ITEC 320 Lecture 12 Higher level usage of pointers

Pointers Review Linked list –Pointer usage –Package design

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 Cell phones How do they work (communication side)

Pointers Cell Networks

Pointers Other scenarios Computer networks Google maps Facebook friends Gaming

Pointers Rationale How do you model a cell phone network on a computer? Why would you want to simulate a cell phone network?

Pointers Graphs Composed of vertices and edges Vertices –Represent an object in a graph Edges –A connection between two vertices

Pointers Variations Weighted graph –Toll road –Hotel cost –Identifiers Possible usage scenarios?

Pointers Methods of implementation Arrays Pointers Benefits of each approach Downsides of each approach

Pointers Code Should we use a package? What about generics?

Pointers Searching How do you find information in a graph? Destination Start

Pointers Breadth first For each node I am connected to –Is this the node I’m looking for? If I didn’t find it –For each node I am connected to Call breadth first search on it

Pointers Depth first If I am the node searched for, stop and return For each node I am connected to –Call depth first search on that node

Pointers Issues What are some of the issues that might happen with searching? How do you implement each way? –Stacks / Recursion / Packages / ?

Pointers More How do you pick the best path? –Lowest cost –Highest cost –Cover all points with least overlap

Pointers Summary Rationale for graph theory Approach Finding algorithms

Pointers Summary Memory usage at a higher level