装饰器未实现修饰的接口

Question

I have my small project where I wrapped object of one class with another class. Decorated class implements one interface but Decorator class does not implement it. I am curious whether it is still decorator pattern or some other pattern and "Decorator" class should be called Wrapper instead of Decorator in my project.

I have checked iluwatar github repository ( https://github.com/iluwatar/java-design-patterns/tree/master/decorator/src/main/java/com/iluwatar/decorator ) and tutorialspoint ( https://www.tutorialspoint.com/design_pattern/decorator_pattern ). For example in iluwatar there is: Decorator:

public class ClubbedTroll implements Troll

Decorated:

public class SimpleTroll implements Troll

In both cases (iluwatar and tutorialspoint) there is common interface implementation in decorator and decorated class. Does it mean it is mandatory to call it decorator design pattern?

Answer 1

I'd say if you don't implement the interface in your decorator, then it simply cannot act like the original thing (decorated). If you're implementing the interface, you can use the decorator everywhere you could have done it with the original interface if classes. That's why you have to use the interface.

If you just wrap the decorated, you've got a wrapper (delegation pattern).

Answer 2

The essense of Decrator pattern is to add additional functionality to an object without extending it. The key word is additional , which means that the public API (or interface) of the object still stays the same. Without this concept there's no point of using Decorator.

So the question actually is "Does an object still provide the same public API without implementing an interface ?"

IMHO, it could be possible in some other language, but in Java it makes no sense, since you can not guarantee an object has the same public API and, therefore, rely on it.

As to Wrapper - this is another name for Adapter pattern .