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How to read every second line from a file in java

Can someone tell me how to read every second line from a file in java?
BufferedReader br = new BufferedReader(new FileReader(file));
String line = br.readLine();
while(line != null){
//Do something ..
line = br.readLine()
}
br.close

One simple way would be to just maintain a counter of number of lines read:
int count = 0;
String line;
while ((line = br.readLine()) != null) {
if (count % 2 == 0) {
// do something with this line
}
++count;
}
But this still technically reads every line in the file, only choosing to process every other line. If you really only want to read every second line, then something like RandomAccessFile might be necessary.

You can do it in Java 8 fashion with very few lines :
static final int FIRST_LINE = 1;
Stream<String> lines = Files.lines(path);
String secondLine = lines.limit(2).skip(FIST_LINE).collect(Collectors.joining("\n"));
First you stream your file lines
You keep only the two first lines
Skip the first line
Note : In java 8, when using Files.lines(), you are supposed to close the stream afterwards or use it in a try-with-resource block.

This is similar to #Tim Biegeleisen's approach, but I thought I would show an alternative to get every other line using a boolean instead of a counter:
boolean skipOddLine = true;
String line;
while ((line = br.readLine()) != null) {
if (skipOddLine = !skipOddLine) {
//Use the String line here
}
}
This will toggle the boolean value every loop iteration, skipping every odd line. If you want to skip every even line instead you just need to change the initial condition to boolean skipOddLine = false;.
Note: This approach only works if you do not need to extend functionality to skip every 3rd line for example, where an approach like Tim's would be easier to modify. It also has the downside of being harder to read than the modulo approach.

This will help you to do it very well
You can use try with resource
You can use stream api java 8
You can use stream api supplier to use stream object again and again
I already hane added comment area to understand you
try (BufferedReader reader =
new BufferedReader(
new InputStreamReader(
new ByteArrayInputStream(x.getBytes()),
"UTF-8"))) { //this will help to you for various languages reading files
Supplier<Stream<String>> fileContentStream = reader::lines; // this will help you to use stream object again and again
if (FilenameUtils.getExtension(x.getOriginalFilename()).equals("txt")) { this will help you to various files extension filter
String secondLine = lines.limit(2).skip(FIST_LINE).collect(Collectors.joining("\n"));
String secondLine =
fileContentStream
.get()
.limit(2)
.skip(1)// you can skip any line with this action
.collect(Collectors.joining("\n"));
}
else if (FilenameUtils.getExtension(x.getOriginalFilename()).equals("pdf")) {
} catch (Exception ex) {
}

How to increment a while loop to read the next line on a file

I am writing code that
first) asks the user for a file name
second) reads the file and puts each line into an ArrayList
third) prints out the ArrayList
My code is reading the file with a BufferedReader, but it is only printing out the first line 25 times instead of printing out the 25 different lines.
This is what my while loop looks like. I don't know how to increment it though
ArrayList<String> stringArray = new ArrayList<String>();
BufferedReader reader = null;
reader = new BufferedReader(new FileReader(fileName));
String line = reader.readLine();
while(reader.readLine() != null){
stringArray.add(line);
}
return stringArray;
Any thoughts?

You are not reading in the line to the variable on each run, you need to read it in the while loop.
String line = reader.readLine();
while(line != null){
stringArray.add(line);
line = reader.readLine(); // read the next line
}
return stringArray;

This is not the preferred solution. Just showing that it can be done a different way
Or you can use a do...while instead of while...do.
String line;
do {
line = reader.readLine();
if (line != null) {
stringArray.add(line);
}
} while (line != null);
You can see why this isn't the preferred solution. You are doing 2 null checks where you can get away with 1.

while (true) {
String line = reader.readLine();
if (line == null) break;
stringArray.add(line);
}
return stringArray;

Java BufferedReader to String Array

I was looking through a lot of diffrent subjects here on stackoverflow but couldn't find anything helpful so far :/
So this is my problem. I am writing a filecopier. The problem occurs already at reading the file. My test docoument got 3 lines of random text. All those 3 lines should get written in a string array. The problem is that only the 2nd line of the textdocument gets written in the array and I can't figure out why. Already debugged it, but didn't get me any further.
I know there are diffrent solutions for a filecopier with diffrent classes etc. But I would really like to get it running with the classes I used here.
String[] array = new String[5];
String datei = "test.txt";
public String[] readfile() throws FileNotFoundException {
FileReader fr = new FileReader(datei);
BufferedReader bf = new BufferedReader(fr);
try {
int i=0;
//String Zeile = bf.readLine();
while(bf.readLine() != null){
array[i] = bf.readLine();
// System.out.println(array[i]); This line is for testing
i++;
}
bf.close();
} catch (IOException e) {
e.printStackTrace();
}
return array;

You're calling readLine() twice for each iteration of the loop, thereby discarding every other line. You need to capture the value returned by every call to readLine(), because each readLine() call advances the reader's position in the file.
Here's the idiomatic solution:
String line;
while((line = bf.readLine()) != null){
array[i] = line;
i++;
}

Here you read 2 lines:
while(bf.readLine() != null){
array[i] = bf.readLine();
// System.out.println(array[i]); This line is for testing
i++;
}
You have to change your Code to:
String line = null;
while((line =bf.readLine()) != null){
array[i] = line;
// System.out.println(array[i]); This line is for testing
i++;
}

The problem is here :
while(bf.readLine() != null)
readLine() reads a line and returns the same at the same time it moves to the next line.
So instead of just checking if the returned value was null also store it.
String txt = null;
while((txt = bf.readLine()) != null)
array[i++] = txt;

I think its because you are calling readLine() twice. First time in the loop, and then second time when you put it in the array. So, it reads a line at the beginning of the loop (line 1), then first line of code inside the loop (line 2 that you see)

I am use Stream.
Not a. This form only applies to reading text files.
BufferedReader bf = new BufferedReader(fr);
// ...
List<String> lines = bf.lines().collect(Collectors.toList());

Reading a file and performing functions based on the contents of the line

I'm wondering if it's possible to read a file by the line number, each with different values and make a condition where if that line contains a certain string or number specified. If it did it would, for example, take the content specified in that line into a variable?
So in a file line one has Age: 50, line 2 has Age: 23, line 3 has Age: 34. What I'm hoping for is that I look specifically at line 3 and take the number 34 and place it in a variable for use in my program.
If it is possible, how would you go about doing this?

I would say, it is not possible to directly address a specific line unless - perhaps you know the line sizes of your file, etc... to seek through the file. But you can use this to go through your file, line by line:
String line;
BufferedReader br = new BufferedReader(new FileReader(file));
while ((line = br.readLine()) != null) {
// do some cool stuff with this line.
}
br.close();

Possible duplicate: Reading a file and performing functions based on the contents of the line
You can always iterate through each line, keeping track of the line via an int or a short.
some code:
String line;
BufferedReader br = new BufferedReader(new FileReader(FILE_HERE));
int line = 0;
while ((line = br.readLine()) != null) {
line++;
if(line == 3){
//do whatever you want
}
}
br.close();
I will add that getting something from one single line while others also have identical info is bad

you can use the scanner object to read through a file. you would use the delimiter to find the info you want and a counter to keep track of the line, then put it in an arraylist or something. depending on what you want to do.
Scanner in = new Scanner(filename);
int line = 0;
in.useDelimiter("[regex of the info you are looking for]");
while in.hasNext()) {
line++
//do something
}

Reading CSV file using BufferedReader resulting in reading alternative lines

I'm trying to read a csv file from my java code. using the following piece of code:
public void readFile() throws IOException {
BufferedReader br = new BufferedReader(new FileReader(fileName));
lines = new ArrayList<String>();
String newLine;
while ((newLine = br.readLine()) != null) {
newLine = br.readLine();
System.out.println(newLine);
lines.add(newLine);
}
br.close();
}
The output I get from the above piece of code is every alternative line [2nd, 4th, 6th lines] is read and returned by the readLine() method. I'm not sure why this behavior exists. Please correct me if I am missing something while reading the csv file.

The first time you're reading the line without processing it in the while loop, then you're reading it again but this time you're processing it. readLine() method reads a line and displaces the reader-pointer to the next line in the file. Hence, every time you use this method, the pointer will be incremented by one pointing to the next line.
This:
while ((newLine = br.readLine()) != null) {
newLine = br.readLine();
System.out.println(newLine);
lines.add(newLine);
}
Should be changed to this:
while ((newLine = br.readLine()) != null) {
System.out.println(newLine);
lines.add(newLine);
}
Hence reading a line and processing it, without reading another line and then processing.

You need to remove the first line in a loop body
newLine = br.readLine();

In java 8, we can easily achieve it
InputStream is = new ByteArrayInputStream(byteArr);
BufferedReader br = new BufferedReader(new InputStreamReader(is));
List<List<String>> dataList = br.lines()
.map(k -> Arrays.asList(k.split(",")))
.collect(Collectors.toCollection(LinkedList::new));
outer list will have rows and inner list will have corresponding column values