Ch4

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?

3
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
Comparison Operators
Operator Name
< less than
<= less than or equal to
> greater than
>= greater than or equal to
== equal to
!= not equal to

5
Boolean Operators
Operator Name
! not
&& and
|| or
^ exclusive or

6
Truth Table for Operator !
p !p
true false
false true
Example
!(1 > 2) is true, because (1 > 2) is false.
!(1 > 0) is false, because (1 > 0) is true.
If p is true, !p is false
If p is false, !p is true

7
Truth Table for Operator && (AND)
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.
Both p1 and p2 have to be true for p1 && p2
to be true, otherwise p1 && p2 is false

8
Truth Table for Operator || (OR)
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.
Both p1 and p2 have to be false for p1 || p2
to be false, otherwise p1 || p2 is true

9
Truth Table for Operator ^ (exclusive-OR)
p1 p2 p1 ^ p2
false false false
false true true
true false true
true true false
Example
(2 > 3) ^ (5 > 1) is true, because (2 > 3)
is false and (5 > 1) is true.
(3 > 2) ^ (5 > 1) is false, because both (3
> 2) and (5 > 1) are true.
Both p1 and p2 have to be true or both have
to be false for p1 ^ p2 to be false, otherwise
p1 ^ p2 is true

10
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? " +
((number % 2 == 0) ^ (number % 3 == 0)));
If both number divided by 2 and number divided by 3 have a remainder of 0
then true will be displayed, otherwise false will be displayed
If either number divided by 2 or number divided by 3 have a remainder of 0 then
true will be displayed, otherwise false will be displayed
If either number divided by 2 or number divided by 3 have a remainder of 0 but
not both then true will be displayed, otherwise false will be displayed

11
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)

12
LeapYear.java
import java.util.Scanner;
public class LeapYear {
public static void main(String args[]) {
// Create a Scanner
Scanner input = new Scanner(System.in);
System.out.print("Enter a year: ");
int year = input.nextInt();
// Check if the year is a leap year
boolean isLeapYear = (year % 4 == 0 && year % 100 != 0)
|| (year % 400 == 0);
// Display the result in a message dialog box
System.out.println(year + " is a leap year? " + isLeapYear); } }

13
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.

14
AdditionQuiz.java
public class AdditionQuiz {
public static void main(String[] args) {
int number1 = (int)(System.currentTimeMillis() % 10);
int number2 = (int)(System.currentTimeMillis() * 7 % 10);
// Create a Scanner
System.out.print( "What is " + number1 + " + " + number2 + "? ");
int answer = input.nextInt();
System.out.println( number1 + " + " + number2 + " = " + answer + " is "
+ (number1 + number2 == answer));
}
}

15
Selection Statements
 if Statements
 switch Statements
 Conditional Operators

16
Simple if Statements
if (booleanExpression) {
statement(s);
}
if (radius >= 0) {
area = radius * radius * PI;
System.out.println("The area"
+ " for the circle of radius "
+ radius + " is " + area);
}
Boolean
Expression
true
Statement(s)
false
(radius >= 0)
true
area = radius * radius * PI;
System.out.println("The area for the circle of " +
"radius " + radius + " is " + area);
false
(A) (B)

17
Note
if ((i > 0) && (i < 10)) {
System.out.println("i is an " +
+ "integer between 0 and 10");
}
(a)
Equivalent
(b)
if ((i > 0) && (i < 10))
System.out.println("i is an " +
+ "integer between 0 and 10");
Outer parentheses required Braces can be omitted if theblock contains a single
statement

18
Caution
Adding a semicolon at the end of an if clause is a common mistake.
if (radius >= 0);
{
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.
Wrong

19
The if...else Statement
if (booleanExpression) {
statement(s)-for-the-true-case;
}
else {
statement(s)-for-the-false-case;
}
Boolean
Expression
falsetrue
Statement(s) for the false caseStatement(s) for the true case

20
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");
}

21
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';
grade = 'C';
grade = 'D';
else
grade = 'F';

22
Trace if-else statement
if (score >= 90.0)
grade = 'A';
grade = 'B';
grade = 'C';
grade = 'D';
else
grade = 'F';
Suppose score is 70.0 The condition is false
animation

23
if (score >= 90.0)
grade = 'A';
grade = 'B';
grade = 'C';
grade = 'D';
else
grade = 'F';
Suppose score is 70.0 The condition is false
animation

24
if (score >= 90.0)
grade = 'A';
grade = 'B';
grade = 'C';
grade = 'D';
else
grade = 'F';
Suppose score is 70.0 The condition is true
animation

25
if (score >= 90.0)
grade = 'A';
grade = 'B';
grade = 'C';
grade = 'D';
else
grade = 'F';
Suppose score is 70.0 grade is C
animation

26
if (score >= 90.0)
grade = 'A';
grade = 'B';
grade = 'C';
grade = 'D';
else
grade = 'F';
Suppose score is 70.0 Exit the if statement
animation

27
Note
The else clause matches the most recent if clause in the
same block.
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)
Equivalent
(b)
int i = 1;
int j = 2;
int k = 3;
if (i > j)
if (i > k)
else

28
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)
}
else
This statement prints B.

29
TIP
if (number % 2 == 0)
even = true;
else
even = false;
(a)
Equivalent boolean even
= number % 2 == 0;
(b)

30
CAUTION
if (even == true)
System.out.println(
"It is even.");
(a)
Equivalent if (even)
System.out.println(
"It is even.");
(b)

31
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 single-
digit 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.

32
SubtractionQuiz.java
public class SubtractionQuiz {
// 1. Generate two random single-digit integers
int number1 = (int)(Math.random() * 10);
int number2 = (int)(Math.random() * 10);
// 2. If number1 < number2, swap number1 with number2
if (number1 < number2) {
int temp = number1;
number1 = number2;
number2 = temp;
}
// 3. Prompt the student to answer “what is number1 – number2?”
System.out.print ("What is " + number1 + " - " + number2 + "? ");
// 4. Grade the answer and display the result
if (number1 - number2 == answer)
System.out.println("You are correct!");
else
System.out.println("Your answer is wrong.n" + number1 + " - " + number2 + " should be " +
(number1 - number2));
}
}

33
Problem: Lottery
Randomly generates a lottery of a two-digit 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.

34
Lottery.java
public class Lottery {
// Generate a lottery
int lottery = (int)(Math.random() * 100);
// Prompt the user to enter a guess
System.out.print("Enter your lottery pick: ");
int guess = input.nextInt();
// Check the guess
if (guess == lottery)
System.out.println("Exact match: you win $10,000");
else if (guess % 10 == lottery / 10 && guess / 10 == lottery % 10)
System.out.println("Match all digits: you win $3,000");
else if (guess % 10 == lottery / 10 || guess % 10 == lottery % 10 || guess / 10 ==
lottery / 10 || guess / 10 == lottery % 10)
System.out.println("Match one digit: you win $1,000");
else System.out.println("Sorry, no match");
}
}

35
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 serious underweight
16-18 underweight
18-24 normal weight
24-29 overweight
29-35 seriously overweight
above 35 gravely overweight

36
ComputeBMI.java
public class ComputeBMI {
// Prompt the user to enter weight in pounds
System.out.print("Enter weight in pounds: ");
double weight = input.nextDouble();
// Prompt the user to enter height in inches
System.out.print("Enter height in inches: ");
double height = input.nextDouble();
final double KILOGRAMS_PER_POUND = 0.45359237; // Constant
final double METERS_PER_INCH = 0.0254; // Constant
// Compute BMI
double bmi = weight * KILOGRAMS_PER_POUND / ((height * METERS_PER_INCH) * (height *
METERS_PER_INCH));
// Display result
System.out.println("Your BMI is " + bmi);
if (bmi < 16)
System.out.println("You are seriously under weight");
else if (bmi < 18)
System.out.println("You are under weight");
else if (bmi < 24)
System.out.println("You are normal weight");
else if (bmi < 29)
System.out.println("You are over weight");
else if (bmi < 35)
System.out.println("You are seriously over weight");
else
System.out.println("You are gravely over weight");
}
}

37
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 2002
are shown in Table 3.1.

38
Problem: Computing Taxes, cont.
if (status == 0) {
// Compute tax for single filers
}
else if (status == 1) {
// Compute tax for married file jointly
}
// Compute tax for married file separately
}
// Compute tax for head of household
}
else {
// Display wrong status
}

39
ComputeTax.java
public class ComputeTax {
// Create a Scanner
// Prompt the user to enter filing status
System.out.print( "(0-single filer, 1-married jointly,n" + "2-married
separately, 3-head of household)n" + "Enter the filing status: ");
int status = input.nextInt();
// Prompt the user to enter taxable income
System.out.print("Enter the taxable income: ");
double income = input.nextDouble();

40
ComputeTax.java
// Compute tax
double tax = 0;
if (status == 0) {
// Compute tax for single filers
if (income <= 6000)
tax = income * 0.10;
else if (income <= 27950)
tax = 6000 * 0.10 + (income - 6000) * 0.15;
tax = 6000 * 0.10 + (27950 - 6000) * 0.15 + (income - 27950) * 0.27;
tax = 6000 * 0.10 + (27950 - 6000) * 0.15 + (67700 - 27950) * 0.27 +
(income - 67700) * 0.30;
tax = 6000 * 0.10 + (27950 - 6000) * 0.15 + (67700 - 27950) * 0.27 +
(141250 - 67700) * 0.30 + (income - 141250) * 0.35;
else
tax = 6000 * 0.10 + (27950 - 6000) * 0.15 + (67700 - 27950) * 0.27 +
(141250 - 67700) * 0.30 + (307050 - 141250) * 0.35 + (income - 307050) *
0.386;
}

41
ComputeTax.java
// Compute tax for married file jointly
// Left as exercise
}
// Compute tax for married separately
// Left as exercise }
// Compute tax for head of household
// Left as exercise
}
else {
System.out.println("Error: invalid status");
System.exit(0);
}
// Display the result
System.out.println("Tax is " + (int)(tax * 100) / 100.0);
}
}

42
Problem: Guessing Birth Date
The program can guess your birth date. Run
to see how it works.
16 17 18 19
20 21 22 23
24 25 26 27
28 29 30 31
Set1
8 9 10 11
12 13 14 15
24 25 26 27
28 29 30 31
Set2
1 3 5 7
9 11 13 15
17 19 21 23
25 27 29 31
Set3
2 3 6 7
10 11 14 15
18 19 22 23
26 27 30 31
Set4
4 5 6 7
12 13 14 15
20 21 22 23
28 29 30 31
Set5
+
= 19

43
GuessBirthDate.java
public class GuessBirthDate {
String set1 = " 1 3 5 7n" + " 9 11 13 15n" + "17 19 21 23n" + "25 27 29 31";
String set2 = " 2 3 6 7n" + "10 11 14 15n" + "18 19 22 23n" + "26 27 30 31";
String set3 = " 4 5 6 7n" + "12 13 14 15n" + "20 21 22 23n" + "28 29 30 31";
String set4 = " 8 9 10 11n" + "12 13 14 15n" + "24 25 26 27n" + "28 29 30 31";
String set5 = "16 17 18 19n" + "20 21 22 23n" + "24 25 26 27n" + "28 29 30 31";
int date = 0;
// Create a Scanner
// Prompt the user to answer questions
System.out.print("Is your birthdate in Set1?n");
System.out.print(set1);
System.out.print("nEnter 0 for No and 1 for Yes: ");
if (answer == 1)
date += 1;

44
GuessBirthDate.java
System.out.print("nIs your birthdate in Set2?n");
answer = input.nextInt();
if (answer == 1)
date += 2;
System.out.print("Is your birthdate in Set3?n");
if (answer == 1)
date += 4;

45
GuessBirthDate.java
if (answer == 1)
date += 8;
if (answer == 1)
date += 16;
System.out.println("nYour birthdate is " + date + "!");
}
}

46
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);
}

47
switch Statement Flow Chart
status is 0
Compute tax for single filers break
Compute tax for married file jointly break
status is 1
Compute tax for married file separatly break
status is 2
Compute tax for head of household break
status is 3
Default actions
default
Next Statement

48
switch Statement Rules
switch (switch-expression) {
case value1: statement(s)1;
break;
break;
…
case valueN: statement(s)N;
break;
default: statement(s)-for-default;
}
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 switch-
expression. Note that value1, ...,
and valueN are constant
expressions, meaning that they
cannot contain variables in the
expression, such as 1 + x.

49
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.
switch (switch-expression) {
break;
break;
…
case valueN: statement(s)N;
break;
default: statement(s)-for-default;
}
The default case, which is optional,
can be used to perform actions
when none of the specified cases
matches the switch-expression.
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.

50
Trace switch statement
switch (ch) {
case 'a': System.out.println(ch);
case 'b': System.out.println(ch);
case 'c': System.out.println(ch);
}
Suppose ch is 'a':
animation

51
switch (ch) {
}
ch is 'a':
animation

52
switch (ch) {
}
Execute this line
animation

53
switch (ch) {
}
Execute this line
animation

54
switch (ch) {
}
Execute this line
animation

55
switch (ch) {
}
Next statement;
Execute next statement
animation

56
switch (ch) {
break;
break;
}
Suppose ch is 'a':
animation

57
switch (ch) {
break;
break;
}
ch is 'a':
animation

58
switch (ch) {
break;
break;
}
Execute this line
animation

59
switch (ch) {
break;
break;
}
Execute this line
animation

60
switch (ch) {
break;
break;
}
Next statement;
Execute next statement
animation

61
Conditional Operator
if (x > 0)
y = 1
else
y = -1;
is equivalent to
y = (x > 0) ? 1 : -1;
(booleanExpression) ? expression1 : expression2
Ternary operator
Binary operator
Unary operator

62
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”);

63
Conditional Operator, cont.
(booleanExp) ? exp1 : exp2

64
Formatting Output
Use the new JDK 1.5 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.
See URL:
http://java.sun.com/j2se/1.5.0/docs/api/java/util/Formatter.htm
for a discussion of printf statement and list of specifiers
and flags.

65
Frequently-Used Specifiers
Specifier Output Example
%b a boolean value true or false
%c a character 'a'
%d a decimal integer 200
%o octal integer
%x hexadecimal integer
%f a floating-point number 45.460000
%e a number in standard scientific notation 4.556000e+01
%g scientific notation (with an exponent) for float
%a hexadecimal with an exponent for float
%s a string "Java is cool"
%n a new line Equivalent to /n
$ argument index which argument to use

66
Frequently-Used Flags
Flag General Character Integral
Floating
Point
Date/
Time Description
'-' y y y y y The result will be left-justified.
'#' y1 - y3 y -
The result should use a conversion-
dependent alternate form
'+' - - y4 y - The result will always include a sign
' ' - - y4 y -
The result will include a leading space for
positive values
'0' - - y y - The result will be zero-padded
',' - - y2 y5 -
The result will include locale-specific
grouping separators
'(' - - y4 y5 -
The result will enclose negative numbers in
parentheses
1 Depends on the definition of Formattable.
2 For 'd' conversion only.
3 For 'o', 'x', and 'X' conversions only.
4 For 'd', 'o', 'x', and 'X' conversions applied to Big Integer or 'd' applied to byte, Byte, short,
Short, int and Integer, long, and Long.
5 For 'e', 'E', 'f', 'g', and 'G' conversions only. Any characters not explicitly defined
as flags are illegal and are reserved
for future extensions.

67
Frequently-Used Specifiers
int count = 5;
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
items
public class MainClass {
public static void main(String[] a) {
double x = 27.5, y = 33.75;
System.out.printf("x = %f y = %g", x, y);
}
}
x = 27.500000 y = 33.7500

68
printf Examples
int a = 5, b = 15, c = 255;
System.out.printf("a = %d b = %x c = %o", a, b, c);
}
}
a = 5 b = f c = 377
double x = 27.5, y = 33.75;
System.out.printf("x = %15f y = %8g", x, y);
}
}
x = 27.500000 y = 33.7500

69
printf Examples
double x = 27.5, y = 33.75;
System.out.printf("x = %15.2f y = %14.3g", x, y);
}
}
x = 27.50 y = 33.8

70
printf Examples
public class MainClass
{
public static void main( String args[] )
{
System.out.printf( "%dn", 26 );
System.out.printf( "%dn", +26 );
System.out.printf( "%dn", -26 );
System.out.printf( "%(dn", -26 );
System.out.printf( "%on", 26 );
System.out.printf( "%xn", 26 );
System.out.printf( "%Xn", 26 );
}
}
26
26
-26
(26)
32
1a
1A

71
printf Examples
public class MainClass
{
public static void main( String args[] )
{
System.out.printf( "%en", 12345678.9 );
System.out.printf( "%en", +12345678.9 );
System.out.printf( "%en", -12345678.9 );
System.out.printf( "%En", 12345678.9 );
System.out.printf( "%fn", 12345678.9 );
System.out.printf( "%gn", 12345678.9 );
System.out.printf( "%Gn", 12345678.9 );
}
}
1.234568e+07
1.234568e+07
-1.234568e+07
1.234568E+07
12345678.900000
1.23457e+07
1.23457E+07

72
Formatting Output
 Items in format section must match items in the
item list.
public class FormatTest {
/**
* Test format program
*/
boolean b1 = true;
double f1 = 25.2;
int d1 = 65;
System.out.printf("b1 is %b, f1 is %6.2f, d1 is %4d",
b1, f1, d1);
}
}
b1 is true, f1 is 25.20, d1 is 65

73
Format Example
public class PrintfDemo {
/**
* Illustrate several output formats with printf()
*/
double q = 1.0/3.0;
// Print the number with 3 decimal places.
System.out.printf ("1.0/3.0 = %5.3f %n", q);
// Increase the number of decimal places
// Pad with zeros.
q = 1.0/2.0;
// Scientific notation
q = 1000.0/3.0;
System.out.printf ("1000/3.0 = %7.2e %n", q);
// More scientific notation
q = 3.0/4567.0;
System.out.printf ("3.0/4567.0 = %7.2e %n", q);
q = -1.0/0.0;
System.out.printf ("-1.0/0.0 = %7.2e %n", q);
q = 0.0/0.0;
// NaN
System.out.printf ("0.0/0.0 = %5.2e %n", q);
// Multiple arguments
System.out.printf ("pi = %5.3f, e = %5.4f %n", Math.PI, Math.E);
double r = 1.1;
// User the argument index to put the argument values into
// different locations within th string.
System.out.printf ("C = 2 * %1$5.5f * %2$4.1f, "+
"A = %2$4.1f * %2$4.1f * %1$5.5f %n",
Math.PI, r);
}
}
1.0/3.0 = 0.333
1.0/3.0 = 0.33333
1.0/2.0 = 00000.500
1000/3.0 = 3.33e+02
3.0/4567.0 = 6.57e-04
-1.0/0.0 = -Infinity
0.0/0.0 = NaN
pi = 3.142, e = 2.7183
C = 2 * 3.14159 * 1.1, A = 1.1 * 1.1 * 3.14159
Output

74
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)

75
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.

76
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 left-
associative.
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))

77
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
3 + 16 > 35 – 1
19 > 35 – 1
19 > 34
false
(1) inside parentheses first
(2) multiplication
(3) multiplication
(4) addition
(5) subtraction
(6) greater than

78
Operand Evaluation Order
Supplement III.A, “Advanced discussions on
how an expression is evaluated in the JVM.”
Companion
Website

79
(GUI) Confirmation Dialogs
int option = JOptionPane.showConfirmDialog
(null, "Continue");

80
Problem: Guessing Birth Date
GuessBirthDateUsingConfirmationDialogGuessBirthDateUsingConfirmationDialog Run
The program can guess your birth date. Run
to see how it works.
16 17 18 19
20 21 22 23
24 25 26 27
28 29 30 31
Set1
8 9 10 11
12 13 14 15
24 25 26 27
28 29 30 31
Set2
1 3 5 7
9 11 13 15
17 19 21 23
25 27 29 31
Set3
2 3 6 7
10 11 14 15
18 19 22 23
26 27 30 31
Set4
4 5 6 7
12 13 14 15
20 21 22 23
28 29 30 31
Set5
+
= 19

81
GuessBirthDateUsingConfirmationDialog.java
import javax.swing.JOptionPane;
public class GuessBirthDateUsingConfirmationDialog {
String set1 =
" 1 3 5 7n" +
" 9 11 13 15n" +
"17 19 21 23n" +
"25 27 29 31";
String set2 =
" 2 3 6 7n" +
"10 11 14 15n" +
"18 19 22 23n" +
"26 27 30 31";
String set3 =
" 4 5 6 7n" +
"12 13 14 15n" +
"20 21 22 23n" +
"28 29 30 31";
String set4 =
" 8 9 10 11n" +
"12 13 14 15n" +
"24 25 26 27n" +
"28 29 30 31";
String set5 =
"16 17 18 19n" +
"20 21 22 23n" +
"24 25 26 27n" +
"28 29 30 31";
int date = 0;

82
GuessBirthDateUsingConfirmationDialog.java
int answer = JOptionPane.showConfirmDialog(null,
"Is your birthdate in these numbers?n" + set1);
if (answer == JOptionPane.YES_OPTION)
date += 1;
answer = JOptionPane.showConfirmDialog(null,
date += 2;
date += 4;
date += 8;
date += 16;
JOptionPane.showMessageDialog(null, "Your birthdate is " + date + "!");
}
}

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