File Processing - Building Java Programs: A Back to Basics Approach - page 382

You can create such a file with an editor like Notepad on a Windows machine or
TextEdit on a Macintosh. Then you might write a program that processes this input
file and produces some kind of report. For example, the following program reads the
first five numbers from the file and reports their sum:
1 // Program that reads five numbers and reports their sum.
2
3 import java.io.*;
4 import java.util.*;
5
6 public class ShowSum1 {
7 public static void main(String[] args)
8 throws FileNotFoundException {
9 Scanner input = new Scanner( new File("numbers.dat"));
10
11 double sum = 0.0;
12 for ( int i = 1; i <= 5; i++) {
13 double next = input.nextDouble();
14 System.out.println("number " + i + " = " + next);
15 sum += next;
16 }
17 System.out.println("Sum = " + sum);
18 }
19 }
This program uses a variation of the cumulative sum code from Chapter 4.
Remember that you need a throws clause in the header for main because there is a
potential FileNotFoundException . The program produces the following output:
number 1 = 308.2
number 2 = 14.9
number 3 = 7.4
number 4 = 2.8
number 5 = 3.9
Sum = 337.19999999999993
Notice that the reported sum is not 337.2. This result is another example of a
roundoff error (also described in Chapter 4).
The preceding program reads exactly five numbers from the file. More typically,
you'll continue to read numbers as long as there are more numbers to read while a
while loop is executing. Remember that the Scanner class includes a series of
hasNext methods that parallel the various next methods. In this case, nextDouble is