Reading a .txt file using Scanner class in Java

Question

I am working on a Java program that reads a text file line-by-line, each with a number, takes each number throws it into an array, then tries and use insertion sort to sort the array. I need help with getting the program to read the text file.

I am getting the following error messages:

java.io.FileNotFoundException: 10_Random (The system cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at java.util.Scanner.<init>(Unknown Source)
at insertionSort.main(insertionSort.java:14)

I have a copy of the .txt file in my "src" "bin" and main project folder but it still cannot find the file. I am using Eclipse by the way.

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

public class insertionSort {

public static void main(String[] args) {

    File file = new File("10_Random");

    try {

        Scanner sc = new Scanner(file);

        while (sc.hasNextLine()) {
            int i = sc.nextInt();
            System.out.println(i);
        }
        sc.close();
    } 
    catch (FileNotFoundException e) {
        e.printStackTrace();
    }
 }
}

Answer 1

At first check the file address, it must be beside your .java file or in any address that you define in classpath environment variable. When you check this then try below.

1. you must use a file name by it's extension in File object constructor, as an example:

   File myFile = new File("test.txt");

2. but there is a better way to use it inside Scanner object by pass the filename absolute address, as an example:

   Scanner sc = new Scanner(Paths.get("test.txt"));

in this way you must import java.nio.file.Paths as well.

Answer 2

You should use either

File file = new File("bin/10_Random.txt");

Or

File file = new File("src/10_Random.txt");

Relative to the project folder in Eclipse.

Answer 3

here are some working and tested methods;

using Scanner

package io;

import java.io.File;
import java.util.Scanner;

public class ReadFromFileUsingScanner {
    public static void main(String[] args) throws Exception {
        File file=new File("C:\\Users\\pankaj\\Desktop\\test.java");
        Scanner sc=new Scanner(file);
        while(sc.hasNextLine()){
            System.out.println(sc.nextLine());
        }
    }
}

Here's another way to read entire file (without loop) using Scanner class

package io;

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

public class ReadingEntireFileWithoutLoop {
    public static void main(String[] args) throws FileNotFoundException {
        File file=new File("C:\\Users\\pankaj\\Desktop\\test.java");
        Scanner sc=new Scanner(file);
        sc.useDelimiter("\\Z");
        System.out.println(sc.next());
    }
}

using BufferedReader

 package io;
import java.io.*;
public class ReadFromFile2 {
    public static void main(String[] args)throws Exception {
        File file=new File("C:\\Users\\pankaj\\Desktop\\test.java");
        BufferedReader br=new BufferedReader(new FileReader(file));
        String st;
        while((st=br.readLine())!=null){
            System.out.println(st);
        }
    }
}

using FileReader

package io;
import java.io.*;
public class ReadingFromFile {
    public static void main(String[] args) throws Exception {
        FileReader fr=new FileReader("C:\\Users\\pankaj\\Desktop\\test.java");
        int i;
        while((i=fr.read())!=-1){
            System.out.print((char) i);
        }
    }
}

Answer 4

Use following codes to read the file

import java.io.File;
import java.util.Scanner;

public class ReadFile {

    public static void main(String[] args) {

        try {
            System.out.print("Enter the file name with extension : ");

            Scanner input = new Scanner(System.in);

            File file = new File(input.nextLine());

            input = new Scanner(file);


            while (input.hasNextLine()) {
                String line = input.nextLine();
                System.out.println(line);
            }
            input.close();

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

}

-> This application is printing the file content line by line

Answer 5

You have to put file extension here

File file = new File("10_Random.txt");