1. Chapter 4: Control Structures I
Java Programming:
Program Design Including Data Structures

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: Program Design Including Data Structures

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 repeating statements
Java Programming: Program Design Including Data Structures

4. Control Structures (continued)
Java Programming: Program Design Including Data Structures

5. Relational Operators Relational operator:
Allows you to make comparisons in a program
Binary operator ( equal to, greater than, … )
Condition is represented by a logical expression in Java
Logical expression: An expression that has a value of either true or false
Java Programming: Program Design Including Data Structures

6. Relational Operators (continued)
Java Programming: Program Design Including Data Structures

7. Relational Operators and Primitive Data Types
Can use with
Integral data types
Floating-point data types
char data type
Unicode Collating Sequence
Java Programming: Program Design Including Data Structures

8. Relational Operators and Primitive Data Types (continued)
Java Programming: Program Design Including Data Structures

9. Relational Operators and Primitive Data Types (continued)
Fragment of the UNICODE table
Java Programming: Program Design Including Data Structures

10. Comparing Strings class String Given string str1 and str2
Method compareTo
Method equals
Given string str1 and str2
Java Programming: Program Design Including Data Structures

11. Comparing Strings (continued)
String str1 = "Hello";
String str2 = "Hi";
String str3 = "Air";
String str4 = "Bill";
String str5 = "Bigger";
Java Programming: Program Design Including Data Structures

12. Comparing Strings (continued)
Java Programming: Program Design Including Data Structures

13. Comparing Strings (continued)
Java Programming: Program Design Including Data Structures

14. Comparing Strings (continued)
Java Programming: Program Design Including Data Structures

15. Comparing Strings (continued)
Java Programming: Program Design Including Data Structures

16. Short-Circuit Evaluation
Computer evaluates a logical expression from left to right and stops as soon as the value of the expression is known
Java Programming: Program Design Including Data Structures

17. Selection One-way selection Two-way selection
Compound (block of) statements
Multiple selections (nested if)
Conditional operator
switch structures
Java Programming: Program Design Including Data Structures

18. One-Way Selection Syntax: Expression called decision maker
if (expression)
statement
Expression called decision maker
Statement called action statement
Java Programming: Program Design Including Data Structures

19. One-Way Selection Example String letterGrade = “P”; Int grade; …
if (grade < 75)
letterGrade = “F”;
Java Programming: Program Design Including Data Structures

20. One-Way Selection (continued)
Example 4-11
//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: Program Design Including Data Structures

21. 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: Program Design Including Data Structures

22. Two-Way Selection Syntax: if (expression) statement1 else statement2
else statement must be paired with an if.
Java Programming: Program Design Including Data Structures

23. Two-Way Selection (continued)
Java Programming: Program Design Including Data Structures

24. Two-Way Selection (continued)
Example 4-14
if (hours > 40.0)
wages = 40.0 * rate * rate * (hours ); else
wages = hours * rate;
Java Programming: Program Design Including Data Structures

25. Compound (Block of) Statements
Syntax: {
statement1
statement2 .
statementn }
Java Programming: Program Design Including Data Structures

26. 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: Program Design Including Data Structures

27. Multiple Selection: Nested if
Syntax:
if (expression1)
statement1
else
if (expression2)
statement2
statement3
Else is associated with the most recent incomplete if
Multiple if statements can be used in place of if…else statements
May take longer to evaluate
Java Programming: Program Design Including Data Structures

28. Multiple Selection: Nested if
Example:
if (studentStatus = “AUDIT”)
letterGrade = “*”;
else
if (grade > 75 )
letterGrade = “P”;
letterGrade = “F”;
Java Programming: Program Design Including Data Structures

29. Conditional (? :) Operator
Ternary operator
Syntax:
expression1 ? expression2 : expression3
If expression1 = true, then the result of the condition is expression2
Otherwise, the result is expression3
Java Programming: Program Design Including Data Structures

30. Conditional (? :) Operator
Example
letterGrade = (finalGrade > 75) ? “Pass” : “Fail”;
Same as
if (finalGrade > 75 )
letterGrade = “Pass”;
Else
letterGrade = “Fail”;
Java Programming: Program Design Including Data Structures

31. switch Structures Expression is also known as selector
switch (expression) {
case value1: statements1
break;
case value2: statements2
...
case valuen: statementsn
default: statements }
Expression is also known as selector
Expression can be an identifier
Value can only be integral
Java Programming: Program Design Including Data Structures

32. switch Structures (continued)
Java Programming: Program Design Including Data Structures

33. switch Structures (continued)
Example 4-24
switch (grade) {
case 'A': System.out.println("The grade is A.");
break;
case 'B': System.out.println("The grade is B.");
case 'C': System.out.println("The grade is C.");
case 'D': System.out.println("The grade is D.");
case 'F': System.out.println("The grade is F.");
default: System.out.println("Grade is invalid."); }
Java Programming: Program Design Including Data Structures

34. 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 the case of business customers)
Output:
Customer’s account number and the billing amount
Java Programming: Program Design Including Data Structures

35. 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 the amount due by each customer
Java Programming: Program Design Including Data Structures

36. Chapter Summary Control structures are used to process programs
Logical expressions and order of precedence of operators are used in expressions
Comparing strings
If statement
if…else statements
switch structures
Proper syntax for using control statements
Java Programming: Program Design Including Data Structures