Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
883 views
in Technique[技术] by (71.8m points)

oop - Differences between Proxy and Decorator Pattern

Can you give any good explanation what is the difference between Proxy and Decorator?

The main difference I see is that when we assume that Proxy uses composition and Decorator uses aggregation then it seems to be clear that by using multiple (one or more) Decorators you can modify/ add functionalities to pre-existing instance (decorate), whereas Proxy has own inner instance of proxied class and delegates to it adding some additional features (proxy behaviour).

The question is - Does Proxy created with aggregation is still Proxy or rather Decorator? Is it allowed (by definition in GoF patterns) to create Proxy with aggregation?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

The real difference is not ownership (composition versus aggregation), but rather type-information.

A Decorator is always passed its delegatee. A Proxy might create it himself, or he might have it injected.

But a Proxy always knows the (more) specific type of the delegatee. In other words, the Proxy and its delegatee will have the same base type, but the Proxy points to some derived type. A Decorator points to its own base type. Thus, the difference is in compile-time information about the type of the delegatee.

In a dynamic language, if the delegatee is injected and happens to have the same interface, then there is no difference.

The answer to your question is "Yes".


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...