深入了解常用的7种Java设计模式

public class Singleton { private static Singleton instance; private Singleton() { // 私有构造函数，防止外部实例化 } public static Singleton getInstance() { if (instance == null) { synchronized (Singleton.class) { if (instance == null) { instance = new Singleton(); } } } return instance; } }

public interface Shape { void draw(); } public class Circle implements Shape { @Override public void draw() { System.out.println("Circle::draw()"); } } public class Rectangle implements Shape { @Override public void draw() { System.out.println("Rectangle::draw()"); } } public class ShapeFactory { public Shape getShape(String shapeType) { if (shapeType == null) { return null; } if (shapeType.equalsIgnoreCase("CIRCLE")) { return new Circle(); } else if (shapeType.equalsIgnoreCase("RECTANGLE")) { return new Rectangle(); } return null; } }

import java.util.ArrayList; import java.util.List; public class Subject { private List 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); } public void update() { System.out.println("Binary String: " + Integer.toBinaryString(subject.getState())); } } public class OctalObserver extends Observer { public OctalObserver(Subject subject) { this.subject = subject; this.subject.attach(this); } public void update() { System.out.println("Octal String: " + Integer.toOctalString(subject.getState())); } } public class HexObserver extends Observer { public HexObserver(Subject subject) { this.subject = subject; this.subject.attach(this); } public void update() { System.out.println("Hex String: " + Integer.toHexString(subject.getState())); } } public class ObserverPatternDemo { public static void main(String[] args) { Subject subject = new Subject(); new BinaryObserver(subject); new OctalObserver(subject); new HexObserver(subject); System.out.println("First state change: 15"); subject.setState(15); System.out.println("Second state change: 10"); subject.setState(10); } }

public class Computer { private String cpu; private String memory; private String disk; // 省略其他属性和方法 } public interface ComputerBuilder { ComputerBuilder setCpu(String cpu); ComputerBuilder setMemory(String memory); ComputerBuilder setDisk(String disk); Computer build(); } public class BasicComputerBuilder implements ComputerBuilder { private Computer computer; public BasicComputerBuilder() { computer = new Computer(); } public ComputerBuilder setCpu(String cpu) { computer.setCpu(cpu); return this; } public ComputerBuilder setMemory(String memory) { computer.setMemory(memory); return this; } public ComputerBuilder setDisk(String disk) { computer.setDisk(disk); return this; } public Computer build() { return computer; } } public class Director { private ComputerBuilder computerBuilder; public Director(ComputerBuilder computerBuilder) { this.computerBuilder = computerBuilder; } public Computer construct() { return computerBuilder .setCpu("i5") .setMemory("8GB") .setDisk("1TB") .build(); } } public class BuilderPatternDemo { public static void main(String[] args) { ComputerBuilder computerBuilder = new BasicComputerBuilder(); Director director = new Director(computerBuilder); Computer computer = director.construct(); System.out.println(computer.toString()); } }

public abstract class Shape implements Cloneable { private String id; protected String type; abstract void draw(); public String getId() { return id; } public void setId(String id) { this.id = id; } public Object clone() { Object clone = null; try { clone = super.clone(); } catch (CloneNotSupportedException e) { e.printStackTrace(); } return clone; } } public class Circle extends Shape { public Circle() { type = "Circle"; } public void draw() { System.out.println("Inside Circle::draw() method."); } } public class Rectangle extends Shape { public Rectangle() { type = "Rectangle"; } public void draw() { System.out.println("Inside Rectangle::draw() method."); } } public class ShapeCache { private static Map shapeMap = new HashMap<>(); public static Shape getShape(String shapeId) { Shape cachedShape = shapeMap.get(shapeId); return (Shape) cachedShape.clone(); } public static void loadCache() { Circle circle = new Circle(); circle.setId("1"); shapeMap.put(circle.getId(), circle); Rectangle rectangle = new Rectangle(); rectangle.setId("2"); shapeMap.put(rectangle.getId(), rectangle); } } public class PrototypePatternDemo { public static void main(String[] args) { ShapeCache.loadCache(); Shape clonedShape1 = ShapeCache.getShape("1"); System.out.println("Shape: " + clonedShape1.getType()); Shape clonedShape2 = ShapeCache.getShape("2"); System.out.println("Shape: " + clonedShape2.getType()); } }

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 { public void playVlc(String fileName) { System.out.println("Playing vlc file. Name: " + fileName); } public void playMp4(String fileName) { // 空实现 } } public class Mp4Player implements AdvancedMediaPlayer { public void playVlc(String fileName) { // 空实现 } public void playMp4(String fileName) { System.out.println("Playing mp4 file. Name: " + fileName); } } public class MediaAdapter implements MediaPlayer { AdvancedMediaPlayer advancedMediaPlayer; public MediaAdapter(String audioType) { if (audioType.equalsIgnoreCase("vlc")) { advancedMediaPlayer = new VlcPlayer(); } else if (audioType.equalsIgnoreCase("mp4")) { advancedMediaPlayer = new Mp4Player(); } } public 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 { MediaAdapter mediaAdapter; public void play(String audioType, String fileName) { if (audioType.equalsIgnoreCase("mp3")) { System.out.println("Playing mp3 file. Name: " + fileName); } else if (audioType.equalsIgnoreCase("vlc") || audioType.equalsIgnoreCase("mp4")) { mediaAdapter = new MediaAdapter(audioType); mediaAdapter.play(audioType, fileName); } else { System.out.println("Invalid media. " + audioType + " format not supported"); } } } public class AdapterPatternDemo { public static void main(String[] args) { AudioPlayer audioPlayer = new AudioPlayer(); audioPlayer.play("mp3", "beyond_the_horizon.mp3"); audioPlayer.play("mp4", "alone.mp4"); audioPlayer.play("vlc", "far_far_away.vlc"); audioPlayer.play("avi", "mind_me.avi"); } }

public interface Strategy { int doOperation(int num1, int num2); } public class OperationAdd implements Strategy { public int doOperation(int num1, int num2) { return num1 + num2; } } public class OperationSubtract implements Strategy { public int doOperation(int num1, int num2) { return num1 - num2; } } public class OperationMultiply implements Strategy { public int doOperation(int num1, int num2) { return num1 * num2; } } public class Context { private Strategy strategy; public Context(Strategy strategy) { this.strategy = strategy; } public int executeStrategy(int num1, int num2) { return strategy.doOperation(num1, num2); } } public class StrategyPatternDemo { public static void main(String[] args) { Context context = new Context(new OperationAdd()); System.out.println("10 + 5 = " + context.executeStrategy(10, 5)); context = new Context(new OperationSubtract()); System.out.println("10 - 5 = " + context.executeStrategy(10, 5)); context = new Context(new OperationMultiply()); System.out.println("10 * 5 = " + context.executeStrategy(10, 5)); } }