Only some thinking to help to think about the Builder Pattern, but it's not so intuitive.
Suppose that we want to save data to files.
class File { /*abstract file*/ };
class FileBuilder
{
public:
virtual bool buildFileHeader() =0;
virtual bool buildFileBody() =0;
virtual bool buildFileTail() =0;
virtual File* getFile() =0;
};
class BmpFile : public File { .... };
class GifFile : public File { .... };
class JpegFile : public File { .... };
//other kinds of files
class BmpFileBuilder : public FileBuilder
{
};
class GifFileBuilder : public FileBuilder
{
};
class JpegFileBuilder : public FileBuilder
{
};
//builders above implement those interfaces from FileBuilder
//other kinds of file builders
//usage
File* buildFile(FileBuilder* fb)
{
fb.buildFileHeader();
fb.buildFileBody();
fb.buildFileTail();
return fb.GetFile();
}
void func()
{
FileBuilder* fb = new SomeFileBuilder();
File* f = buildFile(fb);
//use f
....
}
Key Points:
1. Each builder is responsible for its buildXXX()
2. Each builder builds one kind of File
3. the File would be created in builder's constructor
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// interface
class People
{
public:
virtual void doWhat() =0;
virtual string type() const =0;
};
class Male : public People
{
public:
virtual void doWhat();
virtual string type() const;
static People* creator();
};
class Female : public People
{
public:
virtual void doWhat();
virtual string type() const;
static People* creator();
};
// interface
typedef People* (*CreateFcn)();
class PeopleFactory
{
public:
static People* producePeople(const string& type);
static addCreateFcn(const string& type, CreateFcn creator);
private:
static map<string, CreateFcn> createFcns;
};
People* PeopleFactory::producePeople(const string& type)
{
//***1
CreateFcn creator= createFcns[type];
return creator();
}
---- test ----
void f()
{
//***2
const string t("Male"); //or "Female"
People* p = PeopleFactory::producePeople(t);
p->doWhat();
delete p;
}
---- extension ----
class Hemophrodite : public People
{
virtual void doWhat();
virtual string type() const;
static People* creator();
};
void g()
{
//***3
const string newType = "Hemophrodite";
PeopleFactory::addCreateFcn(newType, Hemophrodite::creator);
// usage
const string t("Hemophrodite");
People* p = PeopleFactory::producePeople(t);
p->doWhat();
delete p;
}
Cool!! OCP!!
---------
Key point:
1. How does the Factory Method create the instance
of classes through their type names?
How could this method follow the OCP?
2. Where does the type name come from?
-- config file
-- registry
-- other method
3. About extension
----------
Interface classes:
People & PeopleFactory
enjoy it!!
]]>
Key point: 澶у眬鎬濇兂 鍒嗗眰鎬濇兂
璁捐錛屾湁寰堝鏂規(guī)硶銆備笉綆″摢縐嶆柟娉曪紝閮介渶瑕佸寰呰璁＄殑瀵硅薄鐨勬繁鍏ョ殑浜?jiǎn)瑙ｃ?br>
瑕佹湁澶у眬鎬濇兂錛屼笉鑳界涓璞癸紝瑙佹湪涓嶈鏋椼?br>
璁捐鏃訛紝涓嶈兘榪囧鑰冭檻緇嗚妭銆傚鏋滈櫡鍦ㄧ粏鑺傞噷錛岃鍙?qiáng)鏃朵腑姝㈠拰閫鍑恒?br>
鑷笂鑰屼笅錛屽眰灞傜粏鍖栨槸涓縐嶄笉閿欑殑鏂規(guī)硶銆?br>
鍙互鍊熺敤涓涓嬪浘褰㈠涓殑“鍒嗗眰嬈＄粏鑺傛ā鍨?#8221;銆?br>
涓嶅悓鐨勫眰嬈″簲璇ユ湁涓嶅悓鐨勭粏鑺傘?br>
緇撴瀯鍖栨湁鍔╀簬鎬濊礬娓呮櫚鍖栥傛爲(wèi)鍨嬬粨鏋勬槸涓縐嶄笉閿欑殑閫夋嫨銆?br>
姣忎釜闃舵鍙仛濂介偅涓樁孌電殑浜嬶紝鍏朵粬鐨勪簨涓寰嬩笉鑳藉仛錛堝敖綆¤兘鍋氭瀬濂戒篃涓嶈錛夈?br>
澶氬拰浜鴻璁哄績(jī)涓殑鎯蟲(chóng)硶銆傚娉ㄦ剰鍒漢鐨勬濊礬錛屼笌宸叉瘮杈冿紝鍙栭暱琛ョ煭銆?br>
閫氬父錛屽浜庨棶棰橈紝瓚婅璁鴻秺娓呮櫚銆?
]]>