Question

My question is regarding Inheritance and Polymorphism.

I have a class A which is the super class. Classes B and C extends A and are subclasses.

Now i have a function in other class(not A or B or C) that takes argument of type A. So polymorphism allows us to pass the argument as A , B or C to that function. Now in that function, inorder to access B s properties, i have to typecast the received argument to B.

是否打造了良好的方案拟订技术? 难道这里使用多吗?

Thanks.

Answer 1

只有当你知道什么可以实现时,才会进行播种。

The use of polymorphism here is that the method in the other class can be written in a generic way, and a single piece of code can thus operate on different types, which, though, have some interface (class A) in common.

因此,......播种(取决于语言文化)是一种非常坏的做法。采用多形态法(取决于......),例如采用B类的论据,采用不同的签字方法->B)。

Update: added Java pseudocode

class A { int m() {} }
class B extends A { int b() {} }
class C extends A {}
class $ { 
  static void x(A $$) {} 
  static void x(B $$) {}
}
public class P {
  public static void main(String[] a) {
    $.x(new A()); //calls $::x(A)
    $.x(new B()); //calls $::x(B)
  }
}

Answer 2

我假定你们想要的是这样的东西(旧法典):

void foo(A obj) {
    if (obj.isOfClass(B)) {
        // Access a property that B has, but A doesn t.
    }
}

In that case you need to typecast:

void foo(A obj) {
    if (obj.isOfClass(B)) {
        ((B)obj).propertyOfB();
    }
}

根据语言,有另一种选择。以Ruby和Pin-C等语文,经常使用所谓的duck打字。想法是:如果它像一个 d子和象一个uck子一样步行,它就必须是一个uck子。换言之,这里重要的是ette/em>一个目标是什么,但该目标是否执行methods:

void foo(Object obj) {
    if (obj.hasMethod(quack)) {
        obj.quack();
    }
}

经常使用uck打字的语文通常更具有“动力”性质。例如,在C++中,它具有非常严格的类型系统,几乎不可能做uck打,而前述的Rub和C目标则属于自然。

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