工厂方法模式

简介

我们接着“简单工厂方法”中生产电脑的模拟场景来看。

在简单工厂方法中，不同供应商的硬盘都由HardDiskFactory创建出来。这种做法存在几个问题：

当供应商很多时，HardDiskFactory就会成为一个“过大类”
假设现在要新引入一家硬盘供应商，那就需要在HardDiskFactory的Create方法中增加一个case分支。
在Create方法中增加case分支的做法违反了“开闭原则”。

我们现在要讲的“工厂方法”可以解决上述问题：

工厂方法针对每一个供应商的硬盘提供一个工厂。通过不同工厂对象来创建不同的产品对象。也就是说，工厂方法不直接定义用于创建对象的类，而是定义一个创建硬盘对象的接口，让子类决定实例化哪一个供应商的硬盘。

当新增一个硬盘供应商时，只需要新增一个工厂对象。不需要在原有工厂中增加代码，所以不违反“开闭原则”，也不会因为不断增加供应商而产生“过大类”。

使用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（与简单工厂方法相同）

Concrete Product: SeagateHardDisk, ToshibaHardDisk

实现不同供应商的硬盘（与简单工厂方法相同）

Factory: HardDiskFactory

声明硬盘工厂方法，具体硬盘对象的创建交给其子类 ConcreteFactory

ConcreteFactory: SeagateHardDiskFactory, ToshibaHardDiskFactory

创建具体硬盘对象

UML

在这里插入图片描述

HardDisk、SeagateHardDisk、ToshibaHardDisk示例代码与简单工厂方法完全一致，此处不再重复

HardDiskFactory代码示例

hard_disk_factory.h

#ifndef HARD_DISK_FACTORY_H
#define HARD_DISK_FACTORY_H

#include "hard_disk.h"

struct HardDiskFactory {
    struct HardDisk* (*Create)(struct HardDiskFactory *this);
    void (*Destroy)(struct HardDiskFactory *this, 
                    struct HardDisk* hardDisk);
};

#endif

SeagateHardDiskFactory代码示例

seagate_hard_disk_factory.h

#define SEAGATE_HARD_DISK_FACTORY_H

#include "hard_disk_factory.h"

struct SeagateHardDiskFactory {
    struct HardDiskFactory hardDiskFactory;
};

// 构造函数
void SeagateHardDiskFactory(struct SeagateHardDiskFactory *this);

// 析构函数
void _SeagateHardDiskFactory(struct SeagateHardDiskFactory *this);

#endif

seagate_hard_disk_factory.c

#include "seagate_hard_disk_factory.h"
#include "seagate_hard_disk.h"
#include "stdio.h"
#include "stdlib.h"

struct HardDisk* SeagateCreate(struct HardDiskFactory *this)
{
    struct SeagateHardDisk *seagateHardDisk = NULL;
    if ((seagateHardDisk = malloc(sizeof(struct SeagateHardDisk))) == NULL) {
        printf("fail in malloc\n");
        return NULL;
    }
    SeagateHardDisk(seagateHardDisk);
    return (struct HardDisk*)seagateHardDisk;
}

void SeagateDestroy(struct HardDiskFactory *this, struct HardDisk *hardDisk)
{
    if (hardDisk != NULL) {
        free(hardDisk);
        hardDisk = NULL;
    }    
}

// 构造函数
void SeagateHardDiskFactory(struct SeagateHardDiskFactory *this)
{
    this->hardDiskFactory.Create = SeagateCreate;
    this->hardDiskFactory.Destroy = SeagateDestroy;
}

// 析构函数
void _SeagateHardDiskFactory(struct SeagateHardDiskFactory *this)
{
    this->hardDiskFactory.Create = NULL;
    this->hardDiskFactory.Destroy = NULL;
}

ToshibaHardDiskFactory代码示例

toshiba_hard_disk_factory.h

#ifndef TOSHIBA_HARD_DISK_FACTORY_H
#define TOSHIBA_HARD_DISK_FACTORY_H

#include "hard_disk_factory.h"

struct ToshibaHardDiskFactory {
    struct HardDiskFactory hardDiskFactory;
};

// 构造函数
void ToshibaHardDiskFactory(struct ToshibaHardDiskFactory *this);

// 析构函数
void _ToshibaHardDiskFactory(struct ToshibaHardDiskFactory *this);

#endif

toshiba_hard_disk_factory.c

#include "toshiba_hard_disk_factory.h"
#include "toshiba_hard_disk.h"
#include "stdio.h"
#include "stdlib.h"

struct HardDisk* ToshibaCreate(struct HardDiskFactory *this)
{
    struct ToshibaHardDisk *toshibaHardDisk = NULL;
    if ((toshibaHardDisk = malloc(sizeof(struct ToshibaHardDisk))) == NULL) {
        printf("fail in malloc\n");
        return NULL;
    }
    ToshibaHardDisk(toshibaHardDisk);
    return (struct HardDisk*)toshibaHardDisk;
}

void ToshibaDestroy(struct HardDiskFactory *this, struct HardDisk *hardDisk)
{
    if (hardDisk != NULL) {
        free(hardDisk);
        hardDisk = NULL;
    }    
}

// 构造函数
void ToshibaHardDiskFactory(struct ToshibaHardDiskFactory *this)
{
    this->hardDiskFactory.Create = ToshibaCreate;
    this->hardDiskFactory.Destroy = ToshibaDestroy;
}

// 析构函数
void _ToshibaHardDiskFactory(struct ToshibaHardDiskFactory *this)
{
    this->hardDiskFactory.Create = NULL;
    this->hardDiskFactory.Destroy = NULL;
}

客户端代码示例

#include "hard_disk.h"
#include "hard_disk_factory.h"
#include "seagate_hard_disk_factory.h"
#include "toshiba_hard_disk_factory.h"
#include "stddef.h"

void main()
{
    struct HardDisk *hardDisk = NULL;
    struct HardDiskFactory *hardDiskFactory;

    struct SeagateHardDiskFactory seagateHardDiskFactory;
    SeagateHardDiskFactory(&seagateHardDiskFactory);
    hardDiskFactory = (struct HardDiskFactory *)&seagateHardDiskFactory;
    // 创建 seagate 硬盘对象
    hardDisk = hardDiskFactory->Create(hardDiskFactory);
    // 使用 seagate 硬盘对象
    hardDisk->Operation(hardDisk);  
    // 销毁 seagate 硬盘对象
    hardDiskFactory->Destroy(hardDiskFactory, hardDisk);
    _SeagateHardDiskFactory(&seagateHardDiskFactory);    

    
    struct ToshibaHardDiskFactory toshibaHardDiskFactory;
    ToshibaHardDiskFactory(&toshibaHardDiskFactory);
    hardDiskFactory = (struct HardDiskFactory *)&toshibaHardDiskFactory;
    // 创建 toshiba 硬盘对象
    hardDisk = hardDiskFactory->Create(hardDiskFactory);
    // 使用 seagate 硬盘对象
    hardDisk->Operation(hardDisk);
    // 销毁 toshiba 硬盘对象
    hardDiskFactory->Destroy(hardDiskFactory, hardDisk);
    _ToshibaHardDiskFactory(&toshibaHardDiskFactory);
}

客户端显示示例

./hard_disk
这是 Seagate 硬盘
这是 Toshiba 硬盘

03设计模式_工厂方法模式_C语言实现

工厂方法模式

简介

使用工厂方法实现硬盘对象创建

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