ITEC 320 Lecture 19 Higher level usage of pointers

Pointers Review Linked list –Pointer usage –Package design HW 1 –Write a doubly linked list that has insert before / after and delete methods –Code will be posted by tomorrow –Due next Monday at 10PM

Pointers Problems What are the major problems with pointers?

Pointers Reference counting Each object has to be uniquely tracked in a system The number of pointers to that object is also counted Whenever a pointer is disposed, the reference count is decreased What happens when it reaches 0? What problem does this resolve?

Pointers Smart pointers Contain regular pointers Also contain number of other pointers that are pointing to the object Or do they… –What if an object contains the number of pointers to itself? –Benefits / downsides Designs for this

Pointers Factories In your words, what are they?

Pointers Approache s Function that returns an object Function that takes an object and returns a pointer Function that takes an id and returns a pointer to it Hash map for memory addresses and # of accesses Others?

Pointers Advantages/ Disadvantage s Why use factories? What do they mean for your code? Benefits Downsides

Pointers Flyweight What does the word bring to mind? One object / pointer reused lots and lots of times Similar to NULL except it is a type / pointer What reasons do you think you would use a flyweight object? Benefits / Downsides

Pointers Disk buffer How many GB does a DVD hold? 3 DVD game How does that game load everything into RAM? Or does it load everything into RAM? Memory Mapping to HD idea

Pointers How it works Several blocks of data reserved in memory Each block maps to a unique block on a HD Data is requested, it is loaded from HD –If it is in list, use it, move to MRU position –If it isn’t, load into least recently used block and move it to the MRU position –Linked list of blocks?

Pointers What it enables

Pointers Design patterns Not language specific features Encompasses a particular idea May or may not be heavily supported in a language –Java supports smart pointers by default –C++ requires a separate class Not a silver bullet

Pointers Command pattern Signals when an action needs to be performed Command Central Command Central Contains pointers to objects Contains list of commands Told to execute X, it actually does it

Pointers Summary Memory usage at a higher level