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设计模式

news 2025/10/6 0:59:35

1. 适配器模式 (Adapter Pattern)

将一个类的接口转换成客户希望的另一个接口，使原本不兼容的类可以一起工作。

// 目标接口
public interface MediaPlayer {void play(String audioType, String fileName);
}// 被适配者
public class Mp3Player {public void playMp3(String fileName) {System.out.println("Playing MP3 file: " + fileName);}
}public class Mp4Player {public void playMp4(String fileName) {System.out.println("Playing MP4 file: " + fileName);}
}// 适配器
public class MediaAdapter implements MediaPlayer {Mp4Player mp4Player;public MediaAdapter(String audioType) {if (audioType.equalsIgnoreCase("mp4")) {mp4Player = new Mp4Player();}}@Overridepublic void play(String audioType, String fileName) {if (audioType.equalsIgnoreCase("mp4")) {mp4Player.playMp4(fileName);}}
}// 适配器实现
public class AudioPlayer implements MediaPlayer {MediaAdapter mediaAdapter;@Overridepublic void play(String audioType, String fileName) {// 内置支持MP3播放if (audioType.equalsIgnoreCase("mp3")) {System.out.println("Playing MP3 file: " + fileName);}// 对于其他格式，使用适配器else if (audioType.equalsIgnoreCase("mp4")) {mediaAdapter = new MediaAdapter(audioType);mediaAdapter.play(audioType, fileName);} else {System.out.println("Invalid media type: " + audioType);}}
}// 使用示例
public class AdapterDemo {public static void main(String[] args) {AudioPlayer audioPlayer = new AudioPlayer();audioPlayer.play("mp3", "song.mp3");audioPlayer.play("mp4", "video.mp4");audioPlayer.play("avi", "movie.avi");}
}

2. 模板方法模式 (Template Method Pattern)

定义一个操作中的算法骨架，而将一些步骤延迟到子类中。

// 抽象模板类
public abstract class Game {// 模板方法，定义游戏流程public final void play() {// 初始化游戏initialize();// 开始游戏startPlay();// 进行游戏endPlay();}// 抽象方法，由子类实现abstract void initialize();abstract void startPlay();abstract void endPlay();// 钩子方法，子类可以选择性重写void endPlay() {System.out.println("Game Finished!");}
}// 具体实现类
public class Cricket extends Game {@Overridevoid initialize() {System.out.println("Cricket Game Initialized! Start playing.");}@Overridevoid startPlay() {System.out.println("Cricket Game Started. Enjoy the game!");}@Overridevoid endPlay() {System.out.println("Cricket Game Finished!");}
}public class Football extends Game {@Overridevoid initialize() {System.out.println("Football Game Initialized! Start playing.");}@Overridevoid startPlay() {System.out.println("Football Game Started. Enjoy the game!");}@Overridevoid endPlay() {System.out.println("Football Game Finished!");}
}// 使用示例
public class TemplatePatternDemo {public static void main(String[] args) {Game game = new Cricket();game.play();System.out.println();game = new Football();game.play();}
}

3. 命令模式 (Command Pattern)

将请求封装成对象，从而使你可以用不同的请求对客户进行参数化。

// 命令接口
public interface Order {void execute();
}// 接收者
public class Stock {private String name = "ABC";private int quantity = 10;public void buy() {System.out.println("Stock [ Name: " + name + ", Quantity: " + quantity + " ] bought");}public void sell() {System.out.println("Stock [ Name: " + name + ", Quantity: " + quantity + " ] sold");}
}// 具体命令
public class BuyStock implements Order {private Stock abcStock;public BuyStock(Stock abcStock) {this.abcStock = abcStock;}public void execute() {abcStock.buy();}
}public class SellStock implements Order {private Stock abcStock;public SellStock(Stock abcStock) {this.abcStock = abcStock;}public void execute() {abcStock.sell();}
}// 调用者
public class Broker {private List<Order> orderList = new ArrayList<Order>();public void takeOrder(Order order) {orderList.add(order);}public void placeOrders() {for (Order order : orderList) {order.execute();}orderList.clear();}
}// 使用示例
public class CommandPatternDemo {public static void main(String[] args) {Stock abcStock = new Stock();BuyStock buyStockOrder = new BuyStock(abcStock);SellStock sellStockOrder = new SellStock(abcStock);Broker broker = new Broker();broker.takeOrder(buyStockOrder);broker.takeOrder(sellStockOrder);broker.placeOrders();}
}

4. 状态模式 (State Pattern)

允许对象在内部状态改变时改变它的行为，对象看起来好像修改了它的类。

// 状态接口
public interface State {void doAction(Context context);
}// 上下文类
public class Context {private State state;public Context() {this.state = null;}public void setState(State state) {this.state = state;}public State getState() {return state;}
}// 具体状态实现
public class StartState implements State {public void doAction(Context context) {System.out.println("Player is in start state");context.setState(this);}public String toString() {return "Start State";}
}public class StopState implements State {public void doAction(Context context) {System.out.println("Player is in stop state");context.setState(this);}public String toString() {return "Stop State";}
}// 使用示例
public class StatePatternDemo {public static void main(String[] args) {Context context = new Context();StartState startState = new StartState();startState.doAction(context);System.out.println(context.getState().toString());StopState stopState = new StopState();stopState.doAction(context);System.out.println(context.getState().toString());}
}

5. 建造者模式 (Builder Pattern)

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。

// 产品类
public class Meal {private List<Item> items = new ArrayList<Item>();public void addItem(Item item) {items.add(item);}public float getCost() {float cost = 0.0f;for (Item item : items) {cost += item.price();}return cost;}public void showItems() {for (Item item : items) {System.out.print("Item : " + item.name());System.out.print(", Packing : " + item.packing().pack());System.out.println(", Price : " + item.price());}}
}// 接口定义
public interface Item {String name();Packing packing();float price();
}public interface Packing {String pack();
}// 包装实现
public class Wrapper implements Packing {@Overridepublic String pack() {return "Wrapper";}
}public class Bottle implements Packing {@Overridepublic String pack() {return "Bottle";}
}// 具体项目
public abstract class Burger implements Item {@Overridepublic Packing packing() {return new Wrapper();}@Overridepublic abstract float price();
}public abstract class ColdDrink implements Item {@Overridepublic Packing packing() {return new Bottle();}@Overridepublic abstract float price();
}public class VegBurger extends Burger {@Overridepublic float price() {return 25.0f;}@Overridepublic String name() {return "Veg Burger";}
}public class ChickenBurger extends Burger {@Overridepublic float price() {return 50.5f;}@Overridepublic String name() {return "Chicken Burger";}
}public class Coke extends ColdDrink {@Overridepublic float price() {return 30.0f;}@Overridepublic String name() {return "Coke";}
}public class Pepsi extends ColdDrink {@Overridepublic float price() {return 35.0f;}@Overridepublic String name() {return "Pepsi";}
}// 建造者
public class MealBuilder {public Meal prepareVegMeal() {Meal meal = new Meal();meal.addItem(new VegBurger());meal.addItem(new Coke());return meal;}public Meal prepareNonVegMeal() {Meal meal = new Meal();meal.addItem(new ChickenBurger());meal.addItem(new Pepsi());return meal;}
}// 使用示例
public class BuilderPatternDemo {public static void main(String[] args) {MealBuilder mealBuilder = new MealBuilder();Meal vegMeal = mealBuilder.prepareVegMeal();System.out.println("Veg Meal");vegMeal.showItems();System.out.println("Total Cost: " + vegMeal.getCost());Meal nonVegMeal = mealBuilder.prepareNonVegMeal();System.out.println("\n\nNon-Veg Meal");nonVegMeal.showItems();System.out.println("Total Cost: " + nonVegMeal.getCost());}
}

6. 代理模式 (Proxy Pattern)

为其他对象提供一种代理以控制对这个对象的访问。

// 接口
public interface Image {void display();
}// 真实对象
public class RealImage implements Image {private String fileName;public RealImage(String fileName) {this.fileName = fileName;loadFromDisk(fileName);}@Overridepublic void display() {System.out.println("Displaying " + fileName);}private void loadFromDisk(String fileName) {System.out.println("Loading " + fileName);}
}// 代理对象
public class ProxyImage implements Image {private RealImage realImage;private String fileName;public ProxyImage(String fileName) {this.fileName = fileName;}@Overridepublic void display() {if (realImage == null) {realImage = new RealImage(fileName);}realImage.display();}
}// 使用示例
public class ProxyPatternDemo {public static void main(String[] args) {Image image = new ProxyImage("test_10mb.jpg");// 图像将从磁盘加载image.display();System.out.println("");// 图像不需要从磁盘加载image.display();}
}

这些设计模式在不同的场景中发挥着重要作用：