Re: Interface Delegation or ??
tam@milkyway.gsfc.nasa.gov wrote:
On Dec 21, 11:12 am, Lew <l...@lewscanon.com> wrote:
/**
* Useful for making things.
**/
interface Factory < R , P , E extends java . lang . Exception >
{
public abstract R make ( final P p ) throws E ;
}
/**
* Can be used to calculate the distance between two Points
**/
interface DistanceMetric < P , R extends java . lang . Comparable < R
{
public abstract R distance ( final P p1 , final P p2 ) ;
}
/**
* Segments have length.
**/
interface Segment < P , R extends java . lang . Comparable < R > >
{
public abstract R length ( ) ;
}
To other readers: take note that these interfaces have package-private access.
This automatically restricts all use of these interfaces to the package (no
need for messy access decorations on the individual methods - Java is
convenient this way.)
--
Lew
Not entirely. As we discussed in another thread, declaring a public
class which implements these interfaces, means all of the interface
methods must also be visible to the public though the existence of the
interfaces themselves may be hidden. You can explicitly hide the
methods using delegation but then you will need to be aware of this
implementation whenever you do want to use the interfaces. A public
class can never explicitly implement an interface and simultaneously
hide the associated methods.
The interface /per se/ is hidden to the public, so cannot be used as a
supertype or otherwise directly accessed outside the package.
It is true that public methods declared to implement the interface in a public
class will be visible to the outside, but that clearly would be a deliberate
decision by the implementor. It would also argue for making the interface
public. If the interface is package-private, it is usually because it is used
only in a package-private context.
It remains true that all uses of the package-private interface will "entirely"
be package-local. There's no way around that. It may well be that other
classes exposes implementing methods to the public; that doesn't change the
truth of the assertion that the interface itself remains hidden.
--
Lew