动态方法调用（继承中的对象和引用） [英] Dynamic Method invocation (Objects and reference in inheritance )

问题描述

假设我有2个类........ A 类是基类和类 B 是派生类，如果我创建一个引用，如： A a = new B（）; 这意味着引用 a 指向 B Class 的对象？如果是的，我怎么能够调用B中的A的重写方法而不是B的其他方法？先谢谢你

Suppose I have 2 classes ........A Class is base class and class B is derived class and if i create a reference such as : A a=new B(); does it mean that reference a points to object of B Class ? If yes than how am i able to call overridden methods of A in B and not other methods of B ? thank you in advance

class A {
    m1() {
    }
}

class B extends A {
    m1() {
    }

    m2() {
    }
}


 A a=new B();
 a.m1(); //it will call overridden m1() in B 
 a.m2(); //it doesnt work if reference "a" points to object of B than why doesnt it call         m2 method ? 

推荐答案

Animal a=new Dog(); // Animal is parent - class, Dog is a child

意味着你有一个动物引用指向狗对象。因此，只有在父类（Animal）中声明的方法可以使用父类引用来调用。

means, you have an animal reference pointing to a Dog Object. So, only the methods which are declared in the parent class (Animal) can be called using a parent- class reference.

在 A类中未定义 m2（），它只定义在 class B 因此，使用 A 的引用，不能调用 m2（）

In your case, m2() is not defined in Class A, it is only defined in class B so, using a reference of A, you can't call m2()

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