Download ch04

Chapter 4:
Control Structures I
Java Programming:
Program Design Including Data Structures
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
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
repeating statements
Java Programming: Program Design Including Data Structures
3
Control Structures (continued)
Java Programming: Program Design Including Data Structures
4
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
5
Relational Operators (continued)
Java Programming: Program Design Including Data Structures
6
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
7
Relational Operators and Primitive
Data Types (continued)
Java Programming: Program Design Including Data Structures
8
Relational Operators and Primitive
Data Types (continued)
Fragment of the UNICODE table
Java Programming: Program Design Including Data Structures
9
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: Program Design Including Data Structures
10
Comparing Strings (continued)
String
String
String
String
String
str1
str2
str3
str4
str5
=
=
=
=
=
"Hello";
"Hi";
"Air";
"Bill";
"Bigger";
Java Programming: Program Design Including Data Structures
11
Comparing Strings (continued)
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
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
16
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
17
One-Way Selection
 Syntax:
if (expression)
statement
 Expression called decision maker
 Statement called action statement
Java Programming: Program Design Including Data Structures
18
One-Way Selection
 Example
String letterGrade = “P”;
Int grade;
…
if
(grade < 75)
letterGrade = “F”;
…
Java Programming: Program Design Including Data Structures
19
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
20
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: Program Design Including Data Structures
21
Two-Way Selection
 Syntax:
if (expression)
statement1
else
statement2
 else statement must be paired with an if.
Java Programming: Program Design Including Data Structures
22
Two-Way Selection (continued)
Java Programming: Program Design Including Data Structures
23
Two-Way Selection (continued)
Example 4-14
if (hours > 40.0)
wages = 40.0 * rate + 1.5 * rate * (hours - 40.0);
else
wages = hours * rate;
Java Programming: Program Design Including Data Structures
24
Compound (Block of) Statements
Syntax:
{
statement1
statement2
.
.
.
statementn
}
Java Programming: Program Design Including Data Structures
25
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
26
Multiple Selection: Nested if
 Syntax:
 Else is associated with the
most recent incomplete if
 Multiple if statements can
if (expression1)
be used in place of
statement1
if…else statements
else
 May take longer to
if (expression2)
evaluate
statement2
else
statement3
Java Programming: Program Design Including Data Structures
27
Multiple Selection: Nested if
 Example:
if (studentStatus = “AUDIT”)
letterGrade = “*”;
else
if (grade > 75 )
letterGrade = “P”;
else
letterGrade = “F”;
Java Programming: Program Design Including Data Structures
28
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
29
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
30
switch Structures
switch (expression)
{
case value1: statements1
break;
case value2: statements2
break;
...
case valuen: statementsn
break;
default: statements
}
Java Programming: Program Design Including Data Structures
 Expression is also
known as selector
 Expression can be an
identifier
 Value can only be
integral
31
switch Structures (continued)
Java Programming: Program Design Including Data Structures
32
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.");
break;
case 'C': System.out.println("The grade is C.");
break;
case 'D': System.out.println("The grade is D.");
break;
case 'F': System.out.println("The grade is F.");
break;
default: System.out.println("Grade is invalid.");
}
Java Programming: Program Design Including Data Structures
33
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
34
Programming Example:
Cable Company Billing
(continued)
Solution:
1. Prompt user for information
2. Use switch statements based on customer’s
type
3. Use an if statement nested within a switch
statement to determine the amount due by
each customer
Java Programming: Program Design Including Data Structures
35
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
36