Components of Proxy Design Pattern

1. Subject

The Subject is an interface or an abstract class that defines the common interface shared by the RealSubject and Proxy classes. It declares the methods that the Proxy uses to control access to the RealSubject.

• Declares the common interface for both RealSubject and Proxy.
• Usually includes the methods that the client code can invoke on the RealSubject and the Proxy.

2. RealSubject

The RealSubject is the actual object that the Proxy represents. It contains the real implementation of the business logic or the resource that the client code wants to access.

• It Implements the operations declared by the Subject interface.
• Represents the real resource or object that the Proxy controls access to.

3. Proxy

The Proxy acts as a surrogate or placeholder for the RealSubject. It controls access to the real object and may provide additional functionality such as lazy loading, access control, or logging.

• Implements the same interface as the RealSubject (Subject).
• Maintains a reference to the RealSubject.
• Controls access to the RealSubject, adding additional logic if necessary.

The Proxy Design Pattern is a structural design pattern that provides a surrogate or placeholder for another object to control access to it. This pattern is useful when you want to add an extra layer of control over access to an object. The proxy acts as an intermediary, controlling access to the real object.

A real-world example can be a cheque or credit card as a proxy for what is in our bank account. It can be used in place of cash and provides a means of accessing that cash when required.

• And that’s exactly what the Proxy pattern does – ” Controls and manages access to the object they are protecting”.
• As in the decorator pattern, proxies can be chained together. The client, and each proxy, believe it is delegating messages to the real server: