212-examplesMethods.pdf

6Methods:

A Deeper Look

OB J ECT IVES

In this chapter you will learn:

How static methods and elds are associated with an

entire class rather than specic instances of the class.

To use common Math methods available in the Java API.

To understand the mechanisms for passing information

between methods.

How the method call/return mechanism is supported by

the method call stack and activation records.

How packages group related classes.

How to use random-number generation to implement

game-playing applications.

To understand how the visibility of declarations is limited

to specic regions of programs.

What method overloading is and how to create

overloaded methods.

The greatest invention of the

nineteenth century was the

invention of the method of

invention.

Alfred North Whitehead

Call me Ishmael.

Herman Melville

When you call me that,

smile!

Owen Wister

Answer me in one word.

William Shakespeare

O! call back yesterday, bid

time return.

William Shakespeare

There is a point at which

methods devour themselves.

Frantz Fanon

Chapter 6 Methods: A Deeper Look 209

Name: Date:

Section:

Assignment Checklist

Exercises Assigned: Circle assignments Date Due

Prelab Activities

Matching YES NO

Fill in the Blank 13, 14, 15, 16, 17, 18, 19, 20, 21,

22

Short Answer 23, 24, 25, 26, 27

Programming Output 28, 29, 30, 31, 32, 33, 34

Correct the Code 35, 36, 37, 38

Lab Exercises

Exercise 1 Minimum YES NO

Follow-Up Question and Activity 1

Exercise 2 Garage YES NO

Follow-Up Question and Activity 1

Exercise 3 Multiplication Test YES NO

Follow-Up Questions and Activities 1, 2

Debugging YES NO

Postlab Activities

Coding Exercises 1, 2, 3, 4, 5, 6

Programming Challenges 1, 2


Prelab Activities

Name: Date:

Section:

Matching

After reading Chapter 6 of Java How to Program: Seventh Edition, answer the given questions. These questions

are intended to test and reinforce your understanding of key Java concepts. You may answer these questions ei-

ther before or during the lab.

For each term in the left column, write the letter for the description that best matches the term from the right

column.

Term Description

E

G

A

I

B

C

H

D

F

K

J

L

1. final

2. class

3. local variables scope

4. Math class

5. return-value-type

6. formal parameter

7. string concatenation

8. promotion rules

9. java.util package

10. arguments in a method call

11. overloaded methods

12. java.lang package

a) Starts from the point of declaration of a variable and continues

to the end of the block.

b) Type of the result returned from a method to its caller.

c) Declared in the parentheses of a method declaration.

d) Describe the allowed implicit conversions between primitive

types.

e) Keyword that appears in declarations of constants.

f) Contains class Random.

g) Scope of a classs fields and methods.

h) Assembling smaller strings into larger strings using operator +.

i) Contains methods that perform commonmathematical calcu-

lations.

j) Methods of the same name must have different sets of param-

eters.

k) Must match in number, type and order with the parameters in

method declaration.

l) Imported by the compiler into all programs.

Prelab Activities Name:

Fill in the Blank


Name: Date:

Section:

Fill in the Blank

Fill in the blanks for each of the following statements:

13. The element of chance can be introduced in a program via an object of class Random .

14. A number added to a randomly generated number to change the starting value in a range of values is known

as the shifting value .

15. A(n) static method is called by preceding the method name with its class name and a dot.

16. If a method does not return a value, the return value type must be void .

17. The arguments passed to a method should match in number , type and order with the parameters in

method declaration.

18. Method nextInt of class Random generates a random int value in the range 2,147,483,648 to

2,147,483,647.

19. Using existing methods as building blocks to create new programs is called software reuse .

20. If more method calls occur than can have their activation records stored on the program execution stack, an

error known as a(n) stack overflow occurs.

21. When a program calls a method, the called method must know how to return to its caller, so the return ad-

dress of the calling method is pushed onto the program execution stack .

22. Local variables are created when program control reaches their declaration; they exist while the block in

which they are declared is active and they are destroyed when the block in which they are declared exits.


Short Answer


Name: Date:

Section:

Short Answer

In the space provided, answer each of the given questions. Your answers should be concise; aim for two or three

sentences.

23. Define the term method.

A method is a program component that performs a specific task. A program may invoke a particular method

many times to perform the methods task. The actual statements defining a method are written only once and

are hidden from other methods.

24. What are the three ways to call a method?

A method in a class can invoke another method in the same class simply by its method name. A method can

invoke an objects method via the reference to the object followed by a dot (.) and the method name. A method

can invoke a static method by following the static methods class name with a dot and the static method

name.

25. What are the similarities between using an enum class and using a set of final variables?

Both can be used to clarify code by providing names for constant values. They also both allow the programmer

to specify a value once and use its name throughout the code.

26. What are overloaded methods? Are methods with the same name that only differ in return type valid over-

loaded methods?

Overloaded methods are methods with the same name but different parameter lists. Methods that differ only in

return type result in a compilation error.

27. Why do identifiers have scope?

An identifiers scope defines where the identifier can be referenced in a program. Some identifiers can be refer-

enced throughout a program, and others can be referenced only from limited portions of a program.


Programming Output


Name: Date:

Section:

Programming Output

For each of the given program segments, read the code, and write the output in the space provided below each

program. [Note: Do not execute these programs on a computer.]

28. What is the output of the following code segment?

Your answer:

29. What is output by the following code segment?

Your answer:

1 int a = 5;

2 int b = -6;

3 System.out.println( Math.max( ( Math.abs( b ) ), a ) );

6

1 int a = -6;

2

3 System.out.println( Math.sqrt( Math.pow( Math.abs( a ), 2 ) ) );

4

5 int a = 6;

6

7 System.out.println( Math.sqrt( Math.pow( Math.abs( a ), 2 ) ) );

6.0

6.0


Programming Output

218 Methods: A Deeper Look Chapter6

Use the following method declaration to answer Questions 30 and 31:


Your answer:


1 public int method1( int x )

2 {

3 if ( x


Programming Output


Your answer:

Given the following class declaration, answer Questions 32, 33 and 34.

12 b = 15;

13

14 System.out.println( method1( method1( a ) ) + method1( b ) );

15

16 a = -10;

17 b = 10;

18

19 System.out.println( method1( method1( a ) ) + method1( b ) );

30

30

10

30

1 import java.util.Scanner;

2

3 public class Greeting

4 {

5 int inputNumber; // number input by user

6 String greetingString; // greeting to display to user

7

8 public void greeting()

9 {

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

11

12 // obtain user input

13 System.out.println(

14 "Enter 1 for an English greeting\nEnter 2 for a Spanish greeting" );

15

16 inputNumber = input.nextInt(); // input integer from user

17

18 greet( inputNumber );

19

20 // call method greet to determine appropriate greeting

21 System.out.println( greetingString );

22 } // end method greeting

23

24 // the greet method

25 public void greet ( int x )

26 {

27 if ( x == 1 )

28 greetingString = "Hello."; // English greeting

29 else if ( x == 2 )

30 greetingString = "Hola."; // spanish greeting

31 else

32 greetingString = "Invalid input";

33 } // end method greet

34 } // end class Greeting


Programming Output


32. What is displayed when the user enters 1?

Your answer:


Your answer:


Your answer:

1 public class GreetingTest

2 {

3 public static void main( String args[] )

4 {

5 Greeting application = new Greeting();

6 application.greeting();

7 } // end main

8 } // end class GreetingTest

Hello.

Hola.

Invalid input


Lab Exercises

Name: Date:

Section:

Lab Exercise 1 Minimum

This problem is intended to be solved in a closed-lab session with a teaching assistant or instructor present. The

problem is divided into six parts:

1. Lab Objectives

2. Description of the Problem

3. Sample Output

4. Program Template (Fig. L 6.1 and Fig. L 6.2)

5. Problem-Solving Tips

6. Follow-Up Question and Activity

The program template represents a complete working Java program, with one or more key lines of code replaced

with comments. Read the problem description and examine the sample output; then study the template code.

Using the problem-solving tips as a guide, replace the /* */ comments with Java code. Compile and execute the

program. Compare your output with the sample output provided. Then answer the follow-up question. The

source code for the template is available at www.deitel.com/books/jhtp7/ and www.prenhall.com/deitel.

Lab Objectives

This lab was designed to reinforce programming concepts from Chapter 6 of Java How to Program: Seventh Edi-

tion. In this lab, you will practice:

Declaring and using methods.

Using Math class methods.

The follow-up question and activity also will give you practice:

Modifying methods to perform different actions.

Description of the Problem

Write a method minimum3 that returns the smallest of three floating-point numbers. Use the Math.min method

to implement minimum3. Incorporate the method into an application that reads three values from the user, de-

termines the smallest value and displays the result.

Sample Output

Type the end-of-file indicator to terminate

On UNIX/Linux/Mac OS X type d then press Enter

On Windows type z then press Enter

Or enter first number: 4

Enter second number: 5

Enter third number: 6

Minimum is 4.000000




Or enter first number: ^Z

Lab Exercises Name:



Program Template

1 // Lab 1: Min.java

2 // Program finds the minimum of 3 numbers


4

5 public class Min

6 {

7 // find the minimum of three numbers

8 public void findMinimum()

9 {


11

12 double one; // first number

13 double two; // second number

14 double three; // third number

15

16 System.out.printf( "%s\n %s\n %s\n",

17 "Type the end-of-file indicator to terminate",

18 "On UNIX/Linux/Mac OS X type d then press Enter",

19 "On Windows type z then press Enter" );

20 System.out.print( "Or enter first number: " );

21

22 while ( input.hasNext() )

23 {

24 one = input.nextDouble();

25

26 /* Write code to get the remainder of the inputs and

27 convert them to double values */

28

29 /* Write code to display the minimum of the three floating-point numbers */

30

31 System.out.printf( "\n%s\n %s\n %s\n",





36 } // end while

37 } // end method findMinimum

38

39 // determine the smallest of three numbers

40 /* write the header for the minimum3 method */

41 {

42 // determine the minimum value

43 return /* Write code to compute the minimum of the three numbers

44 using nested calls to Math.min */

45 } // end method minimum3

46 } // end class Min

Fig. L 6.1 | Min.java.

Lab Exercises Name:



Problem-Solving Tips

1. Method minimum3 should receive three arguments of type double.

2. Method minumum3 should return a double.

3. In order to nest method calls to Math.min, place a method call to Math.min within the argument list of

another call to Math.min. The return value of one Math.min method call will be used as an argument

passed to the other call to method Math.min.

4. Be sure to follow the spacing and indentation conventions mentioned in the text.

5. If you have any questions as you proceed, ask your lab instructor for assistance.

1 // Lab 1: MinTest.java

2 // Test application for class Min

3 public class MinTest

4 {


6 {

7 Min application = new Min();

8 application.findMinimum();

9 } // end main

10 } // end class MinTest

Fig. L 6.2 | MinTest.java

Lab Exercises Name:



Solution




4

5 public class Min

6 {



9 {


11




15






21


23 {


25 System.out.print( "Enter second number: " );

26 two = input.nextDouble();

27 System.out.print( "Enter third number: " );

28 three = input.nextDouble();

29

30 System.out.printf( " Minimum is %f\n",

31 minimum3( one, two, three ) );

32






38 } // end while


40

41 // determine the smallest of three numbers

42 public double minimum3( double one, double two, double three )

43 {

44 // use a nested pair of min statements

45 return Math.min( Math.min( one, two ), three );



Lab Exercises Name:



Follow-Up Question and Activity

1. Modify the program in Lab Exercise 1 to compute the minimum of four double values.




4 {


6 {



9 } // end main


Lab Exercises Name:



Solution




4

5 public class Min

6 {



9 {


11




15 double four; // fourth number

16






22


24 {


26 System.out.print( "Enter second number: " );

27 two = input.nextDouble();

28 System.out.print( "Enter third number: " );

29 three = input.nextDouble();

30 System.out.print( "Enter fourth number: " );

31 four = input.nextDouble();

32

33 System.out.printf( " Minimum is %f\n",

34 minimum4( one, two, three, four ) );

35






41 } // end while


43

44 // determine the smallest of four numbers

45 public double minimum4( double one, double two, double three, double four )

46 {

47 // use a nested pair of min statements

48 return Math.min( Math.min( one, two ), Math.min( three, four ) );



Lab Exercises Name:






4 {


6 {



9 } // end main


Lab Exercises Name:

Lab Exercise 2 Garage


Name: Date:

Section:


This problem is intended to be solved in a closed-lab session with a teaching assistant or instructor present. The

problem is divided into five parts:

1. Lab Objectives

2. Description of the Problem

3. Sample Output

4. Program Template (Fig. L 6.3 and Fig. L 6.4)

5. Problem-Solving Tips

The program template represents a complete working Java program with one or more key lines of code replaced

with comments. Read the problem description and examine the sample output; then study the template code.

Using the problem-solving tips as a guide, replace the /* */ comments with Java code. Compile and execute the

program. Compare your output with the sample output provided. The source code for the template is available

at www.deitel.com/books/jhtp7/ and www.prenhall.com/deitel.

Lab Objectives

This lab was designed to reinforce programming concepts from Chapter 6 of Java How to Program: Seventh Edi-

tion. In this lab, you will practice:

Creating and using methods.

Using Math class methods.

Description of the Problem

A parking garage charges a $2.00 minimum fee to park for up to three hours. The garage charges an additional

$0.50 per hour for each hour or part thereof in excess of three hours. The maximum charge for any given 24-hour

period is $10.00. Assume that no car parks for longer than 24 hours at a time.Write an application that calculates

and displays the parking charges for each customer who parked in the garage yesterday. You should enter the

hours parked for each customer. The program should display the charge for the current customer and should

calculate and display the running total of yesterdays receipts. The program should use the method calculate-

Charges to determine the charge for each customer.

Sample Output

Enter number of hours (a negative to quit): 2

Current charge: $2.00, Total receipts: $2.00

Enter number of hours (a negative to quit): 10

Current charge: $5.50, Total receipts: $7.50

Enter number of hours (a negative to quit): -1

Lab Exercises Name:



Program Template

1 // Lab 2: Garage.java

2 // Program calculates charges for parking


4

5 public class Garage

6 {

7 // begin calculating charges

8 public void startCharging()

9 {


11

12 double totalReceipts = 0.0; // total fee collected for the day

13 double fee; // the charge for the current customer

14 double hours; // hours for the current customer

15

16 // read in the first customer's hours

17 System.out.print(

18 "Enter number of hours (a negative to quit): " );

19 hours = input.nextDouble();

20

21 while ( hours >= 0.0 )

22 {

23 /* Write code here to calculate the fee and assign it to the variable fee */

24

25 /* Write code here to calculate the total receipts */

26

27 System.out.printf(

28 "Current charge: $%.2f, Total receipts: $%.2f\n",

29 fee, totalReceipts );

30

31 // read in the next customer's hours




35 } // end while loop

36 } // end method startCharging

37

38 // determines fee based on time

39 /* Write the header for the calculateCharges method */

40 {

41 // apply minimum charge

42 /* Write a line of code that declares and initializes a variable

43 with the minimum charge of $2 */

44

45 // add extra fees as applicable

46 /* Write an if statement that determines whether hours is greater

47 than 3.0 and, if so, calculates the additional charge. */

48

49 // apply maximum value if needed

50 /* Write code here that determines whether the 10 hour maximum has been reached

51 and if so sets the maximum charge */

52

53 /* Write a line of code that returns the calculated charge */

54 } // end method calculateCharges

55 } // end class Garage

Fig. L 6.3 | Garage.java.

Lab Exercises Name:



Problem-Solving Tips

1. The calculateCharges method should take one argument and return a double.

2. To calculate the fee in line 24, call method calculateCharges and pass it the number of hours input

by the user. Assign the returned value to variable fee.

3. Be sure to follow the spacing and indentation conventions mentioned in the text.

4. If you have any questions as you proceed, ask your lab instructor for assistance.

1 // Lab 2: GarageTest.java

2 // Test application for class Garage

3 public class GarageTest

4 {


6 {

7 Garage application = new Garage();

8 application.startCharging();

9 } // end main

10 } // end class GarageTest

Fig. L 6.4 | GarageTest.java.

Lab Exercises Name:



Solution

1 // Lab 2: Garage.java

2 // Program calculates charges for parking


4

5 public class Garage

6 {

7 // begin calculating charges

8 public void startCharging()

9 {


11

12 double totalReceipts = 0.0; // total fee collected for the day

13 double fee; // the charge for the current customer

14 double hours; // hours for the current customer

15

16 // read in the first customer's hours




20

21 while ( hours >= 0.0 )

22 {

23 // calculate and print the charges

24 fee = calculateCharges( hours );

25 totalReceipts += fee;

26 System.out.printf(

27 "Current charge: $%.2f, Total receipts: $%.2f\n",

28 fee, totalReceipts );

29

30 // read in the next customer's hours




34 } // end while loop

35 } // end method startCharging

36

37 // determines fee based on time

38 public double calculateCharges( double hours )

39 {

40 // apply minimum charge

41 double charge = 2.0;

42

43 // add extra fees as applicable

44 if ( hours > 3.0 )

45 charge = 2.0 + 0.5 * Math.ceil( hours - 3.0 );

46

47 // apply maximum value if needed

48 if ( charge > 10.0 )

49 charge = 10.0;

50

51 return charge;

52 } // end method calculateCharges

53 } // end class Garage

Lab Exercises Name:



1 // Lab 2: GarageTest.java

2 // Test application for class Garage

3 public class GarageTest

4 {


6 {

7 Garage application = new Garage();

8 application.startCharging();

9 } // end main

10 } // end class GarageTest


Postlab Activities

Name: Date:

Section:

Coding Exercises

These coding exercises reinforce the lessons learned in the lab and provide additional programming experience

outside the classroom and laboratory environment. They serve as a review after you have successfully completed

the Prelab Activities and Lab Exercises.

For each of the following problems, write a program or a program segment that performs the specied action:

1. Write a method that takes an integer as an argument and returns the remainder of that value divided by 7.

Incorporate that method into an application that enables the user to enter values to test the method.

1 // Coding Exercise: Question 1:


3

4 public class CodingEX1

5 {

6 public void remainder()

7 {


9

10 System.out.println( "Enter first floating-point value" );

11 int number1 = input.nextInt();

12 int result = modulus( number1 );

13

14 System.out.printf( "result: %d\n", result );

15 } // end method remainder

16

17 public int modulus( int x )

18 {

19 int k = ( x % 7 );

20 return k ;

21 } // end method modulus

22 } // end class CodingEX1


2 public class CodingEx1Test

3 {


5 {

6 CodingEX1 application = new CodingEX1();

7 application.remainder();

8 } // end main

9 } // end class CodingEx1Test

Postlab Activities Name:

Coding Exercises


2. Write a Java application that uses random numbers to simulate 10 flips of a coin.



3 {

4 public void flip()

5 {

6 int tail = 0, head = 0, face;

7

8 for ( int roll = 1; roll


Coding Exercises


3. Write a method multiple that takes two integers as its arguments and returns true if the first integer is di-

visible evenly by the second one (i.e., there is no remainder after division); otherwise, the method should

return false. Incorporate this method into an application that enables the user to enter values to test the

method.



3


5 {

6 public void testDivisibility()

7 {


9

10 int firstNum, secondNum;

11 boolean divides;

12 System.out.println("Please Enter an integer: ");

13 firstNum = input.nextInt();

14

15 System.out.println("Please Enter another integer: ");

16 secondNum = input.nextInt();

17

18 divides = multiple(firstNum, secondNum);

19 System.out.printf( "Is %d divisible by %d? %b\n", firstNum, secondNum, divides );

20 }

21

22 public boolean multiple( int number, int factor )

23 {

24 if ( ( number % factor ) == 0 )

25 return true;

26 else

27 return false;

28 } // end method calculateTotal




3 {


5 {

6 CodingEx3 application = new CodingEx3();

7 application.testDivisibility();

8 } // end main



Coding Exercises


4. Write a method halve that takes one floating-point value of type double as its argument and returns the

value of that number divided by 2. Incorporate this method into an application that enables the user to enter

values to test the method.



3


5 {

6 public void halveNumber()

7 {


9

10 System.out.println( "Please Enter an integer: " );

11 int number = input.nextInt();

12 int half = halve( number );

13

14 System.out.printf( "Half of the number %d is %d\n", number, half );

15 }

16

17 public int halve( int x )

18 {

19 return x / 2;

20 } // end method halve




3 {


5 {


7 application.halveNumber();

8 } // end main



Coding Exercises


5. Write a method diffDouble that takes two floating-point values of type double as arguments and computes

and returns the difference between the first and second number. Incorporate this method into an application

that enables the user to enter values to test the method.

1 // Chapter 6: Coding Exercise: Number 5:


3

4 public class CodingEx5

5 {

6 public void difference()

7 {


9

10 double firstNumber, secondNumber;

11

12 System.out.println( "Please enter your first floating-point number" );

13 firstNumber = input.nextDouble();

14

15 System.out.println( "Please enter your second floating-point number" );

16 secondNumber = input.nextDouble();

17

18 System.out.printf( "The difference between %.2f and %.2f is %.2f\n", firstNumber,

19 secondNumber, diffDouble( firstNumber, secondNumber ) );

20 }

21

22 public double diffDouble( double number1, double number2 )

23 {

24 return number1 - number2;

25 } // end method difference

26 } // end class CodingEx5



3 {


5 {


7 application.difference();

8 } // end main



Coding Exercises


6. Write a method area that computes and returns the area of a square. Incorporate this method into an ap-

plication that allows the user to enter the length of one side of the square.

1 // Chapter 6: Coding Exercise: Number 6:


3

4 public class CodingEx6

5 {

6 public void square()

7 {


9

10 double squareSide;

11

12 System.out.println( "Please enter the side of the square: " );

13 squareSide = input.nextDouble();

14

15 System.out.printf( "The area of the square is %.2f\n", area( squareSide ) );

16 } // end method square

17

18 public double area( int side )

19 {

20 return side * side;

21 } // end method areaSquare

22 } // end class CodingEx6



3 {


5 {


7 application.difference();

8 } // end main



Programming Challenges


Name: Date:

Section:


The Programming Challenges are more involved than the Coding Exercises and may require a significant amount

of time to complete. Write a Java program for each of the problems in this section. The answers to these problems

are available at www.deitel.com/books/jhtp7/ and www.prenhall.com/deitel. Pseudocode, hints or sample

outputs are provided for each problem to aid you in your programming.

1. Write method distance to calculate the distance between two points (x1, y1) and (x2, y2). All numbers and

return values should be of type double. Incorporate this method into an application that enables the user to

enter the coordinates of the points.

Hints:

The distance between two points can be calculated by taking the square root of

( x2 - x1 )

2

+ ( y2 - y1 )

2

Use Math class methods to compute the distance.

Your output should appear as follows:

Solution




Or Enter X1: 1

Enter Y1: 1

Enter X2: 4

Enter Y2: 5

Distance is 5.000000




Or Enter X1: ^Z

1 // Programming Challenge 1: Points.java

2 // Program calculates the distance between two points.


4

5 public class Points

6 {

7 // calculates the distance between two points

8 public void calculateDistance()

9 {


11








16 System.out.print( "Or Enter X1: " );

17

18 // continually read in inputs until the user terminates


20 {

21 double x1 = input.nextDouble();

22 System.out.print( "Enter Y1: " );

23 double y1 = input.nextDouble();

24 System.out.print( "Enter X2: " );

25 double x2 = input.nextDouble();

26 System.out.print( "Enter Y2: " );

27 double y2 = input.nextDouble();

28

29 double distance = distance( x1, y1, x2, y2 );

30 System.out.printf( "Distance is %f\n\n", distance );

31





36 System.out.print( "Or Enter X1: " );

37 } // end while

38 } // end method calculateDistance

39

40 // calculate distance between two points

41 public double distance( double x1, double y1, double x2, double y2 )

42 {

43 return Math.sqrt( Math.pow( ( x1 - x2 ), 2 ) +

44 Math.pow( ( y1 - y2 ), 2 ) );

45 } // end method distance

46 } // end class Points

1 // Programming Challenge 1: PointsTest.java

2 // Test application for class Points

3 public class PointsTest

4 {


6 {

7 Points application = new Points();

8 application.calculateDistance();

9 } // end main

10 } // end class PointsTest

Deitel: Copyright 1992-2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

212-examplesMethods.pdf

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