C/C++中组合详解及其作用介绍

概述

组合 (Composition) 指在一个类中另一类的对象作为数据成员.

C/C++中组合详解及其作用介绍

案例

在平面上两点连成一条直线, 求直线的长度和直线中点的坐标.
要求:

基类: Dot
派生类: Line (同时组合)
派生类 Line 从基类 Dot 继承的 Dot 数据, 存放直线的中点坐标
Line 类再增加两个 Dot 对象, 分别存放两个端点的坐标

Dot 类:

#ifndef PROJECT5_DOT_H
#define PROJECT5_DOT_H

#include <iostream>
using namespace std;

class Dot {
public:
  double x, y;
  Dot(double a, double b) : x(a), y(b) {};
  void show() {
      cout << "x: " << x << endl;
      cout << "y: " << y << endl;
  };
};

#endif //PROJECT5_DOT_H

Line 类:

#ifndef PROJECT5_LINE_H
#define PROJECT5_LINE_H

#include "Dot.h"

class Line : public Dot {
private:
  Dot d1;
  Dot d2;
public:
  Line(const Dot &d1, const Dot &d2) : Dot(0, 0), d1(d1), d2(d2) {
      x = (d1.x + d2.x) / 2;
      y = (d1.y + d2.y) / 2;
  }

  void show(){
      Dot::show();
      cout << "dot1: (" << d1.x << ", " << d1.y << ")" << endl;
      cout << "dot2: (" << d2.x << ", " << d2.y << ")" << endl;
  }
};

#endif //PROJECT5_LINE_H

main:

#include <iostream>
#include "Dot.h"
#include "Line.h"
using namespace std;

int main() {
  double a, b;
  cout << "Input Dot1: \n";
  cin >> a >> b;
  Dot dot1(a,b);
  cout << "Input Dot2: \n";
  cin >> a >> b ;
  Dot dot2(a,b);
  Line l1(dot1, dot2);
  l1.show();

  return 0;
}

输出结果: