Object-Based Programming. Programming with Objects

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1 ITEC1620 Object-Based Programming g Lecture 8 Programming with Objects

2 Review Sequence, Branching, Looping Primitive datatypes Mathematical operations Four-function calculator Scientific calculator Don t program the functions yourself 2

3 Math Class Java set of pre-defined mathematical functions and constants Constants (E, PI) Basic functions round, floor, ceil, min, max, abs Trigonometric functions sin, cos, tan, asin, acos, atan Exponential funcions pow, log 3

4 Functions Blocks of JAVA code that provide a specific, reusable functionality static double sqrt (double a) static double pow (double a, double b) 4

5 Functions and APIs Application Programmer Interfaces (APIs) list the available functionality of a class An API includes Constants, constructors, and methods Datatypes Argument lists with datatypes Descriptions of functionality 5

6 Constants static double PI The double value that t is closer than any other to pi, the ratio of the circumference of a circle to its diameter. static global variable double datatype PI variable name (identifier) 6

7 Functions static double sqrt (double a) Returns the correctly rounded d positive square root of a double value. static stateless function double datatype of result sqrt name (identifier) of method double a datatype of parameter 7

8 Sample Program I Calculate the radius or a circle with area = 1 area = πr 2 r = sqrt(area/π) 8

9 Program public class Radius { public static void main (String[] args) { double temp = 1/Math.PI; double radius = Math.sqrt(temp); } } 9

10 Keyboard Input Scanner class Provides functionality in Java to get user (keyboard) input Constructors Build new Scanner objects Methods Read d data 10

11 Methods to Read Data int nextint() Scans the next token of the input as an int. int datatype of result nextint name (identifier) of method Not static! 11

12 static vs. non-static methods I static Same result for same parameters, every time stateless non-static Result depends on state 12

13 static vs. non-static methods II nextint() Should this method always return the same result? Which input source? Which item in input series? Proper operation of method requires state information State information stored in objects 13

14 Creating Objects Scanner (InputStream source) Constructs t a new Scanner that t produces values scanned from the specified input stream. Scanner type of object being created source state information for new object 14

15 Example import java.util.scanner; public class Input { public static void main (String[] args) { Scanner scan = new Scanner (System.in); int input = scan.nextint(); } } 15

16 Random Numbers Random class Provides functionality in Java to generate (pseudo) random numbers Constructors Build new Random objects Methods Generate t (pseudo) random numbers 16

17 Creating Objects Random (long seed) Creates a new random number generator using a single long seed Random type of object being created seed random number sequence Two Random objects with the same seed will produce the same sequence of random numbers 17

18 Example import java.util.random; public class RandomNumbers { public static void main (String[] args) { Random generator = new Random (1); int randomint = generator.nextint(); } } 18

19 Function Names int input = scan.nextint(); Gets next input from user int randomint = generator.nextint(); nextint(); Generates next random number The meaning of nextint() depends on context 19

20 Sample Program I Simulate the rolling of two six-sided dice 20

21 Program import java.util.*; public class TwoDice { public static void main (String[] args) { Random generator = new Random (); } } 21

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23 Sample Program II Generate a random Pick3 or Pick4 number 23

24 Data 24

25 Processes 25

26 Program import java.util.*; public class Lotto { public static void main (String[] args) { Scanner scan = new Scanner (System.in); Random generator = new Random (); } } 26

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28 Sample Program III Generate a random number between 1 and d10, and dtake user guesses until they guess the number. Output the number of guesses. 28

29 Data 29

30 Processes 30

31 Program import java.util.*; public class GuessingGame { public static void main (String[] args) { Scanner scan = new Scanner (System.in); Random generator = new Random (); } } 31

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33 Readings and Assignments Text sections (5 th, 6 th, or 7 th edition) 2.6, 3.4, 3.5 Tutorials Branching Programs in JAVA Tutorials Looping Programs in JAVA Mid-term Sample 1 Lab Assignment 3 33

Chapter 4 Classes in the Java Class Libraries

Programming Fundamental I ACS-1903 Chapter 4 Classes in the Java Class Libraries 1 Random Random The Random class provides a capability to generate pseudorandom values pseudorandom because the stream of