0
Chapter 3 Selections

1

Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rig...
Motivations
If you assigned a negative value for radius in
Listing 2.1, ComputeArea.java, the program would
print an inval...
Objectives
To declare boolean type and write Boolean expressions using comparison operators (§3.2).
To program AdditionQui...
The boolean Type and Operators
Often in a program you need to compare two
values, such as whether i is greater than j. Jav...
Comparison Operators
Operator Name
<

less than

<=

less than or equal to

>

greater than

>=

greater than or equal to
...
Problem: A Simple Math Learning Tool
This example creates a program to let a first grader
practice additions. The program ...
One-way if Statements
if (boolean-expression) {
statement(s);
}

Boolean
Expression

false

if (radius >= 0) {
area = radi...
Note
if i > 0 {
System.out.println("i is positive");
}

if (i > 0) {
System.out.println("i is positive");
}

(a) Wrong

if...
Simple if Demo
Write a program that prompts the user to enter an integer. If the
number is a multiple of 5, print HiFive. ...
Problem: Guessing Birthday
The program can guess your birth date. Run
to see how it works.
= 19
+

1 3 5 7
9 11 13 15
17 1...
Mathematics Basis for the Game
19 is 10011 in binary. 7 is 111 in binary. 23 is 11101 in binary
10000
10
+
1
10011

10000
...
The Two-way if Statement
if (boolean-expression) {
statement(s)-for-the-true-case;
}
else {
statement(s)-for-the-false-cas...
if...else Example
if (radius >= 0) {
area = radius * radius * 3.14159;
System.out.println("The area for the “
+ “circle of...
Multiple Alternative if Statements
if (score >= 90.0)
grade = 'A';
else
if (score >= 80.0)
grade = 'B';
else
if (score >= ...
animation

Trace if-else statement

Suppose score is 70.0

The condition is false

if (score >= 90.0)
grade = 'A';
else if...
animation

Trace if-else statement

Suppose score is 70.0

The condition is false

if (score >= 90.0)
grade = 'A';
else if...
animation

Trace if-else statement

Suppose score is 70.0

The condition is true

if (score >= 90.0)
grade = 'A';
else if ...
animation

Trace if-else statement

Suppose score is 70.0

grade is C

if (score >= 90.0)
grade = 'A';
else if (score >= 8...
animation

Trace if-else statement

Suppose score is 70.0

Exit the if statement

if (score >= 90.0)
grade = 'A';
else if ...
Note
The else clause matches the most recent if clause in the
same block.
int i = 1;
int j = 2;
int k = 3;

Equivalent

if...
Note, cont.
Nothing is printed from the preceding statement. To
force the else clause to match the first if clause, you mu...
Common Errors
Adding a semicolon at the end of an if clause is a common
mistake.
if (radius >= 0);
Wrong
{
area = radius*r...
TIP
if (number % 2 == 0)
even = true;
else
even = false;

Equivalent

boolean even
= number % 2 == 0;
(b)

(a)

23

Liang,...
CAUTION
if (even == true)
System.out.println(
"It is even.");

Equivalent

if (even)
System.out.println(
"It is even.");
(...
Problem: An Improved Math Learning Tool
This example creates a program to teach a
first grade child how to learn subtracti...
Problem: Body Mass Index
Body Mass Index (BMI) is a measure of health on
weight. It can be calculated by taking your weigh...
Problem: Computing Taxes
The US federal personal income tax is calculated
based on the filing status and taxable income.
T...
Problem: Computing Taxes, cont.
if (status == 0) {
// Compute tax for single filers
}
else if (status == 1) {
// Compute t...
Logical Operators
Operator Name
!

not

&&

and

||

or

^

exclusive or

29

Liang, Introduction to Java Programming, Eig...
Truth Table for Operator !
p

!p

Example (assume age = 24, gender = 'M')

true

false

!(age > 18) is false, because (age...
Truth Table for Operator &&
p1

p2

p1 && p2

Example (assume age = 24, gender = 'F')

false

false

false

false

true

f...
Truth Table for Operator ||
p1

p2

p1 || p2

Example (assume age = 24, gender = 'F')

false

false

false

false

true

t...
Examples
Here is a program that checks whether a number is divisible by 2
and 3, whether a number is divisible by 2 or 3, ...
Truth Table for Operator !
p

!p

true

false

!(1 > 2) is true, because (1 > 2) is false.

false

true

!(1 > 0) is false...
Truth Table for Operator &&
p1

p2

p1 && p2

false

false

false

false

true

false

true

false

false

true

true

tru...
Truth Table for Operator ||
p1

p2

p1 || p2

false

false

false

false

true

true

true

false

true

true

true

true
...
Truth Table for Operator ^
p1

p2

p1 ^ p2

Example (assume age = 24, gender = 'F')

false

false

false

false

true

tru...
Examples
System.out.println("Is " + number + " divisible by 2 and 3? " +
((number % 2 == 0) && (number % 3 == 0)));

Syste...
Companion
Website

The & and | Operators

Supplement III.B, “The & and | Operators”

39

Liang, Introduction to Java Progr...
Companion
Website

The & and | Operators

If x is 1, what is x after this
expression?
(x > 1) & (x++ < 10)
If x is 1, what...
Problem: Determining Leap Year?
This program first prompts the user to enter a year as
an int value and checks if it is a ...
Problem: Lottery
Write a program that randomly generates a lottery of a twodigit number, prompts the user to enter a two-d...
switch Statements
switch (status) {
case 0: compute taxes for single filers;
break;
case 1: compute taxes for married file...
switch Statement Flow Chart
status is 0

Compute tax for single filers

break

Compute tax for married file jointly

break...
switch Statement Rules
The switch-expression must
yield a value of char, byte,
short, or int type and must
always be enclo...
switch Statement Rules
The keyword break is optional,
but it should be used at the end of
each case in order to terminate ...
animation

Trace switch statement

Suppose ch is 'a':

switch
case
case
case
}

(ch)
'a':
'b':
'c':

{
System.out.println(...
animation

Trace switch statement
ch is 'a':

switch
case
case
case
}

(ch)
'a':
'b':
'c':

{
System.out.println(ch);
Syst...
animation

Trace switch statement
Execute this line

switch
case
case
case
}

(ch)
'a':
'b':
'c':

{
System.out.println(ch...
animation

Trace switch statement
Execute this line

switch
case
case
case
}

(ch)
'a':
'b':
'c':

{
System.out.println(ch...
animation

Trace switch statement
Execute this line

switch
case
case
case
}

(ch)
'a':
'b':
'c':

{
System.out.println(ch...
animation

Trace switch statement
Execute next statement

switch
case
case
case
}

(ch)
'a':
'b':
'c':

{
System.out.print...
animation

Trace switch statement

Suppose ch is 'a':

switch (ch) {
case 'a': System.out.println(ch);
break;
case 'b': Sy...
animation

Trace switch statement
ch is 'a':

switch (ch) {
case 'a': System.out.println(ch);
break;
case 'b': System.out....
animation

Trace switch statement
Execute this line

switch (ch) {
case 'a': System.out.println(ch);
break;
case 'b': Syst...
animation

Trace switch statement
Execute this line

switch (ch) {
case 'a': System.out.println(ch);
break;
case 'b': Syst...
animation

Trace switch statement
Execute next statement

switch (ch) {
case 'a': System.out.println(ch);
break;
case 'b':...
Conditional Operator
if (x > 0)
y=1
else
y = -1;
is equivalent to
y = (x > 0) ? 1 : -1;
(boolean-expression) ? expression1...
Conditional Operator
if (num % 2 == 0)
System.out.println(num + “is even”);
else
System.out.println(num + “is odd”);
Syste...
Conditional Operator, cont.
(boolean-expression) ? exp1 : exp2

60

Liang, Introduction to Java Programming, Eighth Editio...
Formatting Output
Use the printf statement.
System.out.printf(format, items);
Where format is a string that may consist of...
Frequently-Used Specifiers
Specifier Output

Example

%b

a boolean value

true or false

%c

a character

'a'

%d

a deci...
Operator Precedence
var++, var-+, - (Unary plus and minus), ++var,--var
(type) Casting
! (Not)
*, /, % (Multiplication, di...
Operator Precedence and Associativity
The expression in the parentheses is evaluated first.
(Parentheses can be nested, in...
Operator Associativity
When two operators with the same precedence
are evaluated, the associativity of the operators
deter...
Example
Applying the operator precedence and associativity rule,
the expression 3 + 4 * 4 > 5 * (4 + 3) - 1 is evaluated a...
Companion
Website

Operand Evaluation Order

Supplement III.A, “Advanced discussions on
how an expression is evaluated in ...
(GUI) Confirmation Dialogs
int option = JOptionPane.showConfirmDialog
(null, "Continue");

68

Liang, Introduction to Java...
Problem: Guessing Birth Date
The program can guess your birth date. Run
to see how it works.
= 19
+

1 3 5 7
9 11 13 15
17...
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Java™ (OOP) - Chapter 3: "Selections"

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To declare boolean type and write Boolean expressions using comparison operators (§3.2).
To program AdditionQuiz using Boolean expressions (§3.3).
To implement selection control using one-way if statements (§3.4)
To program the GuessBirthday game using one-way if statements (§3.5).
To implement selection control using two-way if statements (§3.6).
To implement selection control using nested if statements (§3.7).
To avoid common errors in if statements (§3.8).
To program using selection statements for a variety of examples (BMI, ComputeTax, SubtractionQuiz) (§3.9-3.11).
To generate random numbers using the Math.random() method (§3.9).
To combine conditions using logical operators (&&, ||, and !) (§3.12).
To program using selection statements with combined conditions (LeapYear, Lottery) (§§3.13-3.14).
To implement selection control using switch statements (§3.15).
To write expressions using the conditional operator (§3.16).
To format output using the System.out.printf method and to format strings using the String.format method (§3.17).
To examine the rules governing operator precedence and associativity (§3.18).
(GUI) To get user confirmation using confirmation dialogs (§3.19).

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Transcript of "Java™ (OOP) - Chapter 3: "Selections""

  1. 1. Chapter 3 Selections 1 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  2. 2. Motivations If you assigned a negative value for radius in Listing 2.1, ComputeArea.java, the program would print an invalid result. If the radius is negative, you don't want the program to compute the area. How can you deal with this situation? 2 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  3. 3. Objectives To declare boolean type and write Boolean expressions using comparison operators (§3.2). To program AdditionQuiz using Boolean expressions (§3.3). To implement selection control using one-way if statements (§3.4) To program the GuessBirthday game using one-way if statements (§3.5). To implement selection control using two-way if statements (§3.6). To implement selection control using nested if statements (§3.7). To avoid common errors in if statements (§3.8). To program using selection statements for a variety of examples (BMI, ComputeTax, SubtractionQuiz) (§3.9-3.11). To generate random numbers using the Math.random() method (§3.9). To combine conditions using logical operators (&&, ||, and !) (§3.12). To program using selection statements with combined conditions (LeapYear, Lottery) (§§3.13-3.14). To implement selection control using switch statements (§3.15). To write expressions using the conditional operator (§3.16). To format output using the System.out.printf method and to format strings using the String.format method (§3.17). To examine the rules governing operator precedence and associativity (§3.18). (GUI) To get user confirmation using confirmation dialogs (§3.19). 3 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  4. 4. The boolean Type and Operators Often in a program you need to compare two values, such as whether i is greater than j. Java provides six comparison operators (also known as relational operators) that can be used to compare two values. The result of the comparison is a Boolean value: true or false. boolean b = (1 > 2); 4 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  5. 5. Comparison Operators Operator Name < less than <= less than or equal to > greater than >= greater than or equal to == equal to != not equal to 5 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  6. 6. Problem: A Simple Math Learning Tool This example creates a program to let a first grader practice additions. The program randomly generates two single-digit integers number1 and number2 and displays a question such as “What is 7 + 9?” to the student. After the student types the answer, the program displays a message to indicate whether the answer is true or false. Run AdditionQuiz 6 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  7. 7. One-way if Statements if (boolean-expression) { statement(s); } Boolean Expression false if (radius >= 0) { area = radius * radius * PI; System.out.println("The area" + " for the circle of radius " + radius + " is " + area); } (radius >= 0) false true true Statement(s) (A) area = radius * radius * PI; System.out.println("The area for the circle of " + "radius " + radius + " is " + area); (B) 7 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  8. 8. Note if i > 0 { System.out.println("i is positive"); } if (i > 0) { System.out.println("i is positive"); } (a) Wrong if (i > 0) { System.out.println("i is positive"); } (b) Correct Equivalent if (i > 0) System.out.println("i is positive"); (b) (a) 8 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  9. 9. Simple if Demo Write a program that prompts the user to enter an integer. If the number is a multiple of 5, print HiFive. If the number is divisible by 2, print HiEven. Run SimpleIfDemo 9 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  10. 10. Problem: Guessing Birthday The program can guess your birth date. Run to see how it works. = 19 + 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Set1 2 10 18 26 3 11 19 27 6 14 22 30 Set2 7 15 23 31 4 5 6 7 12 13 14 15 20 21 22 23 28 29 30 31 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31 Set3 Set4 GuessBirthday 16 20 24 28 17 21 25 29 18 22 26 30 19 23 27 31 Set5 Run 10 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  11. 11. Mathematics Basis for the Game 19 is 10011 in binary. 7 is 111 in binary. 23 is 11101 in binary 10000 10 + 1 10011 10000 1000 100 + 1 11101 00110 10 + 1 00111 19 7 23 = 19 + 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Set1 2 10 18 26 3 11 19 27 6 14 22 30 Set2 7 15 23 31 4 5 6 7 12 13 14 15 20 21 22 23 28 29 30 31 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31 Set3 Set4 16 20 24 28 17 21 25 29 18 22 26 30 19 23 27 31 Set5 11 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  12. 12. The Two-way if Statement if (boolean-expression) { statement(s)-for-the-true-case; } else { statement(s)-for-the-false-case; } true Statement(s) for the true case Boolean Expression false Statement(s) for the false case 12 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  13. 13. if...else Example if (radius >= 0) { area = radius * radius * 3.14159; System.out.println("The area for the “ + “circle of radius " + radius + " is " + area); } else { System.out.println("Negative input"); } 13 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  14. 14. Multiple Alternative if Statements if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; Equivalent if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; 14 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  15. 15. animation Trace if-else statement Suppose score is 70.0 The condition is false if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; 15 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  16. 16. animation Trace if-else statement Suppose score is 70.0 The condition is false if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; 16 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  17. 17. animation Trace if-else statement Suppose score is 70.0 The condition is true if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; 17 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  18. 18. animation Trace if-else statement Suppose score is 70.0 grade is C if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; 18 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  19. 19. animation Trace if-else statement Suppose score is 70.0 Exit the if statement if (score >= 90.0) grade = 'A'; else if (score >= 80.0) grade = 'B'; else if (score >= 70.0) grade = 'C'; else if (score >= 60.0) grade = 'D'; else grade = 'F'; 19 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  20. 20. Note The else clause matches the most recent if clause in the same block. int i = 1; int j = 2; int k = 3; Equivalent if (i > j) if (i > k) System.out.println("A"); else System.out.println("B"); int i = 1; int j = 2; int k = 3; if (i > j) if (i > k) System.out.println("A"); else System.out.println("B"); (a) (b) 20 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  21. 21. Note, cont. Nothing is printed from the preceding statement. To force the else clause to match the first if clause, you must add a pair of braces: int i = 1; int j = 2; int k = 3; if (i > j) { if (i > k) System.out.println("A"); } else System.out.println("B"); This statement prints B. 21 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  22. 22. Common Errors Adding a semicolon at the end of an if clause is a common mistake. if (radius >= 0); Wrong { area = radius*radius*PI; System.out.println( "The area for the circle of radius " + radius + " is " + area); } This mistake is hard to find, because it is not a compilation error or a runtime error, it is a logic error. This error often occurs when you use the next-line block style. 22 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  23. 23. TIP if (number % 2 == 0) even = true; else even = false; Equivalent boolean even = number % 2 == 0; (b) (a) 23 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  24. 24. CAUTION if (even == true) System.out.println( "It is even."); Equivalent if (even) System.out.println( "It is even."); (b) (a) 24 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  25. 25. Problem: An Improved Math Learning Tool This example creates a program to teach a first grade child how to learn subtractions. The program randomly generates two singledigit integers number1 and number2 with number1 > number2 and displays a question such as “What is 9 – 2?” to the student. After the student types the answer in the input dialog box, the program displays a message dialog box to indicate whether the answer is correct. SubtractionQuiz Run 25 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  26. 26. Problem: Body Mass Index Body Mass Index (BMI) is a measure of health on weight. It can be calculated by taking your weight in kilograms and dividing by the square of your height in meters. The interpretation of BMI for people 16 years or older is as follows: BMI Interpretation below 16 16-18 18-24 24-29 29-35 above 35 serious underweight underweight normal weight overweight seriously overweight gravely overweight ComputeBMI Run 26 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  27. 27. Problem: Computing Taxes The US federal personal income tax is calculated based on the filing status and taxable income. There are four filing statuses: single filers, married filing jointly, married filing separately, and head of household. The tax rates for 2009 are shown below. Married Filing Jointly Marginal Married Filing Tax Rate Single or Qualified Widow(er) Head of Household Separately 10% $0 – $8,350 $0 – $16,700 $0 – $8,350 $0 – $11,950 15% $8,351– $33,950 $16,701 – $67,900 $8,351 – $33,950 $11,951 – $45,500 25% $33,951 – $82,250 $67,901 – $137,050 $33,951 – $68,525 $45,501 – $117,450 28% $82,251 – $171,550 $137,051 – $208,850 $68,525 – $104,425 $117,451 – $190,200 33% $171,551 – $372,950 $208,851 – $372,950 $104,426 – $186,475 $190,201 - $372,950 35% $372,951+ $372,951+ $186,476+ $372,951+ 27 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  28. 28. Problem: Computing Taxes, cont. if (status == 0) { // Compute tax for single filers } else if (status == 1) { // Compute tax for married file jointly } else if (status == 2) { // Compute tax for married file separately } else if (status == 3) { // Compute tax for head of household } else { // Display wrong status } ComputeTax 28 Run Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  29. 29. Logical Operators Operator Name ! not && and || or ^ exclusive or 29 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  30. 30. Truth Table for Operator ! p !p Example (assume age = 24, gender = 'M') true false !(age > 18) is false, because (age > 18) is true. false true !(gender != 'F') is true, because (grade != 'F') is false. 30 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  31. 31. Truth Table for Operator && p1 p2 p1 && p2 Example (assume age = 24, gender = 'F') false false false false true false (age > 18) && (gender == 'F') is true, because (age > 18) and (gender == 'F') are both true. true false false true true true (age > 18) && (gender != 'F') is false, because (gender != 'F') is false. 31 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  32. 32. Truth Table for Operator || p1 p2 p1 || p2 Example (assume age = 24, gender = 'F') false false false false true true (age > 34) || (gender == 'F') is true, because (gender == 'F') is true. true false true true true true (age > 34) || (gender == 'M') is false, because (age > 34) and (gender == 'M') are both false. 32 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  33. 33. Examples Here is a program that checks whether a number is divisible by 2 and 3, whether a number is divisible by 2 or 3, and whether a number is divisible by 2 or 3 but not both: TestBooleanOperators Run 33 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  34. 34. Truth Table for Operator ! p !p true false !(1 > 2) is true, because (1 > 2) is false. false true !(1 > 0) is false, because (1 > 0) is true. Example 34 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  35. 35. Truth Table for Operator && p1 p2 p1 && p2 false false false false true false true false false true true true Example (3 > 2) && (5 >= 5) is true, because (3 > 2) and (5 >= 5) are both true. (3 > 2) && (5 > 5) is false, because (5 > 5) is false. 35 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  36. 36. Truth Table for Operator || p1 p2 p1 || p2 false false false false true true true false true true true true Example (2 > 3) || (5 > 5) is false, because (2 > 3) and (5 > 5) are both false. (3 > 2) || (5 > 5) is true, because (3 > 2) is true. 36 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  37. 37. Truth Table for Operator ^ p1 p2 p1 ^ p2 Example (assume age = 24, gender = 'F') false false false false true true (age > 34) ^ (gender == 'F') is true, because (age > 34) is false but (gender == 'F') is true. true false true true true false (age > 34) || (gender == 'M') is false, because (age > 34) and (gender == 'M') are both false. 37 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  38. 38. Examples System.out.println("Is " + number + " divisible by 2 and 3? " + ((number % 2 == 0) && (number % 3 == 0))); System.out.println("Is " + number + " divisible by 2 or 3? " + ((number % 2 == 0) || (number % 3 == 0))); System.out.println("Is " + number + " divisible by 2 or 3, but not both? " + TestBooleanOperators ((number % 2 == 0) ^ (number % 3 == 0))); Run 38 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  39. 39. Companion Website The & and | Operators Supplement III.B, “The & and | Operators” 39 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  40. 40. Companion Website The & and | Operators If x is 1, what is x after this expression? (x > 1) & (x++ < 10) If x is 1, what is x after this expression? (1 > x) && ( 1 > x++) How about (1 == x) | (10 > x++)? (1 == x) || (10 > x++)? 40 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  41. 41. Problem: Determining Leap Year? This program first prompts the user to enter a year as an int value and checks if it is a leap year. A year is a leap year if it is divisible by 4 but not by 100, or it is divisible by 400. (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0) LeapYear Run 41 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  42. 42. Problem: Lottery Write a program that randomly generates a lottery of a twodigit number, prompts the user to enter a two-digit number, and determines whether the user wins according to the following rule: • If the user input matches the lottery in exact order, the award is $10,000. • If the user input matches the lottery, the award is $3,000. • If one digit in the user input matches a digit in the lottery, the award is $1,000. Lottery Run 42 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  43. 43. switch Statements switch (status) { case 0: compute taxes for single filers; break; case 1: compute taxes for married file jointly; break; case 2: compute taxes for married file separately; break; case 3: compute taxes for head of household; break; default: System.out.println("Errors: invalid status"); System.exit(0); } 43 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  44. 44. switch Statement Flow Chart status is 0 Compute tax for single filers break Compute tax for married file jointly break Compute tax for married file separatly break Compute tax for head of household break status is 1 status is 2 status is 3 default Default actions Next Statement 44 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  45. 45. switch Statement Rules The switch-expression must yield a value of char, byte, short, or int type and must always be enclosed in parentheses. The value1, ..., and valueN must have the same data type as the value of the switch-expression. The resulting statements in the case statement are executed when the value in the case statement matches the value of the switchexpression. Note that value1, ..., and valueN are constant expressions, meaning that they cannot contain variables in the expression, such as 1 + x. switch (switch-expression) { case value1: statement(s)1; break; case value2: statement(s)2; break; … case valueN: statement(s)N; break; default: statement(s)-for-default; } 45 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  46. 46. switch Statement Rules The keyword break is optional, but it should be used at the end of each case in order to terminate the remainder of the switch statement. If the break statement is not present, the next case statement will be executed. The default case, which is optional, can be used to perform actions when none of the specified cases matches the switch-expression. switch (switch-expression) { case value1: statement(s)1; break; case value2: statement(s)2; break; … case valueN: statement(s)N; break; default: statement(s)-for-default; } The case statements are executed in sequential order, but the order of the cases (including the default case) does not matter. However, it is good programming style to follow the logical sequence of the cases and place the default case at the end. 46 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  47. 47. animation Trace switch statement Suppose ch is 'a': switch case case case } (ch) 'a': 'b': 'c': { System.out.println(ch); System.out.println(ch); System.out.println(ch); 47 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  48. 48. animation Trace switch statement ch is 'a': switch case case case } (ch) 'a': 'b': 'c': { System.out.println(ch); System.out.println(ch); System.out.println(ch); 48 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  49. 49. animation Trace switch statement Execute this line switch case case case } (ch) 'a': 'b': 'c': { System.out.println(ch); System.out.println(ch); System.out.println(ch); 49 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  50. 50. animation Trace switch statement Execute this line switch case case case } (ch) 'a': 'b': 'c': { System.out.println(ch); System.out.println(ch); System.out.println(ch); 50 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  51. 51. animation Trace switch statement Execute this line switch case case case } (ch) 'a': 'b': 'c': { System.out.println(ch); System.out.println(ch); System.out.println(ch); 51 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  52. 52. animation Trace switch statement Execute next statement switch case case case } (ch) 'a': 'b': 'c': { System.out.println(ch); System.out.println(ch); System.out.println(ch); Next statement; 52 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  53. 53. animation Trace switch statement Suppose ch is 'a': switch (ch) { case 'a': System.out.println(ch); break; case 'b': System.out.println(ch); break; case 'c': System.out.println(ch); } 53 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  54. 54. animation Trace switch statement ch is 'a': switch (ch) { case 'a': System.out.println(ch); break; case 'b': System.out.println(ch); break; case 'c': System.out.println(ch); } 54 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  55. 55. animation Trace switch statement Execute this line switch (ch) { case 'a': System.out.println(ch); break; case 'b': System.out.println(ch); break; case 'c': System.out.println(ch); } 55 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  56. 56. animation Trace switch statement Execute this line switch (ch) { case 'a': System.out.println(ch); break; case 'b': System.out.println(ch); break; case 'c': System.out.println(ch); } 56 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  57. 57. animation Trace switch statement Execute next statement switch (ch) { case 'a': System.out.println(ch); break; case 'b': System.out.println(ch); break; case 'c': System.out.println(ch); } Next statement; 57 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  58. 58. Conditional Operator if (x > 0) y=1 else y = -1; is equivalent to y = (x > 0) ? 1 : -1; (boolean-expression) ? expression1 : expression2 Ternary operator Binary operator Unary operator 58 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  59. 59. Conditional Operator if (num % 2 == 0) System.out.println(num + “is even”); else System.out.println(num + “is odd”); System.out.println( (num % 2 == 0)? num + “is even” : num + “is odd”); 59 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  60. 60. Conditional Operator, cont. (boolean-expression) ? exp1 : exp2 60 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  61. 61. Formatting Output Use the printf statement. System.out.printf(format, items); Where format is a string that may consist of substrings and format specifiers. A format specifier specifies how an item should be displayed. An item may be a numeric value, character, boolean value, or a string. Each specifier begins with a percent sign. 61 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  62. 62. Frequently-Used Specifiers Specifier Output Example %b a boolean value true or false %c a character 'a' %d a decimal integer 200 %f a floating-point number 45.460000 %e a number in standard scientific notation 4.556000e+01 %s a string "Java is cool" int count = 5; items double amount = 45.56; System.out.printf("count is %d and amount is %f", count, amount); display count is 5 and amount is 45.560000 62 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  63. 63. Operator Precedence var++, var-+, - (Unary plus and minus), ++var,--var (type) Casting ! (Not) *, /, % (Multiplication, division, and remainder) +, - (Binary addition and subtraction) <, <=, >, >= (Comparison) ==, !=; (Equality) ^ (Exclusive OR) && (Conditional AND) Short-circuit AND || (Conditional OR) Short-circuit OR =, +=, -=, *=, /=, %= (Assignment operator) 63 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  64. 64. Operator Precedence and Associativity The expression in the parentheses is evaluated first. (Parentheses can be nested, in which case the expression in the inner parentheses is executed first.) When evaluating an expression without parentheses, the operators are applied according to the precedence rule and the associativity rule. If operators with the same precedence are next to each other, their associativity determines the order of evaluation. All binary operators except assignment operators are left-associative. 64 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  65. 65. Operator Associativity When two operators with the same precedence are evaluated, the associativity of the operators determines the order of evaluation. All binary operators except assignment operators are leftassociative. a – b + c – d is equivalent to ((a – b) + c) – d Assignment operators are right-associative. Therefore, the expression a = b += c = 5 is equivalent to a = (b += (c = 5)) 65 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  66. 66. Example Applying the operator precedence and associativity rule, the expression 3 + 4 * 4 > 5 * (4 + 3) - 1 is evaluated as follows: 3 + 4 * 4 > 5 * (4 + 3) - 1 3 + 4 * 4 > 5 * 7 – 1 3 + 16 > 5 * 7 – 1 (1) inside parentheses first (2) multiplication (3) multiplication 3 + 16 > 35 – 1 19 > 35 – 1 19 > 34 false (4) addition (5) subtraction (6) greater than 66 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  67. 67. Companion Website Operand Evaluation Order Supplement III.A, “Advanced discussions on how an expression is evaluated in the JVM.” 67 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  68. 68. (GUI) Confirmation Dialogs int option = JOptionPane.showConfirmDialog (null, "Continue"); 68 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
  69. 69. Problem: Guessing Birth Date The program can guess your birth date. Run to see how it works. = 19 + 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Set1 2 10 18 26 3 11 19 27 6 14 22 30 Set2 7 15 23 31 4 5 6 7 12 13 14 15 20 21 22 23 28 29 30 31 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31 Set3 Set4 16 20 24 28 17 21 25 29 18 22 26 30 19 23 27 31 Set5 Run GuessBirthDateUsingConfirmationDialog 69 Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
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