Java/ c++对象创建顺序

Java/C++ Object creation order

本文关键字:创建 顺序 对象 c++ Java      更新时间:2023-10-16

请看下面这段代码:

class Parent {
    Parent() {
        printFunction();
    }
    public void printFunction() {
        System.out.println("Parent Print");
    }
    class ParentInner {
       ParentInner() {
          InnerPrint();
       }
       void InnerPrint() {
          System.out.println("Parent Inner print");
       }
    }
}
class Child extends Parent {
    ChildInner ci;
    Child() {
        super();
        ci = new ChildInner();
    }
    @Override
    public void printFunction() {
        System.out.println("Child Print");
    }
    class ChildInner extends ParentInner {
       ChildInner() {
          super();
       }
       @Override
       void InnerPrint() {
          System.out.println("Child Inner print");
       }
    }
    public static void main(String[] args) {
        Child c = new Child();
    }
}

Java编译器(eclipse和linux)的输出是:

Child print
Child Inner print

这个,在c++ (gcc)

#include <iostream>
#include <new>
using namespace std;
class Parent {
    public:
    Parent() {
        printFunction();
    }
    virtual void printFunction() {
        cout << "Parent printn";
    }
    class ParentInner {
       public:
       ParentInner() {
          InnerPrint();
       }
       virtual void InnerPrint() {
          cout << "Parent Inner printn";
       }
    };
};
class Child : public Parent {
    public:
    Child():Parent() {
        ci = new ChildInner();
    }
    void printFunction() {
        cout << "Child printn";
    }
    class ChildInner : public ParentInner {
       public:
       ChildInner():ParentInner() {
       }
       void InnerPrint() {
          cout << "Child Inner printn";
       }
    };
    ChildInner *ci;
};
int main(int argc, char* argv[]) {
   Child *c = new Child();
   return 0;
}

打印:

Parent print
Parent Inner print

说什么?我认为基类首先被创建,然后子- gcc是合乎逻辑的。Java发生了什么?

正如你所料。当你从Child构造函数初始化列表中调用Parent构造函数时,Child对象还没有完全创建。所以在某种程度上,还没有Child对象,只有Parent对象。