多态性 + 重载 - 如何调用子类的多态/重载方法？

Question

我有一个 Shape 和 Square 类：

public class Shape {..}
public class Square extends Shape {...}

我有一个父子类，它们具有处理形状/正方形的方法：

public class Parent(){
    public void doSomething(Shape a){
        print("Parent doSomething called");
    }
}

public class Child extends Parent(){

    @Override
    public doSomething(Shape a){
        print("Child doSomething for SHAPE called");
    }


    public doSomething(Square a){
        print("Child doSomething for SQUARE called");
    }
}

现在，当我执行此操作时：

Shape square = new Square();

Parent parent = new Child();

parent.doSomething(square);

正如预期的那样，“Child doSomething for SHAPE called”是输出。

有没有办法通过纯多态性来获得“SQUARE 的子 doSomething 调用”输出，而无需在 Parent 类中定义 doSomething(Square a) 并使用@Override 在孩子中？

不用说，我试图避免使用运算符实例和额外的铸件进行任何 if/else 检查。

Answer 1

您要做的是让每个形状负责打印/返回消息本身，即：

class Shape {
    public String doSomething(){
        return "doSomething for SHAPE called";
    }
}

class Square extends Shape {
    @Override
    public String doSomething(){
        return "doSomething for SQUARE called";
    }
}

这是你的父子类：

class Parent{
public void doSomething(Shape a){
    System.out.println("Parent doSomething called");
        }
}

class Child extends Parent{

@Override
public void doSomething(Shape a){
            System.out.println("Child "+a.doSomething());
        }
}

执行：

Shape square = new Square();
Parent parent = new Child();
parent.doSomething(square);

希望这是有道理的。

Answer 2

下面的工作正常

public class PloyM {
    public static void main(String[] args) {
        Child c = new Child();
        c.doSomething(new Shape());
        c.doSomething(new Square());
    }
}

class Shape { }
class Square extends Shape {}

class Parent {
    public void doSomething(Shape a){
        System.out.println("Parent doSomething called");
    }
}

class Child extends Parent {
    @Override
    public void doSomething(Shape a){
        System.out.println("Child doSomething for SHAPE called");
    }

    public void doSomething(Square a){
        System.out.println("Child doSomething for SQUARE called");
    }
}