【b站黑马程序员C++视频学习笔记-多态案例一-计算器类】

多态案例一-计算器类

一、普通方式实现计算器

//多态案例
//普通写法
class Caculator
{
public:
	int getResult(string oper){
		if (oper == "+") {
			return mNum1 + mNum2;
		}
		else if (oper == "-") {
			return mNum1 - mNum2;
		}
		else if (oper == "*") {
			return mNum1 * mNum2;
		}

		//如果想扩展新的功能，需要修改源码
		//在真正的开发中，提倡开闭原则，即对扩展进行开放，对修改进行关闭
	}

	int mNum1, mNum2;
};

void test01() {
	//创建计算器对象
	Caculator c;
	c.mNum1 = 10;
	c.mNum2 = 10;
	cout << c.mNum1 << "+" << c.mNum2 << "=" << c.getResult("+") << endl;
	cout << c.mNum1 << "-" << c.mNum2 << "=" << c.getResult("-") << endl;
	cout << c.mNum1 << "*" << c.mNum2 << "=" << c.getResult("*") << endl;
}

二、多态方式

//利用多态实现计算器
// 多态带来的好处
// 1、组织结构清晰
// 2、可读性强
// 3、利用前期和后期的扩展及维护
//实现计算器抽象类
class AbstractCaculator
{
public:
	virtual int getResult() {//虚函数
		return 0;
	}
	int mNum1;
	int mNum2;
};

//加法类计算器
class AddCaculator :public AbstractCaculator
{
public:
	int getResult() {//重写
		return mNum1 + mNum2;
	}
};

//减法类计算器
class SubCaculator :public AbstractCaculator
{
public:
	int getResult() {
		return mNum1 - mNum2;
	}
};

//乘法类计算器
class MulCaculator :public AbstractCaculator
{
public:
	int getResult() {
		return mNum1 * mNum2;
	}
};

void test02() {
	//多态使用条件
	//父类指针或者引用指向子类对象

	//加法运算
	AbstractCaculator* abc = new AddCaculator;//父类指针指向子类对象
	abc->mNum1 = 100;
	abc->mNum2 = 100;
	cout << abc->mNum1 << "+" << abc->mNum2 << "=" << abc->getResult() << endl;
	//用完后记得销毁
	delete abc;

	//减法运算
	abc = new SubCaculator;
	abc->mNum1 = 100;
	abc->mNum2 = 100;
	cout << abc->mNum1 << "-" << abc->mNum2 << "=" << abc->getResult() << endl;
	delete abc;

	//乘法运算
	abc = new MulCaculator;
	abc->mNum1 = 100;
	abc->mNum2 = 100;
	cout << abc->mNum1 << "*" << abc->mNum2 << "=" << abc->getResult() << endl;
	delete abc;
}