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();  
    }  
}