Reading from a file using ArrayList in Java

Question

I have an assignment that ask me to read from a file, us an ArrayList to organize and declare the numbers, and then calculate the average of those numbers and print them in a new file. I know that I need 3 parts for this which would be the Reader, Writer and the Array List but i get an error when compiling when I try to read from the scaner. Can someone help with how to read from the file with the ArrayList and likewise, how to write into a new file.

import java.util.ArrayList;
import java.util.Collections;
import java.io.*; //Replaces the scanner
import java.io.BufferedReader; 
import java.util.Scanner;
import java.io.FileReader; // Used by the BufferedReader import java.util.Scanner;
import java.io.FileNotFoundException; //
import java.io.IOException; //

    class SD9 {
         public static void main( String[] args ) {  
           try{
             FileReader Fr = new FileReader( "Patriots.txt" ); 
              // the file reader bridges the program and the .txt file together. 
              BufferedReader Br = new BufferedReader( Fr );
              String line = Br.readLine();
              // BufferredReaders can only read one line at a time.
               FileWriter fw = new FileWriter( "PatriotsStat.txt" );
               BufferedWriter bw = new BufferedWriter( fw );
                while( line != null ) {
              //BufferredReaders return null once they've reached     the end of the file.
                ArrayList<Double> Patriots = new ArrayList<Double>();
            for(int i = 0; i < 23; ++i ) {
                  Patriots.add( scan.nextDouble() ); 
                        }       

                 /* String Line1 = "2014 PreSeason:";
                 bw.write(  " "  );
                 bw.newLine();
                  /*String Line3 = " FinalAvg: " + finalAvg;
                  bw.write( Line3 );
                  bw.newLine();*/

               }
                              bw.close();
                   }catch( FileNotFoundException F ) {
               //.....
              }   catch( IOException I ) {
           }

        }
        }

Patriots.add(Double.parseDouble(line) ; // assuming your file only has the numbers — Ace McCloud
– Ace McCloud, Commented Apr 17, 2015 at 4:50
Do u want to compute average for all numbers on each line ? or is your input file having only one number per line ?? Or do u want the average of all the nos in the whole file ? — Ace McCloud
– Ace McCloud, Commented Apr 17, 2015 at 4:52
You seem to be calling scan.nextDouble() but I don't see you creating a Scanner object? — Richard
– Richard, Commented Apr 17, 2015 at 4:52
Awesome thanks. The file I am reading from also has letters...how can i make the Patriots.add for numbers and strings? and i want to compute the average for lines seperatley. For example the file i read from has the name of a team and their scores fro a season. This includes preseason,regular season, and post season games. I have to calculate the average for preseason,regular season, and post season games seperately. — Dante Messi Tapia
– Dante Messi Tapia, Commented Apr 17, 2015 at 4:55

Prashant G · Accepted Answer · 2015-04-17 04:53:08Z

This should work:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Scanner;

class SD9 {
    public static void main(String[] args) throws FileNotFoundException {

        Scanner scanner = new Scanner(new File("Patriots.txt"));
        PrintWriter writer = new PrintWriter(new File("PatriotsStat.txt"));
        ArrayList<Double> Patriots = new ArrayList<Double>();
        double sum = 0;
        while (scanner.hasNext()) {
            double num = scanner.nextDouble();
            sum += num;
            Patriots.add(num);
        }
        scanner.close();
        for (int i = 0; i < Patriots.size(); i++) {
            writer.write(Patriots.get(i)+"\n");
        }
        double average = sum / Patriots.size();

        writer.write("Average : "+average);
        writer.close();
    }
}

Oğuz K · Accepted Answer · 2015-04-17 04:52:05Z

0

I believe this will help.

File fr = new File("Patriots.txt");
Scanner sc = new Scanner(fr); 
ArrayList<Double> patriots = new ArrayList<Double>(); 
while(sc.hasNextDouble()){
    patriots.add(sc.nextDouble);
}
sc.close();

answered Apr 17, 2015 at 4:52

Oğuz K

4004 silver badges7 bronze badges

3 Comments

Dante Messi Tapia Over a year ago

Thanks!!!!What if the file I am reading froma also has letters? I would be needing strings and doubles. How do I do that with array List.

Oğuz K Over a year ago

Then, you can read them all as String using next() or nextLine() methods. Then you can use parseDouble() method for doubles.

Dante Messi Tapia Over a year ago

How would the syntax look like?

Cody Maust · Accepted Answer · 2015-04-17 04:59:17Z

0

The code is failing to compile because your code does not follow the correct Java syntax for a try...catch block

In Java, a try...catch block follows the following form:

try {

    // do something...

} catch (Exception e) {

    // handle the exception...

}

In your code, you will see that you have code in between your try block and your catch block:

The bw.close() line is the culprit.

try {
    // code
}

bw.close();

} catch( FileNotFoundException F ) {
    //.....
} catch( IOException I ) {

}

Assuming you are doing this in an IDE (NetBeans, Eclipse, etc.), this relevant information can be found in the 'Build Output' window

answered Apr 17, 2015 at 4:59

Cody Maust

1878 bronze badges

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