Question
Write a program that takes its input from a binary file of numbers of
type double. The file contains nothing but numbers of type double
written to the file with writeDouble. The program outputs to the
screen the average and standard deviation of the numbers in the file.
The standard deviation of a list of numbers
,
,
,
and so forth is defined as the square root of the average of the
following numbers:
,
,
,
and so forth.
The number a is the average of the numbers
,
,
,
and so forth. Hint: Write your program so that it first reads the
entire file and computes the average of all the numbers, then closes
the file, and then reopens the file and computes the standard
deviation. You will find it helpful to first do Programming Project
10.8 and then modify that program in order to obtain the program for
this project.
Answer
import java.io.*;
public class FileDemo
{
public static void main(String args[])
{
double avg = 0;
int number = 10;
double value;
double dev = 0;
double nextNum;
try
{
ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream("numbersFile.dat"));
for (int i = 0; i < 10; i++) {
value = Math.random() * 20 + 1;
System.out.println("Number contains: " + value);
os.writeDouble(value);
}
os.close();
ObjectInputStream is = new ObjectInputStream(new FileInputStream("numbersFile.dat"));
try {
while (true) {
avg += is.readDouble();
}
} catch (IOException e) {
avg /= number;
System.out.println("Average: " + avg);
}
is.close();
is = new ObjectInputStream(new FileInputStream("numbersFile.dat"));
try
{
while (true)
{
nextNum = is.readDouble();
dev += (nextNum - avg) * (nextNum - avg);
}
} catch (IOException e)
{
System.out.println("Standard deviation:" + Math.sqrt(dev / number));
}
} catch (IOException e)
{
System.out.println("Error....");
}
}
}
Output:
