Java Programming: From Problem Analysis to Program Design, 3e Chapter 4 Control Structures I: Selection

2Java Programming: From Problem Analysis to Program Design, 3e 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

3Java Programming: From Problem Analysis to Program Design, 3e 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)

4Java Programming: From Problem Analysis to Program Design, 3e Flow of Execution

5Java Programming: From Problem Analysis to Program Design, 3e 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

6Java Programming: From Problem Analysis to Program Design, 3e Relational Operators in Java

7Java Programming: From Problem Analysis to Program Design, 3e 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

8Java Programming: From Problem Analysis to Program Design, 3e Relational Operators and the Unicode Collating Sequence

9Java Programming: From Problem Analysis to Program Design, 3e Comparing Strings class String –Method compareTo –Method equals Given string str1 and str2

10Java Programming: From Problem Analysis to Program Design, 3e Comparing Strings (continued) String str1 = "Hello"; String str2 = "Hi"; String str3 = "Air"; String str4 = "Bill"; String str5 = "Bigger";

11Java Programming: From Problem Analysis to Program Design, 3e Comparing Strings (continued)

12Java Programming: From Problem Analysis to Program Design, 3e Comparing Strings (continued)

13Java Programming: From Problem Analysis to Program Design, 3e Logical (Boolean) Operators

14Java Programming: From Problem Analysis to Program Design, 3e Logical (Boolean) Operators (continued)

15Java Programming: From Problem Analysis to Program Design, 3e Logical (Boolean) Operators (continued)

16Java Programming: From Problem Analysis to Program Design, 3e Logical (Boolean) Operators (continued)

17Java Programming: From Problem Analysis to Program Design, 3e Precedence of Operators

18Java Programming: From Problem Analysis to Program Design, 3e 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

19Java Programming: From Problem Analysis to Program Design, 3e Selection One-Way Selection Two-Way Selection Compound (Block of) Statements Multiple Selections (Nested if) Conditional Operator switch Structures

20Java Programming: From Problem Analysis to Program Design, 3e One-Way Selection Syntax: if (expression) statement Expression referred to as decision maker Statement referred to as action statement

One-Way Selection (continued) Java Programming: From Problem Analysis to Program Design, 3e21

22Java Programming: From Problem Analysis to Program Design, 3e Example 4-11 //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)

23Java Programming: From Problem Analysis to Program Design, 3e 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); } One-Way Selection (continued)

24Java Programming: From Problem Analysis to Program Design, 3e Two-Way Selection Syntax: if (expression) statement1 else statement2 else statement must be paired with an if

25Java Programming: From Problem Analysis to Program Design, 3e Two-Way Selection (continued)

26Java Programming: From Problem Analysis to Program Design, 3e Two-Way Selection (continued) Example 4-14 if (hours > 40.0) wages = 40.0 * rate * rate * (hours ); else wages = hours * rate;

27Java Programming: From Problem Analysis to Program Design, 3e Example 4-15 if (hours > 40.0); //Line 1 wages = 40.0 * rate * rate * (hours ); //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 Two-Way Selection (continued)

28Java Programming: From Problem Analysis to Program Design, 3e Compound (Block of) Statements Syntax

29Java Programming: From Problem Analysis to Program Design, 3e 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."); }

30Java Programming: From Problem Analysis to Program Design, 3e 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

31Java Programming: From Problem Analysis to Program Design, 3e 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 expression3

32Java Programming: From Problem Analysis to Program Design, 3e switch Structures

33Java Programming: From Problem Analysis to Program Design, 3e 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 integral, that is, an integer switch Structures (continued)

Integral values also include values of type char 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, 3e34

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, 3e35

36Java Programming: From Problem Analysis to Program Design, 3e switch Structures (continued)

37Java Programming: From Problem Analysis to Program Design, 3e switch Structures (continued)

38Java Programming: From Problem Analysis to Program Design, 3e Example 4-24 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; switch Structures (continued)

39Java Programming: From Problem Analysis to Program Design, 3e 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."); } switch Structures (continued)

40Java Programming: From Problem Analysis to Program Design, 3e 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

41Java Programming: From Problem Analysis to Program Design, 3e 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 switch statement to determine amount due by each customer

42Java Programming: From Problem Analysis to Program Design, 3e Chapter Summary Control structures are used to process programs Logical expressions and order of precedence of operators are used in expressions Compare strings If statements if … else statements switch structures Proper syntax for using control statements