriding, and Hiding

CLASSES

8.4.6.3

Requirements in Overriding and Hiding

If a method declaration overrides or hides the declaration of another method, then

a compile time error occurs if they have different return types or if one has a

return type and the other is

void

. Moreover, a method declaration must not have a

throws

 clause that conflicts ( 8.4.4) with that of any method that it overrides or

hides; otherwise, a compile time error occurs. In these respects, overriding of

methods differs from hiding of fields ( 8.3), for it is permissible for a field to hide

a field of another type.

The access modifier ( 6.6) of an overriding or hiding method must provide at

least as much access as the overridden or hidden method, or a compile time error

occurs. In more detail:

If the overridden or hidden method is

public

, then the overriding or hiding

method must be

public

; otherwise, a compile time error occurs.

If the overridden or hidden method is

protected

, then the overriding or hid 

ing method must be

protected

 or

public

; otherwise, a compile time error

occurs.

If the overridden or hidden method has default (package) access, then the

overriding or hiding method must not be

private

; otherwise, a compile time

error occurs.

Note that a

private

 method is never accessible to subclasses and so cannot be

hidden or overridden in the technical sense of those terms. This means that a sub 

class can declare a method with the same signature as a

private

 method in one of

its superclasses, and there is no requirement that the return type or

throws

 clause

of such a method bear any relationship to those of the

private

 method in the

superclass.

8.4.6.4

Inheriting Methods with the Same Signature

It is possible for a class to inherit more than one method with the same signature

( 8.4.6.4). Such a situation does not in itself cause a compile time error. There are

then two possible cases:

If one of the inherited methods is not

abstract

, then there are two subcases:

N

If the method that is not

abstract

 is

static

, a compile time error occurs.

N

Otherwise, the method that is not

abstract

 is considered to override, and

therefore to implement, all the other methods on behalf of the class that

inherits it. A compile time error occurs if, comparing the method that is not

abstract

 with each of the other of the inherited methods, for any such pair,

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