BCS2182 Object Oriented Programming

1
MODULE 3 FLOW OF CONTROL

• COURSE CODE BCS2143
• COURSE NAME OBJECT ORIENTED PROGRAMMING
• LECTURER KHAIRUL ANWAR AJID
• CONTACT NO 2127 (ext)

2
OBJECTIVES

• learn about Java branching statements
• learn about loops
• learn about the type boolean
• learn to use color and other graphic enhancements

3
OUTLINE

• Branching Statements
• Java Loop Statements
• Programming with Loops
• The Type boolean
• Graphics Supplement

4
FLOW OF CONTROL

• Flow of control is the order in which a program
  performs actions.
• Up to this point, the order has been sequential.
• A branching statement chooses between two or more
  possible actions.
• A loop statement repeats an action until a
  stopping condition occurs.

5
BRANCHING STATEMENTS OUTLINE

• The if-else Statement
• Introduction to Boolean Expressions
• Nested Statements and Compound Statements
• Multibranch if-else Statements
• The switch Statament

6
The if-else Statement

• A branching statement that chooses between two
  possible actions.
• syntax
• if (Boolean_Expression)
• Statement_1
• else
• Statement_2
• example
• if (count lt 3)
• total 0
• else
• total total count

7
The if-else Statement, cont.

• class BankBalance

8
COMPOUND STATEMENTS

• To include multiple statements in a branch,
  enclose the statements in braces.
• if (count lt 3)
• total 0
• count 0

9
Omitting the else Part

• If the else part is omitted and the expression
  after the if is false, no action occurs.
• syntax
• if (Boolean_Expression)
• Statement
• example
• if (weight gt ideal)
• caloriesPerDay - 500

10
INTRODUCTION TO BOOLEAN EXPRESSIONS

• The value of a boolean expression is either true
  or false.
• examples
• time lt limit
• balance lt 0

11
JAVA COMPARISON OPERATORS
12
COMPOUND BOOLEAN EXPRESSIONS

• Boolean expressions can be combined using the
  and () operator.
• example
• if ((score gt 0) (score lt 100))
• ...
• not allowed
• if (0 lt score lt 100)
• ...

13
COMPOUND BOOLEAN EXPRESSIONS, cont.

• syntax
• (Sub_Expression_1) (Sub_Expression_2)
• Parentheses often are used to enhance
  readability.
• The larger expression is true only when both of
  the smaller expressions are true.

14
COMPOUND BOOLEAN EXPRESSIONS, cont.

• Boolean expressions can be combined using the
  or () operator.
• example
• if ((quantity gt 5) (cost lt 10))
• ...
• syntax
• (Sub_Expression_1) (Sub_Expression_2)

15
COMPOUND BOOLEAN EXPRESSIONS, cont.

• The larger expression is true
• when either of the smaller expressions is true
• when both of the smaller expressions are true.
• The Java version of or is the inclusive or
  which allows either or both to be true.
• The exclusive or allows one or the other, but not
  both to be true.

16
NEGATING A BOOLEAN EXPRESSION

• A boolean expression can be negated using the
  not (!) operator.
• syntax
• !(Boolean_Expression)
• example
• (a b) !(a b)
• which is the exclusive or
• Is it not true that programs which do not use the
  not (!) operator are not easier to read?

17
USING

• is appropriate for determining if two integers
  or characters have the same value.
• if (a 3)
• where a is an integer type
• is not appropriate for determining if two
  objects have the same value.
• if (s1 s2), where s1 and s2 refer to strings,
  determines only if s1 and s2 refer the a common
  memory location.
• To test the equality of objects of class String,
  use method equals.
• s1.equals(s2) or s2.equals(s1)
• To test for equality ignoring case, use method
  equalsIgnoreCase.
• (Hello.equalsIgnoreCase(hello))

18
equals and equalsIgnoreCase

• Syntax
• String.equals(Other_String)
• String.equalsIgnoreCase(Other_String)

19
TESTING STRINGS FOR EQUALITY

• class StringEqualityDemo

20
QUESTIONS

• Suppose goals is a variable of type int. Write an
  if-else statement that outputs the word Wow if
  the value of the variable goals is greater than
  10 and outputs the words Oh Well if the value of
  goals is at most 10.
• Suppose goals and errors are variables of type
  int. Write an if-else statement that outputs the
  word Wow if the value of the variable goals is
  greater than 10 and the value of errors is zero.
  Otherwise, the if-else statement outputs the
  words Oh Well.
• Suppose salary and deductions are variables of
  type double that have been given values. Write an
  if-else statement that outputs OK and sets the
  variable net equal to salary minus deductions,
  provided that salary is at least as large as
  deductions. If, however, salary is less than
  deductions, the if-else statement simply outputs
  the word Crazy and does not change the value of
  any variables.

21
ANSWERS

• if (goals gt 10)
• System.out.println("Wow")
• else
• System.out.println("Oh Well")
• if ((goals gt 10) (errors 0))
• System.out.println("Wow")
• else
• System.out.println("Oh Well")
• if (salary gt deductions)
• System.out.println("OK")
• net salary - deductions
• else
• System.out.println("Crazy")

22
NESTED STATEMENTS

• An if-else statement can contain any sort of
  statement within it.
• In particular, it can contain another if-else
  statement.
• An if-else may be nested within the if part.
• An if-else may be nested within the else part.
• An if-else may be nested within both parts.

23
NESTED STATEMENTS, cont.

• Syntax
• if (Boolean_Expression_1)
• if (Boolean_Expression_2)
• Statement_1)
• else
• Statement_2)
• else
• if (Boolean_Expression_3)
• Statement_3)
• else
• Statement_4)

24
NESTED STATEMENTS, cont.

• Each else is paired with the nearest unmatched
  if.
• If used properly, indentation communicates which
  if goes with which else.
• Braces can be used like parentheses to group
  statements.

25
COMPOUND STATEMENTS

• When a list of statements is enclosed in braces
  (), they form a single compound statement.
• syntax
• Statement_1
• Statement_2
• A compound statement can be used wherever a
  statement can be used.
• example
• if (total gt 10)
• sum sum total
• total 0

26
Multibranch if-else Statements

• Syntax
• if (Boolean_Expression_1)
• Statement_1
• else if (Boolean_Expression_2)
• Statement_2
• else if (Boolean_Expression_3)
• Statement_3
• else if
• else
• Default_Statement

27
Multibranch if-else Statements, cont.

• class Grader

28
Multibranch if-else Statements, cont.

• equivalent code

29
QA

• What output is produced by the following code?
• int time 2, tide 3
• if (time tide gt 6)
• System.out.println("Time and tide wait for
  no one.")
• else
• System.out.println("Time and tide wait for
  me.")
• Ans Time and tide wait for me.
• 2. What output is produced by the following code?
• int time 4, tide 3
• if (time tide gt 6)
• System.out.println("Time and tide wait for no
  one.")
• else
• System.out.println("Time and tide wait for
  me.")
• Ans Time and tide wait for no one.
• 3. What output is produced by the following code?

30
The switch Statement

• The switch statement is a mutltiway branch that
  makes a decision based on an integral (integer or
  character) expression.
• The switch statement begins with the keyword
  switch followed by an integral expression in
  parentheses and called the controlling
  expression.
• A list of cases follows, enclosed in braces.
• Each case consists of the keyword case followed
  by
• a constant called the case label
• a colon
• a list of statements.

31
The switch Statement, cont.

• The list is searched for a case label matching
  the controlling expression.
• The action associated with a matching case label
  is executed.
• If no match is found, the case labeled default is
  executed.
• The default case is optional, but recommended,
  even if it simply prints a message.
• Repeated case labels are not allowed.

32
The switch Statement, cont.

• class MultipleBirths

33
The switch Statement, cont.

• The action for each case typically ends with the
  word break.
• The optional break statement prevents the
  consideration of other cases.
• The controlling expression can be anything that
  evaluates to an integral type.
• Syntax
• switch (Controlling_Expression)
• case Case_Label
• Statement(s)
• break
• case Case_Label
• default

34
QA

• 1. What output is produced by the following code?
• int code 2
• switch (code)
• case 1
• System.out.println("Hello.")
• case 3
• System.out.println("Good-bye.")
• break
• default
• System.out.println("Till we meet again.")
• break
• 2. Suppose you change the code in question 12 so
  that the first line is the following
• int code 1
• What output would be produced?
• 3. What output is produced by the following code?

35

• Ans Till we meet again.
• Ans
• Hello
• Good-bye
• Ans Some kind of B.

36
JAVA LOOP STATEMENTS OUTLINE

• the while Statement
• the do-while Statement
• the for Statement

37
JAVA LOOP STATEMENTS, cont.

• A portion of a program that repeats a statement
  or a group of statements is called a loop.
• The statement or group of statements to be
  repeated is called the body of the loop.
• (e.g.)A loop could be used to compute grades for
  each student in a class.
• There must be a means of exiting the loop.

38
The while Statement

• also called a while loop
• A while statement repeats until a controlling
  boolean expression becomes false.
• If the controlling boolean expression is false
  initially, the while loop is not executed.
• The loop body typically contains a statement that
  ultimately causes the controlling boolean
  expression to become false.

39
The while Statement, cont.

• class WhileDemo

40
The while Statement, cont.

• Syntax
• while (Boolean_Expression)
• Body_Statement
• or
• while (Boolean_Expression)
• First_Statement
• Second_Statement

41
The while Statement, cont.
42
The do-while Statement

• also called a do-while loop
• similar to a while statement, except that the
  loop body is executed at least once
• syntax
• do
• Body_Statement
• while (Boolean_Expression)
• dont forget the semicolon!

43
The do-while Statement, cont.

• class DoWhileDemo

44
The do-while Statement, cont.

• First, the loop body is executed.
• Then the boolean expression is checked.
• As long as it is true, the loop is executed
  again.
• If it is false, the loop is exited.
• equivalent while statement
• Statement(s)_S1
• while (Boolean_Condition)
• Statement(s)_S1

45
The do-while Statement, cont.
46
QA

• 1. What output will be produced by the following
  code?
• int count 0
• while (count lt 5)
• System.out.println(count)
• count
• System.out.println("count after loop "
  count)
• 2. Can the body of a while loop execute zero
  times? Can the body of a do-while loop execute
  zero times?
• 3. What output will be produced by the following
  code?
• int count 0
• do
• System.out.println(count)
• count
• while (count lt 0)
• System.out.println("count after loop " count)

47
Answer

• 1.
• 0
• 1
• 2
• 3
• 4
• count after loop 5
• 2. Yes, the body of a while loop can execute zero
  times. No, the body of a dowhile loop must
  execute at least once.
• 3.
• 0
• count after loop 1

48
The for Statement

• A for statement executes the body of a loop a
  fixed number of times.
• example
• for (count 1 count lt 3 count)
• System.out.println(count)
• System.out.println(Done)
• syntax
• for (Initialization, Condition, Update)
• Body_Statement
• Body_Statement can be either a simple statement
  or a compound statement in .
• corresponding while statement
• Initialization
• while (Condition)
• Body_Statement_Including_Update

49
The for Statement, cont.

• class ForDemo

50
The for Statement, cont.
51
Multiple Initialization, etc.

• example
• for (n 1, p 1 n lt 10 n)
• p p n
• Only one boolean expression is allowed, but it
  can consist of s, s, and !s.
• Multiple update actions are allowed, too.
• for (n 1, p 1 n lt 10 n, p n)

52
The Empty while Statement

• What is printed by
• int product 1, number 1
• while (number lt 2)
• product product number
• number
• System.out.println(product)
• The last semicolon in
• while (number lt 10)
• produces an empty while loop body.

53
Choosing a Loop Statement

• If you know how many times the loop will be
  iterated, use a for loop.
• If you dont know how many times the loop will be
  iterated, but
• it could be zero, use a while loop
• it will be at least once, use a do-while loop.
• Generally, a while loop is a safe choice.

54
QA

• 1. What output is produced by the following code?
• int n
• for (n 1 n lt 4 n)
• System.out.println(n)
• 2. What output is produced by the following code?
• int n
• for (n 1 n gt 4 n)
• System.out.println(n)
• 3. What output is produced by the following code?
• int n
• for (n 4 n gt 0 n--)
• System.out.println(n)
• 4. What output is produced by the following code?
• int n
• for (n 4 n gt 0 n--)
• System.out.println(n)

55
Answer

• 1.
• 1
• 2
• 3
• 4
• 2. This loop causes no output. The boolean
  expression n gt 4 is not satisfied the first
• time through the loop, so the loop ends without
  iterating its body.
• 3.
• 4
• 3
• 2
• 1
• 4. The only output is
• 0
• Be sure to notice the semicolon that was added
  at the end of the first line of the for loop.

56
The break Statement in Loops

• A break statement can be used to end a loop
  immediately.
• The break statement ends only the innermost loop
  or switch statement that contains the break
  statement.
• break statements make loops more difficult to
  understand.
• Use break statements sparingly (if ever).

57
The break Statement in Loops, cont.

• class BreakDemo

58
The exit Method

• Sometimes a situation arises that makes
  continuing the program pointless.
• A program can be terminated normally by
• System.exit(0).
• example
• if (numberOfWinners 0)
• System.out.println(/ by 0)
• System.exit(0)

59
Questions

• 1. What output is produced by the following code?
• int n
• for (n 1 n lt 5 n)
• if (n 3)
• break
• System.out.println("Hello")
• System.out.println("After the Loop.")
• 2. What output is produced by the following code?
• int n
• for (n 1 n lt 5 n)
• if (n 3)
• System.exit(0)
• System.out.println("Hello")
• System.out.println("After the Loop.")

Ans Hello Hello After the Loop
Ans Hello Hello
60
QA

• 3. What output is produced by the following code?
• int n
• for (n 1 n lt 3 n)
• switch (n)
• case 1
• System.out.println("One.")
• break
• case 2
• System.out.println("Two.")
• break
• case 3
• System.out.println("Three.")
• break
• default
• System.out.println("Default case.")
• break

Ans One Two Three After the Loop.
61
Programming with Loops Outline

• The Loop Body
• Initializing Statements
• Ending a Loop
• Loop Bugs
• Tracing Variables

62
The Loop Body

• To design the loop body, write out the actions
  the code must accomplish.
• Then look for a repeated pattern.
• The pattern need not start with the first action.
• The repeated pattern will form the body of the
  loop.
• Some actions may need to be done after the
  pattern stops repeating.

Output instructions to the user. Initialize
variables. Do the following for the appropriate
number of times Read a number into the
variable next. sum sum next
Output the number and the sum so far.
63
Initializing Statements
Output instructions to the user. Initialize
variables. Do the following for the appropriate
number of times Read a number into the
variable next. sum sum next
Output the number and the sum so far.

• Some variables need to have a value before the
  loop begins.
• Sometimes this is determined by what is supposed
  to happen after one loop iteration.
• Often variables have an initial value of zero or
  one, but not always.
• Other variables get values only while the loop is
  iterating.

for (count 1 count lt n count) Read a
number into the variable next. product
product next
64
Ending a Loop
double next, average, sum 0 int count Scanner
keyboard new Scanner(System.in) for (count
1 count lt numberOfStudents count)
next keyboard.nextDouble() sum sum
next if (numberOfStudents gt 0) average
sum/numberOfStudents else
System.out.println("No scores to average.")

• If the number of iterations is known before the
  loop starts, the loop is called a
  count-controlled loop.
• use a for loop.
• Asking the user before each iteration if it is
  time to end the loop is called the
  ask-before-iterating technique.
• appropriate for a small number of iterations
• Use a while loop or a do-while loop.

do System.out.println("Enter price ")
price keyboard.nextDouble()
System.out.print("Enter number purchased ")
number keyboard.nextInt()
System.out.println(number " items at "
price) System.out.println("Total cost "
pricenumber) System.out.println("Want to
make another purchase?")
System.out.println("Enter yes or no.")
answer keyboard.next() while
(answer.equalsIgnoreCase("yes"))
65
Ending a Loop, cont.

• For large input lists, a sentinel value can be
  used to signal the end of the list.
• The sentinel value must be different from all the
  other possible inputs.
• A negative number following a long list of
  nonnegative exam scores could be suitable.
• 100
• 90
• 10
• -1

System.out.println("Enter scores for all
students.") System.out.println("Enter a negative
number after") System.out.println("you have
entered all the scores.") Scanner keyboard new
Scanner(System.in) double max
keyboard.nextDouble() double min max//The max
and min so far are the first score. double next
keyboard.nextDouble() while (next gt 0)
if (next gt max) max next if (next
lt min) min next next
keyboard.nextDouble() System.out.println("The
highest score is " max) System.out.println("The
lowest score is " min)
66
Ending a Loop, cont.

• class ExamAverager

67
Nested Loops

• The body of a loop can contain any kind of
  statements, including another loop.
• In the previous example
• the average score was computed using a while
  loop.
• This while loop was placed inside a do-while loop
  so the process could be repeated for other sets
  of exam scores.

68
Declaring Variables Outside Loop Bodies

• The declaration of variables inside a loop body
  is repeated with each execution of the loop body.
• This can be inefficient, depending on the
  compiler.
• It the declaration of variables can be moved
  outside the loop body, generally it is
  appropriate to do so. (refer slide 66)

69
QA

• Write a Java loop statement that will output the
  phrase "One more time." to the screen four times.
  Also, give any declarations or initializing
  statements that are needed.
• Ans int time
• for (time 1 time lt 4 time)
• System.out.println("One more time.")
• Give a Java loop statement that will set the
  variable result equal to 25. Do this with a loop
  that starts out with the value of result equal to
  1 and multiplies the value of result by 2 for
  each of 5 loop iterations. Also, give any
  declarations or initializing statements that are
  needed.
• Ans int result 1
• int count
• for (count 1 count lt 5 count)
• result 2result

70

• What output is produced by the following code
• int count, innerCount
• for (count 0 count lt 3 count)
• for (innerCount 0 innerCount lt count
  innerCount)
• System.out.println(innerCount)
• Ans
• 0
• 0
• 1
• 0
• 1
• 2

71
Loop Bugs

• Common loop bugs
• unintended infinite loops
• off-by-one errors
• testing equality of floating-point numbers

72
Subtle Infinite Loops

• Subtle infinite loops
• The loop may terminate for some input values, but
  not for others.
• For example (refer to figure below), you cant
  get out of debt when the monthly penalty exceeds
  the monthly payment.
• Verify that the monthly payment exceeds the
  penalty, for example, before entering a loop to
  determine the number of payments needed to get
  out of debt.

if (payment lt penalty) System.out.println("p
ayment is too small.") else count 0
while (balance lt 0) balance balance -
penalty balance balance payment count
System.out.println("You will have a
nonnegative balance in count"
months.")
count 0 while (balance lt 0) balance
balance - penalty balance balance
deposit count System.out.println("You
will have a nonnegative balance in
"count" months.") e.g., testing input
penalty 15, deposit 50
73
Off-by-One Errors

• The loop body is repeated one too many times or
  one too few times.
• examples
• lt is used when lt should be used or lt is used
  when lt should be used
• using the index of the last character of a string
  instead of the length of the string (or vice
  versa)
• easy to overlook

74
Testing Equality of Floating-point Numbers

• works satisfactorily for integers and
  characters.
• is not reliable for floating-point numbers
  (which are approximate quantities).
• Use lt or gt rather than or !.

75
Tracing Variables

• Tracing variables means watching the variables
  change while the program is running.
• Simply insert temporary output statements in your
  program to print of the values of variables of
  interest
• or, learn to use the debugging
• facility that may be provided
• by your system.

count 0 System.out.println("count "
count)//trace System.out.println("balance "
balance)//trace System.out.println("penalty "
penalty)//trace System.out.println("deposit
" deposit)//trace while (balance lt 0)
balance balance penalty
System.out.println("balance penalty "
balance)//trace balance balance -
deposit System.out.println("balance -
deposit " balance)//trace count
System.out.println("count "
count)//trace System.out.println("Nonnegative
balance in count "
months.")
count 0 while (balance lt 0) balance
balance penalty balance balance -
deposit count System.out.println("Nonne
gative balance in " count "
months.")
76
The Type Boolean.

• The type boolean is a primitive type with only
  two values true and false.
• Boolean variables can make programs more
  readable.

if ((temperature lt 100) (thrust gt 12000)
(cabinPressure gt 30)) System.out.println("
Initiate launch sequence.") else
System.out.println("Abort launching sequence.")
if (systemsAreOK) System.out.println("Init
iate launch sequence.") else
System.out.println("Abort launching sequence.")
77
Boolean Expressions and Variables

• Variables, constants, and expressions of type
  boolean all evaluate to either true or false.
• A boolean variable can be given the value of a
  boolean expression by using an assignment
  operator.

boolean isPositive (number gt 0) if
(isPositive) System.out.println("The number
is positive.") else System.out.println("The
number is negative or zero.")
is equivalent to
if (number gt 0) System.out.println("The number is
positive.") else System.out.println("The number
is negative or zero.")
78
Naming Boolean Variables

• Choose a statement that will be true when the
  value of the boolean expression is true, such as
  isPositive or systemsAreOk.
• Avoid names that do not unambiguously describe
  the meaning of the value of the variable. Such as
  numberSign, systemStatus.

79
Truth Tables
80
Precedence Rules

• Parentheses should be used to indicate the order
  of operations.
• When parentheses are omitted, the order of
  operation is determined by precedence rules.
• Operations with higher precedence are performed
  before operations with lower precedence.
• Operations with equal precedence are done
  left-to-right (except for unary operations which
  are done right-to-left).

81
Precedence Rules, cont.
82
Precedence Rules, cont.

• In what order are the operations performed?
• score lt min/2 - 10 score gt 90
• score lt (min/2) - 10 score gt 90
• score lt ((min/2) - 10) score gt 90
• (score lt ((min/2) - 10)) score gt 90
• (score lt ((min/2) - 10)) (score gt 90)

83
Short-circuit Evaluation

• Sometimes only part of a boolean expression needs
  to be evaluated to determine the value of the
  entire expression.
• If the first operand associated with an is
  true, the expression is true.
• If the first operand associated with an is
  false, the expression is false.
• This is called short-circuit or lazy evaluation.

84
Short-circuit Evaluation, cont.

• Short-circuit evaluation is not only efficient,
  sometimes it is essential!
• A run-time error can result, for example, from an
  attempt to divide by zero.
• if ((number ! 0) (sum/number gt 5))
• Complete evaluation can be achieved by
  substituting for or for .

85
Input and Output of Boolean Values

• The values true and false of the type boolean can
  be input and output in the same way that values
  of the other primitive types, such as int and
  double,
• example
• boolean booleanVar false
• System.out.println(booleanVar)
• System.out.println("Enter a boolean value")
• Scanner keyboard new Scanner(System.in)
• booleanVar keyboard.nextBoolean()
• System.out.println("You entered " booleanVar)
• dialog
• false
• Enter a boolean value
• true
• You entered true

86
Using a Boolean Variable to End a Loop

• Example
• boolean numbersLeftToRead true
• while (numbersLeftToRead)
• next keyboard.nextInt()
• if (next lt 0)
• numbersLeftToRead false
• else
• Process_Next_Number

87
Using a Boolean Variable to End a Loop, cont

• class BooleanDemo

88

• What output is produced by the following
  statements?
• int number 7
• boolean isPositive (number gt 0)
• if (number gt 0)
• number - 100
• if (isPositive)
• System.out.println("Positive.")
• else
• System.out.println("Not positive.")
• What output is produced by the following
  statements?
• System.out.println(true false)
• System.out.println(true false)
• System.out.println(true (x gt 0))

89
Graphics Supplement Outline

• Specifying a Drawing Color
• The drawString Method
• A JOptionPane Yes/No Window

90
Specifying a Drawing Color

• When drawing a shape inside an applets paint
  method, think of the drawing being done with a
  pen that can change colors.
• The method setColor changes the color of the
  pen.
• canvas.setColor(Color.YELLOW)
• Drawings done later appear on top of drawings
  done earlier.

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Specifying a Drawing Color, cont.
92
Specifying a Drawing Color, cont.
93
Programming Example

• class MultipleFaces

94
Programming Example, cont.

• class MultipleFaces, contd.

95
Programming Example, cont.
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The drawString Method

• similar to other drawing methods, but used to
  draw text
• canvas.drawString(Hello,10,20)
• syntax
• Graphics_Object.drawString(String, X, Y)

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A JOptionPane Yes/No Window

• used to present the user with a yes/no question
• The window contains
• the question text
• two buttons labeled Yes and No.

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A JOptionPane Yes/No Window, cont.

• example
• int answer JOptionPane.showConfirmDialog(null,
  End program?, End Check, JOptionPane.YES_NO_OP
  TION)
• if (answer JOptionPane.YES_OPTION)
• System.exit(0)
• else
• System.out.println(once more)

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A JOptionPane Yes/No Window, cont.
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A JOptionPane Yes/No Window, cont.

• JOptionPane.showConfirmDialog returns an int
  value named either YES_OPTION or NO_OPTION, but
  you do not need to think of them as ints.
• The second argument (End program? in our
  example) appears in the window.
• The third argument (End Check in our example)
  is displayed as the title of the window.

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A JOptionPane Yes/No Window, cont.

• The last argument (JOptionPane.YES_NO_OPTION in
  our example) requests a window with yes and no
  buttons.
• The first argument (null in our example) affects
  the placement of the window on the screen.
• Simply use null for now.

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Summary

• You have learned about Java branching statements.
• You have learned about loops.
• You have learned about the type boolean.
• You have learned to use color and the JOptionPane
  yes/no window.