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Transcript

  • 1. Proxy
  • 2.  
  • 3. Proxy
    • Category
      • Structural
    • Intent
      • Provide a surrogate or placeholder for another object to control access to it
    • Also known as
      • Surrogate
  • 4. Proxy Pattern Motivation
  • 5. Proxy Applicability
      • A remote proxy provides a local representative for an object in a different address space
      • A virtual proxy creates expensive objects on demand
      • A protection proxy controls access to the original object, in order to enforce access rights
      • A smart reference is a replacement for a bare pointer that performs additional actions when an object is accessed
  • 6. Proxy Pattern Structure
  • 7. Proxy Pattern Participants
    • Proxy (ImageProxy)
      • maintains a reference that lets the proxy access the real subject
      • provides an interface identical to Subject’s so that a proxy can be substituted for the real subject
      • controls access to the real subject and may be responsible for creating and deleting it
  • 8. Proxy Participants (continued)
    • Subject (Graphic)
      • defines the common interface for RealSubject and Proxy so that a Proxy can be used anywhere a RealSubject is expected
    • RealSubject (Image)
      • defines the real object that the proxy represents
  • 9. Proxy Consequences
    • Consequences
      • A remote proxy can hide the fact that an object resides in a different address space
      • A virtual proxy can perform optimizations such as creating an object on demand
      • Both protection proxies and smart references allow additional housekeeping tasks when an object is accessed