大话设计模式8—建造者模式（建造小人）
- 1.需求：建造小人
- 2.普通实现
- 3.建造者模式实现
- 4.建造者模式
1.需求：建造小人
假设需要使用画笔和图片画两个小人，小人只需要包含头部、身体和腿就可以。这两个小人一个是瘦人、一个是胖子。现给出画笔和图片两个类如下：
class Pen {
public:
Pen();
};
class Graphics {
public:
Graphics();
};
构造函数
Pen::Pen() {
cout << "use yellow pen" << endl;
}
Graphics::Graphics() {
cout << "start to write" << endl;
}
main函数
int main()
{
Pen *p = new Pen();
Graphics *g = new Graphics();
//自己添加
return 0;
}
请设计BuildThinPerson和BuildFatPerson两个类完成最终需要输出如下。
2.普通实现
设计两个类BuildThinPerson 和BuildFatPerson，这两个类十分相似，都有两个成员变量m_pen和m_graphics指针，来自题设给定的Pen和Graphics 两个类，BuildThinPerson的方法就是画头、身子、腿如下。
class BuildThinPerson {
public:
BuildThinPerson(Pen *pen, Graphics *graphics);
void BuildHead();
void BuildBody();
void BuildLeg();
void BuildThin();
private:
Pen *m_pen;
Graphics *m_graphics;
};
BuildThinPerson 类的实现很简单，由于main函数已经实现了一部分，所以BuildThinPerson 类的构造函数传参即可。在BuildHead(); BuildBody();BuildLeg()三个函数中打印需要的输出，而BuildThin()函数负责调用三个函数封装起来。
BuildThinPerson::BuildThinPerson(Pen * pen, Graphics * graphics) :m_pen(pen), m_graphics(graphics) {
}
void BuildThinPerson::BuildHead() {
cout << "build Head of thin person" << endl;
}
void BuildThinPerson::BuildBody() {
cout << "build Body of thin person" << endl;
}
void BuildThinPerson::BuildLeg() {
cout << "build Leg of thin person" << endl;
}
void BuildThinPerson::BuildThin()
{
BuildHead();
BuildBody();
BuildLeg();
}
BuildFatPerson类的实现只有打印语句和BuildThinPerson不同略去实现。那么补全的main函数如下
int main()
{
Pen *p = new Pen();
Graphics *g = new Graphics();
BuildThinPerson *thin_person = new BuildThinPerson(p, g);
thin_person->BuildThin();
BuildFatPerson *fat_person = new BuildFatPerson(p, g);
fat_person->BuildFat();
return 0;
}
达到建造两个小人的要求
3.建造者模式实现
查看上述代码，可以发现两个类BuildThinPerson 和BuildFatPerson相似度很高，所以第一步，我们考虑把共同的东西放到新设计的父类PersonBuilder中，BuildThinPerson 和BuildFatPerson继承他，三类如下：
class PersonBuilder {
protected:
Pen *m_pen;
Graphics *m_graphics;
public:
PersonBuilder(Pen *pen,Graphics *graphics);
virtual ~PersonBuilder() {};
virtual void BuildHead() {};
virtual void BuildBody() {};
virtual void BuildLeg() {};
};
class BuildThinPerson:public PersonBuilder{
public:
BuildThinPerson(Pen *pen, Graphics *graphics);
virtual void BuildHead();
virtual void BuildBody();
virtual void BuildLeg();
};
class BuildFatPerson:public PersonBuilder {
public:
BuildFatPerson(Pen *pen, Graphics *graphics);
virtual void BuildHead();
virtual void BuildBody();
virtual void BuildLeg();
};
这三个类实现也很简单，子类重写父类的BuildHead(); BuildBody();BuildLeg()函数。
PersonBuilder::PersonBuilder(Pen* pen, Graphics* graphics) : m_pen(pen), m_graphics(graphics) {
}
BuildThinPerson::BuildThinPerson(Pen* pen, Graphics* graphics): PersonBuilder(pen,graphics){
}
void BuildThinPerson::BuildHead() {
cout << "build Head of thin person" << endl;
}
void BuildThinPerson::BuildBody() {
cout << "build Body of thin person" << endl;
}
void BuildThinPerson::BuildLeg() {
cout << "build Leg of thin person" << endl;
}
BuildFatPerson::BuildFatPerson(Pen * pen, Graphics * graphics) :PersonBuilder(pen, graphics){
}
void BuildFatPerson::BuildHead() {
cout << "build Head of fat person" << endl;
}
void BuildFatPerson::BuildBody() {
cout << "build Body of fat person" << endl;
}
void BuildFatPerson::BuildLeg() {
cout << "build Leg of fat person" << endl;
}
重点来了，客户端调用时还是需要知道建造头、身子、腿的方法，我们想要隔绝用户和建造过程的关联，不让用户知道建造的过程和细节。所以我们还需要一个指挥者的类来控制建造过程。
指挥者PersonDirector 类管理抽象建造者类的指针，通过调用CreatPerson进行建造。
class PersonDirector {
private:
PersonBuilder* m_person_builder;
public:
PersonDirector(PersonBuilder* person_builder);
void CreatPerson();
};
PersonDirector类实现，构造函数通过用户告诉指挥者需要建造什么小人，而CreatPerson调用建造过程就行
PersonDirector::PersonDirector(PersonBuilder * person_builder):m_person_builder(person_builder){
}
void PersonDirector::CreatPerson()
{
m_person_builder->BuildHead();
m_person_builder->BuildBody();
m_person_builder->BuildLeg();
}
以上完成了所有类的实现，各类之间关系如下
main函数就很好写出来了，只需要向指挥者传入想创建的小人就行
int main()
{
Pen *p = new Pen;
Graphics *g = new Graphics;
PersonBuilder *build1 = new BuildThinPerson(p,g);
PersonDirector *dir = new PersonDirector(build1);
dir->CreatPerson();
PersonBuilder *build2 = new BuildFatPerson(p, g);
dir = new PersonDirector(build2);
dir->CreatPerson();
delete p;
delete g;
delete build1;
delete dir;
return 0;
}
完成题设要求
所有代码如下：
build.h
#ifndef BUILD_H
#define BUILD_H
class Pen {
public:
Pen();
};
class Graphics {
public:
Graphics();
};
class PersonBuilder {
protected:
Pen *m_pen;
Graphics *m_graphics;
public:
PersonBuilder(Pen *pen,Graphics *graphics);
virtual ~PersonBuilder() {};
virtual void BuildHead() {};
virtual void BuildBody() {};
virtual void BuildLeg() {};
};
class BuildThinPerson:public PersonBuilder{
public:
BuildThinPerson(Pen *pen, Graphics *graphics);
virtual void BuildHead();
virtual void BuildBody();
virtual void BuildLeg();
};
class BuildFatPerson:public PersonBuilder {
public:
BuildFatPerson(Pen *pen, Graphics *graphics);
virtual void BuildHead();
virtual void BuildBody();
virtual void BuildLeg();
};
class PersonDirector {
private:
PersonBuilder* m_person_builder;
public:
PersonDirector(PersonBuilder* person_builder);
void CreatPerson();
};
#endif
build.cpp
#include"build.h"
#include<iostream>
using namespace std;
Pen::Pen(){
cout << "use yellow pen" << endl;
}
Graphics::Graphics(){
cout << "start to write" << endl;
}
PersonBuilder::PersonBuilder(Pen* pen, Graphics* graphics) : m_pen(pen), m_graphics(graphics) {
}
BuildThinPerson::BuildThinPerson(Pen* pen, Graphics* graphics): PersonBuilder(pen,graphics){
}
void BuildThinPerson::BuildHead() {
cout << "build Head of thin person" << endl;
}
void BuildThinPerson::BuildBody() {
cout << "build Body of thin person" << endl;
}
void BuildThinPerson::BuildLeg() {
cout << "build Leg of thin person" << endl;
}
BuildFatPerson::BuildFatPerson(Pen * pen, Graphics * graphics) :PersonBuilder(pen, graphics){
}
void BuildFatPerson::BuildHead() {
cout << "build Head of fat person" << endl;
}
void BuildFatPerson::BuildBody() {
cout << "build Body of fat person" << endl;
}
void BuildFatPerson::BuildLeg() {
cout << "build Leg of fat person" << endl;
}
PersonDirector::PersonDirector(PersonBuilder * person_builder):m_person_builder(person_builder){
}
void PersonDirector::CreatPerson()
{
m_person_builder->BuildHead();
m_person_builder->BuildBody();
m_person_builder->BuildLeg();
}
main.cpp
#include"build.h"
int main()
{
Pen *p = new Pen;
Graphics *g = new Graphics;
PersonBuilder *build1 = new BuildThinPerson(p,g);
PersonDirector *dir = new PersonDirector(build1);
dir->CreatPerson();
PersonBuilder *build2 = new BuildFatPerson(p, g);
dir = new PersonDirector(build2);
dir->CreatPerson();
delete p;
delete g;
delete build1;
delete dir;
return 0;
}
4.建造者模式
建造者模式：将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示。用户只需要指定需要建造的类型就可以的得到他们，而具体的构建过程和细节不需要知道。
如下图所示，Builder是创建小人的抽象类，具体建造者继承他进行构造和装配。
建造者模式主要用于创建一些复杂对象，这些对象内部构造间的顺序通常是稳定的，但对象内部的构造通常面临复杂变化。