为什么不能使用引用子类型实例的父类型引用来调用子类方法? [英] why can't I call a subclass method using a reference of a parent type that refers to an instance of a sub-type?

问题描述

我正在学习Java，同时试图了解继承.我不知道为什么要执行子类walk()的重写方法，而不执行其他xyz()方法.

I am Learning Java, while trying to understand inheritance. I couldn't figure out why the overridden method at the subclass walk() executed but not the other xyz() method.

   class Person{
     public void walk() { System.out.println("walking like a person "); }
   }

   public class Soldier  extends Person{
    @override
    public void walk() { System.out.println("marching like a  soldier "); }
    public void xyz()   { System.out.println("xyzng like a pro"); }

    public static void main(String[] args) {

        Person sp = new Soldier();
        sp.walk(); 
        sp.xyz();
     }
   }

这是我的问题，如果下面的方法调用工作正常并调用Soldier方法walk，

Here is my question, if the following method call works fine and calls the Soldier method walk,

    sp.walk(); 

为什么编译器抱怨此调用?

why the compiler complain about the this call?

    sp.xyz();

推荐答案

在编译时，父类引用"sp"只能看到其中的方法.如果您想以((Soldier)sp).xyz()

At the compile time parent class reference 'sp' can only see method inside it. if you want to access as ((Soldier) sp).xyz()

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