Develop Reference

Reading and splitting data from a text file

So I have a text file that looks like this...
4234
Bob
6858
Joe
I am trying to read the file with java and insert the data into an array. I want to separate the data by that empty line (space). Here is the code that I have come up with to solve the issue, but I am not quite there.
public class Main {
public static void main(String[] args) {
// This name is used when saving the file
BufferedReader input;
String inputLine;
try {
input = new BufferedReader(new FileReader("test.txt"));
while ((inputLine = input.readLine()) != null) {
System.out.println(Arrays.toString(inputLine.split(" ")));
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(1);
}
}
}
The issue that I am coming across is that the output from the code above looks something like this
[4234]
[Bob]
[]
[6858]
[Joe]
The outcome that I would like to achieve, and for the life of me can't think of how to accomplish, is
[4234, Bob]
[6858, Joe]
I feel like with many things that it is a relatively simple code change; I am just not sure what that is.

You need:
2D array
Logic to keep track of where you are in the array position
If your Line is a Number/String
This sounds like hw :) so I wont be solving it, I will just help a bit.
String[][] myData = define your 2D array;
//You need to create a consumer. This is what will take the String line, figure out where to put it into your 2D array.
Consumer<String> processLine = (line) -> {
if(StringUtils.isNumeric(line)){
//Put into array[counter][1]
}
else{
//its a String
//Put into array[counter][0]
}
};
The below try/catch, Opens a File, Reads its Lines, and goes over each one in order (forEachOrdered), ignoring all empty lines, and send it to your processLine consumer.
try (Stream<String> lines = Files.lines(Paths.get("C:/example.txt"), Charset.defaultCharset())) {
lines.filter(line -> !line.isEmpty()).forEachOrdered(processLine);
}
catch (Exception e){
//Handle Exception
}
Used Apache StringUtils http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html
IF you dont want to use any external Libs. You can probably do
Integer.parseInt(line) <-- If that throws an exception, its not a number

Your way of reading the file is not most convenient, in this case.. Scanner would have eased all this work; however, if you insist, that you want to use BufferedReader and FileReader, it's going to be a bit verbose, boilerplate and even ugly code, something like this:
public class Main {
public static void main(String[] args) {
// This name is used when saving the file
BufferedReader input;
String inputLine;
String answer = "";
try {
input = new BufferedReader(new FileReader("path\\to\\your\\test.txt"));
while ((inputLine = input.readLine()) != null) {
answer = answer + "[" + inputLine + ", ";
while ((inputLine = input.readLine()) != null && !inputLine.equals("")) {
answer += inputLine;
}
answer += "]";
System.out.println(answer);
answer = "";
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(1);
}
}
}
This code, with test.txt containing:
4234
Bob
6858
Joe
4234
John
5352
Martin
will output:
[4234, Bob]
[6858, Joe]
[4234, John]
[5352, Martin]

I don't know if it's an actual requirement for you to use arrays of strings, but the better way in the long run is to create a class.
class Person {
public String id;
public String name;
public String toString() { return String.format("[%s, %s]", id, name); }
}
(note: It's a bad idea to actually make the fields public, but this makes the code shorter. You should probably use getters and setters).
Now you can create Persons while reading the file.
List<Person> allInFile = new ArrayList<>();
try (BufferedReader reader = new BufferedReader(new FileReader("path\\to\\your\\test.txt"))) {
String line = reader.readLine();
while (line != null) {
line = line.trim();
// ignore empty lines
if (line.length() == 0) {
continue;
}
// this is an id; create a person and assign id
Person person = new Person();
person.id = line;
// read consecutive field, which is the name
person.name = reader.readLine();
// add the person to the list
allInFile.add(person);
}
}
allInFile.forEach(System.out::println);
Lots of improvements to be done on this, but the main point is to put the two data points into a class.

Try with this code:
it work only when file contains number followed by name otherwise pair would be different format
pair : [number, string]
public static void main(String[] args) {
BufferedReader input;
String inputLine;
List<String> pair = new ArrayList<String>();
List<String> list = new ArrayList<String>();
try {
input = new BufferedReader(new FileReader("Test.txt"));
while ((inputLine = input.readLine()) != null) {
if (!inputLine.isEmpty()) {
pair.add(inputLine);
}
if (pair.size() == 2) {
list.add(pair.toString());
pair.clear();
}
}
for (String s : list) {
System.out.println(s);
}
} catch (IOException e) {
System.out.println(e.getMessage());
System.exit(1);
}
}

After looking at the answers posted by my fellow Stack Overflow members I figured out that there was a very simple way of solving this issue and that was by using Scanner rather than using BufferedReader. I am not sure why I didn't think of this before, but hindsight is 2020. Anyway, the code below is what I used to solve my issue.
public static void main(String[] args) {
ArrayList<String> test = new ArrayList<>();
File file = new File("test.txt");
try {
Scanner sc = new Scanner(file);
while (sc.hasNextLine()) {
test.add(sc.next()); // The id
test.add(sc.next()); // The name
}
sc.close();
System.out.println(test.toString());
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
All this is doing is getting each line with the different data on it and is skipping the blank. From there it is adding it to an ArrayList for later processing. Remember K.I.S.S (Keep It Simple Stupid) no need to overcomplicate anything.

Java - List<String> printing \n instead of showing a line break

I have a .txt file reader, which reads individuals lines of a file and stores them in a List<String> which I then display on a JTextArea. Some of the lines contain \n, because I wanted specific breaking when displaying. However, when I do display the code, the \nare shown instead of breaking the line as they usually do.
I tried replacing the \n's with linebreaks by placing the code str.replaceAll( "\\\\n", System.lineSeperator()); in the while loop, before list.add(str); but it doesn't seem to have any effect.
To reiterate, I simply need a way to change the \n's to linebreaks. Any help would be much appreciated.
The code for the .txt reader is below.
static void parseStringArray(final String filePath, List<String> list){
try {
InputStream input = Text.class.getResourceAsStream(filePath);
BufferedReader reader = new BufferedReader(new InputStreamReader(input));
String str;
while((str = reader.readLine()) != null){
list.add(str);
}
} catch (IOException e) {
e.printStackTrace();
}
}
**Edit - I have updated the post to include a bit more code.
The List I send in as an argument is initialized before the method. It is
protected static List<String> textfiles = new ArrayList<String>();
An example of a line from the .txt file is
Welcome!\n\n If you wish to proceed, please type the password below.\nEnjoy your stay!
The code to display this text is below. (Pardon formatting)
Timer teletypeTimer = null;
public static void animateTeletype(final JTextArea displayArea)
{
final String[] s = new String[1];
s[0] = "";
final int[] i = new int[2];
i[0] = 0;
i[1] = 0;
teletypeTimer = new Timer(20, new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
if(i[0]==0)
displayArea.setText("");
s[0] = TTqueue[i[1]].substring(i[0], i[0]+1);
i[0]++;
displayArea.append(s[0]);
if(displayArea.getText().equals(TTqueue[i[1]]))
{
i[1]++;
if(TTqueue[i[1]] !=null)
{
teletypeTimer.stop();
i[0] = 0;
timerRestart(5000, teletypeTimer);
}
else
{
Arrays.fill(TTqueue, null);
complete=true;
teletypeTimer.stop();
}
}
}
});
teletypeTimer.start();
}

(Posted on behalf of the OP).
I switched replaceAll() with replace() and worked with Pshemo and Nick Vanderhoven's points. I added the line of code str = str.replace("\\n", System.lineSeparator()); as suggested by Pshemo, and that's done the trick. Cheers!

Reading textfile line by line and put in object array

I have to make an EPG app using java, but I am kind of new in programming and it's due tomorrow and it's still not working properly.
I have a question about a small part: I have to read the programs from a text file. Each line contains multiple things, the channel, the title of the program, a subtitle, a category, etcetera.
I have to make sure that I can read the separate parts of each line, but it's not really working, it's only printing the parts from the first line.
I am trying, but I can't find why it's not printing all the parts from all the lines in stead of printing only the parts from the first line. Here's the code:
BufferedReader reader = new BufferedReader(newFileReader(filepath));
while (true) {
String line = reader.readLine();
if (line == null) {
break;
}
}
String[] parts = line.split("\\|", -1);
for(int i = 0; i < parts.length; i++) {
System.out.println(parts[i]);
}
reader.close();
Does anybody know how to get all the lines in stead of only the first?
Thank you!

readLine() only reads one line, so you need to loop it, as you said.
BUT with reading to the String inside of the while loop you always overwrite that String.
You would need to declare the String above the while loop that you can access it from outside, too.
BTW, it seems that your braces for the if don't match.
Anyway, I'd fill the information into an ArrayList, look below:
List<String> list = new ArrayList<>();
String content;
// readLine() and close() may throw errors, so they require you to catch it…
try {
while ((content = reader.readLine()) != null) {
list.add(content);
}
reader.close();
} catch (IOException e) {
// This just prints the error log to the console if something goes wrong
e.printStackTrace();
}
// Now proceed with your list, e.g. retrieve first item and split
String[] parts = list.get(0).split("\\|", -1);
// You can simplify the for loop like this,
// you call this for each:
for (String s : parts) {
System.out.println(s);
}

Use apache commons lib
File file = new File("test.txt");
List<String> lines = FileUtils.readLines(file);

As ArrayList is Dynamic,try,
private static List<String> readFile(String filepath) {
String line = null;
List<String> list = new ArrayList<String>();
try {
BufferedReader reader = new BufferedReader(new FileReader(filepath));
while((line = reader.readLine()) != null){
list.add(line);
}
} catch (Exception e) {
e.printStackTrace();
}
return list;
}

Using a loop I want to find the value of a column from my CSV file java

Forgive me if this is a basic (or not very well explained) question, I am fairly new to Java and have been reading extensive material as well as trying to understand the relevant Javadoc but to no avail.
To give a brief background as to what I am trying to create, I have created a reader class which reads data in from a csv file (4 lines long) including fields such as Item ID, price, description etc. I have created a separate demo class that displays the details of this csv file (through creating an instance of my reader class) and am now trying to create a method that asks the user to input an Item ID that then displays the corresponding Item, based on the ID input by the user. The part I am stuck on is accessing specific rows/columns in a csv file and then comparing these with a given string (entered by the user which corresponds to a specific field in the csv file)
This is what I have come up with thus far:
input = new Scanner(System.in);
System.out.println("Enter a product code");
String prodC = input.next();
//Here I want to know if there is a way of accessing a field in a csv file
Any ideas would be greatly appreciated.
UPDATE
Thank you for quick responses, am currently reading through and seeing how I can try to implement the various techniques. In response to the comment asking about the file reader, this is how I have set that out:
public CatalogueReader(String filename) throws FileNotFoundException {
this.filename = filename;
this.catalogue = new Catalogue();
Scanner csvFile;
try {
csvFile = new Scanner(new File(filename));
} catch (FileNotFoundException fnf) {
throw new FileNotFoundException("File has not been found!");
}
csvFile.useDelimiter("\n");
boolean first = true;
String productCode;
double price;
String description;
double weight;
int rating;
String category;
boolean ageRestriction;
String csvRows;
while (csvFile.hasNextLine()) {
csvRows = csvFile.nextLine();
if (first) {
first = false;
continue;
}
System.out.println(csvRows);
String[] fields = csvRows.split(",");
productCode = (fields[0].trim());
price = Double.parseDouble(fields[1].trim());
description = fields[2].trim();
weight = Double.parseDouble(fields[3].trim());
rating = Integer.parseInt(fields[4].trim());
category = fields[5].trim();
ageRestriction = Boolean.parseBoolean(fields[6].trim());
catalogue.addAProduct(new Item(productCode, price, description, weight, rating, category, ageRestriction));
}
csvFile.close();
}
}

ok so for a CSV file like this:
"1.0.0.0","1.0.0.255","16777216","16777471","AU","Australia"
"1.0.1.0","1.0.3.255","16777472","16778239","CN","China"
"1.0.4.0","1.0.7.255","16778240","16779263","AU","Australia"
"1.0.8.0","1.0.15.255","16779264","16781311","CN","China"
"1.0.16.0","1.0.31.255","16781312","16785407","JP","Japan"
"1.0.32.0","1.0.63.255","16785408","16793599","CN","China"
"1.0.64.0","1.0.127.255","16793600","16809983","JP","Japan"
"1.0.128.0","1.0.255.255","16809984","16842751","TH","Thailand"
here is a sample of how to read using Java Native Libraries
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class CSVReader {
public static void main(String[] args) {
CSVReader obj = new CSVReader();
obj.run();
}
public void run() {
String csvFile = YOURFILEPATHHERE ;
BufferedReader br = null;
String line = "";
String cvsSplitBy = ",";
try {
br = new BufferedReader(new FileReader(csvFile));
while ((line = br.readLine()) != null) {
// use comma as separator
String[] country = line.split(cvsSplitBy);
System.out.println("Country [code= " + country[4]
+ " , name=" + country[5] + "]");
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
System.out.println("Done");
}
}
does this help?

If you are just doing a single look-up and then exiting then just remember the String you are looking for. As you parse the lines compare to see if you have a match and if you do then return that line.
For repeated searches that would be very inefficient though. Assuming your data set is not too large for memory you would be better off parsing the file and putting it into a Map:
Map<String, Data> dataMap = new HashMap<>();
Parse the file, putting all the lines into the map
Then the lookup just becomes:
Data d = dataMap.get(lineKey);
If d is null then there is no matching line. If it not null then you have found your line.

You can create an array list of object. An object for each line in the CSV. Then search the array object with your search criteria.
User CSVReader framework to read the csv file. Sample code (not exactly what you want)
FileInputStream fis = new FileInputStream(file);
CSVReader reader = new CSVReader(new BufferedReader( new InputStreamReader(fis, "UTF-8" )));
ArrayList<String> row = new ArrayList<String>();
ArrayList<Entry> entries = new ArrayList<Entry>();
// a line = ID, Name, Price, Description
while (!reader.isEOF()) {
reader.readFields(row);
if( row.size() >= 4)
entries.add(new Entry(row.get(0), row.get(1), row.get(2), row.get(3)));
}
System.out.println("Size : "+entries);

Unusual output from using split()

I'm reading from a file that has the following format:
name : symptoms : causes : treatments : rate : prognosis
There are a total of 21 entries but when I try to read from the file and use .split(":");, the output changes each time but is always along the lines of: [Ljava.lang.String;#614951ff. I'm guessing it's the pointer or memory address but I want the String value. I'm not getting any exceptions though so I'm not sure where I've gone wrong. The purpose of the method is to read the file and split into an array using the delimiter for the given file row selected.
public String[] readCancer(int row) {
cancers = new String[22];
FileInputStream fis;
InputStreamReader isr;
BufferedReader br = null;
String eachCancer;
String[] splitCancer = null;
int j = 0;
try {
fis = new FileInputStream(myData);
isr = new InputStreamReader(fis);
br = new BufferedReader(isr);
input = new Scanner(br);
while(input.hasNext() && j < 23) {
cancers[j++] = input.nextLine();
}
eachCancer = cancers[row].toString();
splitCancer = eachCancer.split(":");
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem with file input");
} finally {
try {
if(br != null) {
br.close();
}
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem closing the file");
}
}
return splitCancer;
}

To print the contents of array :
1) System.out.println(Arrays.deepToString(splitCancer));
2) System.out.println(Arrays.toString(splitCancer));
3) System.out.println(Arrays.asList(splitCancer));

If you want to display the string array, you should use:
System.out.println(Arrays.toString(splitCancer));
Because when you print splitCancer you'll get the address of the array and not the content of it.
Of course you can print the content in other ways:
for(String str : splitCancer) {
System.out.println(str);
}

Currently I have the following:
public String[] readCancer() {
cancers = new String[22];
split = new String[22];
FileInputStream fis;
InputStreamReader isr;
BufferedReader br = null;
String eachCancer;
int j = 0;
try {
fis = new FileInputStream(myData);
isr = new InputStreamReader(fis);
br = new BufferedReader(isr);
input = new Scanner(br);
while(input.hasNext() && j < 23) {
cancers[j] = input.nextLine().toString();
//cancers[j] = input.nextLine();
split[j] = cancers[j].split(":");
//split[j] = "blah"; this line works
j++;
}
System.out.println(Arrays.toString(split));
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem with file input");
} finally {
try {
if(br != null) {
br.close();
}
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem closing the file");
}
}
return split;
//return split[j]; does not work
}
In my while loop, I keep getting compile errors saying it requires a String but found Stirng[] for split. When I try something simpler, such as split[j] = "blah";, there are no compile errors. I can return cancers perfectly but I need to split by the : delimiter and that seems to be something I cant get my head around. When I try return split[j], then I get another compile error saying it requires a String[] but found String. I've been at this for more than an hour, read through examples in my textbook and tutorials online for using split but it still isn't working. This is the only part of my program that I'm not sure how to do.

I tried pasting the entire file but it came a horrid block of text, so here are 2 lines from it. Each line has the same format but differing lengths:
The general format of the file is name : symptoms : causes : treatment : rate : prognosis
The rate is a String since it is unknown for some diseases and when it is known, the rate is not always out of 250,000. Sometimes it is out of 1,000,000 or 100,000, etc... .
acute promyelocytic leukemia : easy bruising, rapid internal bleeding, fatigue, anemia, frequent fever, infection, blood clots : PML and RARA genes : Medications, chemotherapy : 1 in 250,000 : Good
familial cylindromatosis : numerous skin tumours, ulcers, infection, impaired eyesight, hearing, smell, balance : CYLD gene : Surgery, chemotherapy : Unknown : Unknown
My most recent code attempt is at Unusual output from using split()
The 2 arrays of cancers and split are private String[] as field variables declared outside any of the methods. The variable myData is a private File also declared as a field variable outside any of the methods. I have checked and already verified the file path is correct.
The main method that calls the method:
public static void main(String[] args) {
CancerGUI _gui = new CancerGUI();
String[] resultCancer;
resultCancer = _gui.readCancer();
//System.out.println(resultCancer);
System.out.println(Arrays.toString(resultCancer));
}
I am only calling it in the main method to test whether it correctly returns the String[]. Once it does, then I will call it in a different method that adds the data to a GUI (this part I am reasonably confident I know how to do and have examples from my instructor and textbook to follow).