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ITEC 320. Lecture 12 Higher level usage of pointers. Review. Linked list Pointer usage Package design. Problems. What are the major problems with pointers?. Reference counting. Each object has to be uniquely tracked in a system The number of pointers to that object is also counted
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ITEC 320 Lecture 12 Higher level usage of pointers
Review • Linked list • Pointer usage • Package design
Problems • What are the major problems with 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?
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
Factories • In your words, what are they?
Approaches • 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?
Advantages/Disadvantages • Why use factories? • What do they mean for your code? • Benefits • Downsides
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
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
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?
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
Command pattern • Signals when an action needs to be performed Command Central Contains pointers to objects Contains list of commands Told to execute X, it actually does it
Cell phones • How do they work (communication side)
Other scenarios • Computer networks • Google maps • Facebook friends • Gaming
Rationale • How do you model a cell phone network on a computer? • Why would you want to simulate a cell phone network?
Graphs • Composed of vertices and edges • Vertices • Represent an object in a graph • Edges • A connection between two vertices
Variations • Weighted graph • Toll road • Hotel cost • Identifiers • Possible usage scenarios?
Methods of implementation • Arrays • Pointers • Benefits of each approach • Downsides of each approach
Code • Should we use a package? • What about generics?
Searching • How do you find information in a graph? Start Destination
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
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
Issues • What are some of the issues that might happen with searching? • How do you implement each way? • Stacks / Recursion / Packages / ?
More • How do you pick the best path? • Lowest cost • Highest cost • Cover all points with least overlap
Summary • Rationale for graph theory • Approach • Finding algorithms
Summary • Memory usage at a higher level