Fundamentals of Computer Science II

Transcription

1 Fundamentals of Computer Science II Keith Vertanen Museum CSCI 136: Fundamentals of Computer Science II Keith Vertanen

2 Textbook Resources Head First Java First 5 chapters are review But worth reading anyway Covers more advanced topics Exceptions File I/O Inheritance Interfaces Networking Object serialization Graphical User Interfaces (GUIs) 2

3 Where we've been Already covered most of the Java language & various class APIs primitive data types boolean expressions if-else statements switch-case for-loop while-loop do-while loop arrays, 1D, 2D static methods instance variables instance methods enumerations recursive methods Math String ArrayList Double Integer 3

4 1: More on algorithms Course topics Steps we take to solve a problem Cleverness that solves correctly and efficiently Smart algorithm + right data structure Makes the seemingly impossible possible (but still can't do everything) 4

5 Travelling salesman Travelling salesman problem (TSP) Locations of a bunch of cities Find shortest possible tour visiting each city exactly once, returning home 1000 cities optimal tour 5

6 SW Sweden Computation Log Instance Created: July 29, 2001 Number of Cities: 24,978 Optimal Value: 855,597 Solution Method: Concorde, CPlex 6.5 LP Solver, LKH Solution Time: 84.8 years, Intel Xeon 2.8 GHz 6

7 Travelling salesman Travelling salesman problem (TSP) Finding optimal tour is easy Try all combinations: exponential! This takes an enormous amount of time! Can we find optimal tour faster? Most people think the answer is no No one has proved it! 7

8 Approximate solution TSP algorithm 1 Data structure = linked list Makes it quick to insert next city anywhere in the list Algorithm = add city next to closest existing city Heuristic, not provably optimal but usually does okay File with locations of US cities. 8

9 Algorithm 1: nearest neighbor Tour distance =

10 Approximate solution TSP algorithm 2 Data structure = linked list Makes it quick to insert next city anywhere in the list Algorithm = add city wherever it causes least increase in total tour length Better heuristic, still not provably optimal File with locations of US cities. 10

11 Algorithm 2: smallest increase Tour distance =

12 Your own game AI 12

13 Your own game AI 13

14 Course topics 2: More abstract data types (ADTs) How we store and organize data in our programs "I will, in fact, claim that the difference between a bad programmer and a good one is whether he considers his code or his data structures more important. Bad programmers worry about the code. Good programmers worry about data structures and their relationships." -Linus Torvalds, creator of Linux Opens up the types of programs we can build Not everything works if shoved into an array! 14

15 Abstract Data Types Queue Stack List Set Hash Table Tree Graph int [] x = new int [7]; private class Node { private int num; private Node next; } 15

16 An ADT application: predictive keyboard % java PredictiveKeyboard 5 wiki_200k.txt % java PredictiveKeyboard 5 mobydick.txt 16

17 Training the language model Call me Ishmael. Some years ago- never mind how long preciselyhaving little or no money in my purse, and nothing particular to interest me on shore, I thought I would sail about a little and see the watery part of the world. It is a way I have of driving off the spleen and regulating the circulation. Step 1: Create a map between each unique word and an integer count. Efficient ADT for this job = map Step 2: Create a map between all prefixes of every word to the most frequent word. t the th the the the tho thought to to Efficient ADT for this job = map word count to 1 thought 1 sail 1 ago 1 and 3 the 4 little 2 prefix word t the th the the the tho thought to to 17

18 Course topics 3: More Object Oriented Programming (OOP) Inheritance Share code between related data types Similar objects can live in same bucket Interfaces Guarantee a class implements a certain API Commonly used for sorting, threading, serializing, 18

19 Course topics 4: File input/output and exceptions File I/O more flexible than standard input/output Exceptions handle unexpected problems e.g. file not found, hostname unreachable, 19

20 5: More recursion Course topics Methods calling themselves Often useful technique for solving a problem Divide-and-conquer: e.g. merge sort 20

21 Course topics 6: Threads and concurrency One program with multiple threads of execution Sometimes can help simplify program e.g. background thread to animate progress bar CPUs no longer getting faster, just more cores Use multiple cores, splitting up calculation 21

22 ns/concurrency-ddj.htm 22

23 Course topics 7: Networking and socket communication Send data between two programs On the same computer On computers next to each other On computers on different sides of the globe e.g. Building a multi-player network game 23

24 Course topics 8: Graphical User Interfaces (GUIs) Building interfaces with buttons, etc. Dealing with events Draw ourselves rather than relying on StdDraw 24

25 Course topics 9: Mobile app development Build your own Android app! Java: command-and-control XML: defines user interface 25

26 Course topics 10: Programming Languages Comparison of types: Byte code (intermediate) Compiled Interpreted C / C++ primer 26