CS 340 Data Structures

1. CS 340 Data Structures Instructor: Xenia Mountrouidou

2. Course Objectives • At the end of this class you will be able to: • Make design decisions on which data structure is best to use regarding • performance, • memory, and • implementation efficiency. • Devise or use the most efficient algorithm in your projects. • Understand algorithmic complexity. • Think analytically and identify complexity of a program.

3. Course Objectives (cont.) • At the end of this class you will be able to: • Apply object oriented programming principles when you develop software. • Use and understand third party code. • Detect inefficiency of data structures and algorithms of third party code. • Develop projects using agile test driven approach (Junit). • Employ the Java API. CS 340

4. Why do you need CS 340? • Scenario: • You are a senior developer for e-bay. • You are working on their e-commerce application server! • You drop code, you are a java guru, OO programming is second nature to you… but you do not understand data structures and algorithms. • BIG DEAL! Everything runs perfectly. Until one day… • You need to use a sorting algorithm to sort all potential sellers of a product based in price or ranking. CS 340

5. Why do you need CS 340? • Scenario (cont.): • On every click for a product search, your sorting algorithm will be used. • You choose bubble sort. After all, it has a cool name! • Let’s see what happens: • http://www.cs.bu.edu/teaching/alg/sort/demo Software is not just coding… It is design, performance, memory consumption It is an art, a riddle to be solved with every project CS 340

6. Lectures • We meet at 15:00-16:45, every Tues/Thurs, at Merritt Penticoff Science Bld, Room 130 • Attendance will have a part in your grade. • Attendance means: active participation! • Check the schedule in our webpage • Reading and examples will be posted online. • Check the webpage for news frequently. CS 340

7. How to get help • Join my office hours! • Join the conversation on Piazza. • Check our website frequently. • Use the textbook: • “Data Structures: Abstraction and Design Using Java”, Second Edition by Elliot B. Koffman, Paul A. T. Wolfgang • Experiment with code. It’s fun… CS 340

8. Grading • Homework and Programming projects will be posted online CS 340

9. Programming Projects • They involve • Design • Coding • Testing • Debugging • Some of these can be done in pairs • Both team members will need to answer detailed questions about the implementation • Each team member will evaluate his/her team mate CS 340

10. Principles of Pair Programming CS 340

11. Principles of Pair Programming • All I Really Need to Know about pair programming I Learned in Kindergarten • Share everything. • Play fair. • Don’t hit people. • Put things back where you found them. • Clean up your own mess. • Don’t take things that aren’t yours. • Say you’re sorry when you hurt somebody. CS 340

12. Principles of Pair Programming • Wash your hands before you eat. • Flush. • Warm cookies and cold milk are good for you. • Live a balanced life – learn some and think some and draw and paint and sing and • Dance and play and work every day some. • Take a nap every afternoon. • When you go out into the world, watch out for traffic, hold hands and stick together. • Be aware of wonder. CS 340

13. Policies • Read the collaboration policy carefully. • Late policy: • 1st day late: 10% off • 10% is reduced by every day the homework is late CS 340

14. Java… a bit of history CS 340

15. Java timeline • http://www.youtube.com/watch?v=WAy9mgEYb6o CS 340

16. Java Design Goals • Simple, object oriented, and familiar • Robust and secure • Architecture neutral and portable • High performance • Interpreted, threaded, and dynamic CS 340

17. Java abbreviations • JDK: Java Development Kit • JSDK: Java Servlet Development Kit • JVM: Java Virtual Machine • J2EE: Java Platform, Enterprise Edition. Awidely used platform for server programming. CS 340

18. OOP or… Object Oriented Programming CS 340

19. Object-Oriented Programming • Object-oriented programming (OOP) is popular because: • enables reuse of previous code • saves time • If a new class is similar to an existing class, the existing class can be extended • This is called inheritance CS 340

20. Java is object oriented • Old programming languages: • code was executed line by line and accessed variables or records • Java • objectsthat come with their own methods • When coding in Java one is always thinking about “which object is running this code?” CS 340

21. Inheritance • Meat is a Food • Meat has all the data fields and methods defined by Food • Food is the superclass of Meat • Meat is a subclass of Food • Meat may define other variables and methods that are not contained in Food Food expirationDate() Meat percentageOfProtein() CS 340

22. A Superclass and Subclass Example • Robot • A robot has a • manufacturer • processor • disk • parts • processor speed Write the robot class CS 340

23. A Superclass and Subclass Example (cont.) • Robot • A robot has a • manufacturer • processor • disk • parts • processor speed Robot String manufacturer String processor intdiskSize intnumberOfParts double processorSpeed CS 340

24. A Superclass and Subclass Example (cont.) Robot String manufacturer String processor intdiskSize intnumberOfParts double processorSpeed intgetDiskSize() double getProcessorSpeed() intgetParts() String toString() CS 340

25. A Superclass and Subclass Example (cont.) • Cylon • A Cylon has all the properties of Robot, • manufacturer • processor • disk • parts • processor speed • plus, • vision (pixels) • hands (battle speed) What is a Cylon class? CS 340

26. A Superclass and Subclass Example (cont.) Robot String manufacturer String processor intdiskSize intnumberOfParts double processorSpeed Cylon double pixels double battleSpeed intgetDiskSize() double getProcessorSpeed() intgetParts() String toString() CS 340

27. A Superclass and Subclass Example (cont.) • The constructor of a subclass begins by initializing the data fields inherited from the superclass(es) super(man, proc, parts, disk, procSpeed); which invokes the superclass constructor with thesignature Robot(String man, String processor, int parts, int disk, double procSpeed) CS 340

28. A Superclass and Subclass Example (cont.) /** Class that represents a robot */ public class Robot { private String manufacturer; private String processor; private intnumParts; private intdiskSize; private double processorSpeed; public Robot(String man, String processor, intnumParts, int disk, double procSpeed) { //constructor manufactuer = man; this.processor = processor; this.numParts = numParts; diskSize = disk; processorSpeed = procSpeed; } } Write the methods’ code

29. A Superclass and Subclass Example (cont.) public double getProcessorSpeed() { return processorSpeed; } public intgetDiskSize() { return diskSize; } public intgetParts() { return numParts; } public String toString() { String result = "Manufacturer: " + manufacturer + "\nCPU: " + processor + "\nBody parts: " + numParts + "\nDisk: " + diskSize + " gigabytes" + "\nProcessor speed: " + processorSpeed + " gigahertz"; return result; } } CS 340

30. A Superclass and Subclass Example (cont.) public class Cylon extends Robot { private double pixels; private double battleSpeed; public Cylon(String man, String processor, int parts, int disk, double procSpeed, double pix, double bSpeed) { super(man, proc, parts, disk, procSpeed); pixels = pix; battleSpeed= bSpeed; } } CS 340

31. Protected Visibility for Superclass Data Fields • Variables with private visibility (defined by the keyword private) cannot be accessed by a subclass • Variables with protected visibility (defined by the keyword protected) are accessible by any subclass or any class in the same package • By default variables are public, i.e., they can be accessed by any package CS 340

32. Is-a versus Has-a Relationships • In an is-a or inheritance relationship, one class is a subclass of the other class • In a has-a or aggregation relationship, one class has the other class as an attribute CS 340

33. Is-a versus Has-a Relationships (cont.) public class Robot { private Memory mem; ... } public class Memory { private int size; private int speed; private String kind; ... } A Robot has only one Memory But a Robot is not a Memory (i.e. not an is-a relationship) If a Cylonextends Robot,thenthe Cylonis-aRobot CS 340