METHODS - Introduction to Java Programming: Comprehensive Version - page 239

/** Return the area of the triangle. */
public static double area(
double side1, double side2, double side3)

Write a test program that reads three sides for a triangle and computes the area if
the input is valid. Otherwise, it displays that the input is invalid. The formula for
computing the area of a triangle is given in Programming Exercise 2.19.

*6.20

( Count the letters in a string ) Write a method that counts the number of letters in
a string using the following header:

public static int countLetters(String s)

Write a test program that prompts the user to enter a string and displays the num-
ber of letters in the string.

*6.21

( Phone keypads ) The international standard letter/number mapping for telephones
is shown in Programming Exercise 4.15. Write a method that returns a number,
given an uppercase letter, as follows:

int getNumber( char uppercaseLetter)

Write a test program that prompts the user to enter a phone number as a string.
The input number may contain letters. The program translates a letter (uppercase
or lowercase) to a digit and leaves all other characters intact. Here is a sample run
of the program:

Enter a string: 1-800-Flowers
1-800-3569377

Enter a string: 1800flowers
18003569377

**6.22

( Math: approximate the square root ) There are several techniques for implement-
ing the sqrt method in the Math class. One such technique is known as the
Babylonian method. It approximates the square root of a number, n , by repeatedly
performing a calculation using the following formula:

nextGuess = (lastGuess + n / lastGuess) / 2

When nextGuess and lastGuess are almost identical, nextGuess is the
approximated square root. The initial guess can be any positive value (e.g., 1 ).
This value will be the starting value for lastGuess . If the difference between
nextGuess and lastGuess is less than a very small number, such as 0.0001 ,
you can claim that nextGuess is the approximated square root of n . If not, next-
Guess becomes lastGuess and the approximation process continues. Imple-
ment the following method that returns the square root of n .

public static double sqrt( long n)

*6.23

( Occurrences of a specified character ) Write a method that finds the number of
occurrences of a specified character in a string using the following header:

public static int count(String str, char a)