1、定义一个接口Component

public interface Component {  void operation();  
}

2、创建一个实现了Component接口的简单类SimpleComponent

public class SimpleComponent implements Component {  @Override  public void operation() {  System.out.println("SimpleComponent operation.");  }  
}

3、创建一个装饰器基类Decorator，它也实现了Component接口，并持有一个对Component对象的引用

public abstract class Decorator implements Component {  protected Component component;  public Decorator(Component component) {  this.component = component;  }  @Override  public void operation() {  if (component != null) {  component.operation();  }  }  
}

4、创建一个具体的装饰器类，例如ConcreteDecoratorA，它添加了一些额外的功能

public class ConcreteDecoratorA extends Decorator {  public ConcreteDecoratorA(Component component) {  super(component);  }  @Override  public void operation() {  super.operation(); // 调用被装饰对象的operation方法  addedFunctionA(); // 添加额外的功能A  }  private void addedFunctionA() {  System.out.println("ConcreteDecoratorA added function.");  }  
}

5、编写一个测试类来展示如何使用装饰器

public class DecoratorPatternDemo {  public static void main(String[] args) {  // 创建一个简单组件  Component simpleComponent = new SimpleComponent();  // 使用装饰器A装饰简单组件  Component decoratedComponent = new ConcreteDecoratorA(simpleComponent);  // 调用被装饰后的组件的operation方法  decoratedComponent.operation();  }  
}