Java Programming: From Problem Analysis to Program Design, 5e PDF

Java Programming: From Problem Analysis to Program Design, 5e Chapter 4 Control Structures I: Selection  Chapter Objectives Learn about control structures Examine relational and logical operators Explore how to form and evaluate logical (Boolean) ex...

Java Programming: From Problem Analysis to Program Design, 5e Chapter 4 Control Structures I: Selection  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  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  Flow of Execution Java Programming: From Problem Analysis to Program Design, 5e 4  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  Relational Operators in Java Java Programming: From Problem Analysis to Program Design, 5e 6  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 Java Programming: From Problem Analysis to Program Design, 5e 8 Java Programming: From Problem Analysis to Program Design, 5e 9  Relational Operators and the Unicode Collating Sequence Java Programming: From Problem Analysis to Program Design, 5e 10  Logical (Boolean) Operators Java Programming: From Problem Analysis to Program Design, 5e 11  Logical (Boolean) Operators (continued) 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  Precedence of Operators Java Programming: From Problem Analysis to Program Design, 5e 15  Precedence of Operators (continued) Java Programming: From Problem Analysis to Program Design, 5e 16 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  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  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  One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 22  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  One-Way Selection (continued) if (number < 0) //Line 4 number = -number; //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  if (number < 0) //Line 4 number = -number; //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  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  Two-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 5e 27  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  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  Two-Way Selection (continued) Assume that you will create a program that calculates the wages of an employee based on their worked hours and considers overtime, if hours exceed the standard 40 hours per week. His rate is 500 per hour. Overtime multiplier is 1.5. Java Programming: From Problem Analysis to Program Design, 5e 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("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 33  Multiple Selection: Nested if Syntax Else associated with most recent incomplete if (expression1) if statement1 else if (expression2) Multiple if statements statement2 can be used in place of else if…else statements statement3 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) To avoid excessive indentation, the code in Example 4-15 can be rewritten as follows: Java Programming: From Problem Analysis to Program Design, 5e 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  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 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  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 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) 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 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 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 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  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 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 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 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 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 an integer  0 if string str1  str2  str1.compa reTo(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 66  Comparing Strings (continued) String str1 = "Hello"; String str2 = "Hi"; String str3 = "Air"; String str4 = "Bill"; String str5 = "Bigger"; 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 70