工厂模式是属于创建模式, 大体可以分为三种,简单的工厂模式, 工厂方法模式, 抽象工厂模式
一:简单工厂模式
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// 简单工厂模式
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// 优点, 简单
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// 缺点, 当需要增加新的类的时候, 需要修改工厂类, 违反开发封闭的原则, 软件实体(类, 函数, 模块)
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// 可以扩展, 最好不要修改, 可以使用factory methond 去优化
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#include<iostream>
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using namespace std;
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enum PTYPE { PRODUCT_A, PRODUCT_B };
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class Product {
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public:
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virtual ~Product() {};
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virtual void show() = 0;
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};
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class ProductA : public Product {
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public:
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void show() {
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cout << "product a\n";
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}
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};
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class ProductB : public Product {
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public:
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void show() {
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cout << "product b\n";
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}
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};
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class Factory {
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public:
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Product* Create(PTYPE type) {
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if (type == PRODUCT_A) {
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return new ProductA();
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} else if (type == PRODUCT_B) {
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return new ProductB();
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} else {
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return NULL;
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}
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}
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};
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int main(int argc, char* argv[]) {
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Factory *pF = new Factory();
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Product *pP = pF->Create(PRODUCT_A);
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pP->show();
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delete pF;
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return 0;
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}
二:工厂方法模式, 是对简单工厂模式的优化改进, 解决新增产品, 需要修改工厂类的问题
2.1 目的
主要是定义一个用于创建对象的接口,让子类来决定实例化哪一个类, Factory Method 让一个类的实例化延迟到了子类
2.2 使用场景:
1 当一个类不知道他必须创建的类的对象的时候
2 当一个类希望由他的子类来决定他所创建的对象时候
这个模式可以 把实例化延时到子类中决定
简单的代码
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// 简单工厂模式
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#include<iostream>
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using namespace std;
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// 实例化延迟到子类
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// 缺点 , 新增产品, 就需要新增工厂, 类比较多, 可以优化-- 抽象工厂模式
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enum PTYPE { PRODUCT_A, PRODUCT_B };
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class Product {
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public:
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virtual ~Product() {};
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virtual void show() = 0;
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};
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class ProductA : public Product {
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public:
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virtual ~ProductA() {};
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void show() {
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cout << "product a\n";
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}
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};
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class ProductB : public Product {
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public:
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void show() {
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cout << "product b\n";
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}
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};
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class Factory {
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public:
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virtual ~Factory() {};
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virtual Product* Create() = 0;
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};
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class FactoryA : public Factory {
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public:
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Product* Create() {
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return new ProductA();
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}
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};
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class FactoryB : public Factory {
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public:
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Product* Create() {
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return new ProductB();
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}
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};
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int main(int argc, char* argv[]) {
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Factory *pF = new FactoryA();
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Product *pP = pF->Create();
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pP->show();
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delete pF;
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return 0;
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}
缺点: 新增一个产品, 就需要增加一个工厂类, 如果产品比较多的话, 那么类就比较多。
三:抽象工厂模式
提供一个创建一系列相关或者互相依赖对象的接口, 而无需指定他们具体的类
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// 简单工厂模式
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#include<iostream>
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using namespace std;
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// 实例化延迟到子类
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class Product {
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public:
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virtual ~Product() {};
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virtual void show() = 0;
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};
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class ProductA : public Product {
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public:
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virtual ~ProductA() {};
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void show() {
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cout << "product a\n";
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}
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};
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class Car {
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public:
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virtual ~Car() {};
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virtual void show() = 0;
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};
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class Ben : public Car {
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public:
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void show() { cout << " Ben car \n"; }
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};
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class BMW : public Car {
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public:
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void show() { cout << " BMW car \n"; }
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};
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class ProductB : public Product {
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public:
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void show() {
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cout << "product b\n";
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}
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};
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class Factory {
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public:
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virtual ~Factory() {};
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virtual Product* Create() = 0;
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virtual Car* CreateCar() = 0;
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};
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class FactoryA : public Factory {
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public:
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Product* Create() {
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return new ProductA();
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}
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Car* CreateCar() {
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return new BMW();
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}
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};
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class FactoryB : public Factory {
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public:
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Product* Create() {
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return new ProductB();
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}
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Car* CreateCar() {
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return new Ben();
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}
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};
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int main(int argc, char* argv[]) {
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Factory *pF = new FactoryA();
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Product *pP = pF->Create();
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Car *pC = pF->CreateCar();
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pP->show();
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pC->show();
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delete pF;
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return 0;
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}
备注
手绘UML图
运行环境:
以上代码运行于linux环境, Makefile如下
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# set CPUS for Linux or FreeBSD
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CPUS := $(shell cat /proc/cpuinfo|grep -c processor)
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GCC472_PATH=/usr/local/gcc-4.7.2
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CXX := env LD_LIBRARY_PATH=$(GCC472_PATH)/lib:/usr/local/mpc/lib $(GCC472_PATH)/bin/g++
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CXXFLAGS := -g3 -O2 -fno-strict-aliasing -Wall -Werror -fPIC \
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-isystem /usr/local/include \
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-isystem /usr/include
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LDFLAGS := -pthread \
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-L/usr/local/lib64/ \
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-L/usr/local/lib/
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RTFLAGS := \
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-Wl,-rpath=.. \
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-Wl,-rpath=/$(GCC472_PATH)/lib64
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LIBS := -lpthread
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SRC := $(wildcard *.cc)
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OBJ := $(patsubst %.cc, %.o, $(SRC))
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DEP := $(patsubst %.o, %.d, $(OBJ))
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TARGET := main_test
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all:
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$(MAKE) -j$(CPUS) target
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main_test: $(OBJ)
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$(CXX) $^ -o $@ $(RTFLAGS) $(LDFLAGS) $(LIBS)
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target: $(TARGET)
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%.o : %.cc
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$(CXX) -c $(CXXFLAGS) $< -o $@
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%.d : %.cc
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@$(CXX) -MM $< $(CXXFLAGS) | sed 's/$(notdir $*)\.o/$(subst /,\/,$*).o $(subst /,\/,$*).d/g' > $@
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clean:
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-rm -rf $(OBJ) $(TARGET) *.core $(DEP) *_unittest
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test: all
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./main_test
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.PHONY: all target clean test
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