Control Structures: Part 2

© 2003 Prentice Hall, Inc. All rights reserved.
1
Chapter 5 – Control Structures: Part 2
Outline
5.1 Introduction
5.2 Essentials of Counter-Controlled Repetition
5.3 for Repetition Statement
5.4 Examples Using the for Statement
5.5 do…while Repetition Statement
5.6 switch Multiple-Selection Statement
5.7 break and continue Statements
5.8 Labeled break and continue Statements
5.9 Logical Operators
5.10 Structured Programming Summary
5.11 (Optional Case Study) Thinking About Objects: Identifying
Objects’ States and Activities

2
5.1 Introduction
• Continue structured-programming discussion
– Introduce Java’s remaining control structures

3
5.2 Essentials of Counter-Controlled
Repetition
• Counter-controlled repetition requires:
– Control variable (loop counter)
– Initial value of the control variable
– Increment/decrement of control variable through each loop
– Condition that tests for the final value of the control variable

© 2003 Prentice Hall, Inc.
All rights reserved.
Outline
4
WhileCounter.ja
va
Line 14
Line 16
Line 18
1 // Fig. 5.1: WhileCounter.java
2 // Counter-controlled repetition.
3 import java.awt.Graphics;
4
5 import javax.swing.JApplet;
6
7 public class WhileCounter extends JApplet {
8
9 // draw lines on applet’s background
10 public void paint( Graphics g )
11 {
12 super.paint( g ); // call paint method inherited from JApplet
13
14 int counter = 1; // initialization
15
16 while ( counter <= 10 ) { // repetition condition
17 g.drawLine( 10, 10, 250, counter * 10 );
18 ++counter; // increment
19
20 } // end while
21
22 } // end method paint
23
24 } // end class WhileCounter
Increment for counter
Condition tests for
counter’s final value
Control-variable name is counter
Control-variable initial value is 1

5
5.3 for Repetition Statement
• Handles counter-controlled-repetition details

Outline
6
ForCounter.java
Line 16
int counter =
1;
Line 16
counter <= 10;
Line 16
counter++;
1 // Fig. 5.2: ForCounter.java
2 // Counter-controlled repetition with the for statement.
4
6
7 public class ForCounter extends JApplet {
8
9 // draw lines on applet’s background
11 {
13
14 // for statement header includes initialization,
15 // repetition condition and increment
16 for ( int counter = 1; counter <= 10; counter++ )
17 g.drawLine( 10, 10, 250, counter * 10 );
18
20
21 } // end class ForCounter
Condition tests for
counter’s final valueControl-variable name is counter
Control-variable initial value is 1
Increment for counter

7
Fig. 5.3 for statement header components.
for ( int counter = 1; counter <= 10; counter++ )
Increment of control
variable
Control
variable
Final value of control
variable for which the
condition is true
for
keyword
Loop-continuation
condition
Initial value of
control variable
Required
semicolon
separator
Required
semicolon
separator

8
5.3 for Repetition Structure (cont.)
for ( initialization; loopContinuationCondition; increment )
statement;
can usually be rewritten as:
initialization;
while ( loopContinuationCondition ) {
statement;
increment;
}

9
Fig. 5.4 for statement activity diagram.
[counter <= 10]
[counter > 10]
int counter = 1
counter++Determine whether
the final value of
control variable has
been reached
g.drawLine(
10, 10, 250,
counter * 10 );
Establish initial value of
control variable
Draw a line on the
applet
Increment the
control variable

10
5.4 Examples Using the for Statement
• Varying control variable in for statement
– Vary control variable from 1 to 100 in increments of 1
• for ( int i = 1; i <= 100; i++ )
– Vary control variable from 100 to 1 in increments of –1
• for ( int i = 100; i >= 1; i-- )
– Vary control variable from 7 to 77 in increments of 7
• for ( int i = 7; i <= 77; i += 7 )

Outline
11
Sum.java
Line 12
1 // Fig. 5.5: Sum.java
2 // Summing integers with the for statement.
3 import javax.swing.JOptionPane;
4
5 public class Sum {
6
7 public static void main( String args[] )
8 {
9 int total = 0; // initialize sum
10
11 // total even integers from 2 through 100
12 for ( int number = 2; number <= 100; number += 2 )
13 total += number;
14
15 // display results
16 JOptionPane.showMessageDialog( null, "The sum is " + total,
17 "Total Even Integers from 2 to 100",
18 JOptionPane.INFORMATION_MESSAGE );
19
20 System.exit( 0 ); // terminate application
21
22 } // end main
23
24 } // end class Sum
increment number by 2 each iteration

Outline
12
Interest.java
Lines 13-15
Line 18
Line 19
1 // Fig. 5.6: Interest.java
2 // Calculating compound interest.
3 import java.text.NumberFormat; // class for numeric formatting
4 import java.util.Locale; // class for country-specific information
5
7 import javax.swing.JTextArea;
8
9 public class Interest {
10
12 {
13 double amount; // amount on deposit at end of each year
14 double principal = 1000.0; // initial amount before interest
15 double rate = 0.05; // interest rate
16
17 // create NumberFormat for currency in US dollar format
18 NumberFormat moneyFormat =
19 NumberFormat.getCurrencyInstance( Locale.US );
20
21 // create JTextArea to display output
22 JTextArea outputTextArea = new JTextArea();
23
24 // set first line of text in outputTextArea
25 outputTextArea.setText( "YeartAmount on depositn" );
26
Java treats floating-points as
type double
NumberFormat can format
numeric values as currency
Display currency values with
dollar sign ($)

Outline
13
Interest.java
Lines 28-31
27 // calculate amount on deposit for each of ten years
28 for ( int year = 1; year <= 10; year++ ) {
29
30 // calculate new amount for specified year
31 amount = principal * Math.pow( 1.0 + rate, year );
32
33 // append one line of text to outputTextArea
34 outputTextArea.append( year + "t" +
35 moneyFormat.format( amount ) + "n" );
36
37 } // end for
38
39 // display results
40 JOptionPane.showMessageDialog( null, outputTextArea,
41 "Compound Interest", JOptionPane.INFORMATION_MESSAGE );
42
43 System.exit( 0 ); // terminate the application
44
45 } // end main
46
47 } // end class Interest
Calculate amount with for
statement

14
5.5 do…while Repetition Statement
• do…while structure
– Similar to while structure
– Tests loop-continuation after performing body of loop
• i.e., loop body always executes at least once

Outline
15
DoWhileTest.jav
a
Lines 16-20
1 // Fig. 5.7: DoWhileTest.java
2 // Using the do...while statement.
4
6
7 public class DoWhileTest extends JApplet {
8
9 // draw lines on applet
11 {
13
14 int counter = 1; // initialize counter
15
16 do {
17 g.drawOval( 110 - counter * 10, 110 - counter * 10,
18 counter * 20, counter * 20 );
19 ++counter;
20 } while ( counter <= 10 ); // end do...while
21
23
24 } // end class DoWhileTest
Oval is drawn before testing
counter’s final value

16
Fig. 5.8 do…while repetition statement activity diagram.
action state
[true]
[false]
condition

17
5.6 switch Multiple-Selection Statement
• switch statement
– Used for multiple selections

Outline
18
SwitchTest.java
Lines 16-21:
Getting user’s input
1 // Fig. 5.9: SwitchTest.java
2 // Drawing lines, rectangles or ovals based on user input.
4
5 import javax.swing.*;
6
7 public class SwitchTest extends JApplet {
8 int choice; // user's choice of which shape to draw
9
10 // initialize applet by obtaining user's choice
11 public void init()
12 {
13 String input; // user's input
14
15 // obtain user's choice
16 input = JOptionPane.showInputDialog(
17 "Enter 1 to draw linesn" +
18 "Enter 2 to draw rectanglesn" +
19 "Enter 3 to draw ovalsn" );
20
21 choice = Integer.parseInt( input ); // convert input to int
22
23 } // end method init
24
25 // draw shapes on applet's background
27 {
29
30 for ( int i = 0; i < 10; i++ ) { // loop 10 times (0-9)
31
Get user’s input in JApplet

Outline
19
SwitchTest.java
Line 32:
controlling
expression
Line 32:
switch statement
Line 48
32 switch ( choice ) { // determine shape to draw
33
34 case 1: // draw a line
35 g.drawLine( 10, 10, 250, 10 + i * 10 );
36 break; // done processing case
37
38 case 2: // draw a rectangle
39 g.drawRect( 10 + i * 10, 10 + i * 10,
40 50 + i * 10, 50 + i * 10 );
42
43 case 3: // draw an oval
44 g.drawOval( 10 + i * 10, 10 + i * 10,
45 50 + i * 10, 50 + i * 10 );
47
48 default: // draw string indicating invalid value entered
49 g.drawString( "Invalid value entered",
50 10, 20 + i * 15 );
51
52 } // end switch
53
54 } // end for
55
57
58 } // end class SwitchTest
default case for invalid entries
switch statement determines
which case label to execute,
depending on controlling expression
user input (choice) is
controlling expression

Outline
20
SwitchTest.java

Outline
21
SwitchTest.java

22
Fig. 5.10 switch multiple-selection statement activity diagram with break statements.
case a action(s) break
default action(s)
[true]
case b action(s) break
case z action(s) break
.
.
.
[false]
case a
[true]
[true]
case b
case z
[false]
[false]

23
5.7 break and continue Statements
• break/continue
– Alter flow of control
• break statement
– Causes immediate exit from control structure
• Used in while, for, do…while or switch statements
• continue statement
– Skips remaining statements in loop body
– Proceeds to next iteration
• Used in while, for or do…while statements

Outline
24
BreakTest.java
Line 12
Lines 14-15
1 // Fig. 5.11: BreakTest.java
2 // Terminating a loop with break.
4
5 public class BreakTest {
6
8 {
9 String output = "";
10 int count;
11
12 for ( count = 1; count <= 10; count++ ) { // loop 10 times
13
14 if ( count == 5 ) // if count is 5,
15 break; // terminate loop
16
17 output += count + " ";
18
19 } // end for
20
21 output += "nBroke out of loop at count = " + count;
22 JOptionPane.showMessageDialog( null, output );
23
25
26 } // end main
27
28 } // end class BreakTest
Loop 10 times
exit for structure (break)
when count equals 5

Outline
25
ContinueTest.ja
va
Line 11
Lines 13-14
1 // Fig. 5.12: ContinueTest.java
2 // Continuing with the next iteration of a loop.
4
5 public class ContinueTest {
6
8 {
10
11 for ( int count = 1; count <= 10; count++ ) { // loop 10 times
12
13 if ( count == 5 ) // if count is 5,
14 continue; // skip remaining code in loop
15
16 output += count + " ";
17
18 } // end for
19
20 output += "nUsed continue to skip printing 5";
21 JOptionPane.showMessageDialog( null, output );
22
24
25 } // end main
26
27 } // end class ContinueTest
Loop 10 times
Skip line 16 and proceed to
line 11 when count equals 5

26
5.8 Labeled break and continue
Statements
• Labeled block
– Set of statements enclosed by {}
– Preceded by a label
• Labeled break statement
– Exit from nested control structures
– Proceeds to end of specified labeled block
• Labeled continue statement
– Skips remaining statements in nested-loop body
– Proceeds to beginning of specified labeled block

Outline
27
BreakLabelTest.
java
Line 11
Line 14
Line 17
Lines 19-20
1 // Fig. 5.13: BreakLabelTest.java
2 // Labeled break statement.
4
5 public class BreakLabelTest {
6
8 {
10
11 stop: { // labeled block
12
13 // count 10 rows
14 for ( int row = 1; row <= 10; row++ ) {
15
16 // count 5 columns
17 for ( int column = 1; column <= 5 ; column++ ) {
18
19 if ( row == 5 ) // if row is 5,
20 break stop; // jump to end of stop block
21
22 output += "* ";
23
24 } // end inner for
25
26 output += "n";
27
28 } // end outer for
29
Loop 10 times
stop is the labeled block
Exit to line 35 (next slide)
Nested loop 5 times

Outline
28
BreakLabelTest.
java
30 // following line is skipped
31 output += "nLoops terminated normally";
32
33 } // end labeled block
34
35 JOptionPane.showMessageDialog( null, output,
36 "Testing break with a label",
38
40
41 } // end main
42
43 } // end class BreakLabelTest

Outline
29
ContinueLabelTe
st.java
Line 11
Line 14
Line 17
Lines 21-22
1 // Fig. 5.14: ContinueLabelTest.java
2 // Labeled continue statement.
4
5 public class ContinueLabelTest {
6
8 {
10
11 nextRow: // target label of continue statement
12
13 // count 5 rows
14 for ( int row = 1; row <= 5; row++ ) {
15 output += "n";
16
17 // count 10 columns per row
18 for ( int column = 1; column <= 10; column++ ) {
19
20 // if column greater than row, start next row
21 if ( column > row )
22 continue nextRow; // next iteration of labeled loop
23
24 output += "* ";
25
26 } // end inner for
27
28 } // end outer for
nextRow is the labeled block
Loop 5 times
Nested loop 10 times
continue to line 11 (nextRow)

Outline
30
ContinueLabelTe
st.java
29
30 JOptionPane.showMessageDialog( null, output,
31 "Testing continue with a label",
33
35
36 } // end main
37
38 } // end class ContinueLabelTest

31
5.9 Logical Operators
• Logical operators
– Allows for forming more complex conditions
– Combines simple conditions
• Java logical operators
– && (conditional AND)
– & (boolean logical AND)
– || (conditional OR)
– | (boolean logical inclusive OR)
– ^ (boolean logical exclusive OR)
– ! (logical NOT)

32
expression1 expression2 expression1 &&
expression2
false false false
false true false
true false false
true true true
Fig. 5.15 && (conditional AND) operator truth table.
expression1 expression2 expression1 ||
expression2
false false false
false true true
true false true
true true true
Fig. 5.16 || (conditional OR) operator truth table.

33
expression1 expression2 expression1 ^
expression2
false false false
false true true
true false true
true true false
Fig. 5.17 ^ (boolean logical exclusive OR) operator truth table.
expression !expression
false true
true false
Fig. 5.18 ! (logical negation, or logical NOT) operator truth table.

Outline
34
LogicalOperator
s.java
Lines 16-20
Lines 23-27
1 // Fig. 5.19: LogicalOperators.java
2 // Logical operators.
3 import javax.swing.*;
4
5 public class LogicalOperators
6
8 {
9 // create JTextArea to display results
10 JTextArea outputArea = new JTextArea( 17, 20 );
11
12 // attach JTextArea to a JScrollPane so user can scroll results
13 JScrollPane scroller = new JScrollPane( outputArea );
14
15 // create truth table for && (conditional AND) operator
16 String output = "Logical AND (&&)" +
17 "nfalse && false: " + ( false && false ) +
18 "nfalse && true: " + ( false && true ) +
19 "ntrue && false: " + ( true && false ) +
20 "ntrue && true: " + ( true && true );
21
22 // create truth table for || (conditional OR) operator
23 output += "nnLogical OR (||)" +
24 "nfalse || false: " + ( false || false ) +
25 "nfalse || true: " + ( false || true ) +
26 "ntrue || false: " + ( true || false ) +
27 "ntrue || true: " + ( true || true );
28
Conditional AND truth table
Conditional OR truth table

Outline
35
LogicalOperator
s.java
Lines 30-34
Lines 37-41
Lines 44-48
Lines 51-53
29 // create truth table for & (boolean logical AND) operator
30 output += "nnBoolean logical AND (&)" +
31 "nfalse & false: " + ( false & false ) +
32 "nfalse & true: " + ( false & true ) +
33 "ntrue & false: " + ( true & false ) +
34 "ntrue & true: " + ( true & true );
35
36 // create truth table for | (boolean logical inclusive OR) operator
37 output += "nnBoolean logical inclusive OR (|)" +
38 "nfalse | false: " + ( false | false ) +
39 "nfalse | true: " + ( false | true ) +
40 "ntrue | false: " + ( true | false ) +
41 "ntrue | true: " + ( true | true );
42
43 // create truth table for ^ (boolean logical exclusive OR) operator
44 output += "nnBoolean logical exclusive OR (^)" +
45 "nfalse ^ false: " + ( false ^ false ) +
46 "nfalse ^ true: " + ( false ^ true ) +
47 "ntrue ^ false: " + ( true ^ false ) +
48 "ntrue ^ true: " + ( true ^ true );
49
50 // create truth table for ! (logical negation) operator
51 output += "nnLogical NOT (!)" +
52 "n!false: " + ( !false ) +
53 "n!true: " + ( !true );
54
55 outputArea.setText( output ); // place results in JTextArea
56
Logical NOT truth table
Boolean logical exclusive
OR truth table
Boolean logical inclusive
OR truth table
Boolean logical AND
truth table

Outline
36
LogicalOperator
s.java
57 JOptionPane.showMessageDialog( null, scroller,
58 "Truth Tables", JOptionPane.INFORMATION_MESSAGE );
59
61
62 } // end main
63
64 } // end class LogicalOperators

37
Operators Associativity Type
++ -- right to left unary postfix
++ -- + - !
(type)
right to left unary
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right equality
& left to right boolean logical AND
^ left to right boolean logical exclusive OR
| left to right boolean logical inclusive OR
&& left to right conditional AND
|| left to right conditional OR
?: right to left conditional
= += -= *= /= %= right to left assignment
Fig. 5.20 Precedence/associativity of the operators discussed so far.

38
5.10 Structured Programming Summary
• Sequence structure
– “built-in” to Java
• Selection structure
– if, if…else and switch
• Repetition structure
– while, do…while and for

39
Fig. 5.21 Java’s single-entry/single-exit sequence, selection and repetition statements.
[t]
[f]
[f]
[t]
break
break
[t]
break
[t]
[f]
[t]
[f]
[t]
[f]
[t]
[f]
Repetition
while statement do while statement for statement
SelectionSequence
if else statement
(double selection)
if statement (single
selection)
switch statement
(multiple selection)
.
.
.
[t][f]
default

40
Rules for Forming Structured Programs
1)
Begin with the “simplest activity diagram” (Fig. 5.23).
2)
Any action state can be replaced by two action states in sequence.
3)
Any action state can be replaced by any control statement (sequence,
if, if else, switch, while, do while or for).
4)
Rules 2 and 3 can be applied as often as you like and in any order.
Fig. 5.22 Rules for forming structured programs.
action state
Fig. 5.23 Simplest activity diagram.

41
Fig. 5.24 Repeatedly applying rule 2 of Fig. 5.22 to the simplest activity diagram.
.
.
.action state
action state
apply
Rule 2
apply
Rule 2
apply
Rule 2
action state
action state
action state
action state
action state
action state

42
Fig. 5.25 Applying rule 3 of Fig. 5.22 to the simplest activity diagram.
action state
apply
Rule 3
apply
Rule 3
apply
Rule 3 action stateaction state
action stateaction state action stateaction state
[f] [t]
[f] [t]
[f] [t][f] [t]

43
Fig. 5.26 Activity diagram with illegal syntax.
action state
action state
action state
action state

445.11 (Optional Case Study) Thinking About
Objects: Identifying Objects’ States and
Activities
• State
– Describes an object’s condition at a given time
• Statechart diagram (UML)
– Express how an object can change state
– Express under what conditions an object can change state
– Diagram notation (Fig. 5.28)
• States are represented by rounded rectangles
– e.g., “Not Pressed” and “Pressed”
• Solid circle (with attached arrowhead) designates initial state
• Arrows represent transitions (state changes)
– Objects change state in response to messages
• e.g., “buttonPressed” and “buttonReset”

45
Fig. 5.27 Statechart diagram for FloorButton and ElevatorButton objects.
buttonReset
buttonPressed
PressedNot pressed

465.11 (Optional Case Study) Thinking About
Objects: Identifying Objects’ States and
Activities (cont.):
• Activity diagram (UML)
– Models an object’s workflow during program execution
– Models the actions that an object will perform
– Diagram notation (Fig. 5.28)
• Activities are represented by ovals
• Solid circle designates initial activity
• Arrows represents transitions between activities
• Small diamond represents branch
– Next transition at branch is based on guard condition

47
Fig. 5.28 Activity diagram for a Person object.
[floor door closed]
press elevator button
enter elevator
move toward floor button
wait for door to open
press floor button
wait for door to open
[floor door open]
exit elevator
wait for passenger to exit elevator
[passenger on elevator]
[no passenger on
elevator]

48
Fig. 5.29 Activity diagram for the Elevator object.
close elevator door
ring bell
reset elevator button
[elevator idle][button on destination
floor
pressed]
open elevator door
[elevator moving]
[button on
current floor
pressed]
[floor button
pressed]
[elevator button
pressed]
[summoned]
[not summoned]
set summoned to true
set summoned to false
move to destination floor
[button on
destination
floor
pressed]
[button on
current floor
pressed]

Control Structures: Part 2

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Control Structures: Part 2