CSE 113 Introduction to Computer Programming

1. CSE 113Introduction toComputer Programming Lecture slides for Week 7 Monday, October 10th, 2011 Instructor: Scott Settembre

2. Section 1 Course Administration University at Buffalo: CSE 113 Instructor: Scott Settembre

3. For Project Assistance • You can find the up-to-date hours and locations in the “Contact” section of UBLearns. • Here are the names, emails, and office hours as of 10/10/2011: (Also come to additional labs if you need help) University at Buffalo: CSE 113 Instructor: Scott Settembre

4. You are behind the class if… • If you have not: • completed chapter 1-5, then you are behind the rest of the class. • made significant progress on your project, then you are behind the rest of the class. • experienced how to construct an “if” statement or a “while” statement, then you are going to have problems on the test. • Please do the following: • Complete chapter 1-5 in Bell 101. • Finish your project by Friday. University at Buffalo: CSE 113 Instructor: Scott Settembre

5. Lecture and Lab this Week • Lectures will go over the following: • Chapter 6 concepts • Abstract classes • Overloading method names • The keyword “this” – referring to the current object • Shared variables – use of the keyword “static” • Constants – use of the keyword “final” • Lab will have you do the following: • Finish completely chapters 1-5 if you haven’t • Finish your Project 1 • Begin chapter 6 up to and including 6.4 • Lab Quiz on chapters 1-5 (not 6) University at Buffalo: CSE 113 Instructor: Scott Settembre

6. Section 2 Midterm / Final exam / Project University at Buffalo: CSE 113 Instructor: Scott Settembre

7. Midterm exam (15%) • The midterm exam will be held in lecture on October 21st. • It will cover chapters 1-6.4, including the exercises in the chapter that you do in lab. • It will be a series of true/false, multiple choice, and code examination (running the code in your head), similar to the quizzes that you will have taken. University at Buffalo: CSE 113 Instructor: Scott Settembre

8. Final Exam (25%) • The final exam will be during class during the last week of class. • It may span two days (I may give half on one day and half the next day). • It will consist of questions like the quizzes, as well as some code reading and understanding. • More on this in November. University at Buffalo: CSE 113 Instructor: Scott Settembre

9. Project 1 • Due date: October 14th, 2011 at or before 11:59:59 PM • Get’r done! • Submit appropriately, using the steps outlined in the Course Documents – Submission Steps .pdf file. University at Buffalo: CSE 113 Instructor: Scott Settembre

10. Section 3 Chapter 6 University at Buffalo: CSE 113 Instructor: Scott Settembre

11. The “double” type • A “double” type is declared like so: doublepi; // pi is declared as a floating point number pi = 3.14159; // pi now equals 3.14159 • It can be a value that ranges between a negative and positive range of numbers. • Typically, it is any 7 place decimal number between -1038 and +1038. • You can set its initial value when you declare it: doublepi = 3.14159; // pi declared & set to 3.14159 University at Buffalo: CSE 113 Instructor: Scott Settembre

12. What is an “abstract” class? • A class that you cannot make an instance (i.e. an object) from. • Why? • Well, the code acts more like an “outline” or a summary, but has no real substance. • It is meant to get you started with your sub-class, providing you with some code, some method names, and some instance variables. University at Buffalo: CSE 113 Instructor: Scott Settembre

13. The abstract keyword • You can always tell if a class is an abstract class, by looking at the class signature: import greenfoot.*; // (World, Actor, GreenfootImage, and Greenfoot) /** * A variation of an actor that maintains precise location (using doubles for the co-ordinates * instead of ints). It also maintains a current movement in form of a movement vector. * * @author PoulHenriksen * @author Michael Kolling */ public abstract class SmoothMoverextends Actor { private Vector movement; private double exactX; private double exactY; publicSmoothMover() … This abstract keyword indicates that this class can only be a super-class of other classes, it cannot be instanced into an object. University at Buffalo: CSE 113 Instructor: Scott Settembre

14. Abstract class example Abstract class. Code from this class can only be used from a subclass. Actor Vehicle Car Boat Bicycle University at Buffalo: CSE 113 Instructor: Scott Settembre

15. Why can’t you make an instanceout of “Vehicle” then? • Well, if you look at the “vehicle” code, you will probably not find anything specific about a specific type of vehicle. • Instead, you will find generic methods and instance variables like “move”, “wheels”, or “getPassengerList”. • Creating an object out of that, may not make any sense because you can’t ask the object to “do” anything. University at Buffalo: CSE 113 Instructor: Scott Settembre

16. Let’s look at another class • The “Car” class has a constructor: public class Car extends Vehicle { private intwheels; private intcolor; public Car() { wheels = 4; // Default to 4 wheels color = 0; // Default to color ‘0’ – which == black } } This is called the “default constructor” of a class. It has no parameters in the parameter list. University at Buffalo: CSE 113 Instructor: Scott Settembre

17. What is “overloading”? • When you write two or more methods that use the SAME name, you are overloading a method. • When you “overload” a method, • You use the same name as an already defined method. • You must change the parameter list so the compiler knows which method definition to use. University at Buffalo: CSE 113 Instructor: Scott Settembre

18. Why should we overload? • It is a useful technique, so that you can use the same code. • It allows you to “ask” or “command” the object the same thing, in different ways. University at Buffalo: CSE 113 Instructor: Scott Settembre

19. Overloading example public class Car extends Vehicle { private intwheels; private intcolor; public Car() { wheels = 4; // Default to 4 wheels color = 0; // Default to color ‘0’ } public Car ( intinitialColor ) { wheels = 4; color = initialColor; } } Notice that the method has the same name, but the parameter list is different. This means, you can initialize the car two different ways: either by giving no information to the constructor, or by giving color information to the constructor. University at Buffalo: CSE 113 Instructor: Scott Settembre

20. Let’s take a different lookat this example public class Car extends Vehicle { private intwheels; private intcolor; public Car() { wheels = 4; // Default to 4 wheels color = 0; // Default to color ‘0’ } public Car ( int color ) { wheels = 4; color = color; } } I have changed the name from “initialColor” to “color”. Now how will the compiler know which color I am referring to? The “color” from the paramter list or the private instance “color”? University at Buffalo: CSE 113 Instructor: Scott Settembre

21. The this keyword • There is a keyword called this, which allows the code to refer to the current object running. • Remember, if you have more than one object of a specific class, each object runs the SAME code, but has different instance variables. University at Buffalo: CSE 113 Instructor: Scott Settembre

22. Bunch of cars Car 1 wheels = 4 color = 0 Car 2 wheels = 4 color = 255 Car 3 wheels = 4 color = 59 All these private instance variables values exist in memory at different locations, but the constructor code exists in only one location. public Car () {…} Public Car (int color) {…} So if we are in this code here, how do we know where to put the “color” value? University at Buffalo: CSE 113 Instructor: Scott Settembre

23. Using this keyword public class Car extends Vehicle { private intwheels; private intcolor; public Car() { wheels = 4; // Default to 4 wheels color = 0; // Default to color ‘0’ } public Car ( int color ) { wheels = 4; this.color = color; // Assign color to the instance variable. } } Now how will the compiler know which color I am referring to? “this.color” refers to the current object’s instance variable, whereas the “color” is the “color” value from the parameter list of the method. University at Buffalo: CSE 113 Instructor: Scott Settembre

24. Another use of this • this can also be used to call the constructor of a class. • Yes, I know I told you that you cannot call the constructor of a class, except once at the creation of the object, but this is an exception. • You must call it from within an overloaded constructor, thus it really is a constructor calling a constructor. University at Buffalo: CSE 113 Instructor: Scott Settembre

25. Using this keywordto call a constructor public class Car extends Vehicle { private intwheels; private intcolor; public Car() { this (0); // call the Car overloaded constructor with default value for color } public Car ( int color ) { wheels = 4; // Default to 4 wheels this.color = color; // Assign color to the instance variable. } } The default constructor will now call the overloaded constructor with a default value for color. University at Buffalo: CSE 113 Instructor: Scott Settembre

26. Section 4 Preview for project 2 University at Buffalo: CSE 113 Instructor: Scott Settembre

27. Project 2 - Discussion • I’ll release the description of project 2 on Monday and I will discuss it in class. • Project 2 will further explore your programming skills, but more importantly, it will show you the power of Object Oriented Programming (OOP) • You don’t need a CS degree to work magic! University at Buffalo: CSE 113 Instructor: Scott Settembre

28. Micro-mouse Competitions • Academic based competitions to encourage autonomous robot development. • Here are some links: • Very fast final solution run: http://www.youtube.com/watch?v=eVh644Asb9o&feature=related • Shows learning phase & @4min the final solution run: http://www.youtube.com/watch?v=ZszTOpILeP0&feature=related University at Buffalo: CSE 113 Instructor: Scott Settembre

29. DARPA Grand Challenge • The DARPA Grand Challenge is a government prize-backed challenge to encourage development of autonomous vehicles. • Autonomous vehicles are vehicles that can drive on their own, WITHOUT human supervision. • This is different than Remotely Operated Vehicles (ROV), in that ROV’s have humans remotely telling the aircraft what to do. University at Buffalo: CSE 113 Instructor: Scott Settembre

30. DARPA Grand Challenge Videos • http://www.youtube.com/watch?v=-xibwwNVLgg&feature=related • @13:38 challenge rules explained • http://www.youtube.com/watch?v=lULl63ERek0 • @ :45 is hardware review, you can skip. • @1:20 is a good background explanation of what the challenge had. Good vehicle video. • http://www.youtube.com/watch?v=SQFEmR50HAk • No voiceover, pure video caps. • http://www.youtube.com/watch?v=0eMJaHQGhtQ • Team Buffalo!!! University at Buffalo: CSE 113 Instructor: Scott Settembre

31. What will you need to do? • Stay tuned and find out on Monday! University at Buffalo: CSE 113 Instructor: Scott Settembre

32. Robotic Car – Think about it Actor Robot RobotCar Sensor BumpSensor University at Buffalo: CSE 113 Instructor: Scott Settembre