How does "Proxy" differ from "Decorator"?

Design PatternsMiddle~1 min read

Proxy and Decorator look similar on the surface - both "wrap" an object and implement the same interface. But their goals and purposes differ.

1. Purpose

Proxy controls access to an object. → decides when, how, and whether the real object can be called.
Decorator extends the behavior of an object. → adds new functionality on top of the existing one.

2. Context of Use

Situation	Proxy	Decorator
The object is heavy or remote	Lazy loading, cache	Not intended for this
Need to add new behavior (logging, encryption)	Possible, but not the main goal	The main goal
Access control / security	Yes	No
The client should think it is working with the "real object"	Mandatory	Not always

3. An Example of the Difference

Proxy (access control):

java

class SecuredFileProxy implements FileAccess {
    private RealFile realFile;
    private String userRole;

    public void read() {
        if (userRole.equals("admin")) realFile.read();
        else System.out.println("Access denied");
    }
}

Decorator (behavior extension):

java

class LoggingFileDecorator implements FileAccess {
    private FileAccess wrappee;
    public void read() {
        System.out.println("Reading file...");
        wrappee.read();
    }
}

4. Transparency

Proxy aims to be unnoticeable: the client should not know it is working with an intermediary.
Decorator is a deliberate wrapper: the client knows that new behavior has been added.

5. Analogy

Proxy is like a guard at the door, deciding who gets in.
Decorator is like a designer, decorating a room without changing its foundation.

Conclusion

Criterion	Proxy	Decorator
Main purpose	Access control	Behavior extension
Transparency for the client	Full	Partial
Type of behavior	Controlling	Additive
Example	Lazy loading, protection, cache	Logging, encryption, formatting

Summary: Proxy protects or controls, Decorator adds and decorates.

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How does "Proxy" differ from "Decorator"?

#1. Purpose

#2. Context of Use

#3. An Example of the Difference

#4. Transparency

#5. Analogy

#Conclusion