2005 pearson education, inc. all rights reserved. 1 part 2 control statements

2005 Pearson Education, Inc. All rights reserved.

1

Part 2

Control Statements


2

OBJECTIVES

In this Part you will learn:

To use the if and if else selection statements to choose among alternative actions.

To use the while repetition statement to execute statements in a program repeatedly.

To use counter-controlled repetition and sentinel-controlled repetition.

To use the assignment, increment and decrement operators.


3

Sequence structure activity diagram.

Solid circle represents the activity’s initial state

Solid circle surrounded by a hollow circle represents the activity’s final state


4

Control Structures (Cont.)

• Selection Statements– if statement

• Single-selection statement

– if…else statement• Double-selection statement

– switch statement• Multiple-selection statement


5

Control Structures (Cont.)

• Repetition statements– Also known as looping statements

– Repeatedly performs an action while its loop-continuation condition remains true

– while statement• Performs the actions in its body zero or more times

– do…while statement• Performs the actions in its body one or more times

– for statement• Performs the actions in its body zero or more times


6

if Single-Selection Statement

•if statements– Execute an action if the specified condition is true

– Can be represented by a decision symbol (diamond) in a UML activity diagram

• Transition arrows out of a decision symbol have guard conditions

– Workflow follows the transition arrow whose guard condition is true


7

Fig. 4.2 | if single-selection statement UML activity diagram.

Diamonds

Decision symbols (explained in section 4.5)


8

if…else Double-Selection Statement

•if…else statement– Executes one action if the specified condition is true or a

different action if the specified condition is false

if else double-selection statement UML activity diagram.


9

if ( testScore < 70 )

JOptionPane.showMessageDialog(null, "You did not pass" );

else

JOptionPane.showMessageDialog(null, "You did pass " );

Syntax for the if Statementif ( <boolean expression> )

<then block>

else

<else block>

Then BlockThen Block

Else BlockElse Block

Boolean ExpressionBoolean Expression


10

Control Flow

JOptionPane.showMessageDialog(null, "You did pass");

JOptionPane.showMessageDialog(null, "You did pass");

falsetestScore < 70 ?

testScore < 70 ?

JOptionPane.showMessageDialog(null, "You did not pass");

JOptionPane.showMessageDialog(null, "You did not pass");

true


11

testScore < 80

testScore * 2 >= 350

30 < w / (h * h)

x + y != 2 * (a + b)

2 * Math.PI * radius <= 359.99

Relational Operators

< //less than

<= //less than or equal to

== //equal to

!= //not equal to

> //greater than

>= //greater than or equal to


12

Decision Making: Equality and Relational Operators

• Condition– Expression can be either true or false

•if statement– Simple version in this section, more detail later

– If a condition is true, then the body of the if statement executed

– Control always resumes after the if statement

– Conditions in if statements can be formed using equality or relational operators (next slide)


13

Fig. 14 | Equality and relational operators.

Standard algebraic equality or relational operator

Java equality or relational operator

Sample Java condition

Meaning of Java condition

Equality operators == x == y x is equal to y != x != y x is not equal to y Relational operators > x > y x is greater than y < x < y x is less than y >= x >= y x is greater than or equal to y ≤ <= x <= y x is less than or equal to y


14

if ( testScore < 70 )

JOptionPane.showMessageDialog(null, "You did not pass" );

else

JOptionPane.showMessageDialog(null, "You did pass " );

Syntax for the if Statementif ( <boolean expression> )

<then block>

else

<else block>





15

Outline• Comparison.java

• (1 of 2)

1 // Fig. 2.15: Comparison.java 2 // Compare integers using if statements, relational operators 3 // and equality operators. 4 import java.util.Scanner; // program uses class Scanner 5 6 public class Comparison 7 { 8 // main method begins execution of Java application 9 public static void main( String args[] ) 10 { 11 // create Scanner to obtain input from command window 12 Scanner input; Input = new Scanner( System.in ); 13 14 int number1; // first number to compare 15 int number2; // second number to compare 16 17 System.out.print( "Enter first integer: " ); // prompt 18 number1 = input.nextInt(); // read first number from user 19 20 System.out.print( "Enter second integer: " ); // prompt 21 number2 = input.nextInt(); // read second number from user 22 23 if ( number1 == number2 ) 24 System.out.print( number1 + " Equal " + number2 + “\n” ); 25 26 if ( number1 != number2 ) 27 System.out.printf( "%d != %d\n", number1, number2 ); 28 29 if ( number1 < number2 ) 30 System.out.printf( "%d < %d\n", number1, number2 );

Test for equality, display result using printf.

Compares two numbers using relational operator <.


16

Outline

• Comparison.java

• (2 of 2)

• Program output

31 32 if ( number1 > number2 ) 33 System.out.printf( "%d > %d\n", number1, number2 );

34

35 if ( number1 <= number2 )

36 System.out.printf( "%d <= %d\n", number1, number2 );

37

38 if ( number1 >= number2 )

39 System.out.printf( "%d >= %d\n", number1, number2 );

40

41 } // end method main

42

43 } // end class Comparison Enter first integer: 777 Enter second integer: 777 777 == 777 777 <= 777 777 >= 777 Enter first integer: 1000 Enter second integer: 2000 1000 != 2000 1000 < 2000 1000 <= 2000

Enter first integer: 2000 Enter second integer: 1000 2000 != 1000 2000 > 1000 2000 >= 1000

Compares two numbers using relational operator >, <= and >=.


17

Common Programming Error 9

• Placing a semicolon immediately after the right parenthesis of the condition in an if statement is normally a logic error.


18

Decision Making: Equality and Relational Operators (Cont.)

– Line 6: begins class Comparison declaration

– Line 12: declares Scanner variable input and assigns it a Scanner that inputs data from the standard input

– Lines 14-15: declare int variables

– Lines 17-18: prompt the user to enter the first integer and input the value

– Lines 20-21: prompt the user to enter the second integer and input the value

1 // Fig. 2.15: Comparison.java 2 // Compare integers using if statements, relational operators 3 // and equality operators. 4 import java.util.Scanner; // program uses class Scanner 5 6 public class Comparison 7 { 8 // main method begins execution of Java application 9 public static void main( String args[] ) 10 { 11 // create Scanner to obtain input from command window 12 Scanner input = new Scanner( System.in ); 13 14 int number1; // first number to compare 15 int number2; // second number to compare 16 17 System.out.print( "Enter first integer: " ); // prompt 18 number1 = input.nextInt(); // read first number from user 19 20 System.out.print( "Enter second integer: " ); // prompt 21 number2 = input.nextInt(); // read second number from user 22 23 if ( number1 == number2 ) 24 System.out.printf( "%d == %d\n", number1, number2 ); 25 26 if ( number1 != number2 ) 27 System.out.printf( "%d != %d\n", number1, number2 ); 28 29 if ( number1 < number2 ) 30 System.out.printf( "%d < %d\n", number1, number2 );


19

Decision Making: Equality and Relational Operators (Cont.)

– if statement to test for equality using (==)• If variables equal (condition true)

– Line 24 executes

• If variables not equal, statement skipped

• No semicolon at the end of if statement

• Empty statement– No task is performed

– Lines 26-27, 29-30, 32-33, 35-36 and 38-39• Compare number1 and number2 with the operators !=, <, >, <= and >=, respectively

23 if ( number1 == number2 )

24 System.out.printf( "%d == %d\n", number1, number2 );


20


• Confusing the equality operator, ==, with the assignment operator, =, can cause a logic error or a syntax error.

• The equality operator should be read as “is equal to,” and the assignment operator should be read as “gets” or “gets the value of.” To avoid confusion, some people read the equality operator as “double equals” or “equals equals.”


21


• It is a syntax error if the operators ==, !=, >= and <= contain spaces between their symbols, as in = =, ! =, > = and < =, respectively.


• Reversing the operators !=, >= and <=, as in =!, => and =<, is a syntax error.


22

Good Programming Practice 8

• A lengthy statement can be spread over several lines. If a single statement must be split across lines, choose breaking points that make sense, such as after a comma in a comma-separated list, or after an operator in a lengthy expression. If a statement is split across two or more lines, indent all subsequent lines until the end of the statement.


23

Good Programming Practice 8

• Refer to the operator precedence chart (see the complete chart in Appendix A) when writing expressions containing many operators. Confirm that the operations in the expression are performed in the order you expect. If you are uncertain about the order of evaluation in a complex expression, use parentheses to force the order, exactly as you would do in algebraic expressions. Observe that some operators, such as assignment, =, associate from right to left rather than from left to right.


24

Fig. 2.16 | Precedence and associativity of operations discussed.

Operators Associativity Type

* / % left to right multiplicative

+ - left to right additive

< <= > >= left to right relational

== != left to right equality

= right to left assignment


25

if (testScore < 70)

{

JOptionPane.showMessageDialog(null, "You did not pass“ );

JOptionPane.showMessageDialog(null, “Try harder next time“ );

}

else

{

JOptionPane.showMessageDialog(null, “You did pass“ );

JOptionPane.showMessageDialog(null, “Keep up the good work“ );

}

Compound Statements• Use braces if the <then> or <else> block has multiple statements.




26

if ( <boolean expression> ) {

…

}

else {

…

}

Style Guide

if ( <boolean expression> )

{

…

}

else

{

…

}

Style 1Style 1

Style 2Style 2


27

The if-then Statementif ( <boolean expression> )

<then block>

if ( testScore >= 95 )

JOptionPane.showMessageDialog(null,"You are an honor student");Then BlockThen Block



28

Control Flow of if-then

testScore >= 95?

testScore >= 95?

falseJOptionPane.showMessageDialog (null, "You are an honor student");

JOptionPane.showMessageDialog (null, "You are an honor student");

true


29

The Nested-if Statement

• The then and else block of an if statement can contain any valid statements, including other if statements. An if statement containing another if statement is called a nested-if statement.

if (testScore >= 70) {

if (studentAge < 10) {

System.out.println("You did a great job");

} else {

System.out.println("You did pass"); //test score >= 70

} //and age >= 10

} else { //test score < 70

System.out.println("You did not pass");

}


30

Control Flow of Nested-if Statement

messageBox.show("You did not pass");

messageBox.show("You did not pass");

false inner if

messageBox.show("You did pass");

messageBox.show("You did pass");

false

testScore >= 70 ?

testScore >= 70 ?

true

studentAge < 10 ?

studentAge < 10 ?

messageBox.show("You did a great job");

messageBox.show("You did a great job");

true


31

Writing a Proper if Controlif (num1 < 0)

if (num2 < 0)

if (num3 < 0)

negativeCount = 3;

else

negativeCount = 2;

else

if (num3 < 0)

negativeCount = 2;

else

negativeCount = 1;

else

if (num2 < 0)

if (num3 < 0)

negativeCount = 2;

else

negativeCount = 1;

else

if (num3 < 0)

negativeCount = 1;

else

negativeCount = 0;

negativeCount = 0;

if (num1 < 0)

negativeCount++;

if (num2 < 0)

negativeCount++;

if (num3 < 0)

negativeCount++;

The statement

negativeCount++;

increments the variable by one

The statement

negativeCount++;

increments the variable by one

What is the values of negativeCount when executing the fragment code shown and num1, num2, and num3 values as shown

num1 = -2, num2 = -2, num3 = 2

num1 = 2, num2 = -2, num3 = 2

num1 = -2, num2 = -2, num3 =-2

num1 = 2, num2 = 2, num3 = -2

num1 = -2, num2 = -2, num3 = 2


32

if – else if Control

if (score >= 90)

System.out.print("Your grade is A");

else if (score >= 80)

System.out.print("Your grade is B");


System.out.print("Your grade is C");


System.out.print("Your grade is D");

else

System.out.print("Your grade is F");

Test Score Grade90 score A

80 score 90

B

70 score 80

C

60 score 70

D

score 60 F


33

Matching else

if (x < y)

if (x < z)

System.out.print("Hello");

else

System.out.print("Good bye");

AA

if (x < y)

if (x < z)


else


BB

Are and different?AA BB

if (x < y) {

if (x < z) {


} else {


}

}

Both and means…AA BB


34

5.1 Introduction

Introduce Java’s remaining control structures

for, while , do…while


35

Fig. 5.3 | for statement header components.


36

Outline

1 // Fig. 5.2: ForCounter.java

2 // Counter-controlled repetition with the for repetition statement.

3

4 public class ForCounter

5 {

6 public static void main( String args[] )

7 {

8 // for statement header includes initialization,

9 // loop-continuation condition and increment

10 for ( int counter = 1; counter <= 10; counter++ )

11 System.out.printf( "%d ", counter );

12

13 System.out.println(); // output a newline

14 } // end main

15 } // end class ForCounter 1 2 3 4 5 6 7 8 9 10

Control-variable name is counter

Control-variable initial value is 1

Condition tests for counter’s final value

Increment for counter


37

for Repetition Statement (Cont.)

for ( initialization; loopContinuationCondition; increment ) for ( initialization; loopContinuationCondition; increment )

statement;statement;

can usually be rewritten as:can usually be rewritten as:

initialization;initialization;while ( loopContinuationCondition ) while ( loopContinuationCondition )

{{ statement; statement; increment; increment;}}


38

Error-Prevention Tip

Although the value of the control variable can be changed in the body of a for loop, avoid doing so, because this practice can lead to subtle errors.


39

Fig. 5.4 | UML activity diagram for the for statement in Fig. 5.2.

for ( int counter = 1; counter <= 10; counter++ )

System.out.printf( "%d ", counter );


40

Examples Using the for Statement

Varying control variable in for statementVary control variable from 1 to 100 in increments of 1

for ( int i = 1; i <= 100; i++ )Vary co ntrol 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 )Vary control variable from 20 to 2 in decrements of 2

for ( int i = 20; i >= 2; i -= 2 )Vary control variable over the sequence: 2, 5, 8, 11, 14, 17, 20

for ( int i = 2; i <= 20; i += 3 )Vary control variable over the sequence: 99, 88, 77, 66, 55, 44, 33, 22, 11, 0

for ( int i = 99; i >= 0; i -= 11 )


41

Outline

Sum.java

Line 11

1 // Fig. 5.5: Sum.java

2 // Summing integers with the for statement.

3

4 public class Sum

5 {


7 {

8 int total = 0; // initialize total

9

10 // total even integers from 2 through 20

11 for ( int number = 2; number <= 20; number += 2 )

12 total += number;

13

14 System.out.printf( "Sum is %d\n", total ); // display results

15 } // end main

16 } // end class Sum Sum is 110

increment number by 2 each iteration


42

Examples Using the for Statement (Cont.)

Initialization and increment expression can be comma-separated lists of expressions

11 for ( int number = 2; number <= 20; number += 2 )

12 total += number; E.g., lines 11-12 of Fig. 5.5 can be rewritten as

for ( int number = 2; number <= 20; total += number, number += 2 )

; // empty statement


43

Outline

1 // Fig. 5.6: Interest.java

2 // Compound-interest calculations with for.

3

4 public class Interest

5 {


7 {

8 double amount; // amount on deposit at end of each year

9 double principal = 1000.0; // initial amount before interest

10 double rate = 0.05; // interest rate

11

12 // display headers

13 System.out.printf( "%s%20s\n", "Year", "Amount on deposit" );

14

Java treats floating-points as type double

Second string is right justified and displayed with a field width of 20


44

Outline

15 // calculate amount on deposit for each of ten years

16 for ( int year = 1; year <= 10; year++ )

17 {

18 // calculate new amount for specified year

19 amount = principal * Math.pow( 1.0 + rate, year );

20

21 // display the year and the amount

22 System.out.printf( "%4d%,20.2f\n", year, amount );

23 } // end for

24 } // end main

25 } // end class Interest Year Amount on deposit 1 1,050.00 2 1,102.50 3 1,157.63 4 1,215.51 5 1,276.28 6 1,340.10 7 1,407.10 8 1,477.46 9 1,551.33 10 1,628.89

Calculate amount with for statement

Use the comma (,) formatting flag to display the amount with a thousands separator


45

Increment and Decrement Operators

Unary increment and decrement operators

Unary increment operator (++) adds one to its operand

Unary decrement operator (--) subtracts one from its operand

Prefix increment (and decrement) operator

Changes the value of its operand, then uses the new value of the operand in the expression in which the operation appears

Postfix increment (and decrement) operator

Uses the current value of its operand in the expression in which the operation appears, then changes the value of the operand


46

Fig. 4.15 | Increment and decrement operators.

Operator Called Sample expression

Explanation

++ prefix increment ++a Increment a by 1, then use the new value of a in the

expression in which a resides.

++ postfix increment

a++ Use the current value of a in the expression in which a resides, then increment a by 1.

-- prefix decrement

--b Decrement b by 1, then use the new value of b in the expression in which b resides.

-- postfix decrement

b-- Use the current value of b in the expression in which b resides, then decrement b by 1.


47

Outline

Increment.java

1 // Fig. 4.16: Increment.java 2 // Prefix increment and postfix increment operators. 3

4 public class Increment 5 { 6 public static void main( String args[] ) 7 { 8 int c; 9

10 // demonstrate postfix increment operator 11 c = 5; // assign 5 to c 12 System.out.println( c ); // print 5

13 System.out.println( c++ ); // print 5 then postincrement 14 System.out.println( c ); // print 6 15

16 System.out.println(); // skip a line 17

18 // demonstrate prefix increment operator 19 c = 5; // assign 5 to c 20 System.out.println( c ); // print 5 21 System.out.println( ++c ); // preincrement then print 6 22 System.out.println( c ); // print 6 23

24 } // end main 25

26 } // end class Increment

5 5 6 5 6 6

Postincrementing the c variable

Preincrementing the c variable


48

4.11 Compound Assignment Operators

Compound assignment operators

An assignment statement of the form:variable = variable operator expression;

where operator is +, -, *, / or % can be written as:variable operator= expression;

example: c = c + 3; can be written as c += 3;

This statement adds 3 to the value in variable c and stores the result in variable c


49

Fig. 4.14 | Arithmetic compound assignment operators.

Assignment operator

Sample expression

Explanation Assigns

Assume: int c = 3, d = 5, e = 4, f = 6, g = 12; += c += 7 C = c + 7 10 to c -= d -= 4 d = d - 4 1 to d *= e *= 5 e = e * 5 20 to e /= f /= 3 f = f / 3 2 to f

%= g %= 9 g = g % 9 3 to g


50

Common Programming Error 4.9

Attempting to use the increment or decrement operator on an expression other than one to which a value can be assigned is a syntax error.

For example, writing ++(x + 1) is a syntax error because (x + 1) is not a variable.


51

Fig. 4.17 | Precedence and associativity of the operators discussed so far.

Operators Associativity Type ++ -- right to left unary postfix

++ -- + - ( type ) right to left unary prefix * / % left to right Multiplicative + - left to right Additive < <= > >= left to right Relational == != left to right Equality ?: right to left Conditional

= += -= *= /= %= right to left assignment


52

while Repetition Statement

• while statement

–Repeats an action while its loop-continuation condition remains true


53

for Repetition Statement (Cont.)

for ( initialization; loopContinuationCondition; increment ) for ( initialization; loopContinuationCondition; increment )

statement;statement;

can usually be rewritten as:can usually be rewritten as:

initialization;initialization;while ( loopContinuationCondition ) while ( loopContinuationCondition )

{{ statement; statement; increment; increment;}}


54

Outline

WhileCounter.java

1 // Fig. 5.1: WhileCounter.java

2 // Counter-controlled repetition with the while repetition statement.

3

4 public class WhileCounter

5 {


7 {

8 int counter = 1; // declare and initialize control variable

9

10 while ( counter <= 10 ) // loop-continuation condition

11 {


13 ++counter; // increment control variable by 1

14 } // end while

15

16 System.out.println(); // output a newline

17 } // end main

18 } // end class WhileCounter 1 2 3 4 5 6 7 8 9 10

Control-variable name is counter

Control-variable initial value is 1Condition tests for counter’s

final value

Increment for counter


55Calculate.java// Calculate the sum of the integers from 1 to 10

public class Calculate { public static void main( String args[] ) { int sum; int x;

x = 1; // initialize x to 1 for counting sum = 0; // initialize sum to 0 for totaling

while ( x <= 10 ) // while x is less than or equal to 10 { sum += x; // add x to sum sum = sum + x; ++x; // increment x } // end while

System.out.printf( "The sum is: %d\n", sum ); } // end main

} // end class Calculate


56

Mystery.java

Q : What is this program calculate f(x) ?

public class Mystery { public static void main( String args[] ) { int y; int x = 1; int total = 0;

while ( x <= 10 ) { y = x * x; System.out.println( y ); total += y; ++x; } // end while

System.out.printf( "Total is %d\n", total ); } // end main

} // end class Mystery

/**************************************************************


57

Fig. 4.4 | while repetition statement UML activity diagram.

Diamonds

Decision symbols (explained in section 4.5)

Merge symbols (explained in section 4.7) int product = 3;

while (product <= 100)

product = 3 * product


58

Fig. 4.5 | Pseudocode algorithm that uses counter-controlled repetition to solve the class-average problem.

1 Set total to zero

2 Set grade counter to one

3

4 While grade counter is less than or equal to ten

5 Prompt the user to enter the next grade

6 Input the next grade

7 Add the grade into the total

8 Add one to the grade counter

9

10 Set the class average to the total divided by ten

11 Print the class average


59

class GradeBook { // display a welcome message to the GradeBook user

public void displayMessage() {

// getCourseName gets the name of the course

System.out.printf( "Welcome to the grade book\n for \n CSC111 \n!\n\n" );

} // end method displayMessage

} // end class GradeBook


60

// GradeBookTestExample2.java

import java.util.Scanner; // program uses class Scanner

public class GradeBookTestExample2{ public static void main( String args[] ) {

// determine class average based on 10 grades entered by user

int total; // sum of grades entered by user

int gradeCounter; // number of the grade to be entered next

int grade; // grade value entered by user

int average; // average of grades

// create GradeBook object myGradeBook

GradeBook myGradeBook = new GradeBook(); myGradeBook.displayMessage(); // display welcome message


61

// find average of 10 grades

// create Scanner to obtain input from command window Scanner input = new Scanner( System.in );

// initialization phase total = 0; // initialize total gradeCounter = 1; // initialize loop counter // processing phase while ( gradeCounter <= 10 ) // loop 10 times { System.out.print( "Enter grade: " ); // prompt grade = input.nextInt(); // read grade from user total = total + grade; // add grade to total gradeCounter = gradeCounter + 1; // increment counter by 1 } // end while


62

// termination phase average = total / 10; // integer division yields integer result

// display total and average of grades System.out.printf( "\nTotal of all 10 grades is %d\n", total ); System.out.printf( "Class average is %d\n", average );

} // end main

} // end class GradeBookTestExample2


63

// Analysis of examination results.import java.util.Scanner; // class uses class Scanner

public class AnalysisTestExample1 { public static void main( String args[] ) { // create Scanner to obtain input from command window Scanner input = new Scanner( System.in );

// initializing variables in declarations int passes = 0; // number of passes int failures = 0; // number of failures int studentCounter = 1; // student counter int result; // one exam result (obtains value from user)


64

// process 10 students using counter-controlled loop

while ( studentCounter <= 10 ) { // prompt user for input and obtain value from user System.out.print( "Enter result from 00: 100" ); result = input.nextInt();

// if...else nested in while if ( result >= 60 ) // if result >=60, passes = passes + 1; // increment passes; else // else result is < 60, so failures = failures + 1; // increment failures

// increment studentCounter so loop eventually terminates studentCounter = studentCounter + 1;

} // end while


65

// termination phase; prepare and display results

System.out.printf( "Passed: %d\nFailed: %d\n", passes, failures );

// determine whether more than 8 students passed

if ( passes > 8 ) System.out.println( "Raise Tuition" );

} // end main

} // end class AnalysisTest1


Defining Your Own Classes and Methods


67

Standard Input

The technique of using System.in to input data is called standard input.

We can only input a single byte using System.in directly.

To input primitive data values, we use the Scanner class

(from Java 5.0).

Scanner scanner;

scanner = Scanner.create(System.in);

int num = scanner.nextInt();

Standard InputStandard Input


68

Method Example

nextByte( ) byte b = scanner.nextByte( );

nextDouble( ) double d = scanner.nextDouble( );

nextFloat( ) float f = scanner.nextFloat( );

nextInt( ) int i = scanner.nextInt( );

nextLong( ) long l = scanner.nextLong( );

nextShort( ) short s = scanner.nextShort( );

next() String str = scanner.next();

Common Scanner Methods:


69

A class

• A class is the blueprint from which objects are generated. In other words, if we have six cars we do not need to define a car six times. We will define a car once (in a class) and then generate as many objects as we want from this class blueprint.


UML representationUML representation


Sending a Message

myWindow . setVisible ( true ) ;

MoreExamples

account.deposit( 200.0 );student.setName(“john”);car1.startEngine( );

Object NameName of the object to which we are sending a message.

Object NameName of the object to which we are sending a message.

Method NameThe name of the message we are sending.

Method NameThe name of the message we are sending.

ArgumentThe argument we are passing with the message.

ArgumentThe argument we are passing with the message.


Execution Flow

myWindow.width = 300;

Jframe myWindow;

myWindow

myWindow.visible = true;

State-of-Memory Diagram

: JFrame

width

height

title

visible

200

My First Java …

300

true

myWindow = new JFrame( );

myWindow.title = “My First Java Program”;

The diagram shows only four of the many data members of a JFrame object.


Program Code

myWindow.height = 200;


JFrame myWindow;


myWindow.setSize(300, 200);

myWindow.setTitle (“My First Java Program”);

myWindow.setVisible(true);

Execution Flow

myWindow.setSize(300, 200);

Jframe myWindow;

myWindow

myWindow.setVisible(true);

State-of-Memory Diagram

: JFrame

width

height

title

visible

200

My First Java …

300

true


myWindow.setTitle (“My First Java Program”);



Program Code

The effect of the setSize method is changing the value of width and height.

The effect of the setTitle method is changing the title string to the passed argument.

And the effect of setVisible is the changing the value of visible to true, and as a result,

the appearance of the window on the screen.


78

Standard Input

The technique of using System.in to input data is called standard input.

We can only input a single byte using System.in directly.

To input primitive data values, we use the Scanner class

(from Java 5.0).

Scanner scanner;

scanner = Scanner.create(System.in);

int num = scanner.nextInt();

Standard InputStandard Input


The Definition of the Bicycle Class

class Bicycle {

// Data Member public String ownerName;

public float price ;public int size ;

}


Multiple Instances

• Once the Bicycle class is defined, we can create multiple instances. Notice how all the instances have their own copy of data members.

Bicycle bike1, bike2;

bike1 bike2

: Bicycle

ownerName

: Bicycle

ownerName

“Adam Smith” “Ben Jones”

bike1 = new Bicycle( ); bike1.ownerName = "Adam Smith";

bike2 = new Bicycle( );

bike2.ownerName = "Ben Jones";

Sample Code


First Example: Using the Bicycle Class

import java.util.Scanner; // class uses class Scanner

class BicycleRegistration {

public static void main(String[] args) {

Bicycle bike1, bike2;

String owner1, owner2;

float price1, price2;

int size1, size2;


bike1 = new Bicycle( ); //Create and assign values to bike1

// prompt user for input and obtain value from user System.out.print( "Enter the owner name" );

bike1.ownerName = input.next();

owner1 = bike1.ownerName;

bike2 = new Bicycle( ); //Create and assign values to bike2

// prompt user for input and obtain value from user System.out.print( "Enter the owner name" );

bike2.ownerName = input.next();

owner2 = bike2.ownerName;

This sample program shows the main class BicycleRegistration is using the Bicycle class. .

bike1.ownerName = "Adam Smith";

bike2.ownerName = "Ben Jones";



// prompt user for input and obtain value from user System.out.print( "Enter the Price of Bike 1" );

bike1.price = input.nextFloat();

price1 = bike1.price;

// prompt user for input and obtain value from user System.out.print( "Enter the Size of Bike 1" );

bike1.size = input.nextInt();

size1 = bike1.size;

…

System.out.println(owner1 + " owns a bicycle Its price is“

+ bike1.price + “ Its size is “ + bike1.size);

System.out.println(owner2 + " also owns a bicycle.");

}

}


UML representationUML representation


The Program Structure and Source Files

BicycleRegistration Bicycle

There are two source files. Each class definition is stored in a separate file.

There are two source files. Each class definition is stored in a separate file.

BicycleRegistration.java Bicycle.java

To run the program: 1. javac Bicycle.java (compile)

2. javac BicycleRegistration.java (compile)

3. java BicycleRegistration (run)


86

switch Multiple-Selection Statement

switch statementUsed for multiple selections


87

switchswitch multiple-selection statement UML activity diagram multiple-selection statement UML activity diagram

with with breakbreak statements statements.


88

OutlineGradeBook5.java(1 of 5)


89

GradeBook5.java

(2 of 5)

Display prompt

Loop condition uses grade to determine whether there is more data to input


90GradeBook.java

(3 of 5)

(grade / 10 ) is controlling expression

switch statement determines which case label to execute, depending on

controlling expression

default case for grade less than 60


91

OutlineGradeBook.java

(4 of 5)

Line 91 default case


92

Common Programming Error

Forgetting a break statement when one is needed in a switch is a logic error.


93

OutlineGradeBookTest.java

(1 of 2)

Call GradeBook public methods to count grades


94

OutlineGradeBookTest.java

(2 of 2)

Program output


95

Good Programming Practice

Although each case and the default case in a switch can occur in any order, place the default case last. When the default case is listed last, the break for that case is not required. Some programmers include this break for clarity and symmetry with other cases.


96

switch Multiple-Selection Statement (Cont.)

• Expression in each case– Constant integral expression

• Combination of integer constants that evaluates to a constant integer value

– Character constant• E.g., ‘A’, ‘7’ or ‘$’

– Constant variable• Declared with keyword final


97

switch Multiple-Selection Statement (Cont.)

• Expression in each case– Constant integral expression

• Combination of integer constants that evaluates to a constant integer value

– Character constant• E.g., ‘A’, ‘7’ or ‘$’

– Constant variable• Declared with keyword final


98

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


99

Outline 1 // Fig. 5.12: BreakTest.java 2 // break statement exiting a for statement. 3 public class BreakTest 4 { 5 public static void main( String args[] ) 6 { 7 int count; // control variable also used after loop terminates 8 9 for ( count = 1; count <= 10; count++ ) // loop 10 times 10 { 11 if ( count == 5 ) // if count is 5, 12 break; // terminate loop 13 14 System.out.printf( "%d ", count ); 15 } // end for 16 17 System.out.printf( "\nBroke out of loop at count = %d\n", count ); 18 } // end main 19 } // end class BreakTest

1 2 3 4 Broke out of loop at count = 5

Loop 10 times

Exit for statement (break) when count equals 5


1 // Fig. 5.13: ContinueTest.java

2 // continue statement terminating an iteration of a for statement.

3 public class ContinueTest

4 {


6 {

7 for ( int count = 1; count <= 10; count++ ) // loop 10 times

8 {

9 if ( count == 5 ) // if count is 5,

10 continue; // skip remaining code in loop

11

12 System.out.printf( "%d ", count );

13 } // end for

14

15 System.out.println( "\nUsed continue to skip printing 5" );

16 } // end main

17 } // end class ContinueTest 1 2 3 4 6 7 8 9 10 Used continue to skip printing 5

Loop 10 times

Skip line 12 and proceed to line 7 when count equals 5


101

Boolean Operators

• A boolean operator takes boolean values as its operands and returns a boolean value.

• The three boolean operators are– and: &&

– or: ||

– not !

if (temperature >= 65 && distanceToDestination < 2) {System.out.println("Let's walk");

} else {System.out.println("Let's drive");

}


102

Logical Operators

• Logical operators– Allows for forming more complex conditions

– Combines simple conditions

• Java logical operators– && (conditional AND)

– || (conditional OR)

– & (boolean logical AND)

– | (boolean logical inclusive OR)

– ^ (boolean logical exclusive OR)

– ! (logical NOT)


103

Logical Operators (Cont.)

• Conditional AND (&&) Operator– Consider the following if statement

if ( gender == FEMALE && age >= 65 )

++seniorFemales;

– Combined condition is true • if and only if both simple conditions are true

– Combined condition is false • if either or both of the simple conditions are false


104

&& (conditional AND) operator truth table.

expression1 expression2 expression1 && expression2 false false False false true False true false False true true True


105


• Conditional OR (||) Operator– Consider the following if statement– if ( ( semesterAverage >= 90 ) || ( finalExam >= 90 )

System.out.println( “Student grade is A” );

– Combined condition is true • if either or both of the simple condition are true

– Combined condition is false • if both of the simple conditions are false


106

|| (conditional OR) operator truth table.

expression1 expression2 expression1 || expression2 false false false false true true true false true true true true


107


• Short-Circuit Evaluation of Complex Conditions– Parts of an expression containing && or || operators are

evaluated only until it is known whether the condition is true or false

– E.g., ( gender == FEMALE ) && ( age >= 65 )• Stops immediately if gender is not equal to FEMALE


108

Common Programming Error

• For example, in the expression

( i != 0 ) && ( 10 / i == 2 ) , the second condition must appear after the first condition, or a divide-by-zero error might occur.


109


• Boolean Logical AND (&) Operator– Works identically to &&

– Except & always evaluate both operands

• Boolean Logical OR (|) Operator – Works identidally to ||

– Except | always evaluate both operands


110


• Boolean Logical Exclusive OR (^)– One of its operands is true and the other is false

• Evaluates to true

– Both operands are true or both are false• Evaluates to false

• Logical Negation (!) Operator– Unary operator


111

^ (boolean logical exclusive OR) operator truth table.

expression1 expression2 expression1 ^ expression2 false false false false true true true false true true true false


112

! (logical negation, or logical NOT) operator truth table.

expression !expression false true true false


113

Outline 1 // Fig. 5.18: LogicalOperators.java

2 // Logical operators.

3

4 public class LogicalOperators

5 {


7 {

8 // create truth table for && (conditional AND) operator

9 System.out.printf( "%s\n%s: %b\n%s: %b\n%s: %b\n%s: %b\n\n",

10 "Conditional AND (&&)", "false && false", ( false && false ),

11 "false && true", ( false && true ),

12 "true && false", ( true && false ),

13 "true && true", ( true && true ) );

14

15 // create truth table for || (conditional OR) operator


17 "Conditional OR (||)", "false || false", ( false || false ),

18 "false || true", ( false || true ),

19 "true || false", ( true || false ),

20 "true || true", ( true || true ) );

21

22 // create truth table for & (boolean logical AND) operator


24 "Boolean logical AND (&)", "false & false", ( false & false ),

25 "false & true", ( false & true ),

26 "true & false", ( true & false ),

27 "true & true", ( true & true ) );

28

Conditional AND truth table

Conditional OR truth table

Boolean logical AND truth table


114

Outline29 // create truth table for | (boolean logical inclusive OR) operator


31 "Boolean logical inclusive OR (|)",

32 "false | false", ( false | false ),

33 "false | true", ( false | true ),

34 "true | false", ( true | false ),

35 "true | true", ( true | true ) );

36

37 // create truth table for ^ (boolean logical exclusive OR) operator


39 "Boolean logical exclusive OR (^)",

40 "false ^ false", ( false ^ false ),

41 "false ^ true", ( false ^ true ),

42 "true ^ false", ( true ^ false ),

43 "true ^ true", ( true ^ true ) );

44

45 // create truth table for ! (logical negation) operator

46 System.out.printf( "%s\n%s: %b\n%s: %b\n", "Logical NOT (!)",

47 "!false", ( !false ), "!true", ( !true ) );

48 } // end main

49 } // end class LogicalOperators

Boolean logical inclusive OR truth table

Boolean logical exclusive OR truth table

Logical negation truth table


115

Outline Conditional AND (&&) false && false: false false && true: false true && false: false true && true: true Conditional OR (||) false || false: false false || true: true true || false: true true || true: true Boolean logical AND (&) false & false: false false & true: false true & false: false true & true: true Boolean logical inclusive OR (|) false | false: false false | true: true true | false: true true | true: true Boolean logical exclusive OR (^) false ^ false: false false ^ true: true true ^ false: true true ^ true: false Logical NOT (!) !false: true !true: false


Mid Term Exam

116


117

Examples


118


119


120


121

1 from 3


122

2 from 3


123

3 from 3


124


125

Practical trainingPractical training

Read and run the following programs given to you :

ComputeGrade.java

CreditTest.java

LargestTest.java

SecDegEq.java


126

TEST

Write a program to process cars, each car has attributes

model : string

year : int

price : double

1- Write the class Car

2- Write the class TestCar , which has the main method

Ask the user to enter number of cars to process

input car information model, year, price

display the oldest car information

display the average price of cars


Question : We want to write a Java program that processes Vehicles as shown in the UML diagram. A Vehicle has a type that shows whether the vehicle is a car, a track or a bus. The bus has the attributes power and nbPassengers. The truck has the attributes power and load. The car has the attributes power and isLuxury. When the load of the vehicle is more than 2000kg and less than 3000kg, the vehicle is in the category of the MidSize Truck. When the load is more than 3000kg, the vehicle is in the category of the heavy truck.

•

•

• Write the Vehicle class.

• Using the class Vehicle, write the class VehicleProcess, that processes the following tasks:

–Read the required data vehicle.

–Displays the only required data of the processed vehicle

–If the entered data is related to a truck, displays its category according to its load.

127

+type:String+load:int+nbPassengers:int+power:int+isLuxury:Boolean

Vehicle

+main(String[] args):void()

VehicleProcess


• Question 2: We want to write a Java program that manages a Bookstore, we create the shown UML class Book containing the following attributes:

• Author: a string representing the author name of the book

• Price: the price of the book.

• PublishedYear: the publishing year of the book

•

• Write the class Book

• Using the class Book, write the class TestBook that processes the following tasks:

•Read the number of books in the bookStore.

•Read the information of each book.

•Display the number of books that were published before year 2000.

•Display the author name of the book that has the highest price.

128

Book

+ Author: String

+ PublishedYear: int

+ Price: double

TestBook

+ main(String[] args): void




class Book {

// Data Member public String Author;

public int PublishedYear ;public double Price ;

}


130


131


First Example: Using the Bicycle Class


class BicycleRegistration {


// create Scanner to obtain input from command window// create Scanner to obtain input from command window Scanner input = new Scanner( System.in );

int BooksNumber, BooksBefore2000Count = 0 ;

double highestPrice = 0.0;

String name;

// prompt user to // prompt user to Read the number of books in the bookStore.Read the number of books in the bookStore. System.out.print( "Enter the Number of Books in th store" );

BooksNumber = input.nextInt();

Book Mybook;

Mybook = new Book( ); //Create and assign values to Mybook

for ( int counter = 1; counter <= BooksNumber; counter++)

{

System.out.print( "Enter the Author Name of the Book" ); BooksNumber = input.nextInt();

Mybook.Author = input.next();



System.out.print( "Enter Published Year of the Book" );

Mybook. PublishedYear = input.nextInt();

System.out.print( "Enter Price of the Book" );

Mybook.Price = input.nextDouble();

If (Mybook.PublishedYear < 200 )

BooksBefore2000Count++;

If (Mybook.Price > highestPrice)

{ highestPrice = Mybook.Price ;

name = Mybook.Author ;}

} // end for

// Display the number of books that were published before year 2000.

System.out.println( “Number of books were published before year 2000” + BooksBefore2000Count );

// Display the author name of the book that has the highest price.

System.out.println(“The author name of the book that has the highest price” + name );

} // end main

} // end class


Question : Display the output of the following program.

public class Test {


int a=10, b=15, c=30; double x=9;

System.out.println(" Part A: ");

x = a/ 2 + b / 2 + x / 2 + b/ 2.0;

System.out.println(" first: x = "+ x );

if ( a > b || a -1 != 2 * b && b >= c )

{

x = a + c * a + 2;

System.out.println(" TRUE: x = " + x );

}else

System.out.println(" FALSE: x = " + (a+c * a + 2) );

System.out.println(" FINISH" );

}

}

134


135


136


137


138


139

END

of

Training Lecture


140

// GradeBook class

import java.util.Scanner; // program uses class Scanner

class GradeBook

{

// GradeBookTestExample3.java

// Create GradeBook object and invoke its determineClassAverage method.

•GradeBook.java

•(1 of 3)

Create object and invoke its method.Create object and invoke its method.


141

Outline28 // display a welcome message to the GradeBook user

29 public void displayMessage()

30 {

31 //

32 System.out.printf( "Welcome to the grade book for\n CSC111 \n");

33

34 } // end method displayMessage

35

36 // determine class average based on 10 grades entered by user

37 public void determineClassAverage()

38 {

39 // create Scanner to obtain input from command window

40 Scanner input = new Scanner( System.in );

41

42 int total; // sum of grades entered by user

43 int gradeCounter; // number of the grade to be entered next

44 int grade; // grade value entered by user

45 int average; // average of grades

46

47 // initialization phase

48 total = 0; // initialize total

49 gradeCounter = 1; // initialize loop counter

50

•GradeBook.java

•(2 of 3)

Declare method displayMessage

Declare method determineClassAverage

Declare and initialize Scanner variable input

Declare local int variables total, gradeCounter, grade and average


142

Outline51 // processing phase

52 while ( gradeCounter <= 10 ) // loop 10 times

53 {

54 System.out.print( "Enter grade: " ); // prompt

55 grade = input.nextInt(); // input next grade

56 total = total + grade; // add grade to total

57 gradeCounter = gradeCounter + 1; // increment counter by 1

58 } // end while

59

60 // termination phase

61 average = total / 10; // integer division yields integer result

62

63 // display total and average of grades

64 System.out.printf( "\nTotal of all 10 grades is %d\n", total );

65 System.out.printf( "Class average is %d\n", average );

66 } // end method determineClassAverage

67

68 } // end class GradeBook

•GradeBook.java

•(3 of 3)

while loop iterates as long as gradeCounter <= 10

Increment the counter variable gradeCounter

Calculate average grade

Display results


143

Outline 1 // GradeBookTestExample3.java

2 // Create GradeBook object and invoke its determineClassAverage method.

3

4 public class GradeBookTestExample3

5 {


7 {

8 // create GradeBook object myGradeBook

9

10 GradeBook myGradeBook = new GradeBook();

12

13 myGradeBook.displayMessage(); // display welcome message

14 myGradeBook.determineClassAverage(); // find average of 10 grades

15 } // end main

16

17 } // end class GradeBookTest3

Welcome to the grade book for CSC111! Enter grade: 67 Enter grade: 78 Enter grade: 89 Enter grade: 67 Enter grade: 87 Enter grade: 98 Enter grade: 93 Enter grade: 85 Enter grade: 82 Enter grade: 100 Total of all 10 grades is 846 Class average is 84

Create a new GradeBook object

Call GradeBook’s determineClassAverage method

•GradeBookTestExample3.java


144

1 Initialize passes to zero 2 Initialize failures to zero 3 Initialize student counter to one 4 5 While student counter is less than or equal to 10 6 Prompt the user to enter the next exam result 7 Input the next exam result 8 9 If the student passed 10 Add one to passes 11 Else 12 Add one to failures 13 14 Add one to student counter 15 16 Print the number of passes 17 Print the number of failures 18 19 If more than eight students passed 20 Print “Raise tuition”


145

// Analysis of examination results.


class Analysis { public void processExamResults() {


// initializing variables in declarations

int passes = 0; // number of passes

int failures = 0; // number of failures

int studentCounter = 1; // student counter

int result; // one exam result (obtains value from user)

Create object and invoke its method.Create object and invoke its method. AnalysisTestExample2


146

// process 10 students using counter-controlled loop

while ( studentCounter <= 10 ) { // prompt user for input and obtain value from user System.out.print( "Enter result " ); result = input.nextInt();

// if...else nested in while if ( result >= 60 ) // if result >60, passes = passes + 1; // increment passes; else // else result is not >=60, so failures = failures + 1; // increment failures

// increment studentCounter so loop eventually terminates studentCounter = studentCounter + 1;

} // end while


147

// termination phase; prepare and display results

System.out.printf( "Passed: %d\nFailed: %d\n", passes, failures );

// determine whether more than 8 students passed

if ( passes > 8 ) System.out.println( "Raise Tuition" );

} // end method processExamResults

} // end class Analysis


148

// Test program for class Analysis.

public class AnalysisTestExample2 {

public static void main( String args[] ) { Analysis application = new Analysis(); // create Analysis object application.processExamResults(); // call method to process results

} // end main

} // end class AnalysisTestExample2


149

1 Initialize passes to zero 2 Initialize failures to zero 3 Initialize student counter to one 4 5 While student counter is less than or equal to 10 6 Prompt the user to enter the next exam result 7 Input the next exam result 8 9 If the student passed 10 Add one to passes 11 Else 12 Add one to failures 13 14 Add one to student counter 15 16 Print the number of passes 17 Print the number of failures 18 19 If more than eight students passed 20 Print “Raise tuition”


150

Outline 1

2 // Analysis of examination results.

3 import java.util.Scanner; // class uses class Scanner

4

5 class Analysis

6 {

7 public void processExamResults

8 {



11

12 // initializing variables in declarations

13 int passes = 0; // number of passes

14 int failures = 0; // number of failures

15 int studentCounter = 1; // student counter

16 int result; // one exam result (obtains value from user)

17

18 // process 10 students using counter-controlled loop

19 while ( studentCounter <= 10 )

20 {

21 // prompt user for input and obtain value from user

22 System.out.print( "Enter result (1 = pass, 2 = fail): " );

23 result = input.nextInt();

24

Declare processExamResults’ local variables

while loop iterates as long as studentCounter <= 10


151

Outline

•Analysis.java

•(2 of 2)

25 // if...else nested in while

26 if ( result == 1 ) // if result 1,

27 passes = passes + 1; // increment passes;

28 else // else result is not 1, so

29 failures = failures + 1; // increment failures

30

31 // increment studentCounter so loop eventually terminates

32 studentCounter = studentCounter + 1;

33 } // end while

34

35 // termination phase; prepare and display results

36 System.out.printf( "Passed: %d\nFailed: %d\n", passes, failures );

37

38 // determine whether more than 8 students passed

39 if ( passes > 8 )

40 System.out.println( "Raise Tuition" );

41 } // end method processExamResults

42

43 } // end class Analysis

Determine whether this student passed or failed and increment the appropriate variable

Determine whether more than eight students passed the exam


152

Outline 1 // AnalysisTest2.java 2 // Test program for class Analysis. 3 4 public class AnalysisTest2 5 { 6 public static void main( String args[] ) 7 { 8 Analysis application = new Analysis(); // create Analysis object 9 application.processExamResults(); // call method to process results 10 } // end main 11 12 } // end class AnalysisTest2

Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 2 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Passed: 9 Failed: 1 Raise Tuition Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 2 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 2 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 2 Enter result (1 = pass, 2 = fail): 2 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Enter result (1 = pass, 2 = fail): 1 Passed: 6 Failed: 4

Create an Analysis object

More than 8 students passed the exam

AnalysisTest2.java


153

Formulating Algorithms: Sentinel-Controlled Repetition

• Sentinel-controlled repetition– Also known as indefinite repetition

– Use a sentinel value (also known as a signal, dummy or flag value)

• A sentinel value cannot also be a valid input value


154

Fig. 4.8 | Class-average problem pseudocode algorithm with sentinel-controlled repetition.

1 Initialize total to zero

2 Initialize counter to zero

3

4 Prompt the user to enter the first grade

5 Input the first grade (possibly the sentinel)

6

7 While the user has not yet entered the sentinel

8 Add this grade into the running total

9 Add one to the grade counter

10 Prompt the user to enter the next grade

11 Input the next grade (possibly the sentinel)

12

13 If the counter is not equal to zero

14 Set the average to the total divided by the counter

15 Print the average

16 else

17 Print “No grades were entered”


155

Outline

•GradeBook.java

•(1 of 3)

1 // : GradeBook.java

2 // GradeBook class that solves class-average program using

3 // sentinel-controlled repetition.

4 import java.util.Scanner; // program uses class Scanner

5

6 public class GradeBook

7 {


156

Outline

•GradeBook.java

•(2 of 3)

28 // display a welcome message to the GradeBook user

29 public void displayMessage()

30 {

31 // getCourseName gets the name of the course

32 System.out.printf( "Welcome to the grade book for\n CSC111!\n\n",

33 getCourseName() );

34 } // end method displayMessage

35

36 // determine the average of an arbitrary number of grades

37 public void determineClassAverage()

38 {



41

42 int total; // sum of grades

43 int gradeCounter; // number of grades entered

44 int grade; // grade value

45 double average; // number with decimal point for average

46

47 // initialization phase

48 total = 0; // initialize total

49 gradeCounter = 0; // initialize loop counter

50

51 // processing phase

52 // prompt for input and read grade from user

53 System.out.print( "Enter grade or -1 to quit: " );

54 grade = input.nextInt();

55

Declare method displayMessage

Declare method determineClassAverage

Declare and initialize Scanner variable input

Declare local int variables total, gradeCounter and grade and double variable average


157

Outline

•GradeBook.java

•(3 of 3)

56 // loop until sentinel value read from user

57 while ( grade != -1 )

58 {

59 total = total + grade; // add grade to total

60 gradeCounter = gradeCounter + 1; // increment counter

61

62 // prompt for input and read next grade from user

63 System.out.print( "Enter grade or -1 to quit: " );

64 grade = input.nextInt();

65 } // end while

66

67 // termination phase

68 // if user entered at least one grade...

69 if ( gradeCounter != 0 )

70 {

71 // calculate average of all grades entered

72 average = (double) total / gradeCounter;

73

74 // display total and average (with two digits of precision)

75 System.out.printf( "\nTotal of the %d grades entered is %d\n",

76 gradeCounter, total );

77 System.out.printf( "Class average is %.2f\n", average );

78 } // end if

79 else // no grades were entered, so output appropriate message

80 System.out.println( "No grades were entered" );

81 } // end method determineClassAverage

82

83 } // end class GradeBook

while loop iterates as long as grade != the sentinel value, -1

Calculate average grade using (double) to perform explicit conversion

Display average grade

Display “No grades were entered” message


158

Outline 1 // GradeBookTest4.java

2 // Create GradeBook object and invoke its determineClassAverage method.

3

4 public class GradeBookTest4

5 {


7 {

8 // create GradeBook object myGradeBook and

9 // pass course name to constructor

10 GradeBook myGradeBook = new GradeBook();

11

12

13 myGradeBook.displayMessage(); // display welcome message

14 myGradeBook.determineClassAverage(); // find average of grades

15 } // end main

16

17 } // end class GradeBookTest4

Welcome to the grade book for CS111 Enter grade or -1 to quit: 97 Enter grade or -1 to quit: 88 Enter grade or -1 to quit: 72 Enter grade or -1 to quit: -1 Total of the 3 grades entered is 257 Class average is 85.67

Create a new GradeBook object

Call GradeBook’s determineClassAverage method

•GradeBookTest4.java


159

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


160

Outline• DoWhileTest.java

• Line 8• Lines 10-

14

• Program output

1 // Fig. 5.7: DoWhileTest.java

2 // do...while repetition statement.

3

4 public class DoWhileTest

5 {


7 {

8 int counter = 1; // initialize counter

9

10 do

11 {


13 ++counter;

14 } while ( counter <= 10 ); // end do...while

15

16 System.out.println(); // outputs a newline

17 } // end main

18 } // end class DoWhileTest 1 2 3 4 5 6 7 8 9 10

Declares and initializes control variable counter

Variable counter’s value is displayed before testing counter’s final value

161

Fig. 5.8 | do...while repetition statement UML activity diagram.

do {

System.out.printf( "%d ", counter );

++counter;

} while ( counter <= 10 ); // end do...while


162

Good Programming Practice

• Always include braces in a do...while statement, even if they are not necessary. This helps eliminate ambiguity between the while statement and a do...while statement containing only one statement.

2005 pearson education, inc. all rights reserved. 1 part 2 control statements

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