Question

The input file should contain (in order): the weight (a number greater than zero and less than or equal to 1), the number, n, of lowest numbers to drop, and the numbers to be averaged after dropping the lowest n values.

The program should also write to an output file (rather than the console, as in Horstmann). So you should also prompt the user for the name of the output file, and then print your results to an output file with the name that the user specified.

Remember to get the name of the output file from the user; do not hard-code that name into your program.

• Your program should allow the user to re-enter the input file name if an exception is caught in the main method
• Your methods for reading from and printing to a file should each throw a FileNotFoundException, which should be caught in the main method as is done in Horstmann's DataAnalyzer.java (for the input file). Note that you may deal with just a FileNotFoundException in the while loop that tests for correct input. That is, you don't need to deal with either the NoSuchElementException or the IOException as Horstmann does. Also, you should deal with (just) a FileNotFoundException when calling the method that writes to an output file. That method call should be in main, and it should come after the end of the while loop.
• Use try-with-resources statements in your methods for reading and writing data, and so avoid the need to explicitly close certain resources.

Remember to use a try-with-resources statement in your method to write to a file when creating a new PrintWriter.

The inputValues come from a single line in a text file (data.txt) such as the following.

0.5 3 10 70 90 80 20

The output in the output file must give the weighted average, the data and weight that were used to calculate the weighted average, and the number of values dropped before the weighted average was calculated.

Your output should look very much like the following: "The weighted average of the numbers is 42.5, when using the data 10.0, 70.0, 90.0, 80.0, 20.0, where 0.5 is the weight used, and the average is computed after dropping the lowest 3 values." In particular, you should give the weighted average, the data values that the user entered in the order that the user gave them, the weight, and the number of terms that were dropped before computing the weighted average.

Answer 1

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ANSWER:

EXPLANATION:

CODE:

import java.io.File;

public class WeightedAvgDataAnalyzer {

public static void main(String[] args) {

  

ArrayList<Double> input = getData();

System.out.println(input);

double weightedAverage = calcWeightedAvg(input);

printResults(input, weightedAverage);

}

public static ArrayList<Double> getData() {

ArrayList<Double> inputLine = new ArrayList<Double>();

Scanner console = new Scanner(System.in);

System.out.println("Enter 'data.txt' (without the quotes) as the name of the input file: ");

String inputFileName = console.next();

File inputFile = new File(inputFileName);

Scanner in = null;

try {

in = new Scanner(inputFile);

while (in.hasNextDouble()) {

inputLine.add(in.nextDouble());

}

} catch (FileNotFoundException fne) {

String errorString = fne.getMessage();

System.out.println("There was an error when trying to read from file "

+ inputFileName + ": " + errorString);

} finally {

if (in != null) {

in.close();

}

}

return inputLine;

}

public static double calcWeightedAvg(ArrayList<Double> data) {

double enteredWeight = Double.parseDouble(data.get(0).toString());

int numberofLowetValuesDropped =(int) Double.parseDouble(data.get(1).toString());

data.remove(1);

data.remove(0);

Collections.sort(data);

double total = 0;

for(int i=numberofLowetValuesDropped; i<data.size(); i++){

total = total + Double.parseDouble(data.get(i).toString());

}

data.add(0, enteredWeight);

data.add(1, Double.valueOf(numberofLowetValuesDropped));

double avg = total/(data.size() - numberofLowetValuesDropped);

return avg;

  

}

public static void printResults(ArrayList<Double> inputList, double weightedAvg) {

Scanner console = new Scanner(System.in);

System.out.println("Enter the name of the output file: ");

String outputFileName = console.next();

PrintWriter out = null;

if (inputList.size() > 0) { // we have a non-empty inputList

try {

out = new PrintWriter(outputFileName);

String s = "The weighted average of the numbers is "+weightedAvg+", " +

"when using the data "+inputList+", where "+inputList.get(0)+" is the weight used, " +

"and the average is computed after dropping the lowest "+inputList.get(1)+" values.";

out.print(s);

System.out.println("Your output is in the file " + outputFileName + ".");

} catch (FileNotFoundException fne) {

String errorString = fne.getMessage();

System.out.println("There was an error when trying to write to the output file "

+ errorString);

} finally {

if (out != null) {

out.close();

}

}

} else {

System.out.println("Problems reading data from input file; no output written to " + outputFileName);

}

}

  

}

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