Java中较为常用的设计模式代码样例

Java中较为常用的设计模式有很多种，以下是其中几种的代码样例：

1. 单例模式（Singleton Pattern）：

public class Singleton {
    private static Singleton instance;
    
    private Singleton() {}
    
    public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}

2. 工厂模式（Factory Pattern）：

public interface Shape {
    void draw();
}

public class Circle implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a circle");
    }
}

public class Rectangle implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a rectangle");
    }
}

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;
    }
}

3. 观察者模式（Observer Pattern）：

public interface Observer {
    void update();
}

public class ConcreteObserver implements Observer {
    @Override
    public void update() {
        System.out.println("Observer is updated");
    }
}

public interface Subject {
    void attach(Observer observer);
    void detach(Observer observer);
    void notifyObservers();
}

public class ConcreteSubject implements Subject {
    private List<Observer> observers = new ArrayList<>();
    
    @Override
    public void attach(Observer observer) {
        observers.add(observer);
    }
    
    @Override
    public void detach(Observer observer) {
        observers.remove(observer);
    }
    
    @Override
    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update();
        }
    }
}

这些是常见的设计模式的代码样例，每个设计模式都有不同的用途和实现方式，可以根据具体的需求选择适合的设计模式来解决问题。
#### 引用[.reference_title]
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