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Lecture 39: When to Use A Proxy

Computer Science 313 – Advanced Programming Topics. Lecture 39: When to Use A Proxy. Why Do We Use Proxy Pattern?. Discussed word proxy in Wednesday's lecture When and why would we ever use a proxy?. Real-World Uses of Proxy. Real-World Uses of Proxy. Real-World Uses of Proxy.

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Lecture 39: When to Use A Proxy

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  1. Computer Science 313 – Advanced Programming Topics Lecture 39:When to Use A Proxy

  2. Why Do We Use Proxy Pattern? • Discussed word proxy in Wednesday's lecture • When and why would we ever use a proxy?

  3. Real-World Uses of Proxy

  4. Real-World Uses of Proxy

  5. Real-World Uses of Proxy

  6. Real-World Uses of Proxy

  7. Why We Use Proxy • Add level of indirection before real subject • Continue actions, but protect subject from harm • Create plausible deniability – "But it wasn't me!" • Get tasks done, but eliminate need to be local • Improve performance by using saved results • Same design needs met using Proxy Pattern • In all cases, proxy appears identical to real subject • Proxy acts first then lets subject do the real work • Real subject stays hidden – client does not know

  8. Proxy versus… Adapter Proxy Pattern Adapter Pattern

  9. Proxy versus… Adapter Proxy Pattern Adapter Pattern • Client only knows of Proxy • Uses interface client needs • Subject does all work • Interface identical to the real subjects • Does not change each calls' parameters & return value • Cannot access real subject • Client only knows of Adapter • Uses interface client needs • Adaptee(s) does all work • Interface differs with that of adaptee(s) • Modifies, adds or removes parameters & return value • Can access real subject

  10. Proxy versus… Composite Proxy Pattern Composite Pattern

  11. Proxy versus… Composite Proxy Pattern Composite Pattern • Structural pattern • Common interface defined • One of GoF's patterns • Only one subject used • Proxy acts as a gatekeeper • Structural pattern • Common interface defined • One of GoF's patterns • Many leaves can be used • Composite collects leaves

  12. Proxy versus… Decorator Proxy Pattern Decorator Pattern

  13. Proxy versus… Decorator Proxy Pattern Decorator Pattern • Client thinks it has subject • Hides subject from others • Proxy can intercept call • One proxy per pattern • Does not add or modify basic functionality • Client thinks has concept • Hides concept from others • Decorator can intercept call • Many decorators per pattern • Adds or modifies concept's basic functionality

  14. Proxy versus… Observer Proxy Pattern Observer Pattern

  15. Proxy versus… Observer Proxy Pattern Observer Pattern

  16. For Next Class • Last lab due “Friday”; submit until final exam time • Start now == more committing acts involving carrots • Finish reading on our last design pattern • Lots of interesting code on Wednesday • Will be presenting many cool & useful hacks • Follow the white rabbit – they have tricks & carrots ----------censored----------

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