Individual Readiness Assessment Test (irat) 11 questions ~ 11 minutes. Group Readiness Assessment Test (grat)

Transcription

1 INTRODUCTION

2 Today Questions & Answers Chapters 1 and 2 Individual Readiness Assessment Test (irat) 11 questions ~ 11 minutes Group Readiness Assessment Test (grat) 20 ~ 30 minutes Appeal (as needed) Mini-lecture Assignment for next lecture

3 Individual Test Question 1: def reserved word Question 2: syntax vs. semantic Question 3: white spaces Question 4: comments Question 5: escape sequence Question 0: Are you ready? Question 6: print vs println Question 7: order of precedence Question 8: variable Question 9: result =? Question 10: casting Question 11: string concatenation

4 Reserved Words class system static Scanner print public import main this variable results while

5 Syntax vs. Semantic Syntax grammar Semantic sentence meaning

6 White Spaces Are ignored when it is used to separate words (e.g. quotations) Used to improve the program readability (e.g. indentation) Includes blanks, tabs, and newlines (use them wisely)

7 Comments in Java 3 ways in Java // for one line /* for several lines */ /** for Java doc */ api/java/io/printstream.html

8 Escape Sequence The \ is used to indicate that the following character is special. \n = next line \r = return carriage \\ = to be able to put \ in string \( = not needed as brackets can be used in strings directly See page 63 on textbook

9 print vs. println System.out.println( My name is: ); System.out.print( Patricia ); Solution 1: My name is: Patricia Solution 2: My name is: Patricia

10 Order of Precedence Precedence among some of the Java operators (page 78) Precedence level Operator Operation Associates 1 + Unary plus R to L - Unary minus 2 * Multiplication L to R / Division % Remainder 3 + Addition L to R - Subtraction + String concatenation 4 = Assignment R to L

11 Order of Precedence / 5 * 4

12 Variables in Java Must be declared with a specific type Can only hold one value for the entire duration of the program It is a name for a memory location where a value is stored grades students average

13 Casting in Java int total = 100; int count = 8; result = (float) total / count; Vs. result = total / count;

14 Readings / Assignments Prepare exercise PP. 1.9 page 55 Is an individual work will be picked up at the beginning of class. Note: Lab 1 starts on Tuesday. Attendance mandatory for the first lab.

15 CHAPTERS 1 & 2 PRACTICE

16 Today Return of Assignment Correction of PP 1.9 (page 55) on the board Exercise 2.5 (page 106) Variable assignments Coverage of Scanner class Assignment for next lecture

17 Exercise PP 1.9, page 55 * *** ***** ******* ********* ******* ***** *** *

18 EX 2.5 (page 106) What is the output produced by the following statement? Explain. System.out.println ( He thrusts his fists\n\tagainst + the post\nand still insists\n\the sees the \ ghost\ ); He thrusts his fists against the post and still insists he sees the ghost 2 gifts

19 Today Exercise 2.5 (page 106) Correction of PP 1.9 (page 55) on the board Variable assignments Coverage of Scanner class Assignment for next lecture

20 EX 2.10 (page 107) Given the following declarations, what result is stored in each of the listed assignment statements? (a) int iresult, num1 = 25, num4 = 5; iresult = num1 / num4; (d) int num3 = 17, num4 = 5; double fresult = num3 / num4; (e) int num4 = 5; double fresult, val1 = 17.0; fresult = val1 / num4; Team gift

21 Chapter 2 EX 2.10 (Continued) (g) int iresult, num1 = 25, num2 = 40; iresult = num1 / num2; (h) int num1 = 25, num2 = 40; double fresult = (double) num1 / num2; (j) int num1 = 25, num2 = 40; double fresult = (double) (num1 / num2); Team gift

22 Variable assignment EX 2.6 (page 106) What value is contained in the integer variable size after the following statements are executed? size = 18; size = size + 12; size = size * 2; size = size / 4; size += 12; size *= 2; size /= 4; size = 30; size = 60; size = 15; 3 gifts

23 Chapter 2 EX 2.8 What value is contained in the integer variable length after the following statements are executed? length = 5; length *= 2; length *= length; length /= 100; 1 gift

24 EX 2.11 (page 107) For each of the following expressions, indicate the order in which the operators will be evaluated by writing a number beneath each operator. (b) a b + c d (c) a + b / c / d (i) (a (b c)) d (l) a + (b c) * d e (n) (a + b) * (c / d) % 4 Team gift

25 Anatomy of a class public class ANewClass { public static void main (String[] args) { } } //some work is done here

26 Section 2.6 Scanner class Used to get input from user (from keyboard, from a file ). Can get Strings and numbers import java.util.scanner; public class Input { public static void main (String args) { Scanner scan = new Scanner (System.in); String message = scan.nextline(); int number = scan.nextint(); } }

27 Assignment PP 2.11 page 109 Only think at the steps that must be taken to make it happen No java code Only algorithm (English like sentences of step bystep instructions)

28 END OF MODULE

29 Today Algorithms vs. Program Exercise on Scanner object Exercise PP 2.11 Pick up of individual work Team work Submission Coverage of Applets Exercise on Applets Assignment for next lecture

30 Algorithm vs. Program Peanut butter sandwich Algorithm: English like step by step instructions Independent from the programming language Is the first step to program Program: Instructions written in the specific programming language Should follow algorithm instructions, but adapt it to the specificity of the chosen programming language

31 Practice (PP 2.3 page 109) Write an application that prompts for and reads a person s name, university name, and the year. Then print the following paragraph inserting the appropriate data. Dear name, Congratulations on being accepted to university. The semester begins in year.

32 Chapter 2 PP 2.11 Write an application that prompts for and read a double value representing a monetary amount. Then determine the fewest number of each bill and coin needed to represent that amount, starting with the highest (assume that the $10 bill is the maximum size needed). Assume Canadian monies

33 Graphics & Applets Image => Pixels Color => RGB Grayscale => I

34 Coordinate Systems Each pixel can be identified using a two dimensional coordinate system When referring to a pixel in a Java program, we use a coordinate system with the origin in the top left corner (0, 0) 112 X 40 (112, 40) Y Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

35 The Color Class A color in a Java program is represented as an object created from the Color class The Color class also contains several predefined colors, including the following: Object Color.black Color.blue Color.cyan Color.orange Color.white Color.yellow RGB Value 0, 0, 0 0, 0, 255 0, 255, , 200, 0 255, 255, , 255, 0 Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

36 Applets A Java application is a stand alone program with a main method (like the ones we've seen so far) A Java applet is a program that is intended to transported over the Web and executed using a web browser An applet also can be executed using the appletviewer tool of the Java Software Development Kit An applet doesn't have a main method Instead, there are several special methods that serve specific purposes Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

37 Applets The class that defines an applet extends the Applet class This makes use of inheritance, which is explored in more detail in Chapter 8 See Einstein.java An applet is embedded into an HTML file using a tag that references the bytecode file of the applet The bytecode version of the program is transported across the web and executed by a Java interpreter that is part of the browser Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

38 The HTML applet Tag <html> <head> <title>the Einstein Applet</title> </head> <body> <applet code="einstein.class" width=350 height=175> </applet> </body> </html> Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

39 Drawing Shapes Let's explore some of the methods of the Graphics class that draw shapes in more detail A shape can be filled or unfilled, depending on which method is invoked The method parameters specify coordinates and sizes Shapes with curves, like an oval, are usually drawn by specifying the shape s bounding rectangle An arc can be thought of as a section of an oval Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

40 Drawing a Line X Y page.drawline (10, 20, 150, 45); or page.drawline (150, 45, 10, 20); Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

41 Drawing a Rectangle 50 X Y page.drawrect (50, 20, 100, 40); Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

42 Drawing an Oval 175 X 20 bounding rectangle 80 Y 50 page.drawoval (175, 20, 50, 80); Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

43 Set colors of background and graphics setbackground(color.cyan); page.setcolor(color.blue); page.fillrect(0,175,300,50); page.setcolor(color.yellow); page.filloval( 40, 40,80,80);

44 Chapter 2 PP 2.12 Create a revised version of the Snowman applet with the following modifications: Add to red buttons to the upper torso Make the snowman frown instead of smile Move the sun to the upper right corner of the picture GIVEN AS A LAB ASSIGNMENT (LAB 3)

45 Reading assignment Chapter 3 Check on webct for reading guidelines RAT on Tuesday: BRING YOUR CLICKERS Make sure your clicker is registered in WebCT

46 READING 2 TEST

47 Today Reading 2 Test Questions & Answers Individual test Team test Mini Lecture Correction of Exercise done last lecture (if time permits)

48 Reading 2 individual test Question 0 Are you ready? Question 1 Question 2 Question 3 Question 4 Question 5 Question 6 Question 7 Question 8 Question 9 Question 10 Question 11

49 Reading 2 Team test

50 Declaration/Initialization/Instantiation Declaration: int num; String name; Initialization: first time a variable is assigned a value num = 10; name = patricia ; Instantiation: creation of an object scan = new Scanner(System.in);

51 Method Invocation Two ways: Method static ClassName.MethodName() Method non static ObjectName.MethodName()

52 Method invocation: String class (page 119) non static public int length() Returns the number of characters in this string public charcharat (int index) Returns the character at the specified index public int compareto (String str) Returns an integer indicating if this string is lexically before (negative return value), equal to (..), or after the string str.

53 Method invocation: String class (page 119) public int length() Returns the number of characters in this string String name= patricia ; int strlenght = name.length(); strlenght = 8

54 Method invocation: String class (page 119) public char charat (int index) Returns the character at the specified index String name= patricia ; char letter = name.charat(3); Letter =

55 Method invocation: String class (page 119) String name= patricia ; char letter = name.charat(3); name index value p a t r i c i a

56 Method invocation: String class (page 119) public int compareto (String str) Returns an integer indicating if this string is lexically before (negative return value), equal to (..), or after the string str. String name1 = patricia ; String name2 = fred ; int diff = name1.compareto(name2); diff =

57 Method invocation: String class (page 119) int diff = name1.compareto(name2); patricia after Diff > 0 fred fred Diff < 0 patricia patricia Diff = 0 patricia

58 Method invocation static A method is static if the keyword static is in front of return type (e.g. Math class) public static double sqrt (double num) Returns the square root of num, which must be positive. double nb = 100; double value = Math.sqrt (nb);

59 RAT review What is the content of s1 after the following code fragment? String s1 = Lasserre ; s1 = s1.tolowercase(); s1 = Hel + s1.charat(0) + o ;

60 Correction PP 2.9 Algorithm: Ask user to input cash amount Wait for cash amount Separate dollars from cents Compute tens = dollars / 10 Compute fives = (dollars%10) / 5 Compute twonies, loonies (same idea) Compute quarters = cents / 25 Compute dimes = cents % 25)/10 Computer five & pennies (same idea) Print results

61 FUNDAMENTALS OF PROGRAMMING

62 Today Correction of PP 2.9 Coverage of end of Chapter 2 Applets Exercises on Chapter 3 Coverage of Chapter 3 Wrapper classes Frames & Panels Introduction of fundamental programming concepts Reading for next lecture

63 Correction PP 2.9 Algorithm: Ask user to input cash amount Wait for cash amount Separate dollars from cents Compute tens = dollars / 10 Compute fives = (dollars%10) / 5 Compute twonies, loonies (same idea) Compute quarters = cents / 25 Compute dimes = cents % 25)/10 Computer five & pennies (same idea) Print results

64 Today Correction of PP 2.9 Coverage of end of Chapter 2 Applets Exercises on Chapter 3 Coverage of Chapter 3 Wrapper classes Frames & Panels Introduction of fundamental programming concepts Reading for next lecture

65 Chapter 2 Graphics & Applets Image => Pixels Color => RGB Grayscale => I

66 Coordinate Systems Each pixel can be identified using a two dimensional coordinate system When referring to a pixel in a Java program, we use a coordinate system with the origin in the top left corner (0, 0) 112 X 40 (112, 40) Y Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

67 The Color Class A color in a Java program is represented as an object created from the Color class The Color class also contains several predefined colors, including the following: Object Color.black Color.blue Color.cyan Color.orange Color.white Color.yellow RGB Value 0, 0, 0 0, 0, 255 0, 255, , 200, 0 255, 255, , 255, 0 Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

68 Applets A Java application is a stand alone program with a main method (like the ones we've seen so far) A Java applet is a program that is intended to transported over the Web and executed using a web browser An applet also can be executed using the appletviewer tool of the Java Software Development Kit An applet doesn't have a main method Instead, there are several special methods that serve specific purposes Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

69 Applets The class that defines an applet extends the Applet class This makes use of inheritance, which is explored in more detail in Chapter 8 See Einstein.java An applet is embedded into an HTML file using a tag that references the bytecode file of the applet The bytecode version of the program is transported across the web and executed by a Java interpreter that is part of the browser Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

70 The HTML applet Tag <html> <head> <title>the Einstein Applet</title> </head> <body> <applet code="einstein.class" width=350 height=175> </applet> </body> </html> Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

71 Drawing Shapes Let's explore some of the methods of the Graphics class that draw shapes in more detail A shape can be filled or unfilled, depending on which method is invoked The method parameters specify coordinates and sizes Shapes with curves, like an oval, are usually drawn by specifying the shape s bounding rectangle An arc can be thought of as a section of an oval Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

72 Drawing a Line X Y page.drawline (10, 20, 150, 45); or page.drawline (150, 45, 10, 20); Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

73 Drawing a Rectangle 50 X Y page.drawrect (50, 20, 100, 40); Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

74 Drawing an Oval 175 X 20 bounding rectangle 80 Y 50 page.drawoval (175, 20, 50, 80); Copyright 2009 Pearson Education, Inc Publishing as Pearson-Addison Wesley

75 Set colors of background and graphics setbackground(color.cyan); page.setcolor(color.blue); page.fillrect(0,175,300,50); page.setcolor(color.yellow); page.filloval( 40, 40,80,80);

76 Chapter 2 PP 2.14 Create a revised version of the Snowman applet with the following modifications: Add to red buttons to the upper torso Make the snowman frown instead of smile Move the sun to the upper right corner of the picture GIVEN AS A LAB ASSIGNMENT (LAB 3)

77 Today Correction of PP 2.9 Coverage of end of Chapter 2 Applets Exercises on Chapter 3 Coverage of Chapter 3 Wrapper classes Frames & Panels Introduction of fundamental programming concepts Reading for next lecture

78 Exercise EX 3.3 page 156 Write a declaration of a String variable called change and initialize it to the characters stored in another String object called original with all the e changed to j ;

79 Exercise EX 3.8 page 156 Write an assignment statement that computes the square root of the sum of num1 and num2 and assign the result to num3.

80 Exercise EX 3.4 page 156 What output is produced by the following code fragment? String m1, m2, m3; m1 = Quest for the Holy Grail ; m2 = m1.tolowercase(); m3 = m1 + + m2; System.out.println(m3.replace( h, z ));

81 Exercise EX 3.6 page 156 Assuming that a Random object has been created called generator, what is the range of the result of each of the following expressions? a. generator.nextint(20); b. generator.nextint(8) + 1; c. generator.nextint(45) + 10; d. generator.nextint(100) 50;

82 Exercise EX 3.7 page 156 Write code to declare and instantiate an object of the Random class. Then write a list of expressions using the nextint method that generates random numbers in the following specified ranges, including the endpoints. Use the version of the nextint() method that accepts a single integer parameter a. 0 to 10 b. 0 to 500 c. 1 to 10 d. 1 to 500 e. 25 to 50 f. 10 to 15

83 Today Correction of PP 2.9 Coverage of end of Chapter 2 Applets Exercises on Chapter 3 Coverage of Chapter 3 Wrapper classes Frames & Panels Introduction of fundamental programming concepts Reading for next lecture

84 Chapter 3 Wrapper classes Can I transform String value into a number? Wrapper class: Primitive data hidden in a class: one for each primitive data Provides basic casting functions from one type to another, and various format. Integer class (page 141): static int parseint (String str) String n = 10 ; int nb=integer.parseint(n);

85 Autoboxing Automatic conversion between primitive value and corresponding wrapper object Double nb; double val = 23.4; nb = val; //autoboxing or Double nb = new Double (44.1); double val; val = nb; //autoboxing

86 Frames and Panels Frames Java container Used to display GUI based applications Displayed as a separate window Defined by the Jframe class Panels Java container Cannot be displayed on its own Must be added to another container to be displayed Helps organize components in a GUI Defined by the JPanel class

87 Examples JFrame > Window JPanel for content JLabel for text 2 labels added to Panel, and then included in Frame before being displayed.

88 Nested Panels JPanel to create subpanels Text in subpanels done with JLabel JLabel could have both text and image. Subpanels combined in another panel Panel added to Jframe

89 Today Correction of PP 2.9 Coverage of end of Chapter 2 Applets Exercises on Chapter 3 Coverage of Chapter 3 Wrapper classes Frames & Panels Introduction of fundamental programming concepts Reading for next lecture

90 Next Reading Nice to give instruction but pretty limited Only able to give instruction one after the other: Do A Do B Do C What if I want to say: Do C only if a condition is satisfied?

91 Conditional statements Option 1: Do something only if a condition is true Option 2: there is an exclusive choice between two actions based on a condition being true or false Option 3: condition might have more than 2 solutions and one must do something different depending on each of them.

92 Introduction for next reading Flow of program Sequential Block statement Conditional (or selection) statement If else statements Switch statements

93 Reading assignment Chapter 2, 5 & 6 Check on webct for reading guidelines RAT on Tuesday: BRING YOUR CLICKERS

94 Peer review Access through webct. Check forum for link & deadline Comments: Give constructive feedback to team members I will release results once I ve checked that comments are appropriate. No mark given on this one, only for feedback.

95 EXERCISES

96 Today Conditional statements Review of competition Team programming exercises Switch statement Introduction to next reading

97 Competition results Teams average before bonuses: 87% Didn t have time to look at all teams errors found but Lots of errors were correctly found on the ones I ve seen

98 Exercise Write code describe the following conditions: a) Is the integer variable num an even number if (num % 2 == 0)

99 Exercise Write code describe the following conditions: b) Is the integer variable temp between 20 and 25 (degree celsius) if (temp >= 20 && temp <= 25)

100 Exercise Write code describe the following conditions: c) Is the double variable value is within 10% of the variable limit if (Math.abs (value limit)<= 0.1*limit) (value / limit) > 0.9 && (value/ limit) < 1.1)

101 Exercise Write code describe the following conditions: d) Is the integer variable num outside of the range [10, 100] if (num < 10 num > 100)

102 Exercise Write code describe the following conditions: e) Is the character variable letter a letter of the alphabet if ((letter >= A && letter <= Z ) (letter >= a && letter <= z ))

103 Exercise PP 5.1 page 263 What is the condition for being a leap year? Year is divisible by 4 AND Option 1: Year is not divisible by 100 Option 2: Year is divisible by 100 AND Year is divisible by 400

104 Algorithm Prompt user to give a year Get year from keyboard If year in Gregorian calendar If year is leap year Print message is a leap year Else Print message not a leap year Else Print message date not in Gregorian calendar

105 Switch statement System.out.println("Enter a number"); Scanner scan = new Scanner (System.in); int number = scan.nextint(); switch (number/10){ case 0: System.out.println("pear"); break; case 1: System.out.println("apple"); case 2: case 3: case 4: System.out.println("orange"); break; case 5: System.out.println("grape"); break; default: System.out.println("other"); } What output is produced when number = 9? 1. pear 2. apple 3. orange 4. Grape What output is produced when number = 14? 1. pear, apple and orange 2. apple and orange 3. apple 4. Pear What output is produced when number = 33? 1. pear 2. orange 3. grape 4. apple and orange

106 Programming exercise Exercise PP 5.3 page 263 Design and implement an application that determines and prints the number of odd, even and zero digits in an integer value read from the keyboard. We will assume that the number has 4 digits

107 Algorithm Initialize all counters to zero Ask user for a number Read number from keyboard Get the four digits. divide digit by two and take remainder If remainder equals: Zero: increment even counter if digit equal zero, increment zero counter One: increment odd counter Print values of all counters

108

109

110 Introduction to next reading Sequential order of action Conditional statements Repetition statements Also called loops Used to repeat several times the same action(s) Three variations of the loop: While loop Do while loop For loop

111 While loop Init condition; While (condition) { } Action1; Action 2; Change condition; Change condition Init condition Condition evaluated loop Condition false Action 1 Action 2

112 Do While loop Init condition; Do { Init condition Action1; Action 2; Action 1 Change condition; } while (condition); Condition false Condition evaluated loop Action 2 Change condition

113 For loop While loop Init condition; While (condition) { } Action1; Action 2; Change condition; For loop For (init condition; condition; change condition) { Action1; Action2; }

114 Next Lecture Reading assignment on webct BRING YOUR CLICKERS

115 READING 4 TEST

116 Today Reading 4 Test Questions & Answers Individual test Team test Mini Lecture Assignment for next lecture

117 Reading 4 individual test ARE YOU READY? Question 1 Question 2 Question 3 Question 4 Question 5 Question 6 Question 7 Question 8 Question 9 Question 10

118 Reading 2 Team test

119 Questions 1, 4, 6 While loop Do While loop Init condition; Init condition; while (condition) { do{ Action1; Action1; Action 2; Action 2; Change condition; Change condition; } } while (condition) ; For loop for (init condition; condition; change condition) { Action1; Action2; }

120 Question 8 Which of the following is false about this code fragment? for (int count = 0; count < 5; count++){ System.out.println(count); } a) The variable count only exists for the duration of for loop statement. b) The incrementation is done after the body has been executed c) It prints the values 0 to 5 d) It prints the values 0 to 4

121 For loop, the 3 S s for (init condition; condition; change condition) { Action1; Action2; } for (int count = 0; count < 5; count++){ System.out.println(count); } for (start; stop; step) { Action1; Other way: Action2; }

122 Question 9 Which one of these sentences is false about this code fragment? int count = 0; do { count++; System.out.println(count); } while (count < 5); a) The body of the loop is between the curly brackets b) The semi column after the condition will generate a compilation error c) It prints the values 1 to 5 d) If the two statements in the loop are reversed, it would print the values 0 to 4.

123 Question 10 What output is produced by the following code fragment? int num = 0; while (num < 20) { System.out.println(num); num += 4; }

124 EX 6.6 page 295 Write a for loop to print the odd numbers from 1 to 99 for (int count = 1; count < 100; count += 2) System.out.println(count);

125 Exercise 6.5 page 295 Write a do loop that verifies that the user enters an even integer value. Scanner scan = new Scanner (System.in); int number; do { System.out.print ( Give an even number ); number = scan.nextint(); } while (number % 2!= 0);

126 Next assignment Homework for next lecture: Check on webct

127 LOOP EXERCISES

128 Today Pick up of home assignment Loop statements Class exercises Team programming exercises Introduction to next class Marked exercise

129 Exercise: Trace the code import java.util.scanner; public class Trace { public static void main(string[] args) { Scanner scan = new Scanner(System.in); System.out.println("Give a integer number:"); int n = scan.nextint(); System.out.println("Give another integer number:"); int d = scan.nextint(); int q = 0; while (n >= d){ n = d; q++; } int r = n; } } Steps/. variables n d na 3 q na na r na na System.out.println ("q = " + q + \nr = " + r);

130 EX 6.8 page 295 Write a code fragment that reads 10 integer values from the user and prints the highest value entered. Need a Scanner object Read 10 numbers => loop to get user s numbers Highest value entered => test each number to see if it is bigger

131 Solution Scanner scan = new Scanner (System.in); int count = 1, val, highest; System.out.print("Give a number:"); highest = scan.nextint(); while (count < 10){ System.out.print("Give a number:"); val = scan.nextint(); if (val > highest) highest = val; count++; } System.out.println("The highest value is " + highest);

132 Team work Competition: First team to complete the exercise stops the competition My correction is done immediately after 3 exercises to complete > reward to the winning team(s)

133 Exercise EX 6.9 page 295 Write a code fragment that determines and prints the number of times the character a appears in a String object called name. String name = "I want to see if it happens to work"; int count = 0; for (int position = 0; position < name.length(); position++) if (name.charat(position) == 'a') count++; System.out.println("\ a\ is present " + count +" times");

134 Exercise EX 6.10 page 295 Write a code fragment that prints the characters stored in a String object called str backward. String str = "I want to see if it works"; for (int position = str.length()-1; position >= 0; position--) System.out.print(str.charAt(position));

135 Exercise EX 6.11 page 295 Write a code fragment that prints every other character in a String object called word starting with the first character. String word = "I want to see if it works"; for (int position = 0; position < word.length(); position+=2) System.out.print(word.charAt(position));

136 EXERCISES CORRECTION

137 Today Pick up of individual assignments Correction of star exercises Correction of PP 5.8 and 5.16 Introduction of breaking problem into methods

138 Correction of PP 5.13 Algorithm for (a) For 10 lines Display right number of * Go to the next line Display * s Opposite to the line number For star = 10 to line number On the screen ********** ********* ******** ******* ****** ***** **** *** ** *

139 Program for (a) for (int line = 1; line <= 10; line++){ for (int stars = 10; stars >= line; stars--) System.out.print('*'); System.out.println(); }

140 Correction of PP 5.13 Algorithm for (b) For 10 rows Display right number of start at right position Go to the next line Display stars As many stars as line number But 10-line spaces before On the screen * ** *** **** ***** ****** ******* ******** ********* **********

141 Program for (b) for (int line = 1; line <= 10; line++){ for (int space = 10 - line; space >= 0; space--) System.out.print(" "); for (int stars = 1; stars <= line; stars++) System.out.print("*"); System.out.println(); }

142 Correction of PP 5.13 Algorithm for (c) For 10 lines Display right number of stars at right position Go to next line Display stars One less space than line number (for 1 to line-1) Opposite number of stars than lines (For star = 10 to line number) On the screen ********** ********* ******** ******* ****** ***** **** *** ** *

143 Program for (c) for (int line = 1; line <= 10; line++){ for (int spaces = 1; spaces <= line-1; spaces++) System.out.print(" "); for (int stars = 10; stars >= line; stars--) System.out.print("*"); System.out.println(); }

144 Correction of PP 5.13 Algorithm for (d) For 10 lines Display right number of stars at correct position Go to next line Display stars Number of spaces is equal to half number of stars line. Still holds true in negative values for second half of diamond spaces = 5 line Number of stars is dependant on number of spaces. But always odd number: stars = 10 2*spaces -1 On the screen * *** ***** ******* ********* ********* ******* ***** *** *

145 Program for (d) int nbspaces; for (int line = 1; line <= 10; line++){ } nbspaces = Math.abs(5 - line); for (int spaces = 1; spaces <= nbspaces; spaces++) System.out.print(" "); for (int stars = 1; stars <= 10-2*nbSpaces-1 ; stars++) System.out.print("*"); System.out.println();

146 PP 5.16 Rock, Paper, Scissor Algorithm Loop Play Rock Paper Scissor Ask user if wants to quit If yes, display statistics Stop loop when user wants to quit Rock Paper Scissor: Generate random number (rock = 0, paper = 1, scissor = 2) Ask for user choice Difference user - computer If difference = 0 => tie If difference = 1 or -1 => largest value wins If difference = 2 or -2 => smallest value wins Keep stats

147 Program Scanner scan = new Scanner (System.in); int ties = 0, userwin = 0, computerwin = 0, computerchoice, userchoice; Random gen = new Random (); String answer; boolean exit = false; while (!exit) { computerchoice = gen.nextint(3); System.out.print("Give your choice: Rock(0), Paper(1), Scissor(2)"); userchoice = scan.nextint(); System.out.println("Computer = " + computerchoice + ", User = " + userchoice);

148 switch (Math.abs(userChoice - computerchoice)){ case 0: //both are equals ties++; System.out.println("It's a tie"); break; case 1: //the largest value wins if (userchoice > computerchoice){ System.out.println("you win"); userwin++; } else { System.out.println("computer wins"); computerwin++;} break; case 2: //the smallest value wins if (userchoice < computerchoice){ System.out.println("you win"); userwin++; } else { System.out.println("computer wins"); computerwin++; } break; } System.out.print("Continue? Y/N"); answer = scan.next(); if (answer.equalsignorecase("n")) exit = true; } //display statistics }

149 PP 5.8 Hi-Lo guess Algorithm: Loop: Play Hi-Lo Ask user if wants to quit Stop loop when user wants to quit Algorithm Play Hi-Lo Pick a random number between 1 and 100 Loop Ask user for a guess or quit (zero to quit) Compare guess to random number If guess = number, display statistics on number of guesses Else If guess > number, display High Else (necessarily guess < number) display Low increase number of guesses Stop loop if guess = number or number = 0 Display statistics

150 Breakdown of program Two algorithms => Two pieces of code One in the main method. The other??? Can be done in the same file using strategy of method decomposition Method is invoked in main program Method code is separated in another location in the same file

151 Program import java.util.*; public class HiLo { public static void main (String[] args){ Random gen = new Random(); boolean exit = false; while (!exit){ //play one game playhilo(gen); } } } //test if user wants to play again exit = teststop("continue playing? Y/N");

152 Invocation vs. Declaration Use of index to find book in shelf Code as reference for book Use of table of content to find material to read in book Page number as reference for material Method Use of method invocation for method location Use of method header as reference

153 Invocation vs. declaration Declaration in class with main method public static return-type methodname (parameter list) Invocation in main program: With void as return-type methodname (parameter list values);

154 Invocation vs. declaration Invocation (main): playhilo(gen); Declaration (new method in class): public void playhilo (Random g) { //code for play Hi Lo }

155 Code for Hi-Lo public static void playhilo(random g){ Scanner scan = new Scanner (System.in); int randnum = g.nextint(100)+1; //Computer picks a number between 1 and 100 //initialize counter for statistics and game to begin int count = 0, guess; boolean quit = false; do { System.out.print("Guess the number (0 to quit): "); guess = scan.nextint(); if (guess!= 0) { //if does not want to quit count++; //increment the guess counter if (guess == randnum){ // if found System.out.println("You found it in " + count + " guesses"); quit = true; } else if (guess < randnum) //not found high or low System.out.println("The guess is low"); else System.out.println("The guess is high"); } } } while (!quit && guess!= 0); //leave either because found or because user wants to quit

156 Invocation vs. declaration Declaration in class with main method public static return-type methodname (parameter list) Invocation in main program: With something as return-type TypeOfSomething var = methodname (parameter list values); exit = teststop("continue playing? Y/N"); Method declaration?

157 Invocation vs. declaration Invocation: exit = teststop("continue playing? Y/N"); Declaration: public boolean teststop (String str) { //code for test Stop return boolean-value; }

158 Code for TestStop public static boolean teststop(string message) { Scanner scan = new Scanner (System.in); System.out.println(message); String yesno = scan.next(); if (yesno.equalsignorecase("n")) return true; else return false; } Notice: The boolean instead of void means a boolean will be returned, up to the programmer to place it into a variable (or it will be lost) The keyword return is used to return true or false After the keyword return a boolean must be returned (as indicated in the declaration) The String message indicates that this information must be provided for the method to run correctly the message variable is used to print the right message It simplifies both the main method, and the playhilo method as presented on the next slides

159 Recap. public class HiLo { public static void main (String[] args) { Random gen = new Random(); boolean exit = false; while (!exit){ //play one game playhilo(gen); } } //test if user wants to play again exit = teststop("continue playing? Y/N"); public static void playhilo (Random g) { //code for playing one game //invokes also teststop (shown on next slide) } public static boolean teststop (String message) { //code for printing message and getting answer } } //end of class

160 PP 5.16 Rock, Paper, Scissors Algorithm: Loop: Play Rock Paper Scissor Ask user if wants to quit Stop loop when user wants to quit Display win/loss/ties statistics Algorithm Play Rock Paper Scissor Randomly choose Rock (value 0) Paper (value 1) Scissor (value 2) Ask user for its choice Compare computer and user choice Difference = user - computer => value between -2 and 2 If diff = 0 => tie If diff = 1 or -1 => the largest value wins (either computer or user) If diff = 2 or -2 => the smallest value wins (either computer or user)

161 Exercise Write code for House applet such that: Everything is calculated based on the center of the house (x, y) Size of house, door, window may vary Windows are equally spaced Door is centered Roof and bushes codes is provided

162 //house position (center) int x = 100, y = 100; //house dimensions and features int househeight = 60, housewidth = 140; int roofheight = 40; int doorwidth = 20, doorheight = househeight/2; final int MAX_WINDOWS = 4; int nbwindows = MAX_WINDOWS; int windowwidth = 20, windowheight = 20;

163 Bushes code page.setcolor(color.green); //color for bushes int bushwidth, bushheight = doorheight; int spacing = housewidth/2 - doorwidth/2; bushwidth = spacing/3; //left side page.filloval(x - 3*bushWidth - doorwidth/2, y + househeight/2 - bushheight/2, bushwidth, bushheight/2); page.filloval(x - 2*bushWidth - doorwidth/2, y, bushwidth, bushheight); page.filloval(x - 1*bushWidth - doorwidth/2, y + househeight/2 - bushheight/2, bushwidth, bushheight/2);

164 Assignment for next class Will work again with the House applet example Good idea to make it work on your own machine Reading already available Good idea to start before lecture intro on Thursday Reading and RAT on Tuesday

165 DECOMPOSITION IN METHODS

166 Today Last lecture exercises Team discussion [10 min] House applet example Continuation of breaking problem into methods Introduction to object oriented design Introduction of next reading

167 Exercise Code provided 10 minutes to review Transform to have 5 methods that draw: the house outline, the door, the roof, the windows, and the bushes.

168 Invocation vs. declaration Invocation (main): methodname(parameters); Declaration (new method in class): public void methodname (ParameterList) { //code for method }

169 Exercise Create method which draw the following: the house outline, Paint method invokes this method to draw the house.

170 Draw House Idea public void paint(graphics page) {... // draw the house page.setcolor(color.lightgray); page.fillrect(x - housewidth/2, y - househeight/2, housewidth, househeight);... } public void paint(graphics page) {... // draw the house drawhouseoutline(page, x, y, housewidth, househeight);... } //method drawhouseoutline just below //TO DO.

171 Draw House Method Using method decomposition, replace the Java code in the paint method which draws the outline of the house. Method will be named drawhouseoutline. Method will be public and return a void data type. Method will take 5 parameters: Graphics object named page This is the page which the house will be drawn on Integer data named x Specifies the x coordinate for the centre of the house Integer data named y Specifies the y coordinate for the centre of the house Integer data named housewidth Specifies the width of the house Integer data named househeight Specifies the height of the house

172 Draw House Solution public void paint(graphics page) {... // draw the house drawhouseoutline(page, x, y, housewidth, househeight);... } public void drawhouseoutline(graphics page, int x, int y, } int housewidth, int househeight) { // draw the house page.setcolor(color.lightgray); page.fillrect(x - housewidth/2, y - househeight/2, housewidth, househeight);

173 Exercise Create method which draw the following: the house outline, the roof, Paint method invokes each of these methods to draw the house.

174 Draw Roof Method Using method decomposition, replace the Java code which draws the roof. Method will be named drawroof. Method will be public and return a void data type. Method takes 6 parameters: Graphics object named page Integer data named x Integer data named y Integer data named housewidth Integer data named househeight Integer data named roofheight

175 Draw Roof Solution public void paint(graphic page) {... // draw the roof drawroof(page, x, y, housewidth, househeight, roofheight);... } public void drawroof(graphics page, int x, int y, int housewidth, int househeight, int roofheight) { // draw the roof int[] xroof = {x - housewidth/2, x, x + housewidth/2}; int[] yroof = {y - househeight/2, y - househeight/2 roofheight, y - househeight/2}; page.setcolor(color.red); page.fillpolygon(xroof, yroof, xroof.length); }

176 Exercise Create method which draw the following: the house outline, the roof, the door

177 Draw Door Method Using method decomposition, replace the Java code which draws the door. Method will be named drawdoor. Method will take 5 parameters: A Graphics object to draw on, X and Y coordinates of the house, Width and Height of the door.

178 Draw Door Solution public void paint(graphics page) {... // draw the door drawdoor(page, x, y, doorwidth, doorheight);... } public void drawdoor(graphics page, int x, int y, int doorwidth, int doorheight) { // draw the door page.setcolor(color.blue); page.fillrect(x - doorwidth/2, y, doorwidth, doorheight); }

179 Exercise Create method which draw the following: the house outline, the roof, the door, the windows.

180 Draw Windows Method Using method decomposition, replace the Java code which draws the windows. Method will be named drawwindows. Method will take some parameters: The object to draw on, Location of the house, Number of windows to draw, Dimensions of the window and house.

181 Draw Windows Solution public void paint(graphics page) { }... // draw windows drawwindows(page, x, y, nbwindows, windowwidth, windowheight, housewidth, househeight); public void drawwindows(graphics page, int x, int y, int nbwindows, int windowwidth, int windowheight, int housewidth, int househeight) { } //draw windows page.setcolor(color.white); int spacing = housewidth - (nbwindows*windowwidth); for (int i = 0; i < nbwindows; i++){ page.fillrect(x - housewidth/2 + i*windowwidth + spacing*(i+1)/(nbwindows+1), y - househeight/2 + 5, windowwidth, windowheight);

182 Exercise Create method which draw the following: the house outline, the roof, the door, the windows, the bushes.

183 Draw Bushes Method Using method decomposition, replace the Java code which draws the bushes. Method will be named drawbushes. Insert parameters as required.

184 Draw Bushes Solution public void paint(graphics page) {... // bushes (3 per side) drawbushes(page, x, y, housewidth, househeight, doorwidth, doorheight); } public void drawbushes(graphics page, int x, int y, int housewidth, int househeight, int doorwidth, int doorheight) { // bushes (3 per side) page.setcolor(color.green); int bushwidth, bushheight = doorheight; int spacing = housewidth/2 doorwidth/2; bushwidth = spacing/3; page.filloval(x 3*bushWidth doorwidth/2, y + househeight/2 bushheight/2, bushwidth, bushheight/2); page.filloval(x 2*bushWidth doorwidth/2, y, bushwidth, bushheight); page.filloval(x 1*bushWidth doorwidth/2, y + househeight/2 bushheight/2, bushwidth, bushheight/2); page.filloval(x + 2*bushWidth + doorwidth/2, y + househeight/2 bushheight/2, bushwidth, bushheight/2); page.filloval(x + 1*bushWidth + doorwidth/2, y, bushwidth, bushheight); page.filloval(x + 0*bushWidth + doorwidth/2, y + househeight/2 bushheight/2, bushwidth, bushheight/2); }

185 Discussion Easier to read BUT Not much easier to program: Lots of repetition of parameters relative to the graphic page the house measurements Not much readable code as soon as more than one house must be done Not that easy to change color of roof, house, sizes, etc.

186 House Applet example

187 Better approach Object oriented Allows to separate actual application requirements from the various elements needed to complete the work For example in the house applet: Have a class House which stores all information relative to the house Draw the different elements of the house Has a method draw house that calls the drawing methods House applet only draw the house based on characteristics of object created

188 House applet example House Applet paint() method House create house objects: house 1: red roof, bushes, 4 windows house 2: orange roof, 2 windows, cyan door, no bushes house 3: gray roof, 3 windows, pink door, bushes Stores house features such as width, height, position (x,y), Graphics page draw houses house1.draw(); house2.draw(); house3.draw(); methods to: draw roof, house outline, windows, bushes, and entire drawing of the house (draw)

189 House Applet example Imports public class HouseApplet extends Applet{ public void paint(graphics page){ this.setsize(600,400); page.drawstring("my Village", 10, 10); House house1 = new House(page, 150, 150, Color.lightGray, Color.red, Color.blue, 4, true); House house2 = new House(page, 300, 150, Color.darkGray, Color.orange, Color.cyan, 2, false); House house3 = new House(page, 450, 150, Color.blue, Color.gray, Color.magenta, 3, true); House house4 = new House(page, 450, 300, Color.lightGray, Color.green, Color.darkGray, 1, true); House house5 = new House(page, 300, 300, Color.pink, Color.magenta, Color.lightGray, 3, false); house1.draw (); house2.draw (); house3.draw (); house4.draw (); house5.draw (); } }

190 House Applet example BUT where is the code for the House??? In another file called House.java Linked with HouseApplet file made by invocation: House house1 = new House(page, 150, 150, ); house1.draw ();

191 House Applet example Invocation (HouseApplet.java) Header declaration (House.java) House house1 = new House(page, );... house1.draw (); public House (Graphics page, ) { //initialization of variables } public void draw() { //code for drawing house }

192 Important keywords & words Difference Class vs. Objects Public vs. private Method headers Parameters formal/actual Accessors/mutators methods

193 Assignment for next class Chapter 4 reading Reading and RAT on Tuesday

194 OBJECTS AND CLASSES

195 Today Practice writing classes Midterm review Introduction to readings

196 tostring() method Which is easier? System.out.println( Die 1: + die1.getfacevalue()); OR System.out.println( Die 1: + die1 ); System.out.println( Die 1: + die1.tostring())

197 Exercise PP 4.6 page 202 Design and implement a class called Flight that represents an airline flight. It should contain instance data that represent the airline, flight number, and the flight s origin and destination cities Define the Flight constructor to accept and initialize all instance data Include getter and setter methods for all instance data Include a tostring method that returns a one line description of the flight Create a driver class called FlightTest, whose main method instantiates and updates several Flight objects

198 MIDTERM REVIEW

199 Midterm Question 1 Write a method that returns the temperature in Celsius degrees for a temperature value in Fahrenheit degrees. The equation is C=(F 32)*5/9. The returned temperature can be a decimal number. The temperature given in Fahrenheit is an integer value.

200 Midterm Question 2 Write a method that returns the number of occurrences of a given letter for a given string (no assumptions should be made on the string content or the letter chosen, i.e. Parameters).

201 Midterm Question 3 Write a program that reads one integer number and prints if it is prime or not (a prime number is only divisible by one and by itself).

202 Midterm Question 4 Write a program that reads one sentence as user input and prints the number of vowels and consonants used in the sentence. Note that the sentence can contain other elements than letters (e.g., punctuation, apostrophe, ).

203 INTRODUCTION TO NEXT READING

204 Static Static Can be used for a variable or a method Is independent of any object of the class: Variable: the content is shared by all objects of the class Method: no need of an object to call it (use class name) Classic use Counting objects Sharing resources between objects of the same class

205 Overloading Constructor Different number of parameters All instance data initialized no matter what Default values if not provided by parameters Method overloading Same method, different parameters print() and println()

206 The This reference Used to refer to the current object s: Variables Constructors Methods Clarifies what is called: this.variablename this( parameters); this.methodname( ); Helps diminish the number of variable names that programmers have to come up with May reduces amount of coding by referring to already existing code

207 Assignment for Thursday Reading of Chapter 7 See webct for details

208 READING 7 TEST

209 Today Reading 7Test Questions & Answers Individual test Team test Mini lecture

210 Reading 7 Individual test Question 0 Are you ready? Question 1 Question 2 Question 3 Question 4 Question 5 Question 6 Question 7 Question 8 Question 9 Question 10 Question 11

211 Reading 7 Team test

212 Question What is the value of values.length? a) 5 b) 6 c) 18 d) 7 e) 0

213 Question The statement System.out.println(values[7]) will: a) Cause an ArrayOutOfBoundsException to be thrown b) Output nothing c) Cause a syntax error d) Output 18 e) Output 7

214 Question In Java, arrays are: a) primitive data b) primitive data types if the type stored in the array is a primitive data type and objects if the type stored in the array is an object c) Objects d) Strings e) Wrappers classes

215 Question 4 Assume that BankAccount is predefined class and that the declaration BankAccount[] firstempirebank has already been performed. Then the following instruction reserves memory space for: firstempirebank = new BankAccount[1000]; a) A single BankAccount entry b) A reference variable to the memory that stores all 1000 BankAccount entries c) 1000 BankAccount entries d) 1000 reference variables and 1000 BankAccount entries e) 1000 reference variables, each of which point to a single BankAccount entry