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How do i put a Try-catch statement looking for a file in a loop?

I need to put my searching of the file in my readData() method in a loop that catches the fine not found exception then loops to prompt the user again for the file name until the correct one is entered. Once the proper file name is entered, then the return values pass to the other methods to continue the code.
I have tried putting the block of code into a do-while method but it results in a infinite loop. I need assistance with the semantics of this.
private static ArrayList<Double> readData() {
ArrayList<Double> inputValues = new ArrayList<>();
String inputFileName;
double value;
Scanner input = new Scanner(System.in);
System.out.print("Enter the name of the input file: ");
inputFileName = input.nextLine();
File file = new File(inputFileName);
do{
try {
input = new Scanner(file);
while (input.hasNextDouble()) {
value = input.nextDouble();
inputValues.add(value);
}
}
catch (FileNotFoundException e) {
System.out.println("File not found!");
System.out.println("Please enter file name again: ");
}
}
while(!file.exists());
return inputValues;
}
I am expecting this to explain "File not found!" then prompt again for the file name until the correct one is entered. However it only does the try-catch once and then attempts to return the inputValues return value. This causes the program to crash.
I have tried do while loop. But it ends up in an infinite loop
package weightedavgdataanalyzer;
import java.io.*;
import java.util.*;
public class WeightedAvgDataAnalyzer {
public static void main(String[] args) {
ArrayList<Double> inputValues = readData();
double weightedAvg = calcWeightedAvg(inputValues);
printResults(inputValues, weightedAvg);
}
private static void printResults(ArrayList<Double> inputValues, double weightedAvg) {
System.out.print("Enter output file name: ");
Scanner input = new Scanner(System.in);
String outputFile = input.nextLine();
try {
PrintWriter writer = new PrintWriter(outputFile);
writer.print("The weighted average of the numbers is " + weightedAvg + ", when using the data ");
for (int i = 2; i < inputValues.size(); i++) {
writer.print(inputValues.get(i) + ", ");
}
writer.println("where " + inputValues.get(0)
+ " is the weight used, and the average is computed after dropping the lowest "
+ Integer.valueOf((int) inputValues.get(1).doubleValue()) + " values.");
writer.close();
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
}
private static double calcWeightedAvg(ArrayList<Double> inputValues) {
double sum = 0;
double average;
double weight = inputValues.get(0);
int toDrop = Integer.valueOf((int) inputValues.get(1).doubleValue());
ArrayList<Double> newList = new ArrayList<>();
for (int i = 2; i < inputValues.size(); i++) {
newList.add(inputValues.get(i));
}
Collections.sort(newList);
for (int i = (toDrop); i < newList.size(); i++) {
sum += weight * newList.get(i);
}
average = sum / (newList.size() - toDrop);
return average;
}
private static ArrayList<Double> readData() {
ArrayList<Double> inputValues = new ArrayList<>();
String inputFileName;
double value;
Scanner input = new Scanner(System.in);
System.out.print("Enter the name of the input file: ");
inputFileName = input.nextLine();
File file = new File(inputFileName);
do{
try {
input = new Scanner(file);
while (input.hasNextDouble()) {
value = input.nextDouble();
inputValues.add(value);
}
}
catch (FileNotFoundException e) {
System.out.println("File not found!");
System.out.println("Please enter file name again: ");
}
}
while(!file.exists());
return inputValues;
}
}

Move the initialization of File file = new File(inputFileName); inside the loop as well as the "ask for new file name line". And last step is to also check if the file is an directory. You can't read directories with a Scanner, but file.exists() will still return true
private static ArrayList<Double> readData() {
ArrayList<Double> inputValues = new ArrayList<>();
String inputFileName;
double value;
Scanner input = new Scanner(System.in);
File file;
System.out.print("Enter the name of the input file: ");
do {
inputFileName = input.nextLine();
file = new File(inputFileName);
try {
input = new Scanner(file);
while (input.hasNextDouble()) {
value = input.nextDouble();
inputValues.add(value);
}
} catch (FileNotFoundException e) {
System.out.println("File not found!");
System.out.println("Please enter file name again: ");
}
} while (!file.exists() && !file.isDirectory());
return inputValues;
}

The other answers have not addressed that it is bad practice to control the flow of your code using catch and exception. You should reserve using your catch block for typically printing your errors or logging them.
I moved the logic of asking for the file into a loop that does not depend on an exception to correctly execute and placed it into a reusable method.
Here is what this change would look like:
ArrayList<Double> inputValues = new ArrayList<>();
double value;
File file = promptForFile(); //Condensed into a clean reusable single line of code
try {
Scanner input = new Scanner(file);
while (input.hasNextDouble()) {
value = input.nextDouble();
inputValues.add(value);
}
} catch (FileNotFoundException e) {
e.printStackTrace(); //Or log the error
}
And the method you can reuse anywhere for a new prompt:
public static File promptForFile()
{
System.out.print("Enter the name of the input file: ");
Scanner input = new Scanner(System.in);
String inputFileName = input.nextLine();
File file = new File(inputFileName);
while(!file.exists() && !file.isDirectory())
{
System.out.println("File not found!");
System.out.println("Please enter file name again: ");
inputFileName = input.nextLine();
file = new File(inputFileName);
}
return file;
}
Now the logic of your code is separated from searching for the file and the code is extremely reusable and readable.
This couldn't be done before since you had two different logics mixed intertwined.

File myFile = new File("myFile.txt");
while(!myFile.exists()){
//re-enter filename and instantiate myFile as a new object using it as the argument
}
could just check whether the file exists in a loop like so before using it. The issue with looping for the FileNotFoundException is that your writer is what throws that, so you would have to constantly instantiate the writer and check whether the exception is thrown before possibly looping again, which isn't ideal.

The problem is when the exception is caught, you never ask for a new file name, so you are running the code on the same faulty file path over and over again. To fix this, just move this code block:
System.out.print("Enter the name of the input file: ");
inputFileName = input.nextLine();
File file = new File(inputFileName);
inside the loop.
You may also want to eliminate a condition on your loop, and instead add a return; at the end of your try block.
private static ArrayList<Double> readData() {
ArrayList<Double> inputValues = new ArrayList<>();
String inputFileName;
double value;
Scanner input = new Scanner(System.in);
while (true) {
try {
// Get response in the loop, instead of one time-only
System.out.print("Enter the name of the input file: ");
inputFileName = input.nextLine();
File file = new File(inputFileName);
input = new Scanner(file);
while (input.hasNextDouble()) {
value = input.nextDouble();
inputValues.add(value);
}
// Add your return statement here to get rid of the conditional
// loop.
return inputValues;
}
catch (FileNotFoundException e) {
System.out.println("File not found!");
System.out.println("Please enter file name again: ");
}
}
}

You can take input and can return once file is found or else can keep recording error message
public File getFile(){
while(true) {
try (Scanner scanner = new Scanner(System.in)) {
System.out.println("Enter the name of the input file: ");
File file = new File(System.in);
if (file.exists()) {
return file;
}else{
System.out.println("File not found! Please try again ");
}
}
}
}
private List<Double> getData(File file){
List<Double> listOfDoubles = new ArrayList<>();
try(Scanner scanner = new Scanner(file)){
while(scanner.hasNextDouble()) {
listOfDoubles.add(scanner.nextDouble());
}
}
return listOfDoubles;
}
private static ArrayList<Double> readData() {
ArrayList<Double> inputValues = new ArrayList<>();
File inputFile = getFile();
return getData(inputFile);
}

Call the exact value from text File

Hi guys need help for my mini project for schools. How do i compare the user input and match to my database in text file. this is like validity for username and password. I want to call the second line on my data base using account Number and pin.
this is my data base.
0,admin,adminLastName,123456,123456
1,user,userLastName,1234567,123456
0 = id
admin = name
adminLastName = Last Name
1234567 = accountNumber
123456 = pin
and this is my code.
package atm;
import java.io.File;
import java.util.Scanner;
public class Login {
static void verifyLogin(String name, String lastName, String userAccountNumber, String userPin, String filePath){
Scanner inputData = new Scanner(System.in);
boolean isFound = false;
String tempAccountNumber = "";
String tempPin = "";
System.out.print("\nAccount Number: ");
userAccountNumber = inputData.next();
System.out.print("\nPIN: ");
userPin = inputData.next();
try{
Scanner readTextFile = new Scanner(new File("myDataBase.txt")).useDelimiter("[,\n]");
while (readTextFile.hasNext() && !isFound){
tempAccountNumber = readTextFile.next();
tempPin = readTextFile.next();
if (tempAccountNumber.trim().equals(userAccountNumber.trim()) && tempPin.trim().equals(userPin.trim())){
isFound = true;
System.out.println("Welcome " + name+ " " +lastName);
System.out.println("\nLogin Successfully!");
}
else {
System.out.println("You have entered your PIN or ACCOUNT NUMBER incorrectly. Please check your PIN or ACCOUNT NUMBER and try again.\n If you don't have account yet please go to SignUp page!\n");
myMain mainMenu = new myMain();
mainMenu.inputKeyboard();
}
}
readTextFile.close();
}
catch (Exception e){
}
inputData.close();
}
}

If your textfile contains 1 user per line, and you split it with ',' then you can take each line like you do, then split that line into a string[] array and check if i.e. the name corresponds to 'admin'.
public class Main {
static Scanner input = new Scanner(System.in);
public static void main(String[] args) {
Boolean loggedin = false;
String fileName = "accounts.txt";
String line = null;
System.out.println("What's your username?");
String tempUsername = input.nextLine();
System.out.println("What's your password?");
String tempPassword = input.nextLine();
try {
FileReader fileReader = new FileReader(fileName);
BufferedReader bufferedReader = new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null) {
String[] currAccount = line.split(",");
if (currAccount[1].equals(tempUsername) && currAccount[4].equals(tempPassword)) {
loggedin = true;
System.out.println("You have successfully logged in!");
}
}
bufferedReader.close();
}
catch(FileNotFoundException ex) {
ex.printStackTrace();
// Let's create it if file can't be found or doesn't exist, but let's ask first.
String answer;
System.out.print("File not found, do you want to create it? [Y/n]: ");
answer = input.nextLine();
if (answer.equalsIgnoreCase("y")) {
try {
FileWriter fileWriter = new FileWriter(fileName);
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
System.out.println("File has been created!");
} catch (IOException exc) {
exc.printStackTrace();
}
} else {
System.out.println("File was not created!");
}
}
catch(IOException ex) {
ex.printStackTrace();
}
if (!loggedin) {
System.out.println("Your login combination did not exist.");
}
}
}
Please note, I haven't commented a lot, but it should still make sense.
After splitting remember that you start at array index 0, and not 1. So at index 1 the name on the account will be.
Goodluck.

the scanner doesn't allow me to enter file name

I am trying to prompt the user to enter a file name and search for the filename and save it to 2 2-D array.
Example of the file is:
BBBBB
BBBBB
BBBBB
BBBBB
public class maze_2D{
static Scanner s = new Scanner(System.in);
public static void FromFile() throws Exception{//
System.out.println("Enter File name");
String file = s.nextLine();
File f = new java.io.File(file);
Scanner scanner = new Scanner(f);
// Read from file.....
But when I run the program, i get an error
Enter Filename
java.io.FileNotFoundException:
Why is this happening, why this scanner doesn't allow me to enter any file name?

While inputting file name in command prompt give the full path including file name with extension where your file resides in the File System.
System.out.println("Enter File name");
String file = s.nextLine();
File f = new java.io.File(file);
try {
Scanner sc = new Scanner(f);
while (sc.hasNextLine()) {
int i = sc.nextInt();
System.out.println(i);
}
sc.close();
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
}

I made a little class using most of your code ad it worked fine... try examining your path+filename to ensure it is really there.
I have heard of scanner.getInteger forcing you to add a scanner.nextLine() after it but you are using nextLine to the the fileName so this shouldn't be the case.
public class NewClass {
static Scanner s = new Scanner(System.in);
public static void main(String args[]) throws Exception {
FromFile();
}
public static void FromFile() throws Exception {
System.out.println("Enter File name");
// I enter '/Users/myMame/Downloads/testFile.txt'
String file = s.nextLine();
File f = new java.io.File(file);
Scanner scanner = new Scanner(f);
// do your 2D array manipulation
while(scanner.hasNextLine()){
String line = scanner.nextLine();
System.out.println("line: " + line);
}
}
}

File Input and output method issues

So my program is supposed to say what type of a token it is from my input file. My second method is supposed to write whatever input from the keyboard to an output file until the user types stop. The problem is my first method won't output the integers to their right type. My second method will only put stop in the output file. Here is my code. Any help would be much appriciated.
public class R16 {
public void readFile(String inputFile) {
try {
File in = new File(inputFile);
Scanner scan = new Scanner(in);
while (scan.hasNext()) {
if (scan.hasNextInt()) {
System.out.println("Integer: " + scan.nextInt());
}
if (scan.hasNext()) {
System.out.println("String: " + scan.next());
}
if (scan.hasNextDouble()) {
System.out.println("Double: " + scan.nextDouble());
}
}
scan.close();
} catch (IOException e) {
System.out.println("Error, not good");
}
}
public void writeFile(String outputFile) {
try {
File out = new File(outputFile);
PrintWriter w = new PrintWriter(out);
Scanner scan= new Scanner(System.in);
System.out.print("Enter Text: ");
while(!scan.next().equals("stop")){
w.print(scan.next());
}
w.close();
scan.close();
} catch (IOException e) {
System.out.println("Error, it just got real");
}
}
public static void main(String[] args) {
R16 test = new R16();
test.readFile(args[0]);
test.writeFile(args[1]);
}
}

In your loop, you check for stop then throw away all input.
while(!scan.next().equals("stop")){
Try using something like
String input;
while (!(input = scan.next()).equals("stop")) {
w.print(input);
Now within the loop, you have access to the input variable which contains the input string.

read from text file using try/catch blocks

so im trying to read from a file the number of words and adding them up to give and int answer? And help and or suggestions would be nice, and i can only use a try/catch while for loop and if/else/if.... Thanks!
Here what i got so far:
package filereadingexercise2;
import java.io.*;
import java.util.Scanner;
/**
*
* #author theGreggstar
*/
public class FileReadingExercise2
{
/**
* #param args the command line arguments
*/
public static void main(String[] args)
{
Scanner keys = new Scanner(System.in);
String nameOfFile;
System.out.print("Please Enter The Name Of A File Or Directory, or Type Quit To Exit: ");
nameOfFile = keys.nextLine();
Scanner input = null;
try
{
input = new Scanner(new File(nameOfFile));
}
catch(FileNotFoundException s)
{
System.out.println("File does Not Exist Please Try Again: ");
}
while(input.hasNext())
{
String contents = input.next();
int length;
System.out.print(contents);
}
}
}

If I understand you correctly, you want something like this -
public static void main(String[] args) {
Scanner keys = new Scanner(System.in);
for (;;) { // Loop forever.
System.out.print("Please Enter The Name Of A File Or "
+ "Directory, or Type Quit To Exit: ");
String nameOfFile = keys.nextLine().trim(); // get the User input.
if (nameOfFile.equalsIgnoreCase("quit")) { // check for exit condition.
break;
}
File f = new File(nameOfFile); // Construct a File.
if (f.exists()) { // Does it exist?
if (f.isFile() && f.canRead()) { // is it a File and can I read it?
Scanner input = null;
try {
input = new Scanner(f); // The Scanner!
while (input.hasNextLine()) {
String contents = input.nextLine();
System.out.println(contents); // Print the lines.
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} finally {
if (input != null) {
input.close(); // Close the file scanner.
}
}
} else if (f.isDirectory()) { // No, it's a directory!
try {
System.out.println("File "
+ f.getCanonicalPath()
+ " is a directory");
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}