Calculating Average/Max/Min from an array in Java

问题:

I have my code that will read in a a list of numbers in a file called "QuizScores.txt". However, in this file, certain numbers contain letters. I have told my program to simply ignore those instances and move onto the next number. My issue now if that my code is only reading one line at a time where I need it to look at the entire file, read it in, calculate the average, the maximum, and the minimum, and finally output that to a file called "QuizStats.txt". Any help with this would be greatly appreciated! Thanks!

QuizScores:

45
63
74g
34.7
75
4
8
15
16
23
42
67f
34
67

Code:

import java.io.*;

public class ScoreReader {


    public static void main(String[] args) {
        BufferedReader reader = null;

        try {
               String currentLine;

               reader = new BufferedReader(new FileReader("QuizScores.txt"));
               while ((currentLine = reader.readLine()) != null) {

                   int sum = 0;
                   String[] nums = currentLine.split("\\s+");
                   for (int i = 0; i < nums.length; i++) {
                       try{
                           double num = Integer.parseInt(nums[i]);
                           if (num != -1) {
                               sum += num;
                           }
                       } catch( NumberFormatException err )
                       {

                       }
                   }

                   System.out.println(sum);
               }
            } catch (IOException err) {
                err.printStackTrace();
            } 
            catch (NumberFormatException err) {}
            finally {
                try {
                   if (reader != null){
                       reader.close();
                   }
                }
                   catch (IOException err) {
                    err.printStackTrace();
                   }
            }
    }
}

回答1:

Try this code

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ScoreReader {

    public static void main(String[] args) {
        BufferedReader reader = null;
        double average = 200.0;
        double min = Double.MAX_VALUE;
        double max = Double.MIN_VALUE;
        int n = 1;
        String currentLine;
        double c;
        try {
            reader = new BufferedReader(new FileReader("QuizScores.txt"));
            System.out.println("--Quiz Scores--");
            while ((currentLine = reader.readLine()) != null) {
                try {
                    c = Double.parseDouble(currentLine);
                } catch (Exception ex) {
                    continue;
                }
                max = max > c ? max : c;
                min = min < c ? min : c;
                average += (c - average) / n;
                n++;
                System.out.println(c);
            }
            System.out.println("--Summary--");
            System.out.println("Average: " + average);
            System.out.println("Minimum: " + min);
            System.out.println("Maximum: " + max);
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
        try {
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output

--Quiz Scores--
45.0
63.0
34.7
75.0
4.0
8.0
15.0
16.0
23.0
42.0
67.0
34.0
67.0
--Summary--
Average: 37.97692307692308
Minimum: 4.0
Maximum: 75.0

Is this what you are looking for?

回答2:

double min = 0.0;
double max  = 0.0;
int count = 0;



sum += num;
count++;
if (num > max) {
    max = num;
}
if (num < min) {
    min = num;
}
double avg = (double) sum/count;

Then the avg, sum, min, and max are all known. I would probably take a different approach from the beginning, but the code above should work with your code. I have not run it though.

回答3:

Read line by line parsing only the numbers and put those into a list, then pass that list to a function such as:

 public static Float getAverage(ArrayList <Float> x)
 {
    Float sum = 0.0f;

    for (Float a : x )
        sum += a;

    return sum / x.size();
 }

回答4:

 private class Statistics{

    public double min = -1;
    public double max;
    public double avg;
    public long sum;

    Statistics(List<Long> list){

        int count = 0;
        for (Long num : list) {
            sum += num;
            count++;

            if(min == -1) min= num;

            if (num > max) {
                max = num;
            }
            if (num < min) {
                min = num;
            }
        }

        this.avg = sum/(double)count;
    }

}

// USAGE

    Statistics statistics = new Statistics(Arrays.asList(1l, 2l, 3l, 4l));

    System.out.println(statistics.avg);
    System.out.println(statistics.min);
    System.out.println(statistics.max);
    System.out.println(statistics.sum);