行为型模式 - 策略模式

**行为型模式 - 策略模式**

策略模式是一种常见的设计模式，用于定义一系列算法或行为，并使它们可以被交换和使用。这种模式通过封装单独的算法或行为，使得系统能够在不修改原有代码的情况下更改或扩展这些算法或行为。

**问题**

假设我们正在开发一个游戏系统，需要根据不同的玩家选择来改变游戏难度。我们可以定义三个不同难度级别：简单、普通和困难。每个难度级别都对应着一种特定的游戏逻辑。

**策略模式的应用**

在这种情况下，我们可以使用策略模式来封装不同的难度级别的逻辑。我们首先定义一个抽象类 `DifficultyStrategy`，它包含了所有可能的难度级别的方法：

javapublic abstract class DifficultyStrategy {
 public abstract void apply();
}

javapublic class EasyStrategy extends DifficultyStrategy {
 @Override public void apply() {
 System.out.println("Easy difficulty applied.");
 // 适当的游戏逻辑 }
}

public class NormalStrategy extends DifficultyStrategy {
 @Override public void apply() {
 System.out.println("Normal difficulty applied.");
 // 适当的游戏逻辑 }
}

public class HardStrategy extends DifficultyStrategy {
 @Override public void apply() {
 System.out.println("Hard difficulty applied.");
 // 适当的游戏逻辑 }
}

javapublic class Game {
 private DifficultyStrategy strategy;

 public void setDifficulty(DifficultyStrategy strategy) {
 this.strategy = strategy;
 }

 public void play() {
 strategy.apply();
 }
}

javapublic class Main {
 public static void main(String[] args) {
 Game game = new Game();

 // 设置简单难度 DifficultyStrategy easyStrategy = new EasyStrategy();
 game.setDifficulty(easyStrategy);
 game.play(); // 输出 "Easy difficulty applied."

 // 设置普通难度 DifficultyStrategy normalStrategy = new NormalStrategy();
 game.setDifficulty(normalStrategy);
 game.play(); // 输出 "Normal difficulty applied."

 // 设置困难难度 DifficultyStrategy hardStrategy = new HardStrategy();
 game.setDifficulty(hardStrategy);
 game.play(); // 输出 "Hard difficulty applied."
 }
}

java// DifficultyStrategy.javapublic abstract class DifficultyStrategy {
 public abstract void apply();
}

// EasyStrategy.javapublic class EasyStrategy extends DifficultyStrategy {
 @Override public void apply() {
 System.out.println("Easy difficulty applied.");
 // 适当的游戏逻辑 }
}

// NormalStrategy.javapublic class NormalStrategy extends DifficultyStrategy {
 @Override public void apply() {
 System.out.println("Normal difficulty applied.");
 // 适当的游戏逻辑 }
}

// HardStrategy.javapublic class HardStrategy extends DifficultyStrategy {
 @Override public void apply() {
 System.out.println("Hard difficulty applied.");
 // 适当的游戏逻辑 }
}

// Game.javapublic class Game {
 private DifficultyStrategy strategy;

 public void setDifficulty(DifficultyStrategy strategy) {
 this.strategy = strategy;
 }

 public void play() {
 strategy.apply();
 }
}

// Main.javapublic class Main {
 public static void main(String[] args) {
 Game game = new Game();

 // 设置简单难度 DifficultyStrategy easyStrategy = new EasyStrategy();
 game.setDifficulty(easyStrategy);
 game.play(); // 输出 "Easy difficulty applied."

 // 设置普通难度 DifficultyStrategy normalStrategy = new NormalStrategy();
 game.setDifficulty(normalStrategy);
 game.play(); // 输出 "Normal difficulty applied."

 // 设置困难难度 DifficultyStrategy hardStrategy = new HardStrategy();
 game.setDifficulty(hardStrategy);
 game.play(); // 输出 "Hard difficulty applied."
 }
}