java CircleObject不是抽象的，并且不会覆盖图中的抽象方法

Question

编译下面的代码时，出现以下错误：

Abstrct.java:7: error: CircleObject is not abstract and does not override abstract method changePosition(int,int) in Figure
class CircleObject extends Figure
^
Abstrct.java:14: error: Kd is not abstract and does not override abstract method draw() in Figure
class Kd extends Figure
^
2 errors 

使用

abstract class Figure {

    int x, y;

    abstract void changePosition(int newX, int newY);

    abstract void draw();
}

class CircleObject extends Figure {

    void draw() {
        System.out.println("Draw method called");
    }
}

class Kd extends Figure {

    void changePosition(int newX, int newY) {
        System.out.println("Change Position method called");
    }
}

class Abstrct {

    public static void main(String args[]) {
        Figure q = new CircleObject();
        q.draw();
        Figure p = new Kd();
        p.changePosition(2, 4);
    }
}

Answer 1

当您将一个类定义为抽象类时，扩展它的所有类都需要实现所有方法

abstract class Figure {
    int x, y;
    abstract void changePosition(int newX, int newY);
    abstract void draw();
}

class CircleObject extends Figure {
    void draw() {
        System.out.println("Draw method called");
    }
    void changePosition(int newX, int newY){        
    }
}

class Kd extends Figure {
    void changePosition(int newX, int newY) {
        System.out.println("Change Position method called");
    }
    void draw(){        
    }
}

Answer 2

扩展抽象类的类要么实现其父类的所有抽象方法，要么本身是抽象的

所以CircleObject类也必须实现changePosition（），或者本身就是一个抽象类

Kd类也是如此