Why is a decorator a structural rather than a behavioral design pattern?

Question

I consider myself an intermediate knowledge of GoF design patterns. However, I am embarrassed when it comes to classifying these patterns into structural and behavioral models. I have no confusion about the creation patterns.

From wikipedia - Decorator Pattern - in object-oriented programming, the decorator pattern is a design pattern that allows you to add behavior to a single object, statically or dynamically, without affecting the behavior of other objects from the same class.

From the above definition it is clear that we are talking about behavior, then

• Why is the decorator a structural template?
• What are the criteria for a block diagram?
• What are the criteria for behavior?

Thanks.

Answer 1

Behavioral patterns relate to communication between separate objects: things, such as an intermediary, an observer, a chain of responsibility (even a visitor, which is described as “separating the algorithm from the structure of the object on which it works”). They indicate how individual objects interact.

Structural patterns relate to layering and abstraction of layers; these are things like an adapter, bridge, and composite. Decorator is a way of creating functionality, so it comes with structural templates.

Answer 2

If you need an answer in terms of your quote: a change in behavior is associated with a modification of the structure .
That is, you "decorate" the object (through the specific structuring of your class) to achieve the desired behavior (through delegation)