简单工厂方法模式之“构造函数和析构函数”理解

迈不过友情╰ 2022-11-14 14:40 121阅读 0赞

reference: https://blog.csdn.net/weixin\_46826913/article/details/106289647  
[简单工厂模式（C语言实现）][C]  
[简单工厂、工厂方法模式、抽象工厂模式][Link 1]  
[C++ 类构造函数 & 析构函数][C_ _ _]

使用C语言的来模拟C++中的面向对象概念。

## 1 简介 ##

简单工厂方法定义一个用于创建对象的类，该类接受一个参数，通过参数决定创建不同的对象。

GOF并没有把简单工厂方法定义为23种设计模式之一，可以认为简单工厂方法是工厂方法的简化形式。

为了体现简单工厂方法和工厂方法的区别和联系，此处把简单工厂方法先单独讲一下。

## 2 模拟场景 ##

假设你要生产电脑，电脑由硬盘、内存条、CPU、主板的部件组成。你为了保证供应链可靠，每种部件都选择了至少两家供应商。比如：

硬盘供应商 seagate、Toshiba
    内存条供应商 SAMSUNG、Crucial
    CPU供应商 intel、AMD
    主板供应商 intel、AMD

此处列出多个部件是为了后面讲解工厂方法、抽象工厂方法时使用同一个模拟场景。本章讲简单工厂方法暂时不需要涉及这么多部件，所以仅以硬盘这一个部件为例进行讲解。

## 3 使用简单工厂方法实现的思路 ##

硬盘就是要创建的对象（即：产品）。为了让不同供应商提供的硬盘可以通用，要定义一个硬盘产品类，并让不同供应商的硬盘都继承硬盘产品类的接口。

还需要定义一个创建硬盘对象的类（即：工厂）。工厂类根据参数决定创建哪家供应商的硬盘对象。

## 4 使用简单工厂方法实现硬盘对象创建 ##

参与者

Product: HardDisk  
定义硬盘对象的接口

Concrete Product: SeagateHardDisk, ToshibaHardDisk  
实现不同供应商的硬盘

SimpleFactory: HardDiskFactory  
根据参数，创建不同供应商的硬盘对象

UML:![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpbWFuamloZQ_size_16_color_FFFFFF_t_70]  
HardDisk代码示例

hard\_disk.h

#ifndef HARD_DISK_H
    #define HARD_DISK_H
    
    struct HardDisk {
        void (*Operation)(struct HardDisk *this);
    };
    
    #endif

SeagateHardDisk代码示例

seagate_hard_disk.h
    
    #ifndef SEAGATE_HARD_DISK_H
    #define SEAGATE_HARD_DISK_H
    
    #include "hard_disk.h"
    
    struct SeagateHardDisk {
        struct HardDisk hardDisk;
    };
    
    // 构造函数
    void SeagateHardDisk(struct SeagateHardDisk *this);
    
    // 析构函数
    void _SeagateHardDisk(struct SeagateHardDisk *this);
    
    #endif

seagate\_hard\_disk.c

#include "seagate_hard_disk.h"
    #include "stdio.h"
    
    void SeagateOperation(struct SeagateHardDisk *this)
    {
        printf("这是 Seagate 硬盘\n");
    }
    
    void SeagateHardDisk(struct SeagateHardDisk *this)
    {
        this->hardDisk.Operation = (void(*)(struct HardDisk *))SeagateOperation;
    }
    
    void _SeagateHardDisk(struct SeagateHardDisk *this)
    {
        this->hardDisk.Operation = NULL;
    }

ToshibaHardDisk代码示例

toshiba\_hard\_disk.h

#ifndef TOSHIBA_HARD_DISK_H
    #define TOSHIBA_HARD_DISK_H
    
    #include "hard_disk.h"
    
    struct ToshibaHardDisk {
        struct HardDisk hardDisk;
    };
    
    // 构造函数
    void ToshibaHardDisk(struct ToshibaHardDisk *this);
    
    // 析构函数
    void _ToshibaHardDisk(struct ToshibaHardDisk *this);
    
    #endif

toshiba\_hard\_disk.c

#include "toshiba_hard_disk.h"
    #include "stdio.h"
    
    void ToshibaOperation(struct ToshibaHardDisk *this)
    {
        printf("这是 Toshiba 硬盘\n");
    }
    
    void ToshibaHardDisk(struct ToshibaHardDisk *this)
    {
        this->hardDisk.Operation = (void(*)(struct HardDisk *))ToshibaOperation;
    }
    
    void _ToshibaHardDisk(struct ToshibaHardDisk *this)
    {
        this->hardDisk.Operation = NULL;
    }

HardDiskFactory代码示例

hard_disk_factory.h
    
    #ifndef HARD_DISK_FACTORY_H
    #define HARD_DISK_FACTORY_H
    
    #include "hard_disk.h"
    
    enum HARD_DISK_SUPPLIER_E {
        HARD_DISK_SUPPLIER_SEAGATE,
        HARD_DISK_SUPPLIER_TOSHIBA
    };
    
    struct HardDiskFactory {
        struct HardDisk* (*Create)(struct HardDiskFactory *this, 
                                   enum HARD_DISK_SUPPLIER_E supplier);
        void (*Destroy)(struct HardDiskFactory *this, 
                        struct HardDisk* hardDisk);
    };
    
    // 构造函数
    void HardDiskFactory(struct HardDiskFactory *this);
    
    // 析构函数
    void _HardDiskFactory(struct HardDiskFactory *this);
    
    #endif

hard\_disk\_factory.c

#include "hard_disk_factory.h"
    #include "seagate_hard_disk.h"
    #include "toshiba_hard_disk.h"
    #include "stdio.h"
    #include "stdlib.h"
    
    struct HardDisk *Create(struct HardDiskFactory *this, 
                            enum HARD_DISK_SUPPLIER_E supplier) 
    {
        switch (supplier) {
            case HARD_DISK_SUPPLIER_SEAGATE:
            {
                struct SeagateHardDisk *seagateHardDisk = NULL;
                if ((seagateHardDisk = malloc(sizeof(struct SeagateHardDisk))) == NULL) {
                    printf("fail in malloc\n");
                    return NULL;
                }
                SeagateHardDisk(seagateHardDisk);
                return (struct HardDisk *)seagateHardDisk;
            }
            case HARD_DISK_SUPPLIER_TOSHIBA:
            {
                struct ToshibaHardDisk *toshibaHardDisk = NULL;
                if ((toshibaHardDisk = malloc(sizeof(struct ToshibaHardDisk))) == NULL) {
                    printf("fail in malloc\n");
                    return NULL;
                }
                ToshibaHardDisk(toshibaHardDisk);
                return (struct HardDisk *)toshibaHardDisk;
            }
            default:
                printf("未知的供应商\n");
                return NULL;
        }
    }
    
    void Destroy(struct HardDiskFactory *this, struct HardDisk* hardDisk)
    {
        if (hardDisk != NULL) {
            free(hardDisk);
        }
    }
    
    // 构造函数
    void HardDiskFactory(struct HardDiskFactory *this)
    {
        this->Create = Create;
        this->Destroy = Destroy;
    }
    
    // 析构函数
    void _HardDiskFactory(struct HardDiskFactory *this)
    {
        this->Create = NULL;
        this->Destroy = NULL;
    }

客户端代码示例

#include "hard_disk.h"
    #include "hard_disk_factory.h"
    #include "stddef.h"
    
    void main()
    {
        struct HardDisk *hardDisk = NULL;
    
        struct HardDiskFactory hardDiskFactory;
        HardDiskFactory(&hardDiskFactory);
    
        // 创建 seagate 硬盘对象
        hardDisk = hardDiskFactory.Create(&hardDiskFactory, HARD_DISK_SUPPLIER_SEAGATE);
        // 使用 seagate 硬盘对象
        hardDisk->Operation(hardDisk);  
        // 销毁 seagate 硬盘对象
        hardDiskFactory.Destroy(&hardDiskFactory, hardDisk);       
    
        // 创建 toshiba 硬盘对象
        hardDisk = hardDiskFactory.Create(&hardDiskFactory, HARD_DISK_SUPPLIER_TOSHIBA);
        // 使用 seagate 硬盘对象
        hardDisk->Operation(hardDisk);
        // 销毁 toshiba 硬盘对象
        hardDiskFactory.Destroy(&hardDiskFactory, hardDisk);    
    
        _HardDiskFactory(&hardDiskFactory);
    }

客户端显示示例

./hard_disk
    这是 Seagate 硬盘
    这是 Toshiba 硬盘

[C]: https://blog.csdn.net/HMSIWTV/article/details/32352035?utm_medium=distribute.pc_relevant.none-task-blog-2~default~BlogCommendFromMachineLearnPai2~default-2.control&dist_request_id=1328741.41120.16170257155092361&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2~default~BlogCommendFromMachineLearnPai2~default-2.control
[Link 1]: https://blog.csdn.net/weixin_33671935/article/details/85816304?utm_medium=distribute.pc_relevant.none-task-blog-2~default~BlogCommendFromMachineLearnPai2~default-2.control&dist_request_id=&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2~default~BlogCommendFromMachineLearnPai2~default-2.control
[C_ _ _]: https://www.runoob.com/cplusplus/cpp-constructor-destructor.html
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