40. Proxy

• Problem to solve:

  • Consider an object representing expensive resource that is impossible to duplicate:

    • network connection

    • large object in memory, such as a "result set" of the database query

    • an open file

  • How could we emulate "multiple copies" of these complex and unique objects?

• Solution:

  • A proxy class represents indirect reference to the object with concrete services.

    • (The underlying concrete object is often referred to as a subject.)

  • The proxy controls indirect access to another object, while exposing the same interface.