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  • 1. S.Ducasse 1 QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture. Stéphane Ducasse Stephane.Ducasse@univ-savoie.fr http://www.listic.univ-savoie.fr/~ducasse/ Proxy
  • 2. S.Ducasse 2 License: CC-Attribution-ShareAlike 2.0 http://creativecommons.org/licenses/by-sa/2.0/
  • 3. S.Ducasse 3 Proxy • Category • Structural • Intent • Provide a surrogate or placeholder for another object to control access to it • Also known as • Surrogate
  • 4. S.Ducasse 4 Proxy Pattern Motivation
  • 5. S.Ducasse 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. S.Ducasse 6 Proxy Pattern Structure
  • 7. S.Ducasse 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. S.Ducasse 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. S.Ducasse 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
  • 10. S.Ducasse 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