1. 5.3 Multiple Alternatives (Part 1)
The multiway if-else statement is simply a normal if-else statement that nests another if-else statement at every else branch
It is indented differently from other nested statements
All of the Boolean_Expressions are aligned with one another, and their corresponding actions are also aligned with one another
The Boolean_Expressions are evaluated in order until one that evaluates to true is found
The final else is optional
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

2. Multiway if-else Statement
if (Boolean_Expression)
Statement_1
else if (Boolean_Expression)
Statement_2
else if (Boolean_Expression_n)
Statement_n
else
Statement_For_All_Other_Possibilities
. . .
Copyright © 2012 Pearson Addison-Wesley. All rights reserved.

3. Multiway if-else Statement
if (PercentageGrade >= 90)
System.out.println(“Your grade is A.”);
else if (PercentageGrade >= 80)
System.out.println(“Your grade is B.”);
else if (PercentageGrade >= 70)
System.out.println(“Your grade is C.”);
else if (PercentageGrade >= 60)
System.out.println(“Your grade is D.”);
else
System.out.println(“Your grade is F.”);
. . .
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4. The switch Statement
The switch statement is the only other kind of Java statement that implements multiway branching
When a switch statement is evaluated, one of a number of different branches is executed
The choice of which branch to execute is determined by a controlling expression enclosed in parentheses after the keyword switch
The controlling expression must evaluate to a char, int, short, or byte
Copyright © 2012 Pearson Addison-Wesley. All rights reserved.

5. The switch Statement int vehicleClass; double tool; . . .
switch (vehicleClass) {
case 1:
System.out.println(“Passenger car.”);
toll = 0.50;
break;
case 2:
System.out.println(“Bus.”);
toll = 1.50;
case 3:
System.out.println(“Truck.”);
toll = 2.00;
default:
System.out.println(“Unknown vehicle class!”); }
Copyright © 2012 Pearson Addison-Wesley. All rights reserved.
3-5

6. The switch Statement
Each branch statement in a switch statement starts with the reserved word case, followed by a constant called a case label, followed by a colon, and then a sequence of statements
Each case label must be of the same type as the controlling expression
Case labels need not be listed in order or span a complete interval, but each one may appear only once
Each sequence of statements may be followed by a break statement ( break;)
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7. The switch Statement There can also be a section labeled default:
The default section is optional, and is usually last
Even if the case labels cover all possible outcomes in a given switch statement, it is still a good practice to include a default section
It can be used to output an error message, for example
When the controlling expression is evaluated, the code for the case label whose value matches the controlling expression is executed
If no case label matches, then the only statements executed are those following the default label (if there is one)
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8. The switch Statement
The switch statement ends when it executes a break statement, or when the end of the switch statement is reached
When the computer executes the statements after a case label, it continues until a break statement is reached
If the break statement is omitted, then after executing the code for one case, the computer will go on to execute the code for the next case
If the break statement is omitted inadvertently, the compiler will not issue an error message
Copyright © 2012 Pearson Addison-Wesley. All rights reserved.

9. The switch Statement switch (Controlling_Expression) {
case Case_Label_1:
Statement_Sequence_1
break;
case Case_Label_2:
Statement_Sequence_2
case Case_Label_n:
Statement_Sequence_n
default:
Default_Statement Sequence }
. . .
Copyright © 2012 Pearson Addison-Wesley. All rights reserved.

10. 5.3 Multiple Alternatives (Part 2)
Sequences of Comparisons
if (condition1)
statement1;
else if (condition2)
statement2;
...
else
statement4;
The first matching condition is executed
Order matters:
if (richter >= 0) // always passes
r = "Generally not felt by people";
else if (richter >= 3.5) // not tested
r = "Felt by many people, no destruction";
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

11. Multiple Alternatives: Sequences of Comparisons
Don’t omit else:
if (richter >= 8.0)
r = "Most structures fall";
if (richter >= 7.0) // omitted else--ERROR
r = "Many buildings destroyed";
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

12. ch05/quake/Earthquake.java Continued 1 /**
1 /**
2 A class that describes the effects of an earthquake.
3 */
4 public class Earthquake {
5 private double richter; 6
7 /**
Constructs an Earthquake object.
@param magnitude the magnitude on the Richter scale */
public Earthquake(double magnitude){
richter = magnitude; } 14
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

13. ch05/quake/Earthquake.java (cont.)
/**
Gets a description of the effect of the earthquake.
@return the description of the effect */
public String getDescription() {
String r;
if (richter >= 8.0)
r = "Most structures fall";
else if (richter >= 7.0)
r = "Many buildings destroyed";
else if (richter >= 6.0)
r = "Many buildings considerably damaged, some collapse";
else if (richter >= 4.5)
r = "Damage to poorly constructed buildings";
else if (richter >= 3.5)
r = "Felt by many people, no destruction";
else if (richter >= 0)
r = "Generally not felt by people";
else
r = "Negative numbers are not valid";
return r; }
39 }
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

14. ch05/quake/EarthquakeRunner.java Program Run:
1 import java.util.Scanner; 2
3 /**
4 This program prints a description of an earthquake of a given magnitude.
5 */
6 public class EarthquakeRunner {
7 public static void main(String[] args) {
Scanner in = new Scanner(System.in); 9
System.out.print("Enter a magnitude on the Richter scale: ");
double magnitude = in.nextDouble();
Earthquake quake = new Earthquake(magnitude);
System.out.println(quake.getDescription()); }
15 }
Program Run:
Enter a magnitude on the Richter scale: 7.1
Many buildings destroyed
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

15. A sequence of if/else if/else that compares a single value
The switch Statement
A sequence of if/else if/else that compares a single value
against constant alternatives
switch (digit) {
case 1: System.out.print("one"); break;
case 2: System.out.print("two"); break;
case 3: System.out.print("three"); break;
case 4: System.out.print("four"); break;
case 5: System.out.print("five"); break;
case 6: System.out.print("six"); break;
case 7: System.out.print("seven"); break;
case 8: System.out.print("eight"); break;
case 9: System.out.print("nine"); break;
default: System.out.print("error"); break; }
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

16. Multiple Alternatives: Nested Branches
Branch inside another branch:
if (condition1) {
if (condition2)
statement2a;
else
statement2b; }
statement1;
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

17. If your filing status is Single If your filing status is Married
Tax Schedule
If your filing status is Single
If your filing status is Married
Tax Bracket
Percentage
$0 ... $32,000
10%
0 ... $64,000
Amount over $32,000
25%
Amount over $64,000
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

18. Compute taxes due, given filing status and income figure:
Nested Branches
Compute taxes due, given filing status and income figure:
branch on the filing status
for each filing status, branch on income level
The two-level decision process is reflected in two levels of if statements
We say that the income test is nested inside the test for filing status
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

19. Nested Branches Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

20. ch05/tax/TaxReturn.java Continued 1 /**
1 /**
2 A tax return of a taxpayer in 2008.
3 */
4 public class TaxReturn {
5 public static final int SINGLE = 1;
6 public static final int MARRIED = 2; 7
8 private static final double RATE1 = 0.10;
9 private static final double RATE2 = 0.25;
private static final double RATE1_SINGLE_LIMIT = 32000;
private static final double RATE1_MARRIED_LIMIT = 64000; 12
private double income;
private int status; 15
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

21. ch05/tax/TaxReturn.java (cont.)
/**
Constructs a TaxReturn object for a given income and
marital status.
@param anIncome the taxpayer income
@param aStatus either SINGLE or MARRIED */
public TaxReturn(double anIncome, int aStatus){
income = anIncome;
status = aStatus; } 27
public double getTax() {
double tax1 = 0;
double tax2 = 0; 31
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

22. ch05/tax/TaxReturn.java (cont.)
if (status == SINGLE) {
if (income <= RATE1_SINGLE_LIMIT) {
tax1 = RATE1 * income; }
else {
tax1 = RATE1 * RATE1_SINGLE_LIMIT;
tax2 = RATE2 * (income - RATE1_SINGLE_LIMIT); } }
else {
if (income <= RATE1_MARRIED_LIMIT)
tax1 = RATE1 * income; }
else {
tax1 = RATE1 * RATE1_MARRIED_LIMIT;
tax2 = RATE2 * (income - RATE1_MARRIED_LIMIT); } } 52
return tax1 + tax2; }
55 }
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

23. ch05/tax/TaxCalculator.java Continued 1 import java.util.Scanner; 2
3 /**
4 This program calculates a simple tax return.
5 */
6 public class TaxCalculator {
7 public static void main(String[] args) {
Scanner in = new Scanner(System.in); 9
System.out.print("Please enter your income: ");
double income = in.nextDouble(); 12
System.out.print("Are you married? (Y/N) ");
String input = in.next();
int status;
if (input.equalsIgnoreCase("Y"))
status = TaxReturn.MARRIED;
else
status = TaxReturn.SINGLE;
TaxReturn aTaxReturn = new TaxReturn(income, status); 21
System.out.println("Tax: "
aTaxReturn.getTax()); }
25 }
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

24. ch05/tax/TaxCalculator.java (cont.)
Program Run:
Please enter your income: 50000
Are you married? (Y/N) N
Tax:
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.

25. Answer: Yes, if you also reverse the comparisons:
Self Check 5.5
The if/else/else statement for the earthquake strength first tested for higher values, then descended to lower values. Can you reverse that order?
Answer: Yes, if you also reverse the comparisons:
if (richter < 3.5)
r = "Generally not felt by people";
else if (richter < 4.5)
r = "Felt by many people, no destruction";
else if (richter < 6.0)
r = "Damage to poorly constructed buildings";
...