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外观模式(Facade Pattern)及其应用场景

news 2025/8/7 5:56:19

外观模式是一种结构型设计模式，它为复杂的子系统提供了一个简化的接口。这种模式定义了一个高层接口，使得子系统更容易使用。

外观模式的特点

简化接口：为复杂的子系统提供统一的简单接口
解耦：将客户端与子系统解耦，降低依赖性
易用性：使子系统更易于使用和理解

典型应用场景

复杂子系统需要简化接口时
需要将子系统组织成层次结构时
构建多层系统时，外观可以作为每层的入口点
遗留系统集成时提供统一接口

C++ 示例程序

示例1：计算机启动过程

#include <iostream>// 子系统类：CPU
class CPU {
public:void freeze() { std::cout << "CPU freeze\n"; }void jump(long position) { std::cout << "CPU jump to " << position << "\n"; }void execute() { std::cout << "CPU execute\n"; }
};// 子系统类：内存
class Memory {
public:void load(long position, const std::string& data) {std::cout << "Memory load at " << position << ": " << data << "\n";}
};// 子系统类：硬盘
class HardDrive {
public:std::string read(long lba, int size) {std::cout << "HardDrive read " << size << " bytes from " << lba << "\n";return "BOOT_DATA";}
};// 外观类：计算机
class ComputerFacade {
private:CPU cpu;Memory memory;HardDrive hardDrive;static const long BOOT_ADDRESS = 0x7C00;static const long BOOT_SECTOR = 0;static const int SECTOR_SIZE = 512;public:void start() {std::cout << "Computer starting...\n";cpu.freeze();std::string bootData = hardDrive.read(BOOT_SECTOR, SECTOR_SIZE);memory.load(BOOT_ADDRESS, bootData);cpu.jump(BOOT_ADDRESS);cpu.execute();std::cout << "Computer started successfully\n";}
};// 客户端代码
int main() {ComputerFacade computer;computer.start();return 0;
}

示例2：家庭影院系统

#include <iostream>
#include <string>// 子系统类：投影仪
class Projector {
public:void on() { std::cout << "Projector on\n"; }void off() { std::cout << "Projector off\n"; }void wideScreenMode() { std::cout << "Projector in widescreen mode\n"; }
};// 子系统类：DVD播放器
class DvdPlayer {
public:void on() { std::cout << "DVD Player on\n"; }void off() { std::cout << "DVD Player off\n"; }void play(const std::string& movie) {std::cout << "DVD Player playing \"" << movie << "\"\n";}void stop() { std::cout << "DVD Player stopped\n"; }
};// 子系统类：音响系统
class Amplifier {
public:void on() { std::cout << "Amplifier on\n"; }void off() { std::cout << "Amplifier off\n"; }void setVolume(int level) { std::cout << "Amplifier volume set to " << level << "\n"; }
};// 子系统类：灯光控制
class TheaterLights {
public:void dim(int level) { std::cout << "Theater lights dimmed to " << level << "%\n"; }void on() { std::cout << "Theater lights on\n"; }
};// 外观类：家庭影院
class HomeTheaterFacade {
private:Amplifier amp;DvdPlayer dvd;Projector projector;TheaterLights lights;public:void watchMovie(const std::string& movie) {std::cout << "Get ready to watch a movie...\n";lights.dim(10);amp.on();amp.setVolume(5);projector.on();projector.wideScreenMode();dvd.on();dvd.play(movie);}void endMovie() {std::cout << "Shutting movie theater down...\n";lights.on();amp.off();dvd.stop();dvd.off();projector.off();}
};// 客户端代码
int main() {HomeTheaterFacade theater;theater.watchMovie("The Matrix");std::cout << "\nEnjoy the movie...\n\n";theater.endMovie();return 0;
}

示例3：编译器子系统

#include <iostream>
#include <string>
#include <vector>// 子系统类：扫描器
class Scanner {
public:std::vector<std::string> scan(const std::string& source) {std::cout << "Scanning source code...\n";// 简化的扫描过程return {"token1", "token2", "token3"};}
};// 子系统类：解析器
class Parser {
public:void parse(const std::vector<std::string>& tokens) {std::cout << "Parsing tokens...\n";// 简化的解析过程}
};// 子系统类：代码生成器
class CodeGenerator {
public:void generateCode() {std::cout << "Generating object code...\n";// 简化的代码生成过程}
};// 子系统类：优化器
class Optimizer {
public:void optimize() {std::cout << "Optimizing code...\n";// 简化的优化过程}
};// 外观类：编译器
class CompilerFacade {
private:Scanner scanner;Parser parser;CodeGenerator codeGen;Optimizer optimizer;public:void compile(const std::string& source) {std::cout << "Compilation started\n";auto tokens = scanner.scan(source);parser.parse(tokens);codeGen.generateCode();optimizer.optimize();std::cout << "Compilation completed successfully\n";}
};// 客户端代码
int main() {CompilerFacade compiler;compiler.compile("int main() { return 0; }");return 0;
}