策略模式

策略模式作爲一種軟件設計模式，指對象有某個行爲，但是在不同的場景中，該行爲有不同的實現算法。比如每個人都要“交個人所得稅”，但是“在美國交個人所得稅”和“在中華民國交個人所得稅”就有不同的算稅方法。

策略模式：

• 定义了一族算法（业务规则）；
• 封装了每个算法；
• 这族的算法可互换代替（interchangeable）。

结构

 

Strategy Pattern in UML

 

Strategy pattern in LePUS3 ()

示例

C++

#include <iostream> using namespace std; class StrategyInterface {  public:  virtual void execute() = 0; }; class ConcreteStrategyA: public StrategyInterface {  public:  virtual void execute()  {  cout << "Called ConcreteStrategyA execute method" << endl;  } }; class ConcreteStrategyB: public StrategyInterface {  public:  virtual void execute()  {  cout << "Called ConcreteStrategyB execute method" << endl;  } }; class ConcreteStrategyC: public StrategyInterface {  public:  virtual void execute()  {  cout << "Called ConcreteStrategyC execute method" << endl;  } }; class Context {  private:  StrategyInterface *_strategy;  public:  Context(StrategyInterface *strategy):_strategy(strategy)  {  }  void set_strategy(StrategyInterface *strategy)  {  _strategy = strategy;  }  void execute()  {  _strategy->execute();  } }; int main(int argc, char *argv[]) {  ConcreteStrategyA concreteStrategyA;  ConcreteStrategyB concreteStrategyB;  ConcreteStrategyC concreteStrategyC;  Context contextA(&concreteStrategyA);  Context contextB(&concreteStrategyB);  Context contextC(&concreteStrategyC);  contextA.execute();  contextB.execute();  contextC.execute();    contextA.set_strategy(&concreteStrategyB);  contextA.execute();  contextA.set_strategy(&concreteStrategyC);  contextA.execute();  return 0; } 

Java

//StrategyExample test application class StrategyExample {  public static void main(String[] args) {  Context context;  // Three contexts following different strategies  context = new Context(new FirstStrategy());  context.execute();  context = new Context(new SecondStrategy());  context.execute();  context = new Context(new ThirdStrategy());  context.execute();  } } // The classes that implement a concrete strategy should implement this // The context class uses this to call the concrete strategy interface Strategy {  void execute();   } // Implements the algorithm using the strategy interface class FirstStrategy implements Strategy {  public void execute() {  System.out.println("Called FirstStrategy.execute()");  }   } class SecondStrategy implements Strategy {  public void execute() {  System.out.println("Called SecondStrategy.execute()");  }   } class ThirdStrategy implements Strategy {  public void execute() {  System.out.println("Called ThirdStrategy.execute()");  }   } // Configured with a ConcreteStrategy object and maintains a reference to a Strategy object class Context {  Strategy strategy;  // Constructor  public Context(Strategy strategy) {  this.strategy = strategy;  }  public void execute() {  this.strategy.execute();  } } 

C#

using System; namespace Wikipedia.Patterns.Strategy {  // MainApp test application  class MainApp  {  static void Main()  {  Context context;  // Three contexts following different strategies  context = new Context(new ConcreteStrategyA());  context.Execute();  context = new Context(new ConcreteStrategyB());  context.Execute();  context = new Context(new ConcreteStrategyC());  context.Execute();  }  }  // The classes that implement a concrete strategy should implement this  // The context class uses this to call the concrete strategy  interface IStrategy  {  void Execute();  }  // Implements the algorithm using the strategy interface  class ConcreteStrategyA : IStrategy  {  public void Execute()  {  Console.WriteLine( "Called ConcreteStrategyA.Execute()" );  }  }  class ConcreteStrategyB : IStrategy  {  public void Execute()  {  Console.WriteLine( "Called ConcreteStrategyB.Execute()" );  }  }  class ConcreteStrategyC : IStrategy  {  public void Execute()  {  Console.WriteLine( "Called ConcreteStrategyC.Execute()" );  }  }  // Configured with a ConcreteStrategy object and maintains a reference to a Strategy object  class Context  {  IStrategy strategy;  // Constructor  public Context(IStrategy strategy)  {  this.strategy = strategy;  }  public void Execute()  {  strategy.Execute();  }  } } 

ActionScript 3

//invoked from application.initialize private function init() : void {  var context:Context;  context = new Context( new ConcreteStrategyA() );  context.execute();  context = new Context( new ConcreteStrategyB() );  context.execute();  context = new Context( new ConcreteStrategyC() );  context.execute(); } package org.wikipedia.patterns.strategy {  public interface IStrategy  {  function execute() : void ;  } } package org.wikipedia.patterns.strategy {  public final class ConcreteStrategyA implements IStrategy  {  public function execute():void  {  trace( "ConcreteStrategyA.execute(); invoked" );  }  } } package org.wikipedia.patterns.strategy {  public final class ConcreteStrategyB implements IStrategy  {  public function execute():void  {  trace( "ConcreteStrategyB.execute(); invoked" );  }  } } package org.wikipedia.patterns.strategy {  public final class ConcreteStrategyC implements IStrategy  {  public function execute():void  {  trace( "ConcreteStrategyC.execute(); invoked" );  }  } } package org.wikipedia.patterns.strategy {  public class Context  {  private var strategy:IStrategy;    public function Context(strategy:IStrategy)  {  this.strategy = strategy;  }    public function execute() : void  {   strategy.execute();  }  } } 

PHP

<?php class StrategyExample { public function __construct() { $context = new Context(new ConcreteStrategyA()); $context->execute(); $context = new Context(new ConcreteStrategyB()); $context->execute(); $context = new Context(new ConcreteStrategyC()); $context->execute(); } } interface IStrategy { public function execute(); } class ConcreteStrategyA implements IStrategy { public function execute() { echo "Called ConcreteStrategyA execute method\n"; } } class ConcreteStrategyB implements IStrategy { public function execute() { echo "Called ConcreteStrategyB execute method\n"; } } class ConcreteStrategyC implements IStrategy { public function execute() { echo "Called ConcreteStrategyC execute method\n"; } } class Context { var $strategy; public function __construct(IStrategy $strategy) { $this->strategy = $strategy; } public function execute() { $this->strategy->execute(); } } new StrategyExample; ?> 

Objective-C

@protocol Strategy <NSObject> @required - (void)print; @end @interface ConcreteStrategyA : NSObject<Strategy> {   } @end @interface ConcreteStrategyB : NSObject<Strategy> {   } @end @interface Context : NSObject {  id<Strategy> _strategy; } @property (nonatomic, assign) id<Strategy> strategy; -(void)doIt; @end @implementation ConcreteStrategyA - (void)print {  NSLog(@"Test01"); } @end @implementation ConcreteStrategyB - (void)print {  NSLog(@"Test02"); } @end @implementation Context @synthesize strategy = _strategy; -(void)doIt {  [self.strategy print]; } @end