Chapter 4 - Control Structures I: Selection

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  • 1. Java Programming: From Problem Analysis to Program Design, 5e Chapter 4 Control Structures I: Selection
  • 2. Chapter Objectives • Learn about control structures • Examine relational and logical operators • Explore how to form and evaluate logical (Boolean) expressions • Learn how to use the selection control structures if, if…else, and switch in a program Java Programming: From Problem Analysis to Program Design, 5e 2
  • 3. Control Structures • Three methods of processing a program – In sequence – Branching – Looping • Branch: altering the flow of program execution by making a selection or choice • Loop: altering the flow of program execution by repetition of statement(s) Java Programming: From Problem Analysis to Program Design, 5e 3
  • 4. Flow of Execution Java Programming: From Problem Analysis to Program Design, 5e 4
  • 5. Relational Operators • Relational operator – Allows you to make comparisons in a program – Binary operator • Condition is represented by a logical expression in Java • Logical expression: expression that has a value of either true or false Java Programming: From Problem Analysis to Program Design, 5e 5
  • 6. Relational Operators in Java Java Programming: From Problem Analysis to Program Design, 5e 6
  • 7. Relational Operators and Primitive Data Types • Can be used with integral and floating-point data types • Can be used with the char data type • Unicode collating sequence Java Programming: From Problem Analysis to Program Design, 5e 7
  • 8. Java Programming: From Problem Analysis to Program Design, 5e 8
  • 9. Java Programming: From Problem Analysis to Program Design, 5e 9
  • 10. Relational Operators and the Unicode Collating Sequence Java Programming: From Problem Analysis to Program Design, 5e 10
  • 11. Logical (Boolean) Operators Java Programming: From Problem Analysis to Program Design, 5e 11
  • 12. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 12
  • 13. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 13
  • 14. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 14
  • 15. Precedence of Operators Java Programming: From Problem Analysis to Program Design, 5e 15
  • 16. Precedence of Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 16
  • 17. Java Programming: From Problem Analysis to Program Design, 5e 17
  • 18. Java Programming: From Problem Analysis to Program Design, 5e 18
  • 19. Java Programming: From Problem Analysis to Program Design, 5e 19
  • 20. Selection • One-way selection • Two-way selection • Compound (block of) statements • Multiple selections (nested if) • Conditional operator • switch structures Java Programming: From Problem Analysis to Program Design, 5e 20
  • 21. One-Way Selection • Syntax if (expression) statement • Expression referred to as decision maker • Statement referred to as action statement Java Programming: From Problem Analysis to Program Design, 5e 21
  • 22. One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 22
  • 23. One-Way Selection (continued) Example 4-7 //Program to determine the absolute value of an integer import javax.swing.JOptionPane; public class AbsoluteValue { public static void main(String[] args) { int number; int temp; String numString; numString = JOptionPane.showInputDialog ("Enter an integer:"); //Line 1 number = Integer.parseInt(numString); //Line 2 temp = number; //Line 3 Java Programming: From Problem Analysis to Program Design, 5e 23
  • 24. One-Way Selection (continued) if (number < 0) number = -number; //Line 4 //Line 5 JOptionPane.showMessageDialog(null, "The absolute value of " + temp + " is " + number, "Absolute Value", JOptionPane.INFORMATION_MESSAGE); //Line 6 System.exit(0); } Java Programming: From Problem Analysis to Program Design, 5e 24
  • 25. if (number < 0) number = -number; //Line 4 //Line 5 JOptionPane.showMessageDialog(null, "The absolute value of " + temp + " is " + number, "Absolute Value", JOptionPane.INFORMATION_MESSAGE); //Line 6 System.exit(0); } Java Programming: From Problem Analysis to Program Design, 5e 25
  • 26. Two-Way Selection • Syntax if (expression) statement1 else statement2 • else statement must be paired with an if Java Programming: From Problem Analysis to Program Design, 5e 26
  • 27. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 27
  • 28. Two-Way Selection (continued) Example 4-10 if (hours > 40.0) wages = 40.0 * rate + 1.5 * rate * (hours - 40.0); else wages = hours * rate; Java Programming: From Problem Analysis to Program Design, 5e 28
  • 29. Two-Way Selection (continued) Example 4-11 if (hours > 40.0); //Line 1 wages = 40.0 * rate + 1.5 * rate * (hours - 40.0); //Line 2 else //Line 3 wages = hours * rate; //Line 4 • Because a semicolon follows the closing parenthesis of the if statement (Line 1), the else statement stands alone • The semicolon at the end of the if statement (see Line 1) ends the if statement, so the statement at Line 2 separates the else clause from the if statement; that is, else is by itself • Since there is no separate else statement in Java, this code generates a syntax error Java Programming: From Problem Analysis to Program Design, 5e 29
  • 30. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 30
  • 31. Compound (Block of) Statements • Syntax Java Programming: From Problem Analysis to Program Design, 5e 31
  • 32. Compound (Block of) Statements (continued) if (age > 18) { System.out.println("Eligible to vote."); System.out.println("No longer a minor."); } else { System.out.println("Not eligible to vote."); System.out.println("Still a minor."); } Java Programming: From Problem Analysis to Program Design, 5e 32
  • 33. Multiple Selection: Nested if • Syntax if (expression1) statement1 else if (expression2) statement2 else statement3 • Else associated with most recent incomplete if • Multiple if statements can be used in place of if…else statements • May take longer to evaluate Java Programming: From Problem Analysis to Program Design, 5e 33
  • 34. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e 34
  • 35. Multiple Selection: Nested if (continued) To avoid excessive indentation, the code in Example 4-15 can be rewritten as follows: Java Programming: From Problem Analysis to Program Design, 5e 35
  • 36. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e 36
  • 37. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e 37
  • 38. Java Programming: From Problem Analysis to Program Design, 5e 38
  • 39. Java Programming: From Problem Analysis to Program Design, 5e 39
  • 40. Short-Circuit Evaluation • Definition: a process in which the computer evaluates a logical expression from left to right and stops as soon as the value of the expression is known Java Programming: From Problem Analysis to Program Design, 5e 40
  • 41. Short-Circuit Evaluation (continued) Java Programming: From Problem Analysis to Program Design, 5e 41
  • 42. Java Programming: From Problem Analysis to Program Design, 5e 42
  • 43. Java Programming: From Problem Analysis to Program Design, 5e 43
  • 44. Java Programming: From Problem Analysis to Program Design, 5e 44
  • 45. • The preceding program and its output show that you should be careful when comparing floating-point numbers for equality. • One way to check whether two floating-point numbers are equal is to check whether the absolute value of their difference is less than a certain tolerance. For example, suppose the tolerance is . 000001. • Then x and y are equal if the absolute value of (x – y) is less than 0.000001. To find the absolute value, you can use the function Math.abs of the class Math, as shown in the program. • Therefore, the expression Math.abs(x – y) < 0.000001 determines whether the absolute value of (x – y) is less than 0.000001. Java Programming: From Problem Analysis to Program Design, 5e 45
  • 46. Conditional (? :) Operator • Ternary operator • Syntax expression1 ? expression2 : expression3 • If expression1 = true, then the result of the condition is expression 2; otherwise, the result of the condition is expression 3 Java Programming: From Problem Analysis to Program Design, 5e 46
  • 47. Java Programming: From Problem Analysis to Program Design, 5e 47
  • 48. Java Programming: From Problem Analysis to Program Design, 5e 48
  • 49. Java Programming: From Problem Analysis to Program Design, 5e 49
  • 50. Java Programming: From Problem Analysis to Program Design, 5e 50
  • 51. switch Structures Java Programming: From Problem Analysis to Program Design, 5e 51
  • 52. switch Structures (continued) • In Java, switch, case, break, and default are reserved words • In a switch structure, the expression is evaluated first • The value of the expression is then used to perform the actions specified in the statements that follow the reserved word case • The expression is usually an identifier • The value of the identifier or the expression can be only of type int, byte, short, or char Java Programming: From Problem Analysis to Program Design, 5e 52
  • 53. switch Structures (continued) • The expression is sometimes called the selector; its value determines which statements are selected for execution • A particular case value must appear only once • One or more statements may follow a case label, so you do not need to use braces to turn multiple statements into a single compound statement Java Programming: From Problem Analysis to Program Design, 5e 53
  • 54. switch Structures (continued) • The break statement may or may not appear after each statements1, statements2, ..., statementsn • A switch structure may or may not have the default label Java Programming: From Problem Analysis to Program Design, 5e 54
  • 55. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e 55
  • 56. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e 56
  • 57. switch Structures (continued) Example 4-20 switch (grade) { case 'A': System.out.println("The grade is A."); break; case 'B': System.out.println("The grade is B."); break; case 'C': System.out.println("The grade is C."); break; Java Programming: From Problem Analysis to Program Design, 5e 57
  • 58. switch Structures (continued) case 'D': System.out.println("The grade is D."); break; case 'F': System.out.println("The grade is F."); break; default: System.out.println("The grade is invalid."); } Java Programming: From Problem Analysis to Program Design, 5e 58
  • 59. Java Programming: From Problem Analysis to Program Design, 5e 59
  • 60. Java Programming: From Problem Analysis to Program Design, 5e 60
  • 61. Java Programming: From Problem Analysis to Program Design, 5e 61
  • 62. To output results correctly, the switch structure must include a break statement after each println statement, except the last println statement. Java Programming: From Problem Analysis to Program Design, 5e 62
  • 63. Programming Example: Cable Company Billing • Input: customer’s account number, customer code, number of premium channels to which customer subscribes, number of basic service connections (in case of business customers) • Output: customer’s account number and the billing amount Java Programming: From Problem Analysis to Program Design, 5e 63
  • 64. Programming Example: Cable Company Billing (continued) • Solution – Prompt user for information – Use switch statements based on customer’s type – Use an if statement nested within a switch statement to determine amount due by each customer Java Programming: From Problem Analysis to Program Design, 5e 64
  • 65. Comparing Strings • class String – Method compareTo – Method equals • Given string str1 and str2 an integer < 0 if string str1 < str2  str1.compareTo(str2)= 0 if string str1 is equal to string str2 an integer > 0 if string str1 > str2  Java Programming: From Problem Analysis to Program Design, 5e 65
  • 66. Comparing Strings (continued) String String String String String str1 str2 str3 str4 str5 = = = = = "Hello"; "Hi"; "Air"; "Bill"; "Bigger"; Java Programming: From Problem Analysis to Program Design, 5e 66
  • 67. Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e 67
  • 68. Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e 68
  • 69. Chapter Summary • Control structures are used to process programs • Logical expressions and order of precedence of operators are used in expressions • If statements • if…else statements • switch structures • Proper syntax for using control statements • Compare strings Java Programming: From Problem Analysis to Program Design, 5e 69