Develop Reference

Reading a text file into multiple arrays in Java

I'm currently working on a program that reads in a preset text file and then manipulates the data in various ways. I've got the data manipulation to work with some dummy data but I still need to get the text file read in correctly.
The test file looks like this for 120 lines:
Aberdeen,Scotland,57,9,N,2,9,W,5:00,p.m. Adelaide,Australia,34,55,S,138,36,E,2:30,a.m. Algiers,Algeria,36,50,N,3,0,E,6:00,p.m.(etc etc)
So each of these needs to be read into its own array, in order String[] CityName,String[] Country,int[] LatDeg,int[] LatMin,String[] NorthSouth,int[] LongDeg,int LongMin,String[] EastWest,int[] Time.String[] AMPM
So the problem is that while I'm reasonably comfortable with buffered readers, designing this particular function has proven difficult. In fact, I've been drawing a blank for the past few hours. It seems like it would need multiple loops and counters but I can't figure out the precisely how.

I am assuming that you have one city per line type of file structure. If it is not, it will require a bit of tweaking in the following solution:
I will do the following way if I am more comfortable with BufferReader as you say:
List<List<String>> addresses = new ArrayList<List<String>>();
try(BufferedReader br = new BufferedReader(new FileReader(file))) {
for(String line; (line = br.readLine()) != null; ) {
addresses.add(line.split(","));
}
}
Later, let's say you want to retrieve the country information of say 'Adelaid', you can try the following:
for (List<String> cityInfo : addresses) {
if("Adelaid".equals(cityInfo.get(0)) {
country = cityInfo.get(1);
}
}

Instead of creating different arrays (like String[] CityName,String[] Country, etc.,), try using a Domain Object.
Here, you can have a Domain object or Custom class Location with attributes
public class Location
{
private String cityName;
private String country;
private String latDeg;
etc
getters();
setters();
}`
Then you can write a file reader, each line item in the file will be a Location. So result will have
Location[] locations;
or
List locations;`

To carry out this task I should think the first thing you want to do is establish how many lines of data actually exist within the data file. You say it is 120 lines but what if it happens that it will be more or less? We would want to know exactly what it is so as to properly initialize all our different Arrays. We can use a simple method to accomplish this, let's call it the getFileLinesCount() method which will ulitmately return a Integer value that would be the number of text lines the data file holds:
private int getFileLinesCount(final String filePath) {
int lines = 0;
try{
File file =new File(filePath);
if(file.exists()){
FileReader fr = new FileReader(file);
try (LineNumberReader lnr = new LineNumberReader(fr)) {
while (lnr.readLine() != null){ lines++; }
}
}
else {
throw new IllegalArgumentException("GetFileLinesCount() Method Error!\n"
+ "The supplied file path does not exist!\n(" + filePath + ")");
}
}
catch(IOException e){ e.printStackTrace(); }
return lines;
}
Place this method somewhere within your main class. Now you need to Declare and initialize all your Arrays:
String filePath = "C:\\My Files\\MyDataFile.txt";
int lines = getFileLinesCount(filePath);
String[] CityName = new String[lines];
String[] Country = new String[lines];
int[] LatDeg = new int[lines];
int[] LatMin = new int[lines];
String[] NorthSouth = new String[lines];
int[] LongDeg = new int[lines];
int[] LongMin = new int[lines];
String[] EastWest = new String[lines];
int[] Time = new int[lines];
String[] AMPM = new String[lines];
Now to fill up all those Arrays:
public static void main(String args[]) {
loadUpArrays();
// Do whatever you want to do
// with all those Arrays.....
}
private void loadUpArrays() {
// Read in the data file.
try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
String sCurrentLine;
int x = 0;
// Read in one line at a time and Fill the Arrays...
while ((sCurrentLine = br.readLine()) != null) {
// Split each line read into an array upon itself.
String[] fileLine = sCurrentLine.split(",");
// Fill our required Arrays...
CityName[x] = fileLine[0];
Country[x] = fileLine[1];
LatDeg[x] = Integer.parseInt(fileLine[2]);
LatMin[x] = Integer.parseInt(fileLine[3]);
NorthSouth[x] = fileLine[4];
LongDeg[x] = Integer.parseInt(fileLine[5]);
LongMin[x] = Integer.parseInt(fileLine[6]);
EastWest[x] = fileLine[7];
Time[x] = Integer.parseInt(fileLine[8]);
AMPM[x] = fileLine[9];
x++;
}
br.close();
}
catch (IOException ex) { ex.printStackTrace(); }
}
Now, I haven't tested this, I just quickly punched it out but I think you can get the jest of it.
EDIT:
As #Mad Physicist has so graciously pointed out within his comment below, a List can be used to eliminate the need to count file lines therefore eliminating the need to read the data file twice. All the file lines can be placed into the List and the number of valid file lines can be determined by the size of the List. Filling of your desired arrays can now also be achieved by iterating through the List elements and processing the data accordingly. Everything can be achieved with a single method we'll call fillArrays(). Your Arrays declaration will be a little different however:
String[] CityName;
String[] Country;
int[] LatDeg;
int[] LatMin;
String[] NorthSouth;
int[] LongDeg;
int[] LongMin;
String[] EastWest;
String[] Time;
String[] AMPM;
public static void main(String args[]) {
fillArrays("C:\\My Files\\MyDataFile.txt");
// Whatever you want to do with all
// those Arrays...
}
private void fillArrays(final String filePath) {
List<String> fileLinesList = new ArrayList<>();
try{
File file = new File(filePath);
if(file.exists()){
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String strg;
while((strg = br.readLine()) != null){
// Make sure there is no blank line. If not
// then add line to List.
if (!strg.equals("")) { fileLinesList.add(strg); }
}
br.close();
}
}
else {
throw new IllegalArgumentException("GetFileLinesCount() Method Error!\n"
+ "The supplied file path does not exist!\n(" + filePath + ")");
}
// Initialize all the Arrays...
int lines = fileLinesList.size();
CityName = new String[lines];
Country = new String[lines];
LatDeg = new int[lines];
LatMin = new int[lines];
NorthSouth = new String[lines];
LongDeg = new int[lines];
LongMin = new int[lines];
EastWest = new String[lines];
Time = new String[lines];
AMPM = new String[lines];
// Fill all the Arrays...
for (int i = 0; i < fileLinesList.size(); i++) {
String[] lineArray = fileLinesList.get(i).split(",");
CityName[i] = lineArray[0];
Country[i] = lineArray[1];
LatDeg[i] = Integer.parseInt(lineArray[2]);
LatMin[i] = Integer.parseInt(lineArray[3]);
NorthSouth[i] = lineArray[4];
LongDeg[i] = Integer.parseInt(lineArray[5]);
LongMin[i] = Integer.parseInt(lineArray[6]);
EastWest[i] = lineArray[7];
Time[i] = lineArray[8];
AMPM[i] = lineArray[9];
}
}
catch(IOException e){ e.printStackTrace(); }
}
On another note...your Time Array can not be Integer since in data, what is considered the time contains a colon (:) which is a alpha character therefore (in case you haven't noticed) I have changed its declaration to String[]

How to go to a new line while writing text to a RandomAccessFile in java?

I am trying to create a program where the user is able to create a database and add records to it. I am using random access files and with my current code I am able to write on the file. However, if there are other records on the file, I want the new record that the user adds to be appended at the end of the file, on a new line. Right now, it is appended at the end of the file but on the same line as the last record before it. Could you please help me alter my code to do what I am requesting.
Here is the code of enterData().
public static void enterData(String fileName) {
String temp = " ";
try {
RandomAccessFile OUT = new RandomAccessFile(fileName, "rw");
long fileSize = OUT.length();
System.out.print("Id: ");
try {
Id = Integer.parseInt(reader.readLine());
}catch (IOException e) {}
System.out.print("Experience: ");
try{
experience = Integer.parseInt(reader.readLine());
}
catch(IOException e){}
System.out.print("Wage: ");
try {
wage = Integer.parseInt(reader.readLine());
} catch (IOException e) {}
System.out.print("Industry: ");
industry = reader.readLine();
for (int i = 0; i<100 - industry.length(); i++){
StringBuilder sb = new StringBuilder();
sb.append(" ");
sb.append(industry);
industry = sb.toString();
}
FilePointerPosition = Id;
OUT.seek(fileSize);
String formatted = String.format("%20s%20s%20s%40s", Id, experience, wage, industry);
OUT.writeUTF(formatted);
OUT.close();
} catch (IOException e) {}
}

To write the next line of text in the file in a new line, you can simply append a newline character at the end of every record. For this, you can format the String variable formatted by including a "\n" in the end of the format specification.
String formatted = String.format("%20s%20s%20s%40s\n",
Id, experience, wage, industry);
//notice the "\n" in the end of the String format
OUT.writeUTF(formatted);
This will take the cursor in the file to a new line after writing the contents of formatted just as the System.out.println() method takes the cursor to a new line on the VDU after flashing the output.

Editing existing txt file in java

I have class Account which have username, fullName, password, id and points.
All accounts are saved in a file.I have many accounts in my file, not just one. This is example of one account in text file.
Miljan9602 Rakita Miljan miljan123 1463433398614 0.0
username, full name, password, id and points
Now, for example if i want to change points for my username. First thing i would do is go through all lines in file and compare all usernames, if i find equal username. I would change point's. This is my idea how to do it. Just dont know how to edit it in file.
public void edit(String username, double points)
{
File f = new File("Accounts.txt");
// file doesnt exist, return from method
if(!f.exists())
return;
Scanner sc = null;
try
{
sc = new Scanner(f);
while(sc.hasNextLine())
{
String line = sc.nextLine(); // Take whole line
String split[] = line.split(" "); // Split it so i can check username
if(split[0].equals(username))
{
String change = Double.toString(points); // Make string from double
split[5] = change; // on fifth index are points
/* My question is now how to edit file and to replace my new points
* with old points ?
* Miljan9602 Rakita Miljan miljan123 1463433398614 0.0 <- Need to change this 0.0 with split[4];
*/
}
}
}catch(Exception e)
{
e.printStackTrace();
}finally{
// finally will always close file
sc.close();
}

You could use the Apache's Commons IO library. Everything you'll need, and more, can be found there. Also, here is the GitHub mirror of Commons IO. Worth a look through.

{
File f = new File("Accounts.txt");
FileWriter fw = new FileWriter(f);
// file doesnt exist, return from method
if(!f.exists())
return;
Scanner sc = null;
try
{
sc = new Scanner(f);
while(sc.hasNextLine())
{
String line = sc.nextLine(); // Take whole line
String split[] = line.split(" "); // Split it so i can check username
if(split[0].equals(username))
{
String change = Double.toString(points); // Make string from double
split[5] = change; // on fifth index are points
/* My question is now how to edit file and to replace my new points
* with old points ?
* Miljan9602 Rakita Miljan miljan123 1463433398614 0.0 <- Need to change this 0.0 with split[4];
*/
for(int i = 0; i < spit.length(); i++{
fw.write(split[i] + " ");
}
System.getProperty("line.separator");
}
}
}catch(Exception e)
{
e.printStackTrace();
}finally{
// finally will always close file
sc.close();
fw.close();
}
This should work

As one has to write the entire read text back to the file system, use Files.readAllLines().
Path path = Paths.get(".../Accounts.txt");
Charset charset = StandardCharsets.UTF_8;
List<String> lines = new ArrayList<>();
if (Files.exists()) {
Files.readAllLines(path, charset);
for (int i = 0; i < lines.size(); ++i) {
String split[] = lines.get(i).split(" ");
if (split[0].equals(username)) {
String change = String.valueOf(points);
split[5] = change; // on fifth index are points
StringBuilder sb = new StringBuilder();
for (String value : split) {
if (sb.length() != 0) {
sb.append(' ');
}
sb.append(value);
}
lines.set(i, sb.toString()); // Changes the line.
Files.write(path, lines, charset);
break; // leave loop
}
}
}
More explained
To alter a single line of a text file, one in principle has to load the entire text and after altering the line, safe it entirely.
The reason is that the file can shrink or grow, depending on the line changes.
Even with some twists this is not optimal.
Files.readAllLines is a nice method for that. One might also change the format:
Fixed length records (lines) allow a RandomAccessFile. However a text risks being manually edited so the file gets corrupted, and one also has limited field lengths.
The .properties format allows access with the Properties class. Requirement is a key, and a format key = value. Also the text has some escaping (\).
One could keep Accounts.txt in core, say in a class Accounts, representing all as a Map from user name to Account.
class Account {
public final String userName; // Unmodifiable key
public String password;
...
}
class Accounts {
private Map<String, Account> accountsByUserName = new HashMap<>();
public void loadAccounts() throws IOException { ... }
public void saveAccounts() throws IOException { ... }
public Optional<Account> getAccountByUserName(String userName) { ... }
public void deleteAccountByUserName(String userName) { ... }
public void createAccount(Account account) throws AlreadyExistsException { ... }
}

How to load text data into a table using Java

I have a text data like
name = abc
id = 123
Place = xyz
Details = some texts with two line
name = aaa
id = 54657
Place = dfd
Details = some texts with some lines
I need to place them in a table or csv and my output should look like
name id Place Details
abc 123 xyz Some texts
dfd 54657 dfd Some texts
How can I do this with java?

Code for the CSV version :) It reads the input file and create a CSV in the format you asked for:
try {
BufferedReader sc = new BufferedReader(new FileReader("input2.txt"));
ArrayList<String> name = new ArrayList<>();
ArrayList<String> id = new ArrayList<>();
ArrayList<String> place = new ArrayList<>();
ArrayList<String> details = new ArrayList<>();
String line = null;
while ((line = sc.readLine()) !=null) {
if (!line.trim().equals("")) {
System.out.println(line);
if (line.toLowerCase().contains("name")) {
name.add(line.split("=")[1].trim());
}
if (line.toLowerCase().contains("id")) {
id.add(line.split("=")[1].trim());
}
if (line.toLowerCase().contains("location")) {
place.add(line.split("=")[1].trim());
}
if (line.toLowerCase().contains("details")) {
details.add(line.split("=")[1].trim());
}
}
}
PrintWriter pr = new PrintWriter(new File("out.csv"));
pr.println("name;id;Place;Details;");
for (int i = 0; i < name.size(); i++) {
pr.println(name.get(i) + ";" + id.get(i) + ";" + place.get(i) + ";" + details.get(i) + ";");
}
pr.close();
} catch (Exception e) {
e.printStackTrace();
}
Sample file content it processes:
name = abinhav
Location =Bangalore
Id =613636064725610496
Details = infoodnetwork: Q2 is up. You can still join the Megakitchens in India contest and grab some exciting vouchers. RT if you are enjoying…
name = Mathi
Location =Chennai
Id =613636066474508289
Details = i am the drifter Of course they can, but the BBC needs a daily negative story on India.

Reading from text file and writing to csv(comma seperated values) can be achieved using java io.
your logic should once write the headers to a text file with separator as comma and then read the corresponding values from the text may be use split("=") and append to the file with comma separator. You can create new files write the values and save the file with csv extension
try {
BufferedReader bReader = new BufferedReader(new FileReader("input file"));
String line = "";
while ((line = bReader.readLine()) != null) {
String[] strArray = line.split("=");
// write this to file
System.out.println( strArray[1]);
}
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

Parse the text file with a Scanner (doc here)
Create a DefaultTableModel (doc here). DefaultTableModel model = new DefaultTableModel(data, new String[]{"name","id","Place","Details"});, where data is a 2D String array with your data.
Create a JTable (doc here) with the model you just created. JTable table = new JTable(model);
Add the table to a JPanel, or JFrame, with a JScrollPane (if needed): panel.add(new JScrollPane(table));.

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);