设计模式是软件开发中常用的解决问题的可重用模式。它提供了一套经过验证的解决方案，可以帮助开发人员解决常见问题，并提高代码的可维护性和可扩展性。Java中有23种常见的设计模式，可以分为三个类别：创建型模式、结构型模式和行为型模式。
- 创建型模式：用于创建对象的模式，隐藏了对象的创建过程。
- 单例模式（Singleton）：确保一个类只有一个实例，并提供全局访问点。
public class Singleton {private static Singleton instance;private Singleton() {}public static Singleton getInstance() {if (instance == null) {instance = new Singleton();}return instance;}
}
- 工厂模式（Factory）：通过一个工厂类创建对象，将对象的实例化过程封装起来。
public interface Shape {void draw();
}public class Circle implements Shape {@Overridepublic void draw() {System.out.println("Draw a circle");}
}public class Rectangle implements Shape {@Overridepublic void draw() {System.out.println("Draw a rectangle");}
}public class ShapeFactory {public Shape createShape(String shapeType) {if (shapeType.equalsIgnoreCase("circle")) {return new Circle();} else if (shapeType.equalsIgnoreCase("rectangle")) {return new Rectangle();}return null;}
}
- 结构型模式：用于描述如何将对象和类组合成更大的结构。
- 适配器模式（Adapter）：将一个类的接口转换成客户端所期望的接口。
public interface MediaPlayer {void play(String audioType, String fileName);
}public interface AdvancedMediaPlayer {void playVlc(String fileName);void playMp4(String fileName);
}public class VlcPlayer implements AdvancedMediaPlayer {@Overridepublic void playVlc(String fileName) {System.out.println("Playing vlc file: " + fileName);}@Overridepublic void playMp4(String fileName) {// do nothing}
}public class Mp4Player implements AdvancedMediaPlayer {@Overridepublic void playVlc(String fileName) {// do nothing}@Overridepublic void playMp4(String fileName) {System.out.println("Playing mp4 file: " + fileName);}
}public class MediaAdapter implements MediaPlayer {private AdvancedMediaPlayer advancedMediaPlayer;public MediaAdapter(String audioType) {if (audioType.equalsIgnoreCase("vlc")) {advancedMediaPlayer = new VlcPlayer();} else if (audioType.equalsIgnoreCase("mp4")) {advancedMediaPlayer = new Mp4Player();}}@Overridepublic void play(String audioType, String fileName) {if (audioType.equalsIgnoreCase("vlc")) {advancedMediaPlayer.playVlc(fileName);} else if (audioType.equalsIgnoreCase("mp4")) {advancedMediaPlayer.playMp4(fileName);}}
}public class AudioPlayer implements MediaPlayer {private MediaAdapter mediaAdapter;@Overridepublic void play(String audioType, String fileName) {if (audioType.equalsIgnoreCase("mp3")) {System.out.println("Playing mp3 file: " + fileName);} else if (audioType.equalsIgnoreCase("vlc") || audioType.equalsIgnoreCase("mp4")) {mediaAdapter = new MediaAdapter(audioType);mediaAdapter.play(audioType, fileName);} else {System.out.println("Format not supported");}}
}
- 行为型模式：用于描述对象之间的通信方式和职责分配。
- 观察者模式（Observer）：定义对象之间的一对多依赖关系，当一个对象的状态发生变化时，所有依赖它的对象都会收到通知。
import java.util.ArrayList;
import java.util.List;public class Subject {private List<Observer> observers = new ArrayList<>();private int state;public int getState() {return state;}public void setState(int state) {this.state = state;notifyAllObservers();}public void attach(Observer observer) {observers.add(observer);}public void notifyAllObservers() {for (Observer observer : observers) {observer.update();}}
}public abstract class Observer {protected Subject subject;public abstract void update();
}public class BinaryObserver extends Observer {public BinaryObserver(Subject subject) {this.subject = subject;this.subject.attach(this);}@Overridepublic void update() {System.out.println("Binary: " + Integer.toBinaryString(subject.getState()));}
}public class OctalObserver extends Observer {public OctalObserver(Subject subject) {this.subject = subject;this.subject.attach(this);}@Overridepublic void update() {System.out.println("Octal: " + Integer.toOctalString(subject.getState()));}
}public class HexObserver extends Observer {public HexObserver(Subject subject) {this.subject = subject;this.subject.attach(this);}@Overridepublic void update() {System.out.println("Hex: " + Integer.toHexString(subject.getState()));}
}public class Main {public static void main(String[] args) {Subject subject = new Subject();new BinaryObserver(subject);new OctalObserver(subject);new HexObserver(subject);subject.setState(10);subject.setState(15);}
}
