67 lines
1.5 KiB
C++
67 lines
1.5 KiB
C++
// 初尝多态
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#include <iostream>
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#include <cstring>
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#include <cstdlib>
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using namespace std;
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// 抽象类:
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// 至少有一个纯虚函数的类
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// 抽象类不能实现对象
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class AbstractCaculator // 定义计算器
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{
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protected: // 使用保护权限（目的是使子类可以访问，而其他类不可访问）
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int a, b;
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public:
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void setA(int a) { this->a = a; }
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void setB(int b) { this->b = b; }
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public:
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// 扩展功能，让子类去实现
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virtual int getResult() = 0; // 纯虚函数，声明函数并赋值为 0
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};
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class AddCa : public AbstractCaculator
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{
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// 必须要去实现纯虚函数
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int getResult()
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{
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return a + b;
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}
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};
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class SubCa : public AbstractCaculator
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{
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// 必须要去实现纯虚函数
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int getResult()
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{
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return a - b;
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}
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};
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// 多态的体现:
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// 1) 定义函数时，形参的类型为父类对象的指针
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// 2) 调用函数时，实参的类型为子类对象的指针
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int Result(AbstractCaculator *caculator, int a, int b)
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{
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caculator->setA(a);
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caculator->setB(b);
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return caculator->getResult();
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}
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int main()
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{
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// 抽象类型不能去定义对象
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// error: cannot declare variable ‘a1’ to be of abstract type ‘AbstractCaculator’
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// AbstractCaculator a1;
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AddCa *a2 = new AddCa;
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cout << Result(a2, 10, 20) << endl;
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cout << Result(new SubCa, 10, 20) << endl; // new SubCa 返回的是一个临时对象，不需要 delete
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delete a2;
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// delete new SubCa; // error: cannot delete expression of type ‘SubCa’
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return 0;
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}
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