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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
  • 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
  • 4. Flow of Execution Java Programming: From Problem Analysis to Program Design, 5e
  • 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
  • 6. Relational Operators in Java Java Programming: From Problem Analysis to Program Design, 5e
  • 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
  • 8. Java Programming: From Problem Analysis to Program Design, 5e
  • 9. Java Programming: From Problem Analysis to Program Design, 5e
  • 10. Relational Operators and the Unicode Collating Sequence Java Programming: From Problem Analysis to Program Design, 5e
  • 11. Logical (Boolean) Operators Java Programming: From Problem Analysis to Program Design, 5e
  • 12. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 13. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 14. Logical (Boolean) Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 15. Precedence of Operators Java Programming: From Problem Analysis to Program Design, 5e
  • 16. Precedence of Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 17. Java Programming: From Problem Analysis to Program Design, 5e
  • 18. Java Programming: From Problem Analysis to Program Design, 5e
  • 19. Java Programming: From Problem Analysis to Program Design, 5e
  • 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
  • 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
  • 22. One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 23.
    • 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
    One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 24.
    • if (number < 0) //Line 4
    • number = -number; //Line 5
    • JOptionPane.showMessageDialog(null,
    • &quot;The absolute value of &quot; + temp
    • + &quot; is &quot; + number,
    • &quot;Absolute Value&quot;,
    • JOptionPane.INFORMATION_MESSAGE); //Line 6
    • System.exit(0);
    • }
    One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 25.
    • if (number < 0) //Line 4
    • number = -number; //Line 5
    • JOptionPane.showMessageDialog(null,
    • &quot;The absolute value of &quot; + temp
    • + &quot; is &quot; + number,
    • &quot;Absolute Value&quot;,
    • JOptionPane.INFORMATION_MESSAGE); //Line 6
    • System.exit(0);
    • }
    Java Programming: From Problem Analysis to Program Design, 5e
  • 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
  • 27. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 28. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e Example 4-10 if (hours > 40.0) wages = 40.0 * rate + 1.5 * rate * (hours - 40.0); else wages = hours * rate;
  • 29. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • 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
  • 30. Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 31. Compound (Block of) Statements
    • Syntax
    Java Programming: From Problem Analysis to Program Design, 5e
  • 32. Compound (Block of) Statements (continued)
    • if (age > 18)
    • {
    • System.out.println(&quot;Eligible to vote.&quot;);
    • System.out.println(&quot;No longer a minor.&quot;);
    • }
    • else
    • {
    • System.out.println(&quot;Not eligible to vote.&quot;);
    • System.out.println(&quot;Still a minor.&quot;);
    • }
    Java Programming: From Problem Analysis to Program Design, 5e
  • 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
  • 34. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 35. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e To avoid excessive indentation, the code in Example 4-15 can be rewritten as follows:
  • 36. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 37. Multiple Selection: Nested if (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 38. Java Programming: From Problem Analysis to Program Design, 5e
  • 39. Java Programming: From Problem Analysis to Program Design, 5e
  • 40.
    • 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
    Short-Circuit Evaluation Java Programming: From Problem Analysis to Program Design, 5e
  • 41. Short-Circuit Evaluation (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 42. Java Programming: From Problem Analysis to Program Design, 5e
  • 43. Java Programming: From Problem Analysis to Program Design, 5e
  • 44. Java Programming: From Problem Analysis to Program Design, 5e
  • 45. Java Programming: From Problem Analysis to Program Design, 5e
    • 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.
  • 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
  • 47. Java Programming: From Problem Analysis to Program Design, 5e
  • 48. Java Programming: From Problem Analysis to Program Design, 5e
  • 49. Java Programming: From Problem Analysis to Program Design, 5e
  • 50. Java Programming: From Problem Analysis to Program Design, 5e
  • 51. switch Structures Java Programming: From Problem Analysis to Program Design, 5e
  • 52. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • 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
  • 53. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • 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
  • 54. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
    • The break statement may or may not appear after each statements1 , statements2 , ..., statementsn
    • A switch structure may or may not have the default label
  • 55. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 56. switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 57.
    • Example 4-20
    • switch (grade)
    • {
    • case 'A':
    • System.out.println(&quot;The grade is A.&quot;);
    • break ;
    • case 'B':
    • System.out.println(&quot;The grade is B.&quot;);
    • break ;
    • case 'C':
    • System.out.println(&quot;The grade is C.&quot;);
    • break ;
    switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 58.
    • case 'D':
    • System.out.println(&quot;The grade is D.&quot;);
    • break ;
    • case 'F':
    • System.out.println(&quot;The grade is F.&quot;);
    • break ;
    • default :
    • System.out.println(&quot;The grade is invalid.&quot;);
    • }
    switch Structures (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 59. Java Programming: From Problem Analysis to Program Design, 5e
  • 60. Java Programming: From Problem Analysis to Program Design, 5e
  • 61. Java Programming: From Problem Analysis to Program Design, 5e
  • 62. Java Programming: From Problem Analysis to Program Design, 5e To output results correctly, the switch structure must include a break statement after each println statement, except the last println statement.
  • 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
  • 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
  • 65. Comparing Strings
    • class String
      • Method compareTo
      • Method equals
    • Given string str1 and str2
    Java Programming: From Problem Analysis to Program Design, 5e
  • 66. Comparing Strings (continued)
    • String str1 = &quot;Hello&quot;;
    • String str2 = &quot;Hi&quot;;
    • String str3 = &quot;Air&quot;;
    • String str4 = &quot;Bill&quot;;
    • String str5 = &quot;Bigger&quot;;
    Java Programming: From Problem Analysis to Program Design, 5e
  • 67. Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 68. Comparing Strings (continued) Java Programming: From Problem Analysis to Program Design, 5e
  • 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