Develop Reference

Reading a file in Java with Scanner

I'm trying to get a program to read a text file but it's throwing a FileNotFoundException even though I have the potato.txt file set in the project directory.
import java.io.File;
import java.util.Scanner;
public static void main(String[] args) {
String potato = "potato.txt"; // assume this line can't be changed at all
Scanner scan = new Scanner(new File(potato)); // throws FileNotFoundException
while (scan.hasNextLine()) {
String line = scan.nextLine();
System.out.println(line);
}
}
}

Try using the full Path, like this:
File file = new File("C:/temp/potato.txt"); //This is just an example path, look up your files path and put it here.
Scanner scan = new Scanner(file);
Also, don't forget to close your scanner when done (after your while-loop):
scan.close();

Another java.io.FileNotFoundException (The system cannot find the file specified) thread

I've created a basic notepad text file (e.g., text-file.txt) and have tried placing this file in multiple file paths for my code to retrieve, but I can't seem to get this to work. Basically, I'm wanting to take the content of text-file.txt and create a second file where everything is in all caps.
Here is my code:
package abc123;
import java.util.Scanner;
import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
public class abc123
{
public static void main (String [] args) throws IOException
{
Scanner in = new Scanner(System.in);
System.out.print("Please provide the name of your input file: ");
String inFileName = in.nextLine();
System.out.print("Please indicate what you'd like to name your output file: ");
String outFileName = in.nextLine();
FileReader reader = new FileReader(inFileName);
PrintWriter writer = new PrintWriter(outFileName);
Scanner fileReader = new Scanner(reader);
while(fileReader.hasNext())
{
String line = fileReader.nextLine();
line = line.toUpperCase();
writer.println(line);
}
fileReader.close();
writer.close();
System.out.println("The process is now complete. Please check your output file. Thank you.");
}
}
I'm a Java newbie, so a simple solution (and comments, as always) that I can grasp at this point would be super helpful. Thanks!

if the file isn't in the same folder as your java class, you have to give java full-path to find the file. be sure you also type the extension of the file, like ".txt".

Scanning in file

I'm trying to scan the following sentences into my Java program as strings:
The cat in the hat
The cat sat on the mat
Pigs in a blanket
and then read it into a list using whileloop and hasNextLine()method.
My problem is that I am unsure how to read this in as it is not a designated text file and I must utilizeargs [0]
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.ArrayList;
public class Scan {
public static void main(String[] args) throws FileNotFoundException{
//Opens a scanner into the file
File file = new File( args [0] );
try (Scanner scan = new Scanner(file))
{
ArrayList<String> list = new ArrayList<String>();
while(scan.hasNextLine())
{
list.add(scan.nextLine());
}
}
}
}

If you're just trying to output the list, use a for each style loop is the fastest way to check if you're doing it right.
for (String val : list)
{
System.out.println(val);
}

I think you should replace your existing code with the one below:
ArrayList<String> list = new ArrayList<String>();
Scanner scan = new Scanner(System.in);
while (scan.hasNextLine()) {
list.add(scan.nextLine());
}
scan.close();
Use System.in instead of new File(args[0]). System.in reads from the standard input (i.e. whatever is entered in with the keyboard). This should work both on an IDE and with command line input.
I hope this helps.

Scanner- trouble finding file

I'm trying to load a text file into java, but I'm having trouble locating the file within my code.
My file is named 'test.txt' and is saved under src/test.txt , src/fileIOTest/test.txt , and in a resources file, but regardless of how I try to load the file, the program can't seem to locate it. It shows up in the package explorer, but throws a file not found exception.
package fileIOTest;
//This project tests out the scanner system, reading a text file into an array.
import java.io.IOException;
import java.util.Scanner;
import java.io.*;
public class Test {
public void init(){
Scanner sc = null;
try {
sc = new Scanner(new FileReader("/test.txt"));
} catch(IOException e){
e.printStackTrace();// print the error
}
int[] testArray = new int[10];
for(int i = 0; i < 10; i++){
testArray[i] = sc.nextInt();
System.out.println(testArray[i]);
}
}
public static void main(String[] args){
Test fileLoader = new Test();
fileLoader.init();
}
}
Edit: Here's my file system

Ok, try:
File directory = new File("src/test.txt");
Path file = Paths.get(directory.getAbsolutePath());
Scanner sc = new Scanner(file);
Or: Try removing slash might work:
Scanner sc = newScanner(new FileReader("test.txt"));

Modify or Delete Data in a File

Today I was trying the algorithm for modifying and deleting data inside a file using Java in Windows platform.
1st : create a temporaryFile
2nd : write the data you wanted inside the originalFile into a String and to the temporaryFile
3rd : rename temporaryFile to originalFile.
The Code:
import java.io.File;
import java.io.IOException;
import java.io.FileWriter;
import java.util.Scanner;
import java.io.FileNotFoundException;
public class testing{
private static String temp;
public static void main(String [] args)
{
try{
File tempFile = File.createTempFile("haha\\temporary", ".txt"); //create a temporary file in haha folder
FileWriter writer = new FileWriter(tempFile);
Scanner input = new Scanner(new File("haha\\testing.txt")); //get input from testing.txt
temp = input.next();
writer.write(temp);
writer.close();
File origFile = new File("haha\\testing.txt");
tempFile.renameTo(origFile);
}
catch ( FileNotFoundException fileNotFoundException ){}
catch(IOException ioException){}
}
}
In the above code , the textFile to be edited is located inside a folder name haha which is located inside another folder together with the testing.class.I've tried this code to no avail , the originalTextFile has no changes .

If you have your file in the same directory, you don't need to pass the path to the File constructor.
Scanner input = new Scanner(new File("testing.txt"));
This should do it.

You need to close the Scanner object to make the changes, the underlying operating system has a file lock that must be released.
input.close();
File origFile = new File("haha\\testing.txt");