使用 Java 中的 Scanner 类读取 .txt 文件

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

你必须把文件扩展名放在这里

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

Answer 2

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 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());
        }
    }
}

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

1. Make sure the filename is correct (proper capitalisation, matching extension etc - as already suggested).

2. Use the Class.getResource method to locate your file in the classpath - don't rely on the current directory:

    URL url = insertionSort.class.getResource("10_Random"); File file = new File(url.toURI());

3. Specify the absolute file path via command-line arguments:

    File file = new File(args[0]);

In Eclipse:

1. Choose "Run configurations"
2. Go to the "Arguments" tab
3. Put your "c:/my/file/is/here/10_Random.txt.or.whatever" into the "Program arguments" section

Answer 5

1. You need the specify the exact filename, including the file extension, eg 10_Random.txt .
2. The file needs to be in the same directory as the executable if you want to refer to it without any kind of explicit path.
3. While we're at it, you need to check for an int before reading an int . It is not safe to check with hasNextLine() and then expect an int with nextInt() . You should use hasNextInt() to check that there actually is an int to grab. How strictly you choose to enforce the one integer per line rule is up to you, of course.

Answer 6

No one seems to have addressed the fact that your not entering anything into an array at all. You are setting each int that is read to "i" and then outputting it.

for (int i =0 ; sc.HasNextLine();i++)
{
    array[i] = sc.NextInt();
}

Something to this effect will keep setting values of the array to the next integer read.

Than another for loop can display the numbers in the array.

for (int x=0;x< array.length ; x++)
{
    System.out.println("array[x]");
}

Answer 7

File Path Seems to be an issue here please make sure that file exists in the correct directory or give the absolute path to make sure that you are pointing to a correct file. Please log the file.getAbsolutePath() to verify that file is correct.

Answer 8

private void loadData() {

    Scanner scanner = null;
    try {
        scanner = new Scanner(new File(getFileName()));
        while (scanner.hasNextLine()) {
            Scanner lijnScanner = new Scanner(scanner.nextLine());

            lijnScanner.useDelimiter(";");
            String stadVan = lijnScanner.next();
            String stadNaar = lijnScanner.next();
            double km = Double.parseDouble(lijnScanner.next());

            this.voegToe(new TweeSteden(stadVan, stadNaar), km);

        }
    } catch (FileNotFoundException e) {
        throw new DbException(e.getMessage(), e);
    } finally {
        if(scanner != null){
            scanner.close();
        }
    }
}

Answer 9

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 10

The file you read in must have exactly the file name you specify: "10_random" not "10_random.txt" not "10_random.blah", it must exactly match what you are asking for. You can change either one to match so that they line up, but just be sure they do. It may help to show the file extensions in whatever OS you're using.

Also, for file location, it must be located in the working directory (same level) as the final executable (the .class file) that is the result of compilation.

Answer 11

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 12

顺便说一句，值得设置字符编码：

Scanner scanner = new Scanner(new File("C:\\tmp\\edit1.txt"), "UTF-16");