Java Reference
In-Depth Information
Listing 7.3
Successfully resolving with a
uses
clause
Bundle-SymbolicName: Exporter
Export-Package: fancyfoods.special; uses:="fancyfoods.used"
Import-Package: fancyfoods.used; version="[1,2)"
Bundle-SymbolicName: Importer
Import-Package: fancyfoods.special,
fancyfoods.used; version="[1,2)"
In listing 7.3, you can see two bundles. One bundle exports a package,
fancy-
foods.special
, with a
uses
constraint of
fancyfoods.used
. The other bundle
imports the
fancyfoods.special
and
fancyfoods.used
packages. The resolver
knows that the importing bundle
must
be wired to the same instance of
fancy-
foods.used
that the exporting bundle is, as shown here.
Listing 7.4
Successfully resolving with a
uses
clause
Bundle-SymbolicName: Exporter
Export-Package: fancyfoods.special; uses:="fancyfoods.used"
Import-Package: fancyfoods.used; version="[1,2)"
Bundle SymbolicName: Importer
Import-Package: fancyfoods.special
In listing 7.4, you can see two bundles similar to those in listing 7.3—one that exports
package
fancyfoods.special
with a
uses
constraint of
fancyfoods.used
, and
another that imports
fancyfoods.special
but not
fancyfoods.used
. In this case, the
importing bundle can't see the
fancyfoods.used
package at all. Because of this, the
importing bundle is class-space compatible with
any
view of that package. This might
sound odd, but think of it this way: the importing bundle has no way to get the
fancy-
foods.used
package; therefore it can't have an incompatible view! The end result of
this is that, as in the following listing, we can successfully wire these bundles together.
Listing 7.5
Failure to resolve with a
uses
clause
Bundle-SymbolicName: Exporter
Export-Package: fancyfoods.special; uses:="fancyfoods.used"
Import-Package: fancyfoods.used; version="[1,2)"
Bundle SymbolicName: Importer
Import-Package: fancyfoods.special,
fancyfoods.used; version="[2,3)"
Listing 7.5 is another variation on listing 7.3. Again, the
Exporter
hasn't changed, but
the
Importer
has a different import version range for
fancyfoods.used
. In this case,
the importing bundle can see the
fancyfoods.used
package, but can never wire to
the same package that the
Exporter
bundle does. Because of this, you can guarantee
that the
uses
constraint on the
fancyfoods.special
package will
never
be satisfied.
This means that the resolver can't wire the import and export together, even though
they look like they should match.
