METHODS - Introduction to Java Programming: Comprehensive Version - page 234

Q UIZ

Answer the quiz for this chapter online at www.cs.armstrong.edu/liang/intro10e/quiz.html .

P ROGRAMMING E XERCISES

Note
A common error for the exercises in this chapter is that students don't implement
the methods to meet the requirements even though the output from the main pro-
gram is correct. For an example of this type of error see www.cs.armstrong.edu/liang/
CommonMethodErrorJava.pdf .

Sections 6.2-6.9
6.1

( Math: pentagonal numbers ) A pentagonal number is defined as n (3 n -1)/2 for
n

1, 2, . . ., and so on. Therefore, the first few numbers are 1, 5, 12, 22, . . . .
Write a method with the following header that returns a pentagonal number:

=

public static int getPentagonalNumber( int n)

Write a test program that uses this method to display the first 100 pentagonal
numbers with 10 numbers on each line.

*6.2

( Sum the digits in an integer ) Write a method that computes the sum of the digits
in an integer. Use the following method header:

public static int sumDigits( long n)

For example, sumDigits(234) returns 9 (2 4). Hint : Use the % opera-

tor to extract digits, and the / operator to remove the extracted digit. For instance,
to extract 4 from 234, use 234 % 10 (

+ 3 +

= 4). To remove 4 from 234, use 234 / 10

( 23). Use a loop to repeatedly extract and remove the digit until all the digits

are extracted. Write a test program that prompts the user to enter an integer and
displays the sum of all its digits.

=

**6.3

( Palindrome integer ) Write the methods with the following headers

// Return the reversal of an integer, i.e., reverse(456) returns 654
public static int reverse( int number)

// Return true if number is a palindrome
public static boolean isPalindrome( int number)

Use the reverse method to implement isPalindrome . A number is a palin-
drome if its reversal is the same as itself. Write a test program that prompts the
user to enter an integer and reports whether the integer is a palindrome.

*6.4

( Display an integer reversed ) Write a method with the following header to display
an integer in reverse order:

VideoNote
Reverse an integer

public static void reverse( int number)

For example, reverse(3456) displays 6543 . Write a test program that prompts
the user to enter an integer and displays its reversal.

*6.5

( Sort three numbers ) Write a method with the following header to display three
numbers in increasing order:

public static void displaySortedNumbers(
double num1, double num2, double num3)