1. SWE 510: Object Oriented Programming in Java
Branching Mechanism
This slide set was compiled from the Absolute Java textbook slides (Walter Savitch) and the instructor’s class materials.
SWE 510: Object Oriented Programming in Java

2. SWE 510: Object Oriented Programming in Java
Flow of Control
Branching mechanisms
if-else if
switch (break)
Looping mechanisms
while
do while
for
Boolean expressions
evaluate to either true or false and decide
which branch the control should go to
if the control should stay in a loop
SWE 510: Object Oriented Programming in Java

3. SWE 510: Object Oriented Programming in Java
if-else Statement
Prev_Statement
Syntax
Previous_Statement
if ( Boolean_Expression )
Yes_Statement
else
No_Statement
Next_Statement
Examples
if ( time < limit )
System.out.println( “You made it” );
System.out.println( “You missed the deadline” );
if ( side1 + side2 > side3 && side2 + side3 > side1 && side3 + side1 > side2 )
System.out.println( “Forms a triangle” );
System.out.println( “Does not form a triangle” );
Boolean
Expression?
true
Yes_Statement
false
No_Statement
Next_Statement
SWE 510: Object Oriented Programming in Java

4. SWE 510: Object Oriented Programming in Java
Omitting the else Part
Prev_Statement
Syntax
Previous_Statement
if ( Boolean_Expression )
Yes_Statement
Action_Statement
Examples
if ( weight > ideal )
calorieAllotment = calorieAllotment - 500;
if ( mph > 60 )
System.out.println( “Too fast” );
Boolean
Expression?
true
Action_Statement
false
Next_Statement
SWE 510: Object Oriented Programming in Java

5. SWE 510: Object Oriented Programming in Java
Compound Statements
Each Yes_Statement and No_Statement branch of an if-else can be a made up of a single statement or many statements
Syntax
if ( Boolean_Expression ) {
Yes_Statement1;
Yes_statement2;
...; }
else
No_Statement1;
No_Statement2;
Example
if ( myScore > yourScore )
System.out.println( “I win!” );
wager += 100;
System.out.println( “I wish these were golf scores” );
wager = 0;
Yes_Statement1
Yes_Statement2 …
Boolean
Expression?
true
false
No_Statement1
No_Statement2 …
SWE 510: Object Oriented Programming in Java

6. SWE 510: Object Oriented Programming in Java
Nested Statements
if-else statements and if statements both contain smaller statements within them
Example
if ( side1 == side2 ) {
System.out.println( “Isoceles” );
if ( side2 == side3 )
System.out.println( “Equilateral” ); }
Equivalent
if ( side1 == side2 )
System.out.println( “Isoceles” );
if ( side1 == side2 && side2 == side3 (
System.out.println( “Equilateral” );
SWE 510: Object Oriented Programming in Java

7. Multiway if-else Statement
Syntax
if (Boolean_Expression_1)
Statement_1
else if (Boolean_Expression_2)
Statement_2
else if (Boolean_Expression_n)
Statement_n
else
Statement_For_All_Other_Possibilities
Example
if ( testScore >= 95 )
grade = ‘A’;
else if ( testScore >= 85 )
grade = ‘B’;
else if ( testScore >= 75 )
grade = ‘C’;
else if ( testScore >= 65 )
grade = ‘D’;
grade = ‘F’;
System.out.println( “grade = ” + grade );
Expression_1?
Statement_1
Expression_2?
Statement_2
Expression_n?
Statement_n
Other_Statement
SWE 510: Object Oriented Programming in Java

8. SWE 510: Object Oriented Programming in Java
What’s Redundant?
Improve Textbook p101’s code
if ( netIncome <= )
tax = 0;
else if ( ( netIncome > ) && ( netIncome <= ) )
tax = 0.05 * ( netIncome – );
else {
fivePercentTax = 0.05 * 15000;
tenPercentTax = 0.10 * ( netIncome – );
tax = fivePercentTax + tenPercentTax; }
true
netIncome <= 15000
Tax = 0
false
true
netIncome <= 30000
Tax = 0.05 * …
false
Tax = 0.05 * … * ….;
SWE 510: Object Oriented Programming in Java

9. SWE 510: Object Oriented Programming in Java
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
Syntax
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 }
Must be a constant:
char, int, short, or byte
Controlling_Exp
Label_1?
true
Statement_1
false
Label_2?
Statement_2
Label_n?
Statement_n
default_Statement
Optional but recommended
Executed in none of label_1 ~ n
SWE 510: Object Oriented Programming in Java

10. SWE 510: Object Oriented Programming in Java
Example 1 (Textbook p103)
int vehicleClass;
double toll;
...;
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!” ); }
A controlling expression must return
char, int, short, or byte.
Case labels must be a constant.
Recommended to detect error cases.
SWE 510: Object Oriented Programming in Java

11. Example 2 (java.sun.com tutorial)
A controlling expression must return
char, int, short, or byte.
class SwitchDemo {
public static void main(String[] args) {
int month = 8;
switch (month) {
case 1: System.out.println("January"); break;
case 2: System.out.println("February"); break;
case 3: System.out.println("March"); break;
case 4: System.out.println("April"); break;
case 5: System.out.println("May"); break;
case 6: System.out.println("June"); break;
case 7: System.out.println("July"); break;
case 8: System.out.println("August"); break;
case 9: System.out.println("September"); break;
case 10: System.out.println("October"); break;
case 11: System.out.println("November"); break;
case 12: System.out.println("December"); break;
default: System.out.println("Invalid month."); break; }
Case labels must be a constant.
Recommended to detect error cases.
SWE 510: Object Oriented Programming in Java

12. switch Statement without breaks
Syntax
switch (Controlling_Expression) {
case Case_Label_1:
Statement_Sequence_1
case Case_Label_2:
Statement_Sequence_2
break;
case Case_Label_m;
Statement_Sequence_m
case Case_Label_n:
Statement_Sequence_n
default:
Default_Statement Sequence }
Controlling_Exp
Label_1?
true
Statement_1
false
Label_2?
Statement_2
Label_m?
Statement_m
Label_n?
Statement_n
Default_stmt
SWE 510: Object Oriented Programming in Java

13. Example 3 (java.sun.com tutorial)
class SwitchDemo2 {
public static void main(String[] args) {
int month = 2;
int year = 2000;
int numDays = 0;
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
numDays = 31;
break;
case 4:
case 6:
case 9:
case 11:
numDays = 30;
case 2:
if ( ((year % 4 == 0) && !(year % 100 == 0)) || (year % 400 == 0) )
numDays = 29;
else
numDays = 28;
default:
System.out.println("Invalid month."); }
System.out.println("Number of Days = " + numDays);
SWE 510: Object Oriented Programming in Java

14. PITFALL: Forgetting a break
class SwitchDemo2 {
public static void main(String[] args) {
int month = 2;
int year = 2000;
int numDays = 0;
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
numDays = 31;
case 4:
case 6:
case 9:
case 11:
numDays = 30;
case 2:
if ( ((year % 4 == 0) && !(year % 100 == 0)) || (year % 400 == 0) )
numDays = 29;
else
numDays = 28;
default:
System.out.println("Invalid month."); }
System.out.println("Number of Days = " + numDays);
Compiler does not complain about no breaks.
Control continues down to the next case.
SWE 510: Object Oriented Programming in Java

15. SWE 510: Object Oriented Programming in Java
Conditional Operator
A notational variant on certain forms of the if-else statement
Also called the ternary operator or arithmetic if
Syntax
( Boolean_Expression ) ? Yes_Expression : No_Expression;
// if Boolean_Expression is true, evaluate Yes_Expression,
// otherwise evaluate No_Expression, and finally return the
// resulted value.
Example
max = ( n1 > n2 ) ? n1 : n2;
Equivalent
if ( n1 > n2 )
max = n1;
else
max = n2;
SWE 510: Object Oriented Programming in Java