Java程序辅导

6Methods:
A Deeper Look
OB J ECT IVES
In this chapter you will learn:
■ How static methods and fields are associated with an
entire class rather than specific 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 specific 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
Chapter 6 Methods: A Deeper Look 211
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 variable’s 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 class’s 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
Chapter 6 Methods: A Deeper Look 213
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.
Prelab Activities Name:
Short Answer
Chapter 6 Methods: A Deeper Look 215
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 method’s 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 object’s 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 method’s 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 identifier’s 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.
Prelab Activities Name:
Programming Output
Chapter 6 Methods: A Deeper Look 217
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
Prelab Activities Name:
Programming Output
218 Methods: A Deeper Look Chapter6
Use the following method declaration to answer Questions 30 and 31:
30. What is output by the following code segment?
Your answer:
31. What is output by the following code segment?
1 public int method1( int x )
2 {
3 if ( x <= 10 )
4 x += 10;
5 else
6 x -= 10;
7
8 return x;
9 }
1 int a = 6;
2
3 System.out.println( method1( a ) );
4
5 a = 15;
6
7 System.out.println( method1( a ) );
8
9 a = 10;
10
11 System.out.println( method1( a ) );
12
13 a = -10;
14
15 System.out.println( method1( a ) );
16
5
20
0
1 int a = 15;
2 int b = 5;
3
4 System.out.println( method1( method1( a ) ) + method1( b ) );
5
6 a = 0;
7 b = 0;
8
9 System.out.println( method1( method1( a ) ) + method1( b ) );
10
11 a = 5;
Prelab Activities Name:
Programming Output
Chapter 6 Methods: A Deeper Look 219
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
Prelab Activities Name:
Programming Output
220 Methods: A Deeper Look Chapter6
32. What is displayed when the user enters 1?
Your answer:
33. What is displayed when the user enters 2?
Your answer:
34. What is displayed when the user enters 3?
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
Chapter 6 Methods: A Deeper Look 225
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
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: ^Z
Lab Exercises Name:
Lab Exercise 1 — Minimum
226 Methods: A Deeper Look Chapter6
Program Template
1 // Lab 1: Min.java
2 // Program finds the minimum of 3 numbers
3 import java.util.Scanner;
4
5 public class Min
6 {
7 // find the minimum of three numbers
8 public void findMinimum()
9 {
10 Scanner input = new Scanner( System.in );
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",
32 "Type the end-of-file indicator to terminate",
33 "On UNIX/Linux/Mac OS X type  d then press Enter",
34 "On Windows type  z then press Enter" );
35 System.out.print( "Or enter first number: " );
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:
Lab Exercise 1 — Minimum
Chapter 6 Methods: A Deeper Look 227
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 {
5 public static void main( String args[] )
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:
Lab Exercise 1 — Minimum
228 Methods: A Deeper Look Chapter6
Solution
1 // Lab 1: Min.java
2 // Program finds the minimum of 3 numbers
3 import java.util.Scanner;
4
5 public class Min
6 {
7 // find the minimum of three numbers
8 public void findMinimum()
9 {
10 Scanner input = new Scanner( System.in );
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 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
33 System.out.printf( "\n%s\n %s\n %s\n",
34 "Type the end-of-file indicator to terminate",
35 "On UNIX/Linux/Mac OS X type  d then press Enter",
36 "On Windows type  z then press Enter" );
37 System.out.print( "Or enter first number: " );
38 } // end while
39 } // end method findMinimum
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 );
46 } // end method minimum3
47 } // end class Min
Lab Exercises Name:
Lab Exercise 1 — Minimum
Chapter 6 Methods: A Deeper Look 229
Follow-Up Question and Activity
1. Modify the program in Lab Exercise 1 to compute the minimum of four double values.
1 // Lab 1: MinTest.java
2 // Test application for class Min
3 public class MinTest
4 {
5 public static void main( String args[] )
6 {
7 Min application = new Min();
8 application.findMinimum();
9 } // end main
10 } // end class MinTest
Lab Exercises Name:
Lab Exercise 1 — Minimum
230 Methods: A Deeper Look Chapter6
Solution
1 // Lab 1: Min.java
2 // Program finds the minimum of 4 numbers
3 import java.util.Scanner;
4
5 public class Min
6 {
7 // find the minimum of three numbers
8 public void findMinimum()
9 {
10 Scanner input = new Scanner( System.in );
11
12 double one; // first number
13 double two; // second number
14 double three; // third number
15 double four; // fourth number
16
17 System.out.printf( "%s\n %s\n %s\n",
18 "Type the end-of-file indicator to terminate",
19 "On UNIX/Linux/Mac OS X type  d then press Enter",
20 "On Windows type  z then press Enter" );
21 System.out.print( "Or enter first number: " );
22
23 while ( input.hasNext() )
24 {
25 one = input.nextDouble();
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
36 System.out.printf( "\n%s\n %s\n %s\n",
37 "Type the end-of-file indicator to terminate",
38 "On UNIX/Linux/Mac OS X type  d then press Enter",
39 "On Windows type  z then press Enter" );
40 System.out.print( "Or enter first number: " );
41 } // end while
42 } // end method findMinimum
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 ) );
49 } // end method minimum4
50 } // end class Min
Lab Exercises Name:
Lab Exercise 1 — Minimum
Chapter 6 Methods: A Deeper Look 231
1 // Lab 1: MinTest.java
2 // Test application for class Min
3 public class MinTest
4 {
5 public static void main( String args[] )
6 {
7 Min application = new Min();
8 application.findMinimum();
9 } // end main
10 } // end class MinTest
Lab Exercises Name:
Lab Exercise 2 — Garage
Chapter 6 Methods: A Deeper Look 233
Name: Date:
Section:
Lab Exercise 2 — Garage
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 yesterday’s 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:
Lab Exercise 2 — Garage
234 Methods: A Deeper Look Chapter6
Program Template
1 // Lab 2: Garage.java
2 // Program calculates charges for parking
3 import java.util.Scanner;
4
5 public class Garage
6 {
7 // begin calculating charges
8 public void startCharging()
9 {
10 Scanner input = new Scanner( System.in );
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
32 System.out.print(
33 "Enter number of hours (a negative to quit): " );
34 hours = input.nextDouble();
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:
Lab Exercise 2 — Garage
Chapter 6 Methods: A Deeper Look 235
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 {
5 public static void main( String args[] )
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:
Lab Exercise 2 — Garage
236 Methods: A Deeper Look Chapter6
Solution
1 // Lab 2: Garage.java
2 // Program calculates charges for parking
3 import java.util.Scanner;
4
5 public class Garage
6 {
7 // begin calculating charges
8 public void startCharging()
9 {
10 Scanner input = new Scanner( System.in );
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 // 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
31 System.out.print(
32 "Enter number of hours (a negative to quit): " );
33 hours = input.nextDouble();
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:
Lab Exercise 2 — Garage
Chapter 6 Methods: A Deeper Look 237
1 // Lab 2: GarageTest.java
2 // Test application for class Garage
3 public class GarageTest
4 {
5 public static void main( String args[] )
6 {
7 Garage application = new Garage();
8 application.startCharging();
9 } // end main
10 } // end class GarageTest
Chapter 6 Methods: A Deeper Look 253
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 specified 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:
2 import java.util.Scanner;
3
4 public class CodingEX1
5 {
6 public void remainder()
7 {
8 Scanner input = new Scanner( System.in );
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
1 // Coding Exercise: Question 1:
2 public class CodingEx1Test
3 {
4 public static void main( String args[] )
5 {
6 CodingEX1 application = new CodingEX1();
7 application.remainder();
8 } // end main
9 } // end class CodingEx1Test
Postlab Activities Name:
Coding Exercises
254 Methods: A Deeper Look Chapter6
2. Write a Java application that uses random numbers to simulate 10 flips of a coin.
1 // Coding Exercise: Question 2:
2 public class CodingEX2
3 {
4 public void flip()
5 {
6 int tail = 0, head = 0, face;
7
8 for ( int roll = 1; roll <= 10; roll++ ) {
9 face = 1 + ( int ) ( Math.random() * 2 );
10
11 switch ( face )
12 {
13 case 1:
14 ++head;
15 break;
16
17 case 2:
18 ++tail;
19 break;
20 } // end switch
21 } // end for
22
23 System.out.printf( "Tails\tHeads\n%d\t%d\n", tail, head );
24 } // end method flip
25 } // end class CodingEX2
1 // Coding Exercise: Question 2:
2 public class CodingEx2Test
3 {
4 public static void main( String args[] )
5 {
6 CodingEx2 application = new CodingEx2();
7 application.flip();
8 } // end main
9 } // end class CodingEx2Test
Postlab Activities Name:
Coding Exercises
Chapter 6 Methods: A Deeper Look 255
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.
1 // Coding Exercise: Question 3:
2 import java.util.Scanner;
3
4 public class CodingEX3
5 {
6 public void testDivisibility()
7 {
8 Scanner input = new Scanner( System.in );
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
29 } // end class CodingEX3
1 // Coding Exercise: Question 3:
2 public class CodingEx3Test
3 {
4 public static void main( String args[] )
5 {
6 CodingEx3 application = new CodingEx3();
7 application.testDivisibility();
8 } // end main
9 } // end class CodingEx3Test
Postlab Activities Name:
Coding Exercises
256 Methods: A Deeper Look Chapter6
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.
1 // Coding Exercise: Question 4:
2 import java.util.Scanner;
3
4 public class CodingEX4
5 {
6 public void halveNumber()
7 {
8 Scanner input = new Scanner( System.in );
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
21 } // end class CodingEX4
1 // Coding Exercise: Question 4:
2 public class CodingEx4Test
3 {
4 public static void main( String args[] )
5 {
6 CodingEx4 application = new CodingEx4();
7 application.halveNumber();
8 } // end main
9 } // end class CodingEx4Test
Postlab Activities Name:
Coding Exercises
Chapter 6 Methods: A Deeper Look 257
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:
2 import java.util.Scanner;
3
4 public class CodingEx5
5 {
6 public void difference()
7 {
8 Scanner input = new Scanner( System.in );
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
1 // Coding Exercise: Question 5:
2 public class CodingEx5Test
3 {
4 public static void main( String args[] )
5 {
6 CodingEx5 application = new CodingEx5();
7 application.difference();
8 } // end main
9 } // end class CodingEx5Test
Postlab Activities Name:
Coding Exercises
258 Methods: A Deeper Look Chapter6
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:
2 import java.util.Scanner;
3
4 public class CodingEx6
5 {
6 public void square()
7 {
8 Scanner input = new Scanner( System.in );
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
1 // Coding Exercise: Question 6:
2 public class CodingEx6Test
3 {
4 public static void main( String args[] )
5 {
6 CodingEx6 application = new CodingEx6();
7 application.difference();
8 } // end main
9 } // end class CodingEx6Test
Postlab Activities Name:
Programming Challenges
Chapter 6 Methods: A Deeper Look 259
Name: Date:
Section:
Programming Challenges
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
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 X1: 1
Enter Y1: 1
Enter X2: 4
Enter Y2: 5
Distance is 5.000000
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 X1: ^Z
1 // Programming Challenge 1: Points.java
2 // Program calculates the distance between two points.
3 import java.util.Scanner;
4
5 public class Points
6 {
7 // calculates the distance between two points
8 public void calculateDistance()
9 {
10 Scanner input = new Scanner( System.in );
11
Postlab Activities Name:
Programming Challenges
260 Methods: A Deeper Look Chapter6
12 System.out.printf( "%s\n %s\n %s\n",
13 "Type the end-of-file indicator to terminate",
14 "On UNIX/Linux/Mac OS X type  d then press Enter",
15 "On Windows type  z then press Enter" );
16 System.out.print( "Or Enter X1: " );
17
18 // continually read in inputs until the user terminates
19 while ( input.hasNext() )
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
32 System.out.printf( "%s\n %s\n %s\n",
33 "Type the end-of-file indicator to terminate",
34 "On UNIX/Linux/Mac OS X type  d then press Enter",
35 "On Windows type  z then press Enter" );
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 {
5 public static void main( String args[] )
6 {
7 Points application = new Points();
8 application.calculateDistance();
9 } // end main
10 } // end class PointsTest