在java中覆蓋的概念

Question

超類中的方法適用於java中的所有子類....如果子類有自己獨立的方法，我怎樣才能使它工作...

class  Polymorphism3 {

 public static void main(String[] args) {
            // note how these are all considered objects of type Animal by Java
            Animal[] a = new Animal[4];
            a[0] = new Mouse();
            a[1] = new Bird();
            a[2] = new Horse();
            a[3] = new Animal();            
            for (int i=0;i<4;i++) {
                a[i].pullTail();                
            }           

//...       


class Animal {
    public void pullTail() {
        System.out.println("I don't know what to say.");
    }
}

class Mouse extends Animal {
    public void pullTail() {
        System.out.println("fart");
    }
}

class Bird extends Animal {
    public void pullTail() {
        System.out.println("tweet");
    }

    public void fly() {
        System.out.println("flap");
    }
}

class Horse extends Animal {
    public void pullTail() {
        System.out.println("neigh");
    }
}

Answer 1

如果未在Animal中聲明，則無法使其正常工作。
唯一的方法是將動物轉化為鳥類如

（（鳥）一[1]）飛（）;

你也可以從Bird的putTail實現中調用它。

Answer 2

如果這是無法實例化嵌套類：你需要一個封閉類的對象：

public class Polymorphism3 {
    public static void main(String[] args) {
        // note how these are all considered objects of type Animal by Java
        Animal[] a = new Animal[4];
        Polymorphism3 poly = new Polymorphism3();
        a[0] = poly.new Mouse();
        a[1] = poly.new Bird();
        a[2] = poly.new Horse();
        a[3] = poly.new Animal();
        for (int i = 0; i < 4; i++) {
            a[i].pullTail();
        }
    }

    class Animal {
        public void pullTail() {
            System.out.println("I don't know what to say.");
        }
    }

    class Mouse extends Animal {
        public void pullTail() {
            System.out.println("fart");
        }
    }

    class Bird extends Animal {
        public void pullTail() {
            System.out.println("tweet");
        }

        public void fly() {
            System.out.println("flap");
        }
    }

    class Horse extends Animal {
        public void pullTail() {
            System.out.println("neigh");
        }
    }
}