Develop Reference

reading input from file until specific word is read

i am writing a java program to read a file and print output to another string variable.which is working perfectly as intended using is code.
{
String key = "";
FileReader file = new FileReader("C:/Users/raju/Desktop/input.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while (line != null) {
key += line;
line = reader.readLine();
}
System.out.println(key); //this prints contents of .txt file
}
this prints whole text in the file.But i want to only print the lines till word END is encountered in file.
example: if input.txt file contains following text : this test file END extra in
it should print only :
this test file

Just do a simple indexOf to see where it is and if it exists in the line. If the instance is found one option would be using substring to cut off everything up until the index of the keyword. For a bit more control though try using java regular expressions.
String key = "";
FileReader file = new FileReader("C:/Users/raju/Desktop/input.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while ((line = reader.readLine()) != null && line.indexOf("Keyword to look for") == -1)
key += line;
System.out.println(key);

I am not sure why it needs to be any more complicated than this:
BufferedReader re = new BufferedReader(new InputStreamReader(System.in));
while (true) {
String str = re.readLine();
if (str.equals("exit")) break;
// whatever other code.
}

You can do it in many ways. one of them is using indexOf method to specify the start index of "END" in input and then using subString method.
for more information, read documentation of String calss. HERE

This will work for your issue.
public static void main(String[] args) throws IOException {
String key = "";
FileReader file = new FileReader("/home/halil/khalil.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while (line != null) {
key += line;
line = reader.readLine();
} String output = "";
if(key.contains("END")) {
output = key.split("END")[0];
System.out.println(output);
}
}

You have to change your logic to check if the line contains "END".
If END not found in a line, add the line to key stringin your program
If yes, split that line into word array, read the line till you encounter the word "END" and append it to your key string. Consider using Stringbuilder for key.
while (line != null) {
line = reader.readLine();
if(!line.contains("END")){
key += line;
}else{
//Note that you can use split logic like below, or use java substring
String[] words = line.split("");
for(String s : words){
if(s.equals("END")){
return key;
}
key += s;
}
}
}

Java NumberFormatException Error String to Float

Taking in a list of strings and converting them to a float and storing the values. I get this error when hitting the second value I want to store. Below is the code and the text file I'm reading from:
public static void readCities() {
StringBuilder sb = new StringBuilder();
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader("C:/Users/Luke/workspace/Traveling Sales Person/Destinations/11PointDFSBFS.tsp"));
String line;
while ((line = br.readLine()) != null) {
if (sb.length() > 0) {
sb.append("\n");
}
sb.append(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null) {
br.close();
}
} catch (IOException ex) {
ex.printStackTrace();
}
}
String contents = sb.toString();
String[] parts = contents.split("NODE_COORD_SECTION");//splits into locations
String[] locations = parts[1].split(" ");
int counter = 0;
for (int i = 1; i < locations.length; i++) {
cities[counter] = new City(Float.parseFloat(locations[i+1]), Float.parseFloat(locations[i+2]));
counter++;
}
}
Code error:
Exception in thread "main" java.lang.NumberFormatException: For input string: "63.860370
2
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
at sun.misc.FloatingDecimal.parseFloat(FloatingDecimal.java:122)
at java.lang.Float.parseFloat(Float.java:451)
at TSP.readCities(TSP.java:132)
at TSP.main(TSP.java:28)

As all the commenters already said: Without the actual data it's more or less guessing, what is the problem, but with your code and the error-message some things can be said already, what you should do independly:
You read in all the lines and put them into a StringBuilder including a new line-break. Later on you do splits, but you never remove this line-break, so it is going to end up in the data you try to parse as float. This will lead to a parsing error, because spaces and other whitespaces are not removed. The easiest way to do this without changing too much in your code is by trimming the values:
cities[counter] = new City(Float.parseFloat(locations[i+1].trim()), Float.parseFloat(locations[i+2],trim()));
BTW: What's the reason for creating a new variable counter that is essentially i-1 and using i+1 and i+2 later on? Makes reading your code a bit harder, because you expect some additional logic where entries are skipped which isn't there.
According to the error-message the problem is a leading quotation mark and a newline. You can't say if that error occurred for the first or the second of the two values that are parsed and without the original line(s) of the input file it's hard to say, what is going on, but maybe I gave you enough hints to allow you to progress with your code.
If not we need more informations, especially the line(s) that produce this error, so analysing your code becomes possible.

How can I read a specifc column from a text file and calculate the average of this column?

I am a little stuck with a java exercise I am currently working on. I have a text file in this format:
Quio Kla,2221,3.6
Wow Pow,3332,9.3
Zou Tou,5556,9.7
Flo Po,8766,8.1
Andy Candy,3339,6.8
I now want to calculate the average of the whole third column, but I have to extract the data first I believe and store it in an array. I was able to read all the data with a buffered reader and print out the entire file in console, but that did not get me closer to get it into an array. Any suggestions on how I can read in a specific column of a text file with a buffered readder into an array would be highly appreciated.
Thank you very much in advance.

You can split your text file by using this portion of code:
BufferedReader in = null;
try {
in = new BufferedReader(new FileReader("textfile.txt"));
String read = null;
while ((read = in.readLine()) != null) {
String[] splited = read.split(",");
for (String part : splited) {
System.out.println(part);
}
}
} catch (IOException e) {
System.out.println("There was a problem: " + e);
e.printStackTrace();
} finally {
try {
in.close();
} catch (Exception e) {
}
}
And then you'll have all your columns in the array part.

It`s definitely not the best solution, but should be sufficient for you
BufferedReader input = new BufferedReader(new FileReader("/file"));
int numOfColumn = 2;
String line = "";
ArrayList<Integer>lines = new ArrayList<>();
while ((line = input.readLine()) != null) {
lines.add(Integer.valueOf(line.split(",")[numOfColumn-1]));
}
long sum =0L;
for(int j:lines){
sum+=j;
}
int avg = (int)sum/lines.size();

I'm going to assume each data set is separated by newline characters in your text file.
ArrayList<Double> thirdColumn = new ArrayList<>();
BufferedReader in = null;
String line=null;
//initialize your reader here
while ((line = in.readLine())!=null){
String[] split = line.split(",");
if (split.length>2)
thirdColumn.add(Double.parseDouble(split[2]));
}
By the end of the while loop, you should have the thirdColumn ArrayList ready and populated with the required data.
The assumption is made that your data set has the following standard format.
String,Integer,Double
So naturally a split by a comma should give a String array of length 3, Where the String at index 2 contains your third column data.

converting one line string into individual integers

if i have this line in a file: 2 18 4 3
and i want to read it as individual integers, how could i?
i'm using bufferreader:
BufferedReader(new FileReader("mp1.data.txt"));
i have tried to use:
BufferedReader(new RandomAccessFile("mp1.data.txt"));
so i can use the method
.readCahr();
but i got an error
if i use
int w = in.read();
it will read the ASCII, and i want it as it is(in dec.)
i was thinking to read it as a string first, but then could i separate each number?
also i was thinking to let each number in a line, but the file i have is long with numbers

Consider using a Scanner:
Scanner scan = new Scanner(new File("mp1.data.txt"));
You can then use scan.nextInt() (which returns an int, not a String) so long as scan.hasNextInt().
No need for that ugly splitting and parsing :)
However, note that this approach will continue reading integers past the first line (if that's not what you want, you should probably follow the suggestions outlined in the other answers for reading and handling only a single line).
Furthermore, hasNextInt() will return false as soon as a non-integer is encountered in the file. If you require a way to detect and handle invalid data, you should again consider the other answers.

It's important to approach larger problems in software engineering by breaking them into smaller ones. In this case, you've got three tasks:
Read a line from the file
Break it into individual parts (still strings)
Convert each part into an integer
Java makes each of these simple:
Use BufferedReader.readLine() to read the line as a string first
It looks like the splitting is as simple as splitting by a space with String.split():
String[] bits = line.split(" ");
If that's not good enough, you can use a more complicated regular expression in the split call.
Parse each part using Integer.parseInt().
Another option for the splitting part is to use the Splitter class from Guava. Personally I prefer that, but it's a matter of taste.

You can split() the String and then use the Integer.parseInt() method in order to convert all the elements to Integer objects.
try {
BufferedReader br = new BufferedReader(new FileReader("mp1.data.txt"));
String line = null;
while ((line = br.readLine()) != null) {
String[] split = line.split("\\s");
for (String element : split) {
Integer parsedInteger = Integer.parseInt(element);
System.out.println(parsedInteger);
}
}
}
catch (IOException e) {
System.err.println("Error: " + e);
}

Once you read the line using BufferedReader, you can use String.split(regex) method to split the string by space ("\\s").
for(String s : "2 18 4 3".split("\\s")) {
int i = Integer.parseInt(s);
System.out.println(i);
}

If you use Java 7+, you can use this utility method:
List<String> lines = Files.readAllLines(file, Charset.forName("UTF-8"));
for (String line: lines) {
String[] numbers = line.split("\\s+");
int firstNumber = Integer.parseInt(numbers[0]);
//etc
}

Try this;
try{
// Open the file that is the first
FileInputStream fstream = new FileInputStream("textfile.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
String strLine;
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
//split line by whitespace
String[] ints = strLine.split(" ");
int[] integers = new int[ints.length];
// to convert from string to integers - Integer.parseInt ("123")
for ( int i = 0; i < ints.length; i++) {
integers[i] = Integer.parseInt(ints[i]);
}
// now do what you want with your integer
// ...
}
in.close();
} catch (Exception e) {//Catch exception if any
System.err.println("Error: " + e.getMessage());
}

How can I recognize a special delimiter string when reading from a file of strings?

I want to read strings from a file. When a certain string (><) is found, I want to start reading integers instead, and convert them to binary strings.
My program is reading the strings in and saving them in an ArrayList successfully, but
it does not recognise the >< symbol and therefore the reading of the binary strings is not successful.
The Code
try {
FileInputStream fstream = new FileInputStream(fc.getSelectedFile().getPath());
// Get the object of DataInputStream
DataInputStream ino = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(ino));
String ln;
String str, next;
int line, c =0;
while ((ln = br.readLine()) != null) {
character = ln;
System.out.println(character);
iname.add(ln); // arraylist that holds the strings
if (iname.get(c).equals("><")) {
break; // break and moves
// on with the following while loop to start reading binary strings instead.
}
c++;
}
String s = "";
// System.out.println("SEQUENCE of bytes");
while ((line = ino.read()) != -1) {
String temp = Integer.toString(line, 2);
arrayl.add(temp);
System.out.println("telise? oxii");
System.out.println(line);
}
ino.close();
} catch (Exception exc) { }
The file I'm trying to read is for example:
T
E
a
v
X
L
A
.
x
"><"
sequence of bytes.
Where the last part is saved as bytes and in the textfile appears like that. no worries this bit works. all the strings are saved in a new line.

< is two characters and iname.get(c) is only one character.
What u should do is test if ln equals > and then another test if the next character equals < . If both test pass then break out of the loop.
you will have to becarefull

Use a Scanner. It allows you to specify a delimiter, and has methods for reading input tokens as String or int.

Could you not do something like:
while ((ln = br.readLine()) != null){
character=ln;
System.out.println(character);
//
// Look for magic characters >< and stop reading if found
//
if (character.indexOf("><") >= 0) {
break;
}
iname.add(ln);
}
This would work if you didn't want to add the magic symbol to your ArrayList. Your code sample is incomplete - if you're still having trouble you'd need to post the whole class.