Never Call Virtual Functions during Constructio...

为什么80%的码农都做不了架构师？>>>

代码

1. java

class Bird {public Bird() {show();}public void show() {System.out.println("hey, I'm a bird.");}
}class Eagle extends Bird {private String name = "littleEgale";public Eagle(String name) {this.name = name;}@Overridepublic void show() {System.out.println("I'm a bald eagle, my name is " + name + '.');}}public class VirtualTester {public static void main(String[] args) {new Eagle("java");}}

2. c++

#include <iostream>
#include <string>
using namespace std;class Bird {
public:Bird() {show();}virtual void show() {cout << "hey, I'm a bird." << endl;}};class Eagle : public Bird {
private :string name;
public:Eagle(const string &name):name(name){}void show() {cout << "I'm a bald eagle, my name is " << name<< "." <<endl;}
};int main() {Eagle("cPlusPlus");
}

3. python

class Bird():def __init__(self):self.show()def show(self):print("hey, I'm a bird.")class Eagle(Bird):def __init__(self,name):self.__name = name  # 1Bird.__init__(self) # 2def show(self):print("I'm a bald eagle, my name is",self.__name,'.')Eagle('python')

运行结果：

java:      I'm a bald eagle, my name is null.

c++:       hey, I'm a bird.

python:   I'm a bald eagle, my name is python.

分析

Item 9:Never Call Virtual Functions during Construction or Destruction. Effective C++

Puzzle 49: Larger Than Life. Java Puzzlers

结论：

不在构造和析构过程中调用virtual函数, 适用于基类初始化限定在子类初始化之前的语言。一个设计良好的继承体系，应该避免在基类构造函数中直接或间接的调用被子类重载的方法。

转载于:https://my.oschina.net/coda/blog/34971

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Never Call Virtual Functions during Constructio...

代码

1. java

2. c++

3. python

运行结果：

分析

结论：

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