Reading Numbers from a File

Objectives

1. Perform some basic statistics on numbers in a file.

Notes

• A file (numbers.dat) holds a set of integers, for these numbers find the
  • min
  • max
  • average
• We need two concepts
  • The scanner has a hasNext* method
    • hasNextInt()
    • hasNextFloat()
    • hasNextDouble()
    • hasNextLong()
    • ...
    • These all return true if there is one of these available for the scanner.
  • Accumulation
    • Outside of a read loop, set a variable to 0
    • Add to it each time a value is read in the loop.
  • Max/min
    • You really can't properly set it to a default value.
    • This is a little harder
    • I set a boolean flag to be true
    • Then test inside the loop.
  • We will demo both of these as we write the code.

• import java.util.Scanner;
  import java.io.*;
  
  public class NumberReader {
      public static void main(String[] args)  {
          Scanner myScanner;
          int data;
          int count = 0;
          int sum = 0;
          int max = 0;
          int min = 0;
          boolean isFirst = true;
          
          try {
              myScanner = new Scanner(new File("input.dat"));   
          } catch (FileNotFoundException e) {
              System.out.println("Could not open the file");
              return;            
          }
          
          count = 0;
          sum = 0;
          isFirst = true;
          
          while(myScanner.hasNextInt()) {
              data = myScanner.nextInt();
              if (isFirst) {
                 isFirst = false;
                 max = data;
                 min = data;
              } else {
                 if (min > data) {
                     min = data;
                 }
                 if (max < data) {
                     max = data;
                 }
              }
              
              count++;
              sum += data;
              System.out.printf("Item %d is %d \n",count,data);
          }
          
          System.out.println();
          System.out.printf("There were %d numbers in the file.\n",count);
  
          if (count > 0) {
              System.out.printf("The smallest was %d\n",min);
              System.out.printf("The largest was %d\n",max);
              System.out.printf("The sum is %d\n", sum);
              double average = (double) sum /  (double) count;
              System.out.printf("The average was %.3f\n",average);
          }
          
          myScanner.close();
          
         }
  }