Suppose I have:
public class FightingZone<MobileSuitso, Background> {
private MobileSuitCollection<MobileSuitso> msCollection;
private BackgroundInfo<Background> bgInfo;
public FightingZone(MobileSuitCollection<MobileSuitso> newCollection, BackgroundInfo<Background> newInfo) {
this.msCollection = newCollection;
this.bgInfo = newInfo;
}
...
...// inside a method
MobileSuitCollection temporaryCollection = new MobileSuitCollection<MobileSuitso>(); // /!\
}
The problem is MobileSuitCollection is an Interface, so I can't instantiate it. For example, I could do:
MobileSuitCollection temporaryCollection = new GundamMeisterCollection<MobileSuitso>();
MobileSuitCollection temporaryCollection = new InnovatorCollection<MobileSuitso>();
MobileSuitCollection temporaryCollection = new CannonFolderCollection<MobileSuitso>();
etc. However, to manipulate temporaryCollection
, I need it to be of the same type as the one passed via parameter to my Class. So I thought about doing this:
if (msCollection instanceof GundamMeisterCollection) {
...
} else if (msCollection instanceof InnovatorCollection) 开发者_如何学Python{
...
} ...
I realize that is awful however. Is there a better way to do this? Would it be possible to keep a reference to the class used by the initial type and then instantiate the temporaryCollection
with that?
The code that you place in the if-clause can be placed in a Visitor
:
// Generics skipped for brevity
interface MobileSuitCollectionVisitor {
handleCollection(GundamMeisterCollection collection);
handleCollection(InnovatorCollection collection);
handleCollection(CannonFolderCollection collection)
}
class ConcreteVisitor implements MobileSuitCollectionVisitor {
// place all of the logic in the implemented methods
}
and then let MobileSuitCollection
have a method:
void visit(MobileSuitCollectionVisitor visitor);
And in each implementation of MobileSuitCollection
simply have
public void visit(MobileSuitCollectionVisitor visitor) {
visitor.handleCollection(this);
}
A quick and dirty way to do it would be to clone the original collection, then manipulate it as needed. A better way might be to add a newInstance()
method to the interface, or pass in a factory to FightingZone
.
精彩评论