假设我有一个类扩展另一个类并实现一个或多个接口(interface)。如何指定需要这种条件的类型?
例如:
class Eagle extends Animal implements Fly {
}
class Falcon extends Animal implements Fly {
}
public static void main (){
??? anAnimalWhoCanFly;
}
更新:我删除了该列表。假设我想要一个对象,它是扩展 Animal 并实现 Fly 的类的对象。
谢谢
最佳答案
如果您想要一种方法来指定,例如“扩展 Animal 并实现 Fly 的类型”,只需定义一个完全执行此操作的类即可:
public abstract class FlyingAnimal extends Animal implements Fly{ }
现在您已经有了从 FlyingAnimal
扩展的 Eagle
和 Falcon
,而不是直接从 Animal
扩展而来:
public class Falcon extends FlyingAnimal {
public void fly(){ System.out.println("I'm a fast flier");
}
public class Eagle extends FlyingAnimal {
public void fly(){ System.out.println("I'm built for soaring");
}
public class Cat extends Animal {
// I'm a cat; I can't fly
}
现在你可以做这样的事情:
public void flyIt(FlyingAnimal fa){
fa.fly();
}
public void test(){
Falcon falcon = new Falcon();
Animal eagle = new Eagle();
Animal cat = new Cat();
flyIt(falcon); // OK: `Falcon` is a `Falcon`, which is also
// a `FlyingAnimal`
flyIt(cat); // COMPILE ERROR: `cat` is an `Animal`,
// which is not a subclass of `FlyingAnimal`
flyIt(eagle); // COMPILE ERROR: `eagle` is an `Animal`, which is
// not a `FlyingAnimal`
flyIt((Eagle)eagle);
// OK: because we know that `eagle` actually references
// an `Eagle`, we know the type-cast `(Eagle)eagle`
// will succeed at run-time; `Eagle` is a `FlyingAnimal`
// and thus is acceptable as an argument to `flyIt`
flytIt((FlyingAnimal)eagle);
// OK: because we know that `eagle` actually references
// an `Eagle`, which in turn is a `FlyingAnimal`, we
// know the type-cast `(FlyingAnimal)eagle` will
// succeed at run-time
flyIt((FlyingAnimal)cat);
// RUN-TIME ERROR: `cat` references a `Cat`, which is
// an `Animal` but not a `FlyingAnimal`, and so will
// not successfully convert to a `FlyingAnimal` at
// run-time.
关于java - Java中如何同时使用继承和接口(interface)的多态性?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46459454/