Develop Reference

Detect first line of text file separately?

I am designing a program that will load a text file into different media file classes (Media > Audio > mp3, Media > Video > Avi, etc).
Now the first line of my text file is how many files there are in total, as in
3
exmaple.mp3,fawg,gseges
test.gif,wfwa,rgeg
ayylmao.avi,awf,gesg
Now that is what is in my text file, I want to first get the first line separately, then loop through the rest of the files.
Now I understand I can simply count how many files are in by using an int that grows as I loop but I want it clear in the file aswell, and I'm not sure how to go about this.
static public Media[] importMedia(String fileName)
{
try {
BufferedReader reader = new BufferedReader(new FileReader(fileName));
String line = reader.readLine();
while(line != null)
{
//Get the first line of the text file seperatly? (Then maybe remove it? idk)
//Split string, create a temp media file and add it to a list for the rest of the lines
}
//String[] split = s.next().split(",");
} catch (Exception ex) { System.out.println(ex.getMessage()); }
return null;
}
I hope my question is clear, if it TL;DR I want to get the first line of a text file separately, then the rest Id like to loop through.

I wouldn't advice using a for-loop here, since the file might contain additional lines (e.g. comments or blank lines) to make it more human-readable. By examining the content of each line, you can make your processing more robust against this sort of thing.
static public Media[] importMedia(String fileName)
{
try {
BufferedReader reader = new BufferedReader(new FileReader(fileName));
// Get and process first line:
String line = reader.readLine(); // <-- Get the first line. You could consider reader as a queue (sort-of), where readLine() dequeues the first element in the reader queue.
int numberOfItems = Integer.valueOf(line); // <-- Create an int of that line.
// Do the rest:
while((line = reader.readLine()) != null) // <-- Each call to reader.readLine() will get the next line in the buffer, so the first time around this will give you the second line, etc. until there are no lines left to read.
{
// You will not get the header here, only the rest.
if(!line.isEmpty() || line.startsWith("#") {
// If the line is not empty and doesn't start with a comment character (I chose # here).
String[] split = line.split(",");
String fileName = split[0];
// etc...
}
}
} catch (Exception ex) { System.out.println(ex.getMessage()); }
return null;
}

You don't need while loop to read up to end of file. Read first line and convert it to int than loop through.
static public Media[] importMedia(String fileName)
{
try {
BufferedReader reader = new BufferedReader(new FileReader(fileName));
// Get and process first line:
int lineNo=Integer.parseInt(reader.readLine());
// Now read upto lineNo
for(int i=0; i < lineNo; i++){
//Do what you need with other lines.
String[] values = reader.readLine().split(",");
}
} catch (Exception e) {
//Your exception handling goes here
}
}

ReadLine - execute twice?

I need to be able to read each line of the file for multiple arguments, hence the for loop. After the first one, it does not seem to be reading them anymore, seems to skip the try statement. Any ideas? I'm sure Its something silly I am missing but have been playing about with it and unfortunately time is not on my side.
for (int j = 0; j < ags.length; j++){
try{
String nameFromFile = null;
BufferedReader InputReader = new BufferedReader(new InputStreamReader(System.in));
while ((nameFromFile = InputReader.readLine()) != null) {
// Do stuff
} catch (IOException e) {
System.out.println(e.getMessage());
}
}

You appear to have two sources you want to compare System.in and args I suggest you read these individually and then compare them.
Set<String> fromInt = new HashSet<>();
try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
for(String line; (line = br.readLine()) != null;)
fromIn.add(normalise(line));
}
// compare argsList with fromIn.
e.g.
for(String arg: args) {
if (fromIn.contains(normalise(arg))) {
// something
} else {
// something else
}
}

I need to be able to read each line of the file
What file? You're reading from System.in:
BufferedReader InputReader = new BufferedReader(new InputStreamReader(System.in));
Your code will block at this line until you enter something at the console.

You do not read a file, bu the System.in stream.
Every stream has an internal pointer, so the stream nows, which line was read at last.
If the System stream was read once, the pointer is pointing to the end of the stream.
As long as the stream is not reset, the read command will not return anything.
try
InputStream.reset()
or even better, only read the Stream once and cache the result! This is faster and safe, because the Stream input can change during iteration.

Your code will never exit from while loop.
while ((nameFromFile = InputReader.readLine()) != null)
In above loop it will print only one time and at the end of the file it will not be out of the while loop . That's why you are getting only one time output. Since it is not exited from while loop it does not go back into for loop. readLine() return the string and it is terminated by "\n" or "\r\n". Change as below and you will be able to read as ags.length
while ((nameFromFile = InputReader.readLine())=="\n")

How do I quadruple the integer values in a text file? [closed]

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.
Closed 9 years ago.
I guess this comes down to reading and writing to the same file. I would like to be able to return the same text file as is input, but with all integer values quadrupled. Should I even be attempting this with Java, or is it better to write to a new file and overwrite the original .txt file?
In essence, I'm trying to transform This:
12
fish
55 10 yellow 3
into this:
48
fish
220 40 yellow 12
Here's what I've got so far. Currently, it doesn't modify the .txt file.
import java.io.*;
import java.util.Scanner;
public class CharacterStretcher
{
public static void main(String[] args)
{
Scanner keyboard = new Scanner( System.in );
System.out.println("Copy and paste the path of the file to fix");
// get which file you want to read and write
File file = new File(keyboard.next());
File file2 = new File("temp.txt");
BufferedReader reader;
BufferedWriter writer;
try {
// new a writer and point the writer to the file
FileInputStream fstream = new FileInputStream(file);
// Use DataInputStream to read binary NOT text.
reader = new BufferedReader(new InputStreamReader(fstream));
writer = new BufferedWriter(new FileWriter(file2, true));
String line = "";
String temp = "";
int var = 0;
int start = 0;
System.out.println("000");
while ((line = reader.readLine()) != null)
{
System.out.println("a");
if(line.contains("="))
{
System.out.println("b");
var = 0;
temp = line.substring(line.indexOf('='));
for(int x = 0; x < temp.length(); x++)
{
System.out.println(temp.charAt(x));
if(temp.charAt(x)>47 && temp.charAt(x)<58) //if 0<=char<=9
{
if(start==0)
start = x;
var*=10;
var+=temp.indexOf(x)-48; //converts back into single digit
}
else
{
if(start!=0)
{
temp = temp.substring(0, start) + var*4 + temp.substring(x);
//writer.write(line.substring(0, line.indexOf('=')) + temp);
//TODO: Currently writes a bunch of garbage to the end of the file, how to write in the middle?
//move x if var*4 has an extra digit
if((var<10 && var>2)
|| (var<100 && var>24)
|| (var<1000 && var>249)
|| (var<10000 && var>2499))
x++;
}
//start = 0;
}
System.out.println(temp + " " + start);
}
if(start==0)
writer.write(line);
else
writer.write(temp);
}
}
System.out.println("end");
// writer the content to the file
//writer.write("I write something to a file.");
// always remember to close the writer
writer.close();
//writer = null;
file2.renameTo(file); //TODO: Not sure if this works...
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

Given that this is a pretty quick and simple hack of a formatted text file, I don't think you need to be too clever about it.
Your logic for deciding whether you are looking at a number is pretty complex and I'd say it's overkill.
I've written up a basic outline of what I'd do in this instance.
It's not very clever or impressive, but should get the job done I think.
I've left out the overwriting and reading the input form the console so you get to do some of the implementation yourself ;-)
import java.io.*;
public class CharacterStretcher {
public static void main(String[] args) {
//Assumes the input is at c:\data.txt
File inputFile = new File("c:\\data.txt");
//Assumes the output is at c:\temp.txt
File outputFile = new File("c:\\temp.txt");
try {
//Construct a file reader and writer
final FileInputStream fstream = new FileInputStream(inputFile);
final BufferedReader reader = new BufferedReader(new InputStreamReader(fstream));
final BufferedWriter writer = new BufferedWriter(new FileWriter(outputFile, false));
//Read the file line by line...
String line;
while ((line = reader.readLine()) != null) {
//Create a StringBuilder to build our modified lines that will
//go into the output file
StringBuilder newLine = new StringBuilder();
//Split each line from the input file by spaces
String[] parts = line.split(" ");
//For each part of the input line, check if it's a number
for (String part : parts) {
try {
//If we can parse the part as an integer, we assume
//it's a number because it almost certainly is!
int number = Integer.parseInt(part);
//We add this to out new line, but multiply it by 4
newLine.append(String.valueOf(number * 4));
} catch (NumberFormatException nfEx) {
//If we couldn't parse it as an integer, we just add it
//to the new line - it's going to be a String.
newLine.append(part);
}
//Add a space between each part on the new line
newLine.append(" ");
}
//Write the new line to the output file remembering to chop the
//trailing space off the end, and remembering to add the line
//breaks
writer.append(newLine.toString().substring(0, newLine.toString().length() - 1) + "\r\n");
writer.flush();
}
//Close the file handles.
reader.close();
writer.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

You may want to consider one of these:
Build the new file in memory, rather than trying to write to the same file you are reading from. You could use StringBuilder for this.
Write to a new file, then overwrite the old file with the new one. This SO Question may help you there.
With both of these, you will be able to see your whole output, separate from the input file.
Additionally, with option (2), you don't have the risk of the operation failing in the middle and giving you a messed up file.
Now, you certainly can modify the file in-place. But it seems like unnecessary complexity for your case, unless you have really huge input files.
At the very least, if you try it this way first, you can narrow down on why the more complicated version is failing.

You cannot read and simultaneously write to the same file, because this would modify the text you currently read. This means, you must first write a modified new file and later rename it to the original one. You probably need to remove the original file before renameing.
For renaming, you can use File.renameTo or see one of the many SO's questions
You seem to parse integers in your code by collecting single digits and adding them up. You should consider using either a Scanner.nextInt or employ Integer.parseInt.
You can read your file line by line, split the words at white space and then parse them and check if it is either an integer or some other word.

How to write or append string in loop in a file in java?

I'm having memory problem as working with very large dataset and getting memory leaks with char[] and Strings, don't know why! So I am thinking of writing some processed data in a file and not store in memory. So, I want to write texts from an arrayList in a file using a loop. First the program will check if the specific file already exist in the current working directory and if not then create a file with the specific name and start writing texts from the arrayList line by line using a loop; and if the file is already exist then open the file and append the 1st array value after the last line(in a new line) of the file and start writing other array values in a loop line by line.
Can any body suggest me how can I do this in Java? I'm not that good in Java so please provide some sample code if possible.
Thanks!

I'm not sure what parts of the process you are unsure of, so I'll start at the beginning.
The Serializable interface lets you write an object to a file. Any object that implemsents Serializable can be passed to an ObjectOutputStream and written to a file.
ObjectOutputStream accepts a FileOutputStream as argument, which can append to a file.
ObjectOutputstream outputStream = new ObjectOutputStream(new FileOutputStream("filename", true));
outputStream.writeObject(anObject);
There is some exception handling to take care of, but these are the basics. Note that anObject should implement Serializable.
Reading the file is very similar, except it uses the Input version of the classes I mentioned.

Try this
ArrayList<String> StringarrayList = new ArrayList<String>();
FileWriter writer = new FileWriter("output.txt", true);
for(String str: StringarrayList ) {
writer.write(str + "\n");
}
writer.close();

// in main
List<String> SarrayList = new ArrayList<String>();
.....
fill it with content
enter content to SarrayList here.....
write to file
appendToFile (SarrayList);
.....
public void appendToFile (List<String> SarrayList) {
BufferedWriter bw = null;
boolean myappend = true;
try {
bw = new BufferedWriter(new FileWriter("myContent.txt", myappend));
for(String line: SarrayList ) {
bw.write(line);
bw.newLine();
}
bw.flush();
} catch (IOException ioe) {
ioe.printStackTrace();
} finally {
if (bw != null) try {
bw.close();
} catch (IOException ioe2) {
// ignore it or write notice
}
}
}

Unable to write new lines to File

I have a bunch of strings that I'm writing to a file:
private void writeScoreToFile(BlastScore result)
{
try{
FileWriter fstream = new FileWriter(getFilesDir() + CaptureActivity.BLAST_SCORES,true);
BufferedWriter out = new BufferedWriter(fstream);
out.write(Integer.toString(result.getBlastScore()));
out.close();
}catch (Exception e){
System.err.println("Write Error: " + e.getMessage());
}
}
I would like to read it back in as a List.
private List<String> getArrayFromFile(String filename) throws IOException
{
FileReader fileReader = new FileReader(getFilesDir() + filename);
BufferedReader bufferedReader = new BufferedReader(fileReader);
List<String> lines = new ArrayList<String>();
String line = null;
while ((line = bufferedReader.readLine()) != null) {
lines.add(line);
}
bufferedReader.close();
return lines;
}
The list that is being written is:
100
96
100
96
100
When I print the List it looks like
10-28 21:22:31.130: I/System.out(936): Last Score: 1009610096100
Here is the code I am using to print it:
try {
List<String> blastScores = getArrayFromFile(CaptureActivity.BLAST_SCORES);
System.out.println("Last Score: " + blastScores.get(blastScores.size()-1));
} catch (IOException e) {
// TODO Auto-generated catch block
System.err.println("Read Error: " + e.getMessage());
}
I'm trying to get the n-1 element.
I'm not sure what I'm doing wrong.

When you are writing the Integers or Integer Strings you are not putting a new line character after each output. Hence, your file has only one line of data, which line you are getting as a continuous String...
To fix, add a line separator like write.newLine() in between separate write() calls.

The code which writes the scores uses
out.write(Integer.toString(result.getBlastScore()));
This means that if the method is called with scores 12, 100 and 2, your file will look like
121002
since you don't write any separator. How do you want to parse this into three numbers correctly?
Use a PrintWriter that wraps the BufferedWriter, and use its println method to write the score.
Note that writing the scores one by one by opening the file and closing it each time won't be very fast. BTW, using a BufferedWriter just to write a single integer won't gain any benefit. You also have bad exception handling : the streams and readers/writers should always be closed in a finally block.

In your writeScoreToFile function I don't see any new line or any sort of delimiter that would separate each score being written.
In that case your file would in fact contain 1009610096100 on a single line and the loop inside getArrayFromFile would only be executed once:
while ((line = bufferedReader.readLine()) != null) {
lines.add(line);
}
Therefore your List<String> only contains 1 element and the code blastScores.get(blastScores.size()-1) will get the last and only element, that obviously being 1009610096100.