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[英]Is there any way other than instanceof operator for object type comparison in java?
[英]Is there a better/cleaner way to conditionally create a type than using instanceof? [Java]
假设我有:
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>(); // /!\
}
问题是MobileSuitCollection是一个接口,所以我无法实例化它。 例如,我可以这样做:
MobileSuitCollection temporaryCollection = new GundamMeisterCollection<MobileSuitso>();
MobileSuitCollection temporaryCollection = new InnovatorCollection<MobileSuitso>();
MobileSuitCollection temporaryCollection = new CannonFolderCollection<MobileSuitso>();
但是,要操作temporaryCollection
,我需要它与通过参数传递给我的类的类型相同。 所以我想这样做:
if (msCollection instanceof GundamMeisterCollection) {
...
} else if (msCollection instanceof InnovatorCollection) {
...
} ...
我意识到这很糟糕。 有一个更好的方法吗? 是否可以保留对初始类型使用的类的引用,然后用它实例化temporaryCollection
?
您放在if子句中的代码可以放在一个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
}
然后让MobileSuitCollection
有一个方法:
void visit(MobileSuitCollectionVisitor visitor);
而在MobileSuitCollection
每个实现中都有
public void visit(MobileSuitCollectionVisitor visitor) {
visitor.handleCollection(this);
}
快速而肮脏的方法是克隆原始集合,然后根据需要进行操作。 更好的方法可能是在接口中添加newInstance()
方法,或者将工厂传递给FightingZone
。
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