CSE215_Module_02_Elementary_Programming.ppt

Liang, Introduction to Java Programming, Tenth Edition, (c) 2015 Pearson Education, Inc. All
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1
Chapter 2 Elementary Programming

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Motivations
In the preceding chapter, you learned how to
create, compile, and run a Java program. Starting
from this chapter, you will learn how to solve
practical problems programmatically. Through
these problems, you will learn Java primitive data
types and related subjects, such as variables,
constants, data types, operators, expressions, and
input and output.

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Objectives
 To write Java programs to perform simple computations (§2.2).
 To obtain input from the console using the Scanner class (§2.3).
 To use identifiers to name variables, constants, methods, and classes (§2.4).
 To use variables to store data (§§2.5–2.6).
 To program with assignment statements and assignment expressions (§2.6).
 To use constants to store permanent data (§2.7).
 To name classes, methods, variables, and constants by following their naming conventions (§2.8).
 To explore Java numeric primitive data types: byte, short, int, long, float, and double (§2.9.1).
 To read a byte, short, int, long, float, or double value from the keyboard (§2.9.2).
 To perform operations using operators +, -, *, /, and % (§2.9.3).
 To perform exponent operations using Math.pow(a, b) (§2.9.4).
 To write integer literals, floating-point literals, and literals in scientific notation (§2.10).
 To write and evaluate numeric expressions (§2.11).
 To obtain the current system time using System.currentTimeMillis() (§2.12).
 To use augmented assignment operators (§2.13).
 To distinguish between postincrement and preincrement and between postdecrement and predecrement (§2.14).
 To cast the value of one type to another type (§2.15).
 To describe the software development process and apply it to develop the loan payment program (§2.16).
 To write a program that converts a large amount of money into smaller units (§2.17).
 To avoid common errors and pitfalls in elementary programming (§2.18).

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Introducing Programming with an
Example
Listing 2.1 Computing the Area of a Circle
This program computes the area of the circle.
ComputeArea
Run
Animation
IMPORTANT NOTE: If you cannot run the buttons, see
www.cs.armstrong.edu/liang/javaslidenote.doc.

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Trace a Program Execution
public class ComputeArea {
/** Main method */
public static void main(String[] args) {
double radius;
double area;
// Assign a radius
radius = 20;
// Compute area
area = radius * radius * 3.14159;
// Display results
System.out.println("The area for the circle of radius " +
radius + " is " + area);
}
}
no value
radius
allocate memory
for radius
animation

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/** Main method */
double radius;
double area;
// Assign a radius
radius = 20;
// Compute area
// Display results
}
}
no value
radius
memory
no value
area
allocate memory
for area
animation

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/** Main method */
double radius;
double area;
// Assign a radius
radius = 20;
// Compute area
// Display results
}
}
20
radius
no value
area
assign 20 to radius
animation

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/** Main method */
double radius;
double area;
// Assign a radius
radius = 20;
// Compute area
// Display results
}
}
20
radius
memory
1256.636
area
compute area and assign it
to variable area
animation

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/** Main method */
double radius;
double area;
// Assign a radius
radius = 20;
// Compute area
// Display results
}
}
20
radius
memory
1256.636
area
print a message to the
console
animation

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Reading Input from the Console
1. Create a Scanner object
Scanner input = new Scanner(System.in);
2. Use the method nextDouble() to obtain to a double value.
For example,
System.out.print("Enter a double value: ");
double d = input.nextDouble();
ComputeAreaWithConsoleInput
Run
ComputeAverage
Run
Animation

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Identifiers
 An identifier is a sequence of characters that consist of
letters, digits, underscores (_), and dollar signs ($).
 An identifier must start with a letter, an underscore (_),
or a dollar sign ($). It cannot start with a digit.
 An identifier cannot be a reserved word. (See Appendix
A, “Java Keywords,” for a list of reserved words).
 An identifier cannot be true, false, or
null.
 An identifier can be of any length.

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Variables
// Compute the first area
radius = 1.0;
System.out.println("The area is “ +
area + " for radius "+radius);
// Compute the second area
radius = 2.0;
System.out.println("The area is “ +
area + " for radius "+radius);

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Declaring Variables
int x; // Declare x to be an
// integer variable;
double radius; // Declare radius to
// be a double variable;
char a; // Declare a to be a
// character variable;

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Assignment Statements
x = 1; // Assign 1 to x;
radius = 1.0; // Assign 1.0 to radius;
a = 'A'; // Assign 'A' to a;

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Declaring and Initializing
in One Step
 int x = 1;
 double d = 1.4;

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Named Constants
final datatype CONSTANTNAME = VALUE;
final double PI = 3.14159;
final int SIZE = 3;

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Naming Conventions
 Choose meaningful and descriptive names.
 Variables and method names:
– Use lowercase. If the name consists of several
words, concatenate all in one, use lowercase
for the first word, and capitalize the first letter
of each subsequent word in the name. For
example, the variables radius and area, and
the method computeArea.

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Naming Conventions, cont.
 Class names:
– Capitalize the first letter of each word in
the name. For example, the class name
ComputeArea.
 Constants:
– Capitalize all letters in constants, and use
underscores to connect words. For
example, the constant PI and
MAX_VALUE

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Numerical Data Types
Name Range Storage Size
byte –27 to 27 – 1 (-128 to 127) 8-bit signed
short –215 to 215 – 1 (-32768 to 32767) 16-bit signed
int –231 to 231 – 1 (-2147483648 to 2147483647) 32-bit signed
long –263 to 263 – 1 64-bit signed
(i.e., -9223372036854775808 to 9223372036854775807)
float Negative range: 32-bit IEEE 754
-3.4028235E+38 to -1.4E-45
Positive range:
1.4E-45 to 3.4028235E+38
double Negative range: 64-bit IEEE 754
-1.7976931348623157E+308 to -4.9E-324
Positive range:
4.9E-324 to 1.7976931348623157E+308

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Reading Numbers from the Keyboard
int value = input.nextInt();
Method Description
nextByte() reads an integer of the byte type.
nextShort() reads an integer of the short type.
nextInt() reads an integer of the int type.
nextLong() reads an integer of the long type.
nextFloat() reads a number of the float type.
nextDouble() reads a number of the double type.

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Numeric Operators
Name Meaning Example Result
+ Addition 34 + 1 35
- Subtraction 34.0 – 0.1 33.9
* Multiplication 300 * 30 9000
/ Division 1.0 / 2.0 0.5
% Remainder 20 % 3 2

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Integer Division
+, -, *, /, and %
5 / 2 yields an integer 2.
5.0 / 2 yields a double value 2.5
5 % 2 yields 1 (the remainder of the division)

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Remainder Operator
Remainder is very useful in programming. For example, an
even number % 2 is always 0 and an odd number % 2 is always
1. So you can use this property to determine whether a number
is even or odd. Suppose today is Saturday and you and your
friends are going to meet in 10 days. What day is in 10
days? You can find that day is Tuesday using the following
expression:
Saturday is the 6th
day in a week
A week has 7 days
After 10 days
The 2nd
day in a week is Tuesday
(6 + 10) % 7 is 2

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Problem: Displaying Time
Write a program that obtains minutes and
remaining seconds from seconds.
DisplayTime Run

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NOTE
Calculations involving floating-point numbers are
approximated because these numbers are not stored
with complete accuracy. For example,
System.out.println(1.0 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1);
displays 0.5000000000000001, not 0.5, and
System.out.println(1.0 - 0.9);
displays 0.09999999999999998, not 0.1. Integers are
stored precisely. Therefore, calculations with integers
yield a precise integer result.

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Exponent Operations
System.out.println(Math.pow(2, 3));
// Displays 8.0
System.out.println(Math.pow(4, 0.5));
// Displays 2.0
System.out.println(Math.pow(2.5, 2));
// Displays 6.25
System.out.println(Math.pow(2.5, -2));
// Displays 0.16

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Number Literals
A literal is a constant value that appears directly
in the program. For example, 34, 1,000,000, and
5.0 are literals in the following statements:
int i = 34;
long x = 1000000;
double d = 5.0;

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Integer Literals
An integer literal can be assigned to an integer variable as
long as it can fit into the variable. A compilation error
would occur if the literal were too large for the variable to
hold. For example, the statement byte b = 1000 would
cause a compilation error, because 1000 cannot be stored
in a variable of the byte type.
An integer literal is assumed to be of the int type, whose
value is between -231 (-2147483648) to 231–1
(2147483647). To denote an integer literal of the long type,
append it with the letter L or l. L is preferred because l
(lowercase L) can easily be confused with 1 (the digit
one).

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Floating-Point Literals
Floating-point literals are written with a decimal
point. By default, a floating-point literal is treated
as a double type value. For example, 5.0 is
considered a double value, not a float value. You
can make a number a float by appending the letter f
or F, and make a number a double by appending the
letter d or D. For example, you can use 100.2f or
100.2F for a float number, and 100.2d or 100.2D
for a double number.

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double vs. float
The double type values are more accurate than the
float type values. For example,
System.out.println("1.0 / 3.0 is " + 1.0 / 3.0);
displays 1.0 / 3.0 is 0.3333333333333333
16 digits
displays 1.0F / 3.0F is 0.33333334
7 digits
System.out.println("1.0F / 3.0F is " + 1.0F / 3.0F);

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Scientific Notation
Floating-point literals can also be specified in
scientific notation, for example, 1.23456e+2, same
as 1.23456e2, is equivalent to 123.456, and
1.23456e-2 is equivalent to 0.0123456. E (or e)
represents an exponent and it can be either in
lowercase or uppercase.

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Arithmetic Expressions
)
9
4
(
9
)
)(
5
(
10
5
4
3
y
x
x
x
c
b
a
y
x 







is translated to
(3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y)

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Character Data Type
char letter = 'A'; (ASCII)
char numChar = '4'; (ASCII)
char letter = 'u0041'; (Unicode)
char numChar = 'u0034'; (Unicode)
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Four hexadecimal digits.
NOTE: The increment and decrement operators can also be used
on char variables to get the next or preceding Unicode character.
For example, the following statements display character b.
char ch = 'a';
System.out.println(++ch);

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Unicode Format
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Java characters use Unicode, a 16-bit encoding scheme
established by the Unicode Consortium to support the
interchange, processing, and display of written texts in the
world’s diverse languages. Unicode takes two bytes,
preceded by u, expressed in four hexadecimal numbers
that run from 'u0000' to 'uFFFF'. So, Unicode can
represent 65535 + 1 characters.
Unicode u03b1 u03b2 u03b3 for three Greek
letters

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Escape Sequences for Special Characters
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Description Escape Sequence Unicode
Backspace b u0008
Tab t u0009
Linefeed n u000A
Carriage return r u000D
Backslash u005C
Single Quote ' u0027
Double Quote " u0022

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Casting between char and
Numeric Types
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int i = 'a'; // Same as int i = (int)'a';
char c = 97; // Same as char c = (char)97;

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How to Evaluate an Expression
Though Java has its own way to evaluate an
expression behind the scene, the result of a Java
expression and its corresponding arithmetic
expression are the same. Therefore, you can safely
apply the arithmetic rule for evaluating a Java
expression. 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
54 - 1
53
(1) inside parentheses first
(2) multiplication
(3) multiplication
(4) addition
(6) subtraction
(5) addition

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38
Problem: Converting Temperatures
Write a program that converts a Fahrenheit degree
to Celsius using the formula:
FahrenheitToCelsius Run
)
32
)(
(9
5

 fahrenheit
celsius
Note: you have to write
celsius = (5.0 / 9) * (fahrenheit – 32)

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39
Problem: Displaying Current Time
Write a program that displays current time in GMT in the
format hour:minute:second such as 1:45:19.
The currentTimeMillis method in the System class returns
the current time in milliseconds since the midnight, January
1, 1970 GMT. (1970 was the year when the Unix operating
system was formally introduced.) You can use this method
to obtain the current time, and then compute the current
second, minute, and hour as follows.
ShowCurrentTime
Run
Elapsed
time
Unix Epoch
01-01-1970
00:00:00 GMT
Current Time
Time
System.currentTimeMills()

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40
Augmented Assignment Operators

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Increment and
Decrement Operators

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Increment and
Decrement Operators, cont.
int i = 10;
int newNum = 10 * i++; int newNum = 10 * i;
i = i + 1;
Same effect as
int i = 10;
int newNum = 10 * (++i); i = i + 1;
int newNum = 10 * i;
Same effect as

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Increment and
Decrement Operators, cont.
Using increment and decrement operators makes
expressions short, but it also makes them complex and
difficult to read. Avoid using these operators in expressions
that modify multiple variables, or the same variable for
multiple times such as this: int k = ++i + i.

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Assignment Expressions and
Assignment Statements
Prior to Java 2, all the expressions can be used as
statements. Since Java 2, only the following types of
expressions can be statements:
variable op= expression; // Where op is +, -, *, /, or %
++variable;
variable++;
--variable;
variable--;

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Numeric Type Conversion
Consider the following statements:
byte i = 100;
long k = i * 3 + 4;
double d = i * 3.1 + k / 2;

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Conversion Rules
When performing a binary operation involving two
operands of different types, Java automatically
converts the operand based on the following rules:
1. If one of the operands is double, the other is
converted into double.
2. Otherwise, if one of the operands is float, the other is
converted into float.
3. Otherwise, if one of the operands is long, the other is
converted into long.
4. Otherwise, both operands are converted into int.

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Type Casting
Implicit casting
double d = 3; (type widening)
Explicit casting
int i = (int)3.0; (type narrowing)
int i = (int)3.9; (Fraction part is truncated)
What is wrong? int x = 5 / 2.0;
byte, short, int, long, float, double
range increases

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Problem: Keeping Two Digits After
Decimal Points
Write a program that displays the sales tax with two
digits after the decimal point.
SalesTax Run

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Casting in an Augmented Expression
In Java, an augmented expression of the form x1 op=
x2 is implemented as x1 = (T)(x1 op x2), where T is
the type for x1. Therefore, the following code is
correct.
int sum = 0;
sum += 4.5; // sum becomes 4 after this statement
sum += 4.5 is equivalent to sum = (int)(sum + 4.5).

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50
Problem:
Computing Loan Payments
ComputeLoan Run
This program lets the user enter the interest
rate, number of years, and loan amount, and
computes monthly payment and total
payment.
12
)
1
(
1
1 




ars
numberOfYe
erestRate
monthlyInt
erestRate
monthlyInt
loanAmount
ment
monthlyPay

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51
Problem: Monetary Units
This program lets the user enter the amount in
decimal representing dollars and cents and output
a report listing the monetary equivalent in single
dollars, quarters, dimes, nickels, and pennies.
Your program should report maximum number of
dollars, then the maximum number of quarters,
and so on, in this order.
ComputeChange Run

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52
Common Errors and Pitfalls
 Common Error 1: Undeclared/Uninitialized
Variables and Unused Variables
 Common Error 2: Integer Overflow
 Common Error 3: Round-off Errors
 Common Error 4: Unintended Integer Division
 Common Error 5: Redundant Input Objects
 Common Pitfall 1: Redundant Input Objects

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Common Error 1:
Undeclared/Uninitialized Variables
and Unused Variables
double interestRate = 0.05;
double interest = interestrate * 45;

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Common Error 2: Integer Overflow
int value = 2147483647 + 1;
// value will actually be -2147483648

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Common Error 3: Round-off Errors
System.out.println(1.0 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1);
System.out.println(1.0 - 0.9);

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Common Error 4: Unintended Integer
Division
int number1 = 1;
int number2 = 2;
double average = (number1 + number2) / 2;
System.out.println(average);
(a)
int number1 = 1;
int number2 = 2;
double average = (number1 + number2) / 2.0;
System.out.println(average);
(b)

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57
Common Pitfall 1: Redundant Input
Objects
System.out.print("Enter an integer: ");
int v1 = input.nextInt();
Scanner input1 = new Scanner(System.in);
System.out.print("Enter a double value: ");
double v2 = input1.nextDouble();

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The String Type
The char type only represents one character. To represent a string
of characters, use the data type called String. For example,
String message = "Welcome to Java";
String is actually a predefined class in the Java library just like the
System class and JOptionPane class. The String type is not a
primitive type. It is known as a reference type. Any Java class can
be used as a reference type for a variable. Reference data types
will be thoroughly discussed in Chapter 7, “Objects and Classes.”
For the time being, you just need to know how to declare a String
variable, how to assign a string to the variable, and how to
concatenate strings.
58

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String Concatenation
// Three strings are concatenated
String message = "Welcome " + "to " + "Java";
// String Chapter is concatenated with number 2
String s = "Chapter" + 2; // s becomes Chapter2
// String Supplement is concatenated with character B
String s1 = "Supplement" + 'B'; // s1 becomes SupplementB
59

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JOptionPane Input
This book provides two ways of obtaining input.
1. Using the Scanner class (console input)
2. Using JOptionPane input dialogs (you need to import
before your class file with this command
 import javax.swing.*;
60

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Getting Input from Input Dialog Boxes
String input = JOptionPane.showInputDialog(
"Enter an input");
61

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Getting Input from Input Dialog Boxes
String string = JOptionPane.showInputDialog(
null, “Prompting Message”, “Dialog Title”,
JOptionPane.QUESTION_MESSAGE);
62

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Converting Strings to Doubles
To convert a string into a double value, you can use the
static parseDouble method in the Double class as follows:
double doubleValue =Double.parseDouble(doubleString);
where doubleString is a numeric string such as “123.45”.
63

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The showMessageDialog Method
JOptionPane.showMessageDialog(null,
"Welcome to Java!",
"Display Message",
JOptionPane.INFORMATION_MESSAGE);
64

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Two Ways to Invoke the Method
There are several ways to use the showMessageDialog
method. For the time being, all you need to know are
two ways to invoke it.
One is to use a statement as shown in the example:
JOptionPane.showMessageDialog(null, msg,
title, JOptionPane.INFORMATION_MESSAGE);
The other is to use a statement like this:
JOptionPane.showMessageDialog(null, msg);
where x is a string for the text to be displayed.
65

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(GUI) Confirmation Dialogs
int option = JOptionPane.showConfirmDialog
(null, "Continue");
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CSE215_Module_02_Elementary_Programming.ppt

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