Reading a text file in java

Question

How would I read a .txt file in Java and put every line in an array when every lines contains integers, strings, and doubles? And every line has different amounts of words/numbers.

Answer 1

Try the Scanner class which no one knows about but can do almost anything with text.

To get a reader for a file, use

File file = new File ("...path...");
String encoding = "...."; // Encoding of your file
Reader reader = new BufferedReader (new InputStreamReader (
    new FileInputStream (file), encoding));

... use reader ...

reader.close ();

You should really specify the encoding or else you will get strange results when you encounter umlauts, Unicode and the like.

Answer 2

Easiest option is to simply use the Apache Commons IO JAR and import the org.apache.commons.io.FileUtils class. There are many possibilities when using this class, but the most obvious would be as follows;

List<String> lines = FileUtils.readLines(new File("untitled.txt"));

It's that easy.

"Don't reinvent the wheel."

Answer 3

The best approach to read a file in Java is to open in, read line by line and process it and close the strea

// Open the file
FileInputStream fstream = new FileInputStream("textfile.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));

String strLine;

//Read File Line By Line
while ((strLine = br.readLine()) != null)   {
  // Print the content on the console - do what you want to do
  System.out.println (strLine);
}

//Close the input stream
fstream.close();

To learn more about how to read file in Java, check out the article.

Answer 4

Your question is not very clear, so I'll only answer for the "read" part :

List<String> lines = new ArrayList<String>();
BufferedReader br = new BufferedReader(new FileReader("fileName"));
String line = br.readLine();
while (line != null)
{
    lines.add(line);
    line = br.readLine();
}

Answer 5

Common used:

    String line = null;
    File file = new File( "readme.txt" );

    FileReader fr = null;
    try
    {
        fr = new FileReader( file );
    } 
    catch (FileNotFoundException e) 
    {  
        System.out.println( "File doesn't exists" );
        e.printStackTrace();
    }
    BufferedReader br = new BufferedReader( fr );

    try
    {
        while( (line = br.readLine()) != null )
    {
        System.out.println( line );
    }

Answer 6

@user248921 first of all, you can store anything in string array , so you can make string array and store a line in array and use value in code whenever you want. you can use the below code to store heterogeneous(containing string, int, boolean,etc) lines in array.

public class user {
 public static void main(String x[]) throws IOException{
  BufferedReader b=new BufferedReader(new FileReader("<path to file>"));
  String[] user=new String[500];
  String line="";
  while ((line = b.readLine()) != null) {
   user[i]=line; 
   System.out.println(user[1]);
   i++;  
   }

 }
}

Answer 7

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class PredmetTest {

    public static void main(String[] args) {
        // Define the file path to read the subject names and grades from
        String filePath = "path_to_your_file.txt";

        // Create a list to store the subjects
        List<Predmet> predmeti = new ArrayList<>();

        // Read the file and populate the predmeti list
        try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
            String line;
            while ((line = br.readLine()) != null) {
                String[] parts = line.split(" ");
                String subjectName = parts[0];

                // Parse the grades for the subject
                List<Integer> grades = new ArrayList<>();
                for (int i = 1; i < parts.length; i++) {
                    grades.add(Integer.parseInt(parts[i]));
                }

                // Create a new Predmet object with the subject name and grades
                Predmet predmet = new Predmet(subjectName, grades);

                // Add the Predmet object to the list
                predmeti.add(predmet);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Calculate and display the average grade for each subject
        double highestAverage = -1;
        Predmet predmetWithHighestAverage = null;

        for (Predmet predmet : predmeti) {
            // Calculate the average grade for the subject
            double average = predmet.calculateAverage();

            // Update the subject with the highest average if necessary
            if (average > highestAverage) {
                highestAverage = average;
                predmetWithHighestAverage = predmet;
            }

            // Display the subject and its average grade
            System.out.println("Subject: " + predmet.getSubjectName());
            System.out.println("Average grade: " + average);
            System.out.println();
        }

        // Display the subject with the highest average grade
        if (predmetWithHighestAverage != null) {
            System.out.println("Subject with the highest average grade: " + predmetWithHighestAverage.getSubjectName());
        }
    }
}

public class Predmet {
    private String subjectName;
    private List<Integer> grades;

    public Predmet(String subjectName, List<Integer> grades) {
        this.subjectName = subjectName;
        this.grades = grades;
    }

    public String getSubjectName() {
        return subjectName;
    }

    public List<Integer> getGrades() {
        return grades;
    }

    public double calculateAverage() {
        int sum = 0;
        for (int grade : grades) {
            sum += grade;
        }
        return (double) sum / grades.size();
    }
}

Answer 8

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

public class Predmet {
    String naziv;
    float ocjena;

    public Predmet(String naziv, float ocjena) {
        this.naziv = naziv;
        this.ocjena = ocjena;
    }
}

public class PredmetTest {
    public static void main(String[] args) {
        List<Predmet> predmeti = new ArrayList<>();

        // Učitavanje predmeta iz datoteke
        try {
            File file = new File("predmeti.txt");
            Scanner scanner = new Scanner(file);

            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                String[] parts = line.split(" ");
                String naziv = parts[0];
                float ocjena = Float.parseFloat(parts[1]);
                Predmet predmet = new Predmet(naziv, ocjena);
                predmeti.add(predmet);
            }

            scanner.close();
        } catch (FileNotFoundException e) {
            System.out.println("Datoteka nije pronađena.");
            e.printStackTrace();
        }

        // Ispisivanje predmeta i zaključne ocjene
        float najveciProsjek = 0;
        Predmet predmetSaNajvecimProsjekom = null;

        for (Predmet predmet : predmeti) {
            System.out.println("Predmet: " + predmet.naziv);
            System.out.println("Zaključna ocjena: " + predmet.ocjena);
            System.out.println();

            if (predmet.ocjena > najveciProsjek) {
                najveciProsjek = predmet.ocjena;
                predmetSaNajvecimProsjekom = predmet;
            }
        }

        // Ispisivanje predmeta s najvišim prosjekom
        if (predmetSaNajvecimProsjekom != null) {
            System.out.println("Predmet s najvišim prosjekom: " + predmetSaNajvecimProsjekom.naziv);
            System.out.println("Prosjek ocjena: " + predmetSaNajvecimProsjekom.ocjena);
        }
    }
}

Answer 9

This is a nice way to work with Streams and Collectors.

List<String> myList;
try(BufferedReader reader = new BufferedReader(new FileReader("yourpath"))){
    myList = reader.lines() // This will return a Stream<String>
                 .collect(Collectors.toList());
}catch(Exception e){
    e.printStackTrace();
}

When working with Streams you have also multiple methods to filter, manipulate or reduce your input.

Answer 10

For Java 11 you could use the next short approach:

  Path path = Path.of("file.txt");
  try (var reader = Files.newBufferedReader(path)) {
      String line;
      while ((line = reader.readLine()) != null) {
          System.out.println(line);
      }
  }

Or:

var path = Path.of("file.txt");
List<String> lines = Files.readAllLines(path);
lines.forEach(System.out::println);

Or:

Files.lines(Path.of("file.txt")).forEach(System.out::println);