Java issue with reading a text file into an ArrayList

Question

I have created a program that is supposed to read a text file for Integers and put them into an Arraylist, and then there are a bunch of methods to act on it. but, after some trouble shooting I am noticing that my program won't pull the integers from the text file in. Could anyone point me in the right direction?

    package project1;

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

    public class Main {
        public static void main(String[] Args) {
            Main mainObject = new Main();
            mainObject.run();
        }
        public void run() {
            **ArrayList<Integer> list = new ArrayList<>();
            String fileName = "p01-in.txt";
            Scanner in = new Scanner(fileName);
            while (in.hasNextInt()) {
                list.add(in.nextInt());
                int line = in.nextInt();
                System.out.println("%s  %n" + line);
            }
            in.close();**
            ArrayList<Integer> listRunsUpCount = new ArrayList<>();
            ArrayList<Integer> listRunsDnCount = new ArrayList<>();
            Main findRuns = new Main();
            listRunsUpCount = findRuns.FindRuns(list, 0);
            listRunsDnCount = findRuns.FindRuns(list, 1);
            ArrayList<Integer> listRunsCount = new ArrayList<>();
            Main mergeRuns = new Main();
            listRunsCount = mergeRuns.MergeRuns(listRunsUpCount, 
            listRunsDnCount);
            Main Output = new Main();
            Output.Output("p01-runs.txt", listRunsCount);
        }

new Scanner(String) constructs a Scanner that reads from that String (not a File). You probably meant to pass a file there. — Elliott Frisch
– Elliott Frisch, Commented Jul 8, 2018 at 16:30
Every time you call in.nextInt() in your while loop you are pulling in a integer value. You make the call twice, is this intentional. Perhaps what you should be doing is placing what is read into a variable then utilizing that twice instead: int val = in.nextInt(); list.add(val); System.out.println("%s %n" + String.valueOf(val));. OR put int line = in.nextInt(); above list.add(...) and then change list.add(in.nextInt()); to list.add(line);. — DevilsHnd - 退した
– DevilsHnd - 退した, Commented Jul 8, 2018 at 16:42
By the way, it is good practice to follow the Java Naming Conventions. Variables and method names should start with lowercase. So you should refactor the variable names Args and Output and the method names FindRuns, MergeRuns and Output. — MC Emperor
– MC Emperor, Commented Jul 26, 2018 at 14:55

Rupesh Agrawal · Accepted Answer · 2018-07-26 14:34:49Z

1

You can use BufferedReader to read file content line by line.

try {
        BufferedReader reader = new BufferedReader(new FileReader(fileName));
        String line=reader.readLine();
        while (line != null) {
            line = reader.readLine();
            list.add(Integer.parseInt(line.trim()));
        }
        reader.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

answered Jul 26, 2018 at 14:34

Rupesh Agrawal

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