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How to change the value of a file object?

In the following code, I'm trying to create a way to verify if what a user entered is a file that exists, and then prompts them repeatedly until they enter something that does exist.
System.out.print("Input file name: ");
String entry = console.nextLine().toLowerCase();
File f = new File(entry + ".txt");
while(!f.exists()){
System.out.print("File not found. Try again: ");
f.equals(console.next().toLowerCase() + ".txt");
}
Sorry if its a stupid question, I'm just new to java and don't know why this doesn't work. For example, if there's only one file named "testing.txt", and their first entry is "potato", I want it to prompt them until they enter the name of a file that does exist.

Try with below code
public static void main(String[] args) {
System.out.println("Enter File Name: ");
Scanner scanner = new Scanner(System.in);
File file = new File(scanner.nextLine()+".txt");
while(!file.exists())
{
System.out.println("File Not Found. Try Again...");
file = new File(scanner.nextLine()+".txt");
}
System.out.println("File Found. "+file.getName());
scanner.close();
}

Searching a list of names in a text file from user input

I'm currently in an Introductory Java class at University and I'm having a bit of trouble. Last semester we started with Python and I became very acquainted with it and I would say I am proficient now in writing Python; yet Java is another story. Things are alot different. Anyway, Here is my current assignment: I need to write a class to search through a text document (passed as an argument) for a name that is inputted by the user and output whether or not the name is in the list. The first line of the text document is the amount of names in the list.
The text document:
14
Christian
Vincent
Joseph
Usman
Andrew
James
Ali
Narain
Chengjun
Marvin
Frank
Jason
Reza
David
And my code:
import java.util.*;
import java.io.*;
public class DbLookup{
public static void main(String[]args) throws IOException{
File inputDataFile = new File(args[0]);
Scanner stdin = new Scanner(System.in);
Scanner inFile = new Scanner(inputDataFile);
int length = inFile.nextInt();
String names[] = new String[length];
for(int i=0;i<length;i++){
names[i] = inFile.nextLine();
}
System.out.println("Please enter a name that you would like to search for: ");
while(stdin.hasNext()){
System.out.println("Please enter a name that you would like to search for: ");
String input = stdin.next();
for(int i = 0;i<length;i++){
if(input.equalsIgnoreCase(names[i])){
System.out.println("We found "+names[i]+" in our database!");
break;
}else{
continue;
}
}
}
}
}
I am just not getting the output I am expecting and I cannot figure out why.

Try this
You should trim() your values as they have extra spaces
if(input.trim().equalsIgnoreCase(names[i].trim()))
I have run your example it runs perfectly after using trim(), you have missed to trim()

Create a seperate scanner class to read line by line.You can use BufferedReader also.
final Scanner scanner = new Scanner(file);
while (scanner.hasNextLine()) {
final String str= scanner.nextLine();
if(str.contains(name)) {
// Found the input word
System.out.println("I found " +name+ " in file " +file.getName());
break;
}
}

If you use Java 8:
String[] names;
try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
names = stream.skip(1).toArray(size -> new String[size]);
} catch (IOException e) {
e.printStackTrace();
}

Creating mad-lib game in java and receiving NoSuchElementException method [closed]

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Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 7 years ago.
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I'm trying to create a java program that recieves a .txt file and plays the game, then prints it all into a new file (named by the user). I've reached the point where all the words have been chosen but am getting a NoSuchElementException message after that. I have a pretty basic knowledge of java and absolutely no clue how to proceed. Anyone have suggestions?
import java.io.*;
import java.util.*;
public class MadLibs {
public static void main(String[] args) throws FileNotFoundException {
Scanner console = new Scanner(System.in);
intro();
//in order to create the output file first prompts user to decide
//whether they want to create a mad-lib, view their mad-lib or quit
//if 'c' is selected then while loop is exited
String action = "c";
String fileName = "fileName";
while (action.equals("c")) {
System.out.print("(C)reate mad-lib, (V)iew mad-lib, (Q)uit? ");
action = console.nextLine();
action = action.toLowerCase();
File file = new File(fileName);
System.out.print("Input file name: ");
while (!file.exists()) {
fileName = console.nextLine();
file = new File(fileName);
if (!file.exists()) {
System.out.print("File not found. Try again: ");
}
}
//asks for a file to read from for the mad-lib game
//and creates file (named by user) to input the information
System.out.print("Output file name: ");
String outputName = console.nextLine();
System.out.println();
File outputFile = new File(outputName);
PrintStream output = new PrintStream(outputFile);
Scanner tokens = new Scanner(file);
while (tokens.hasNext()) {
String token = tokens.next();
//calls the returned placeHolder
String placeHolder = placeHolder(console, tokens, token);
String newWord = madLib(console, token, placeHolder);
//copies each token and pastes into new output file
}
}
while (action.equals("v")) {
System.out.print("Input file name: ");
fileName = console.nextLine();
File outputFile = new File(fileName);
if (!outputFile.exists()) {
System.out.print("File not found. Try again: ");
fileName = console.nextLine();
} else {
PrintStream output = new PrintStream(outputFile);
output = System.out;
}
}
while (action.equals("q")) {
}
}
public static String madLib(Scanner console, String token, String
placeHolder) throws FileNotFoundException{
String word = placeHolder.replace("<", "").replace(">", ": ").replace("-",
" ");
String startsWith = String.valueOf(word.charAt(0));
if (startsWith.equalsIgnoreCase("a") || startsWith.equalsIgnoreCase("e")
||
startsWith.equalsIgnoreCase("i") || startsWith.equalsIgnoreCase("o")
||
startsWith.equalsIgnoreCase("u")) {
String article = "an ";
System.out.print("Please type " + article + word);
String newWord = console.next();
return newWord;
} else {
String article = "a ";
System.out.print("Please type " + article + word);
String newWord = console.next();
return newWord;
}
}
public static String placeHolder(Scanner console, Scanner tokens, String
token) throws FileNotFoundException {
while(!(token.startsWith("<") && token.endsWith(">"))) {
//not a placeholder!
//continue reading file
token = tokens.next();
}
//outside of this while loop = found a placeholder!!
String placeHolder = token;
//returns placeholder to main
return placeHolder;
}
//method prints out the introduction to the game
public static void intro() {
System.out.println("Welcome to the game of Mad Libs");
System.out.println("I will ask you to provide various words");
System.out.println("and phrases to fill in a story.");
System.out.println("The result will be written to an output file.");
System.out.println();
}
}
Also am currently using a file called simple.txt with the text:
I wannabe a <job> when I grow up.
Just like my dad.
Life is <adjective> like that!
This is the full error message:
Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:862)
at java.util.Scanner.next(Scanner.java:1371)
at MadLibs.placeHolder(MadLibs.java:96)
at MadLibs.main(MadLibs.java:46)

I ran your code and got a NoSuchElementException instead of a NoSuchFileException. To circumvent this exception you need to check if there are any more tokens while in the method placeHolder. Otherwise, after entering every placeholder you would still search for the next placeholder token although there is no next().
Change your code to:
while(tokens.hasNext() && !(token.startsWith("<") && token.endsWith(">"))) {
//not a placeholder!
//continue reading file
System.out.println(token);
token = tokens.next();
}

Replace string text from a source file, save changes into the original file. Append using StringBuilder

Please consider the following code. I'm not very familiar with StringBuilders or reading/writing data. I need to:
1.) Open source file
2.) Grab words and check for old string, if an old string, then append new string
3.) Use PrintWriter and Close. I am revising the following code below:
import java.io.*;
import java.util.*;
public class ReplaceText {
public static void main(String[] args) throws Exception {
// Check command line parameter usage
if (args.length != 4) {
System.out.println(
"Usage: java ReplaceText sourceFile targetFile oldStr newStr");
System.exit(1);
}
// Check if source file exists
File sourceFile = new File(args[0]);
if (!sourceFile.exists()) {
System.out.println("Source file " + args[0] + " does not exist");
System.exit(2);
}
// Check if target file exists
File targetFile = new File(args[1]);
if (targetFile.exists()) {
System.out.println("Target file " + args[1] + " already exists");
System.exit(3);
}
// Create input and output files
Scanner input = new Scanner(sourceFile);
PrintWriter output = new PrintWriter(targetFile);
while (input.hasNext()) {
String s1 = input.nextLine();
String s2 = s1.replaceAll(args[2], args[3]);
output.println(s2);
}
input.close();
output.close();
}
}
I'd also like to ask the user for the source file, old string, and new string at run time instead of using command line arguments.
I know I still need to incorporate StringBuilder. Here is what I have so far:
public class ReplaceText {
public static void main(String [] args) throws Exception {
Scanner scan = new Scanner(System.in);
System.out.println("What is the source file");
java.io.File file = new java.io.File(scan.next());
System.out.println("Enter old line");
String oldLine = scan.nextLine();
System.out.println("Enter new line");
String newLine = scan.nextLine();
//scan.exit;
/** Read one line at a time, append, replace oldLine with
* newLine using a loop */
//Scanner scan2 = new Scanner(file);
//PrintWriter that replaces file
java.io.PrintWriter output = new java.io.PrintWriter(file);
output.println(file);
output.close();
}
}

FileNotFoundException occurs due to my outputStream method

Please bear with me here as I'm new to the site.
below is a program that I've written for my programming in Java class, and while most of it has gone well so far, I can't seem to get rid of a specific bug.
When the program reaches the third if block (choice == 3) it doesn't let the user enter any data, and if the line
"outputStream = openOutputTextFile(newerFileName);"
is present in the if block then a FileNotFoundException occurs. After tinkering around with my code for a while I've found that the error is being thrown because the program cannot find the inputStream anymore. Although I've checked and have found that the program can still find, read, and write to the file that is throwing the error.
I'm thinking that since the error only occurs when I put the outputStream in, and is being thrown by the inputStream, then it probably has something to do with file streams. I just don't know what exactly
Does anyone have any ideas on how I could solve this issue?
public class FileProgram {
public static PrintWriter openOutputTextFile(String fileName)
throws FileNotFoundException {
PrintWriter toFile = new PrintWriter(fileName);
return toFile;
}
public static Scanner readFile(String fileName)
throws FileNotFoundException {
Scanner inputStream = new Scanner(new File(fileName));
return inputStream;
}
public static void main(String args[]) throws FileNotFoundException {
ArrayList<String>fileReader = new ArrayList<String>(10);
PrintWriter outputStream = null;
Scanner inputStream = null;
Scanner keyboard = new Scanner(System.in);
try {
System.out.println("Enter the name of the text file you want to copy.");
String oldFileName = keyboard.nextLine();
inputStream = readFile(oldFileName);
while(inputStream.hasNextLine()) {
String currentLine = inputStream.nextLine();
fileReader.add(currentLine);
}
System.out.println("All data has been collected. Enter the name for the new text file");
String newFileName = keyboard.nextLine();
outputStream = openOutputTextFile(newFileName);
File userFile = new File(newFileName);
if(userFile.exists())
{
System.out.println("The name you entered matches a file that already exists.");
System.out.println("Here are your options to fix this issue.");
System.out.println("Option 1: Shut down the program.");
System.out.println("Option 2: Overwrite the old file with the new empty one.");
System.out.println("Option 3: Enter a different name for the new file.");
System.out.println("Enter the number for the option that you want.");
int choice = keyboard.nextInt();
if(choice == 1) {
System.exit(0);
} else if(choice == 2) {
outputStream = new PrintWriter(newFileName);
} **else if(choice == 3) {
System.out.println("Enter a different name.");
String newerFileName = keyboard.nextLine();
outputStream = openOutputTextFile(newerFileName);
}**
}
for(int i = 0; i < fileReader.size(); i++) {
String currentLine = fileReader.get(i);
outputStream.println(currentLine);
//System.out.println(currentLine);
}
System.out.println("The old file has been copied line-by-line to the new file.");
}
catch(FileNotFoundException e) {
System.out.println("File not found");
System.out.println("Shutting program down.");
System.exit(0);
}
finally {
outputStream.close();
inputStream.close();
}
}
}

You are having trouble getting a line of input from your Scanner object after calling .nextInt(). In response to the numeric choice, the user enters an integer followed by a newline.
This line reads the integer from the input buffer:
int choice = keyboard.nextInt();
However, there's still a newline in the input buffer right after the number. Thus when you call .nextLine():
String oldFileName = keyboard.nextLine();
You get an empty line. You cannot create a file with an empty string for a file name, so a FileNotFoundException is thrown (this is per spec, see the other answer).
One solution is to consistently use .nextLine(), getting a line at a time from the input buffer. When you need an integer, simply parse the string manually:
int choice = Integer.parseInt( keyboard.nextLine() );
By the way, in debugging this sort of issue it's very useful to get into the habit of adding some printout statements to see what's going on:
public static PrintWriter openOutputTextFile(String fileName)
throws FileNotFoundException {
System.out.println( "Trying to create file: '" + fileName + "'" );
PrintWriter toFile = new PrintWriter(fileName);
return toFile;
}
There are more advanced debugging techniques, but this one is extremely simple, and using it is a lot more effective than using nothing at all.