Develop Reference

Creating, writing to and reading files

I know there are many questions related to this, but I still do not follow. I have copied the below code from a tutorial on how to create, write to and read from a file. There is a CreateFile class, a ReadFile class and a Demo class:
CreateFile.java
import java.io.*;
import java.lang.*;
import java.util.*;
public class CreateFile {
private Formatter x;
public void openFile(){
try{
x = new Formatter("chinese.txt");
}
catch(Exception e)
{
System.out.println("You have an error");
}
}
public void addRecords(){
x .format("%s%s%s", "20 ", "bucky ", "robers");
}
public void closeFile(){
x.close();
}
}
ReadFile.java
public class ReadFile {
private Scanner x;
public void openFile()
{
try{
x = new Scanner(new File("words.txt"));
}
catch(Exception e){
System.out.println("could not find file");
}
}
public void readFile()
{
while(x.hasNext())
{
String a = x.next();
String b = x.next();
String c = x.next();
System.out.printf("%s %s %s\n", a,b,c);
}
}
public void closeFile()
{
x.close();
}
}
public class Demo {
public static void main(String[] args) {
CreateFile g = new CreateFile();
g.openFile();
g.addRecords();
g.closeFile();
WordCounter r = new WordCounter();
r.openFile();
r.readFile();
r.closeFile();
}
In Demo.java if I remove the last four statements related to reading the file, the first four statements related to opening and writing to a file run without error. However, once I add
WordCounter r = new WordCounter();
r.openFile();
r.readFile();
r.closeFile();
and run the program, it outputs: Exception in thread "main" could not find file. I am not sure what is going on, is the file chinese.txt never being created?

I'd suggest that you look into serialization it much easier and simpler than writing to .txt files.
But if you really need to do .txt files this is how you write to a .txt file
//This gets your project directory
private String projectPath = System.getProperty("user.dir");
//call save()
String save("test.txt", "This is will be save to a test.txt file");
private boolean save(String textfile String outputtext){
String filepath = projectPath + textfile;
try{
BufferedWriter writer = new BufferedWriter(new FileWriter(filepath));
writer.write(outputtext);
writer.close();
} catch(IOException e) { }
return true;
}
And this is how you read it
private String load(String textfile){
String temp="";
String filepath = projectPath + textfile;
try{
BufferedReader reader =new BufferedReader(new FileReader(filepath));
while(true){
//this will read one line at a time you can append it output
try {
temp+= reader.readLine();
//If no more lines break out of the loop
if(line==null)
break;
}catch(IOException e){}
}
reader.close();
}
catch(IOException e){}
//Return contents of the file you loaded
return temp;
}
I hope that this code is clear enough. If you have any further questions let me know. I'll gladly answer them.

Want to read content from two text files then compare and write to another text file with java

I have text files.
album.txt
new_album.txt
Each text files contains some folder name.
For example,
album.txt contains
#Event1
#Event2
#Event3
and new_album.txt contains
#Event1(update20-05-2015)
#Event2(update03-03-2016)
#Event3(update15-08-2016)
#Event4(update30-07-2017)
I want to compare similar folder name from album.txt with new_album.txt line by line, then put folder name that similar from album.txt to similar.txt and put folder name that not match to not_match.txt .
Output in similar.txt
#Event1
#Event2
#Event3
Output in not_match.txt
#Event4(update30-07-2017)
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
public class CompareFileName {
public static void main(String[] args) throws Exception {
BufferedReader br1 = null;
BufferedReader br2 = null;
String sCurrentLine;
List<String> list1 = new ArrayList<String>();
List<String> list2 = new ArrayList<String>();
br1 = new BufferedReader(new FileReader("album.txt"));
br2 = new BufferedReader(new FileReader("new_album.txt"));
while ((sCurrentLine = br1.readLine()) != null) {
list1.add(sCurrentLine);
}
while ((sCurrentLine = br2.readLine()) != null) {
list2.add(sCurrentLine);
}
//This part is my problem
List <String> list_similar = new ArrayList<String>();
List <String> list_not_match = new ArrayList<String>();
for (String string : list1) {
if(string.matches("list2")){ //I don't know how to compare similar folder name from list2 with list1.
list_similar.add(string);
}else{list_not_match.add(string)}
}
//This part is the part I use for add string to text file but it not complete I want to write string from list_similar to similar.text and list_not_match to not_match.txt
file = new File("similar.txt");
fileName = "similar.txt";
str = file.list();
try{
PrintWriter outputStream = new PrintWriter(fileName);
for(String string:str){
outputStream.println(string);
}
outputStream.close();
System.out.println("get name complete");
}
catch (FileNotFoundException e){
e.printStackTrace();
}
System.out.println("done.");
}

If you want to read something from files, you can use these streams.
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new FileReader(new File("path\\to\\your\\file.txt"))); //or any format
BufferedWriter writer = new BufferedWriter(new FileWriter(new File("path\\to\\your\\second\\file.txt")));
//read one line from your file
String line = reader.readLine();
//write something to your file
writer.write(line);
}
If you want to read folder names you can use this.
File f = f = new File("path\\to\\your\\folder\\with\\files");
File[] files = f.listFiles();
for(File currentFile : files) {
System.out.println(currentFile.getName());
}
If you want to create new files or folders, you can use this.
File f = f = new File("path\\to\\your\\folder\\with\\files");
f.mkdir();
//or
f.mkdirs();
//or if you have File f = new File("myTextFile.txt"); then you can create file using this:
f.createNewFile();

Application (main method)
public class Application {
public static void main(String... aArgs) throws IOException {
InputParser firstListInputParser = new InputParser(new File(/**"Your path to /album.txt"*/));
firstListInputParser.processLineByLine();
List<String> firstList = firstListInputParser.getListWithParsedFolderNames();
firstListInputParser.printMap();
InputParser secondListInputParser = new InputParser(new File(/**"Your path to /new_album.txt"*/));
secondListInputParser.processLineByLine();
List<String> secondList = secondListInputParser.getListWithParsedFolderNames();
secondListInputParser.printMap();
// Create the list with common value and write it to the file
List<String> listWithCommonValues = new ArrayList<String>(firstList);
listWithCommonValues.retainAll(secondList);
Path fileCommon = Paths.get(/**"Your path to /similar.txt"*/);
Files.write(fileCommon, listWithCommonValues, Charset.forName("UTF-8"));
// Create the list with different values and write it to the file
List<String> listWithAllValues = new ArrayList<String>(firstList);
listWithAllValues.addAll(secondList);
//remove the common values from the list with all values
listWithAllValues.removeAll(listWithCommonValues);
Path fileDistincts = Paths.get(/**"Your path to /not_match.txt"*/);
Files.write(fileDistincts, listWithAllValues, Charset.forName("UTF-8"));
}
private static void log(Object aObject){
System.out.println(String.valueOf(aObject));
}
}
Inputparser
/**
* Assumes UTF-8 encoding
*/
public class InputParser {
//create a list to hold the values
List<String> listWithParsedFolderNames = new ArrayList<>();
//private final Path fFilePath;
private final File file;
private final static Charset ENCODING = StandardCharsets.UTF_8;
/**
Constructor.
#param aFileName full name of an existing, readable file.
*/
public InputParser(File aFileName){
//fFilePath = Paths.get(aFileName);
file = aFileName;
}
/**
* Processes each line and calls {#link #processLine(String)}}.
*/
public final void processLineByLine() throws IOException {
try (Scanner fileScanner = new Scanner(file, ENCODING.name())){
while (fileScanner.hasNextLine()){
processLine(fileScanner.nextLine());
}
}
}
/**
Overridable method for processing lines in different ways.
*Parses the line and cuts away the part after '(update'
* Ex1: input line: #Event1(update20-05-2015)
* Ex1: output : #Event1
*
* Ex2: input line: #Event2
* Ex2: output : #Event2
*/
protected void processLine(String aLine){
Scanner scanner = new Scanner(aLine);
if (scanner.hasNext()) {
String name = scanner.next();
String finalName = name.split("\\(update")[0];
//stores the values in the list
listWithParsedFolderNames.add(finalName);
} else {
log("Empty or invalid line. Unable to process.");
}
}
/**
* Prints the content of the listWlistWithParsedFolderNames
*/
public void printMap() {
Iterator it = listWithParsedFolderNames.iterator();
while (it.hasNext()) {
log("The prsed value is: " + it.next());
}
}
/**
* #return the list with values
*/
public List<String > getListWithParsedFolderNames() {
return this.listWithParsedFolderNames;
}
private static void log(Object aObject){
System.out.println(String.valueOf(aObject));
}
}
In the similar.txt it will print:
#Event1
#Event2
#Event3
In the not_match.txt it will print:
#Event4
If you want it to print #Event4(update30-07-2017) into the not_match class you will have to change the list to a key value map that has the parsed input #Event4 as key and the full line #Event4(update30-07-2017) as value. After comparing the keys of the map you can write the values into your file.

How do I get a file to read into an Arraylist, when the file is opened through a filechooser

I am trying to get a file to read into an Arraylist, then take the numbers read from the file and calculate the average. I am having trouble getting it to read the file and I am opening with a JFileChooser. I have spent three days trying to get this to work. I have seen some similar questions on here but none using a JFileChooser.
Here is my code for the JFileChooser. I know how to calculate the average, but I just need to read the numbers in the file.
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import javax.swing.JFileChooser;
import javax.swing.JOptionPane;
public class Week07 {
static JFileChooser fileChooser = new JFileChooser();
public static void main(String[] args) throws IOException {
String theFile;
theFile = getTheFileName();
double theAverage;
theAverage = getTheAverage(theFile);
displayTheResult(theAverage,"The average is: ");
}
public static String getTheFileName() {
String status;
fileChooser.showOpenDialog(null);
status = fileChooser.getSelectedFile().getAbsolutePath(); {
return status;
}
}
private static double getTheAverage(String theFile) throws NumberFormatException, IOException{
String fileName = getTheFileName();
FileReader fr = new FileReader(theFile);
BufferedReader br = new BufferedReader(fr);
so here is what i have, but now i cant get it to display the average.
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFileChooser;
import javax.swing.JOptionPane;
public class Week07 {
static JFileChooser chooser = new JFileChooser();
public static void main(String[] args) throws IOException {
String theFile;
theFile = getTheFileName();
double theAverage;
//theAverage = getTheAverage(theFile);
//displayTheResult(theAverage,"The average is: ");
}
public static String getTheFileName() {
String status;
chooser.showOpenDialog(null);
status = chooser.getSelectedFile().getAbsolutePath(); {
return status;
}
}
public List<String> readFile() throws IOException
{
JFileChooser chooser = new JFileChooser();
int result = chooser.showOpenDialog(null);
//check result
File theFile = chooser.getSelectedFile();
//needs exception handling etc.
BufferedReader br = new BufferedReader(new FileReader(theFile));
List<String> data = new ArrayList<String>();
String line;
while ( (line = br.readLine()) != null)
data.add(line);
br.close();
return data;
}}
public static double average(List<Integer> readFile) {
if (readFile == null || readFile.isEmpty())
return 0.0;
// Calculate the summation of the elements in the list
long sum = 0;
int n = readFile.size();
// Iterating manually is faster than using an enhanced for loop.
for (int i = 0; i < n; i++)
sum += readFile.get(i);
// We don't want to perform an integer division, so the cast is mandatory.
return ((double) sum) / n;
}
}

In Java there is the File class which is used for dealing with, well files. So whether you get the file from a FileChooser or by any other means does not matter.
There are a few things I would do differently in your getTheFileName() methode:
Return the File directly instead of the path
Creating the JFileChooser inside the methode
Check the return value of showOpenDialog (what if the user presses Cancel)
Here is some example code which reads the content of a file in a list of strings:
public List<String> readFile()
{
JFileChooser chooser = new JFileChooser();
int result = chooser.showOpenDialog(null);
//check result
File file = chooser.getSelectedFile();
//needs exception handling etc.
BufferedReader br = new BufferedReader(new FileReader(file));
List<String> data = new ArrayList<String>();
String line;
while ( (line = br.readLine()) != null)
data.add(line);
br.close();
return data;
}
If you are using >= Java 7 you can simply use this:
List<String> data = Files.readAllLines(Path path, Charset cs);
Another way would be to use the Scanner class. This would maybe simplify things, since you can directly check and read integer/double values and sum them up.

Let's start with the proper use of the JFileChooser...
JFileChooser#showOpenDiaog returns an int
Returns: the return state of the file chooser on popdown: JFileChooser.CANCEL_OPTION
JFileChooser.APPROVE_OPTION JFileChooser.ERROR_OPTION if an error
occurs or the dialog is dismissed
This is important, as JFileChooser#getSelectedFile may also return null, which would cause your current code...
public static String getTheFileName() {
String status;
fileChooser.showOpenDialog(null);
status = fileChooser.getSelectedFile().getAbsolutePath(); {
return status;
}
}
To throw a NullPointerException...
Instead, you should consider using something like...
public static File getTheFileName() {
File file = null;
if (fileChooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
file = fileChooser.getSelectedFile();
}
return file;
}
The reason for using the actual File object is it carries much more context and functionality the just a String alone.
The next step is to read the file. Depending on which version of Java you are using you could use...
File file = ...;
List<String> values = new ArrayList<String>(25);
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String text = null;
while ((text = br.readLine()) != null) {
values.add(text);
}
} catch (IOException exp) {
exp.printStackTrace();
}
For Java 7 (using try-with-resources) or
File file = ...;
List<String> values = new ArrayList<String>(25);
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader(file));
String text = null;
while ((text = br.readLine()) != null) {
values.add(text);
}
} catch (IOException exp) {
exp.printStackTrace();
} finally {
try {
br.close();
} catch (Exception e) {
}
}
If you are using Java 6 or earlier. The important thing here is to make sure you are properly closing your resources, if you open, you must make every effort to close it.
Check out Basic I/O and How to use File Choosers for more details

Java: Make a void-method out of this class (textfile changer)

What I want to do: My class copytest reads a textfile, edits one character and save this new file in a new directory. I want to program a void-method out of it, which does exactly the same and can then be used the following way:
copy(String "C:\\Old.txt", String "C:\\New.txt", int 1, int 1)
Now copy does exactly the same as my old class copytest, it reads the old file, edits it and saves it.
My first idea was to have two files as the first to arguments, but this is obviously impossible. My new idea is to give the method two strings of the wanted directories of the old and the new file. It still doesn't work. I hope, you understand, what I want to do and how to solve this problem.
Old class code (works):
import java.io.*;
import java.util.Scanner;
public class copytest {
public static void main(String[] args) throws Exception {
readFile();
}
public static void readFile() throws Exception {
// Location of file to read
File file = new File("...old.txt");
Scanner scanner = new Scanner(file);
int lineNumber=1;
int charNumber=1;
String wantedChar="r";
int i=0;
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
if (i == lineNumber+2) {
if (line.length() >= charNumber) {
line = line.substring(0,charNumber-1) + wantedChar + line.substring(charNumber);
}
}
writeFile(line);
i++;
}
scanner.close();
System.out.println("File copied.");
}
public static void writeFile(String copyText) throws Exception {
String newLine = System.getProperty("line.separator");
// Location of file to output
Writer output = null;
File file = new File("...new.txt");
output = new BufferedWriter(new FileWriter(file, true));
output.write(copyText);
output.write(newLine);
output.close();
}
}
New void code (first try with file as argument):
public void copy(file old, file new, int x, int y) {
public static void readFile() throws Exception {
Scanner scanner = new Scanner(old);
int lineNumber=y;
int charNumber=x;
String wantedChar="r";
int i=0;
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
if (i == lineNumber+2) {
if (line.length() >= charNumber) {
line = line.substring(0,charNumber-1) + wantedChar + line.substring(charNumber);
}
}
writeFile(line);
i++;
}
scanner.close();
System.out.println("File copied.");
}
public static void writeFile(String copyText) throws Exception {
String newLine = System.getProperty("line.separator");
// Location of file to output
Writer output = null;
File file = new File(new.getPath());
output = new BufferedWriter(new FileWriter(file, true));
output.write(copyText);
output.write(newLine);
output.close();
}
readFile();
}
New try with strings as argument, but still doesn't work:
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.Writer;
import java.util.Scanner;
public class copytestnew {
public void copy(String old, String newone, int x, int y) {
// Location of file to read
File file = new File(old);
Scanner scanner = new Scanner(file);
int lineNumber=y;
int charNumber=x;
String wantedChar="r";
int i=0;
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
if (i == lineNumber+2) {
if (line.length() >= charNumber) {
line = line.substring(0,charNumber-1) + wantedChar + line.substring(charNumber);
}
}
String newLine = System.getProperty("line.separator");
// Location of file to output
Writer output = null;
File file2 = new File(newone);
output = new BufferedWriter(new FileWriter(file2, true));
output.write(line);
output.write(newLine);
output.close();
i++;
}
scanner.close();
System.out.println("File copied");
}
}

I remember you! I answeared you last time on how to replace the char at one of the lines.
First, change the decleration to
public static void copy(String old, String newone, int x, int y) throws IOException {
NOTICE the throws statment!
And now when you want to call this method you should use it inside a try-catch block or declear that you throwing exception same as you did at the copy function.

public void copy(file old, file new, int x, int y) {
public static void readFile() throws Exception {
You're defining a function inside a method. As all functions in java are methods (static or non-static), this is not permitted. Try this:
class IDontKnowHowToNameIt {
public static void copy(file old, file new, int x, int y) {
//...
// call readFile from here
// ...
}
private static void readFile() throws Exception {
//...
}
}

How to use data stored in a variable located in a seperate file?

I have two files. One file counts the number of listed events I have in a text file and stores the number of events into the variable "count". I want to then use the value in this variable to do computation in a second file. How do I do this? Do I have to create an object of the class in my first file and then reference it? I need an example please, I cannot seem to get this to work. Here is what I have tried.
My first file:
import java.util.*;
import java.io.*;
public class EventCounter {
public static void main (String [] args) throws IOException{
Scanner file = new Scanner(new File("event.txt"));
int count = 0;
while (file.hasNextLine()) {
count++;
file.nextLine();
}
System.out.println(count); //test
}
}
My Second file:
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
public class ReadEventFile {
private String path;
public ReadEventFile(String file) {
path = file;
}
public String[] OpenFile() throws IOException {
FileReader fr = new FileReader(path);
BufferedReader textReader = new BufferedReader(fr);
EventCounter method = new EventCounter(); //make object?
String[] dataTable = new String[count];
int i;
for (i=0; i<count; i++) { //Why count does not exist?
}
My second file does not know that count is a variable from my first file :-(

You seem to have your process flow backwards. The class with the main method will be created and run by the JVM - therefore it's your entry point.
Your ReadEventFile class therefore needs to be told the count when it is created. Simply add it to the constructor:
public static class ReadEventFile {
private final File eventFile;
private final int count;
public ReadEventFile(final int count, final File eventFile) {
this.eventFile = eventFile;
this.count = count;
}
public String[] openFile() throws IOException {
String[] dataTable = new String[count];
int i;
for (i = 0; i < count; i++) {
}
return dataTable;
}
}
Now your EventCounter needs to create a ReadEventFile instance once it knows the count and call the openFile method on it:
public static void main(String[] args) throws IOException {
final File eventFile = new File("event.txt");
int count = 0;
try (Scanner file = new Scanner(eventFile)) {
while (file.hasNextLine()) {
count++;
file.nextLine();
}
}
final ReadEventFile readEventFile = new ReadEventFile(count, eventFile);
final String[] dataTable = readEventFile.openFile();
}
The ReadEventFile does it's work and then returns the String[] back to your EventCounter.
You don't close any of your resources when you are done with them. This is asking for trouble. I have added a Java 7 try-with-resources around your Scanner in the EventCounter.
The design of this program does seem a little odd. There is no logical reason why the EventCounter should be the entry point to the application. I would recommend you create a BootStrap class that holds the main method and is the entry point that then calls both the EventCounter and the ReadEventFile.
Further, the openFile method on the ReadEventFile class isn't well named - it does more than that. Maybe processEventFile or something along those lines would be more appropriate.

your first Program
package farzi;
import java.util.*;
import java.io.*;
public class EventCounter {
public static void main (String [] args) throws IOException
{
EventCounter object = new EventCounter();
System.out.println(object.returnCount());
}
public int returnCount() throws FileNotFoundException
{
Scanner file = new Scanner(new File("event.txt"));
int count = 0;
while (file.hasNextLine()) {
count++;
file.nextLine();
}
System.out.println(count); //test
return count;
}
}
your second program
package farzi;
import java.io.File;
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
public class ReadEventFile
{
private String path;
public ReadEventFile(String file)
{
String path = file;
}
public String[] OpenFile() throws IOException {
EventCounter eventCounterObject = new EventCounter();
int countLocal = eventCounterObject.returnCount();
FileReader fr = new FileReader(path);
BufferedReader textReader = new BufferedReader(fr);
EventCounter method = new EventCounter(); //make object?
String[] dataTable = new String[countLocal];
int i;
String[] textData = null;
for (i=0; i<countLocal; i++) { //Why count does not exist?
textData[i] = textReader.readLine();
}
return textData;
}
}