CS 180 Problem Solving and Object Oriented Programming Fall 2011

Transcription

1 CS 180 Problem Solving and Object Oriented Programming Fall 2011 hlp:// Notes for Week 2: August 29- September 2, 2011 Aditya Mathur Department of Computer Science Purdue University West LafayeLe, IN, USA

2 Readings and Self- help Exercises for Week 2 Readings: Chapter 2: 2.1, 2.2, 2.3, 2.4 Self help exercises (not to be turned in): 2.1, 2.2, 2.3, 2.4, 2.7, 2.9, 2.12,

3 About Homework All homework problems will be assigned during recitazon. Please make sure you alend your recitazon seczon. Homework assigned during week X is due at the start of your recitazon during week X+1. It is best to use Piazza to ask queszons regarding homework. But please do not post answers to homework problems. Most, but not necessarily all, homework problems will be from the textbook. 3

4 Lab for Week 2 Play with Java programs: IntroducZon to Android- based smart phone IntroducZon to the Finch robot 4

5 Feedback for Week 1 5

6 Q1. I understand the difference between sequenzal soluzon and Concurrent soluzon. (a) Yes (b) No (c) Not sure (d) Missed week 1 lecture (s) 6

7 Q2. I understand the difference between Data Parallelism and Task parallelism. (a) Yes (b) No (c) Not sure (d) Missed week 1 lecture(s) 7

8 DissecZng a Java Program: Preliminaries 8

9 The edit, compile, execute cycle.java file(s) Edit a Java program.class file(s) (byte code) Compile your program No syntax error Execute your program Correct program Syntax Error Run Zme Error or Incorrect Output In CS 180 we shall use DrJava for edizng, compiling and execuzon. DrJava is an Integrated Development Environment also known as an IDE. Eclipse, JBuilder, and IntelliJ IDEA are a few other Java IDEs. For programming the RidgeSoi robot we shall use RoboJDE. 9

10 Classes and Objects Set of real or virtual objects Represent Template in Java Create Objects created Class Animal animal Class Car momscar car student flower Class Student amanda dog Class Flower bruschela Class Dog ziggy 10

11 Classes and Objects Class: Contains alributes and operazons related to some real or virtual object. This object could be abstract or concrete [e.g., a Dog or a Golden Retriever]. Object: Created from a class. Contains specialized properzes (alributes) and operazons related to a more specific real or virtual object, e.g., object mydog created from class Dog has breed as a property that might be different from another object marysdog created from the same class. 11

12 Java program: Structure Package [Contains one or more classes] Class [Data and zero or more methods] Data (alributes) Method Data and statements At least one class must have a method named main(). Data represents properzes of a real, virtual or a Java object. E.g., breed, age, color Methods are operazons that can be performed on an object created from a class. E.g., run(), sit(), down (), no(), goodboy() 12

13 Java program: Classes and Objects class Automobile Data Method make model Data and statements create camry create mazdarx7 Objects derived from Class Automobile make model maxspeed start() make model maxspeed start() 13

14 Elements of a SequenZal Java Program For praczce (try later): Programs to be dissected: Program 2.6 ScannerExample.java Chapter 2 pages Program 2.7 BouncingBall.java in Chapter 2 pages Strategy: Go through this program line by line and alempt to understand the meaning of each line. It is likely this exercise will generate more queszons than answers. 14

15 Elements of a Concurrent Java Program For praczce (try later): Program to be dissected: Program 2.8 AreaMeasuringRobot.java in Chapter 2 pages Strategy: Go through this program line by line and alempt to understand the meaning of each line. It is likely this exercise will generate more queszons than answers. 15

16 Announcements Feast with faculty tonight: 6:30pm in Ford Dining Hall, room on the second floor. Lab makeup policy at the course web site. This week s recitazon: you will learn about the Scanner class and how to map a problem to a Java program. Make sure you alend! Project 1 descripzon will be released via the Schedule page of the course site on Sunday (a day before the announced date). Is Java a pure OO language:? Use Google to find an answer. 16

17 Binary numbers and FloaZng point representazon I hate floazng point and IEEE format!! Knowledge useful in CS 240, CS 314, and several other classes. WriZng programs for engine control, satellite control, aircrai design, integrazon, etc. etc. Understanding why the results of a computazon are not what you expected. 17

18 Types Set of values Set of OperaZons x a b c 18

19 PrimiZve types: int, long Set of integers Set of OperaZons * / % Integer.MAX_VALUE: Integer.MIN_VALUE: Long.MAX_VALUE: Long.MIN_VALUE:

20 PrimiZve types: float, double Set of real numbers Set of OperaZons (sample) Infinity E4 - Infinity + - * == > >= NaN Float.MAX_VALUE: e+38 Float.MIN_VALUE: e- 45 Double.MAX_VALUE: e+308 Double.MIN_VALUE: e

21 PrimiZve types: boolean Set of logical values Set of OperaZons (sample) true false ==!= && 21

22 PrimiZve types: char Set of characters (sample values shown) Set of OperaZons (sample) a & $ ==!= && + 22

23 Operators: ArithmeZc, relazonal, condizonal ArithmeZc operators + - * / % RelaZonal operators == < > <= >=!= Boolean/condiZonal operators && a+b*c- d a/b c%d a==b a<=b a!=b a==b c<d a<=b&&c>d a!=b &&c>d p+1<q 23

24 Operators: bitwise Bitwise operators &: bitwise AND : bitwise OR ^: bitwise exclusive OR ~: bitwise complement Bitwise shii operators <<: bitwise lei shii >>: bitwise right shii >>>: unsigned right shii a & b: logical and of a and b a b: logical OR of a and b a <<3: shii bit palern of a lei by 3 bits a>>2: shii bit palern of a to the right by 2 bits 24

25 Names Used to denote classes, objects, data Contain characters; must start with a leler, or a $ sign or an underscore. Examples: height, area1, Dog, $great Length unlimited, case sensizve. Dog and dog are different names. ConvenZon: All class names begin with an uppercase leler; all other names begin with a lower case leler. 25

26 Constants A constant is something that cannot change during program execuzon. Examples: Integer constants: 0, 1, - 1, +24, 29, , O14, 0x1B FloaZng point constants: 0.0, e28, Boolean constants: true, false Character constants:, a, A, $ String constants:,, Hi!, Alice in Wonderland 26

27 Named Constants A constant can be named and the name used instead of the constant itself. Examples: final float pi= ; final boolean dogsexist=true; 27

28 Variables A variable is something whose value may change during program execuzon. Example: int numstudents; denotes the number of students whose grads have been processed. Its value changes as each student s grade is processed by a grade processing program. Every variable has a name and a type. Example: int hurricanecategory; The name is hurricanecategory and its type is int. Every variable must be declared before it is used. 28

29 Strings: basics A string is any sequence of Unicode characters You may name a string as in the following: String mydogsname; mydogsname is an object of type String. It can take any string as its value. For example, Max, Bently, Jake and Raja are possible values of mydogsname. What is the difference between 29 and 29? 29

30 Strings: assignment You may assign a value to a string object. mydogsname= Bently ; // Assuming that mydogsname has been declared String mycarcolor= Black ; All string objects must be declared before they are used. Thus it would be incorrect to assign a value to mydogsname before it has been declared. 30

31 Strings: Other operazons You may apply a variety of operazons to strings. Examples follow. String commend= Bently, + good girl!; // String catenazon String mycar= It s a Porsche +, and I love it! + but maintenance is expensive. // String catenazon String firstchar=commend.charat(0); // Extract character at posizon 0 31

32 Strings: More operazons There exist a variety of operazons on strings. A few are given below. Statement String commend= Bently, + good girl! ; char firstchar=commend.charat(0); moviename.equals( FugiZve ) Opera+on used CatenaZon Character extraczon using charat() Comparison using equals() String.valueOf(29) Conversion integer 29 to String 29 32

33 DeclaraZons int age; float height, area; String name boolean iamalive; int x=1, y=0; String firstname= Harry ; 33

34 Simple expressions Expressions are used to compute something. float x, y, z; // Declare x, y, z as variables of type float x*y+z; // ArithmeZc expression, results in float value x<y; // Boolean expression, results in boolean value String firstname= Mary, lastname= Jones ; firstname+ +lastname; // Results in a String More in Chapter 2! And yet more to come! 34

35 Assignment statement An assignment statement allows assigning the value of an expression to a variable. float p=x*y+z; // p gets the value of x*y+z boolean q=x<y; // q gets the value of x<y String firstname= Mary, lastname= Jones ; String name= firstname+ +lastname; More in Chapter 2! And yet more to come! 35

36 Back to classes and objects 36

37 CreaZng an object: Mom s car new Car ( Yellow, Mom, 200); public class Car{ String color; String owner; int miles; String color= Yellow ; String owner= Mom ; int miles=200; public int getmiles(){ } 37

38 CreaZng an object: Dad s car new Car ( Black, Dad, ); public class Car{ String color; String owner; int miles; String color= Black ; String owner= Dad ; int miles=200000; public int getmiles(){ } 38

39 CreaZng an object: Instance variables public class Car{ String color; String owner; int miles; Instance variables are copied into the new object. Each object has its own values for these variables. Thus, two objects of the same type have their own copies of instance variables. public int getmiles(){ } 39

40 CreaZng an object: get and set instance variables public class Car{ String color; String owner; int miles; public int getmiles(){ return miles; } public void setmiles(int m ){ miles=m; } Get the value of miles from the object. int dadscarmiles=dadscar.getmiles(); Set the value of miles in an object. momscar.setmiles(300); 40

41 Classes and Objects: Summary Class: Object: Instance variables: Template to create objects. Created from a class; may denote a real world or an abstract object; Inherits all instance variables and methods. Variables that become local to an object. get and set methods Used for geƒng data from and into an object. Constructor Used for creazng objects. 41

42 Week 2: August 29- September 2, 2011 Hope you enjoyed this week! QuesZons? Contact your recitazon instructor. Make full use of our office hours. 42