How to read certain lines of a txt file in java? - java

I want to read only the parts i need to. For example my text file look likes these
Name Age Gender
=====================
Donald 13 Male
John 14 Non-binary
Pooh 42 Female
I only want to read the data but i don't know how because my code reads a .txt file line by line
try {
File myObj = new File("database.txt");
Scanner myReader = new Scanner(myObj);
while (myReader.hasNextLine()) { //to read each line of the file
String data = myReader.nextLine();
String [] array = data.split(" "); //store the words in the file line by line
if(array.length ==5){ // to check if data has all five parameter
people.add(new Person(array[0], array[1],array[2], Double.parseDouble(array[3]), Double.parseDouble(array[4])));
}
}
JOptionPane.showMessageDialog(null, "Successfully Read File","Javank",JOptionPane.INFORMATION_MESSAGE);
myReader.close();
} catch (FileNotFoundException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}

You can simply call myReader.nextLine() twice before entering your loop to ignore the first two lines.
Another approach you can take is to use a RandomAccessFile object instead of a Scanner to process your input. If you know how many characters are in the file before the beginning of your relevant data, you can use the RandomAccessFile object's seek method to skip to the beginning of your input, e.g. if there are 50 characters in the file before your data you can use randomAccessFile.seek(50) and then read the lines with randomAccessFile.readLine().
I would probably recommend using the first method of skipping 2 lines however because it seems more simple and robust.

Related

Can't read integer file

I'm trying to read data from a file that contains integers, but the Scanner doesn't read anything from that file.
I've tried to read the file from the Scanner :
// switch() blablabla
case POPULATION:
try {
while (sc.hasNextInt()) {
this.listePops.add(sc.nextInt());
}
} catch (Exception e) {
System.err.println("~ERREUR~ : " + e.getMessage());
}
break;
And if I try to print each sc.nextInt() to the console, it just prints a blank line and then stops.
Now when I read the same file as a String:
?652432
531345
335975
164308
141220
1094283
328278
270582
// (Rest of the data)
So, I guess it can't read the file as a list of integers since there's a question mark at the beginning, but the problem is that this question mark doesn't appear anywhere in my file, so I can't remove it. What am I supposed to do?
If the first character in the file is a question mark (?) and its original origin is unknown then it is usually the UTF-8 Byte Order Mark (BOM). This means the file was saved as UTF-8. The Microsoft Notepad application will add a BOM to the saved text file if that file was saved in UTF-8 instead of ANSI. There are also other BOM characters for UTF-16, UTF-32, etc.
Reading a text file as String doesn't look like a bad idea now. Changing the save format of the file can work to but that BOM may have actual intended purpose for another application, so, that may not be a viable option. Let's read the file as String lines (read comments in code):
// Variable to hold the value of the UTF-8 BOM:
final String UTF8_BOM = "\uFEFF";
// List to hold the Integer numbers in file.
List<Integer> listePops = new ArrayList<>();
// 'Try With Resources' used to to auto-close file and free resources.
try (Scanner reader = new Scanner(new File("data.txt"))) {
String line;
int lineCount = 0;
while (reader.hasNextLine()) {
line = reader.nextLine();
line = line.trim();
// Skip blank lines (if any):
if (line.isEmpty()) {
continue;
}
lineCount++;
/* Is this the first line and is there a BOM at the
start of this line? If so, then remove it. */
if (lineCount == 1 && line.startsWith(UTF8_BOM)) {
line = line.substring(1);
}
// Validate Line Data:
// Is the line a String representation of an Integer Number?
if (line.matches("\\d+")) {
// Yes... then convert that line to Integer and add it to the List.
listePops.add(Integer.parseInt(line));
}
// Move onto next file line...
}
}
catch (FileNotFoundException ex) {
// Do what you want with this exception (but don't ignore it):
System.err.println(ex.getMessage());
}
// Display the gathered List contents:
for (Integer ints : listePops) {
System.out.println(ints);
}

Reading data from a csv file and storing into an array, my file opens correctly however the file is being read incorrectly

String fileName = "MSFT.csv";
File file = new File(fileName);
try{
Scanner inputStream = new Scanner(file);
while(inputStream.hasNext()){
String data = inputStream.next();
System.out.println(data);
}
inputStream.close();
}
catch(FileNotFoundException e){
e.printStackTrace();
I am attempting to read from a csv file and when I run this code to make sure the file is being read correctly all of the comma separated data displays correctly with the exception of the first line. The first line from the file is being output with each word being on a different line. What am I doing wrong with my initial reading of the file?
An example of my output goes as:
Timestamp,
close,
high,
low,
open,
value,
9:30,57.515,57.57,57.47,57.515,31120
Now all of my words in this case are on the same line in the excel file, but when I run it timestamp, close, high, etc all appear on different lines so I'm not sure why it appears like this.
The Scanner hasNext is defined as follows:
hasNext() Returns true if this scanner has another token in its input.
So when you use it your are reading your csv file token by token and not line by line. Beside that using the Scanner next does the following:
next() Finds and returns the next complete token from this scanner.
And finally using System.out.println will insert a line separator after printing your data, which is why it keeps going to the next line after outputing each token.
Change your code as follows and it should work as expected:
String fileName = "MSFT.csv";
File file = new File(fileName);
try{
Scanner inputStream = new Scanner(file);
while(inputStream.hasNextLine()){
String data = inputStream.nextLine();
System.out.println(data);
}
inputStream.close();
} catch(FileNotFoundException e){
e.printStackTrace();

Read from textfile to textfield java

I have a text file which stores data about a user, from username, password and other details. In the text file, each user's data is stored in one line and separated using ",". I am trying to read from the file and list all the usernames. usernames are first one the line
In the following code, I manage to read and output, but only the last one from the text file. How can I read and output all.
try {
File f = new File("/Users/Nisham/Desktop/javapwd.txt");
Scanner sc = new Scanner(f);
while(sc.hasNextLine()){
String line = sc.nextLine();
String[] details = line.split(",");
String name = details[0];
//int age = Integer.parseInt(details[2]);
jTextArea1.setText(name);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
Each time through the while loop you reset the text to the newly read input, wiping out the previous text. You need to append the text, not set it.
You are overwriting the text in jTextArea1 in while loop
jTextArea1.setText(name);

How to read only integers from file?

I got a problem when I'm trying to read int from text file.
I'm using this kind of code
import java.util.Scanner;
import java.io.*;
File fileName =new File( "D:\\input.txt");
try {
Scanner in = new Scanner(fileName);
c = in.nextInt();
n = in.nextInt();
} catch(Exception e){
System.out.println("File not Found!!!");
}
If my text is edit like this
30
40
So it will work (meaning c=30, n=40).
But if I want to edit the text file that will be like this
c=30
n=40
My code will not work.
How can I change my code to read only the numbers and ignore the "c=" and n="
or any others chars besides the numbers?
You need to read your lines using Scanner.nextLine, split each line on =, and then convert the 2nd part to integer.
Remember to do the check - Scanner.hasNextLine before you read any line. So, you need to use a while loop to read each line.
A Simple implementation, you can extend it according to your need: -
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
String[] tokens = line.split("=");
try {
System.out.println(Integer.parseInt(tokens[1]);
} catch (NumberFormatException e) {
e.printStackTrace();
}
}
Now if you want to use those numbers later on, you can also add them in an ArrayList<Integer>.
Following the format you want to use in the input file then it would be better if you make use of java.util.Properties. You won't need to care about the parsing.
Properties props = new Properties();
props.load(new FileInputStream(new File("D:\\input.txt")));
c = Integer.parseInt(props.getProperty("c"));
n = Integer.parseInt(props.getProperty("n"));
You can read more about the simple line-oriented format.
you could read line by line(Scanner.nextLine) and check every character in the line by asking isDigit()
If your data line will always be in the same format x=12345, use a regex to get the numeric value from the line

Java - Parsing a text file with integers and strings

I have a text file with the following contents (delimiter is a single space):
1231 2134 143 wqfdfv -89 rwq f 8 qer q2
sl;akfj salfj 3 sl 123
My objective is to read the integers and strings seperately. Once I know how to parse them, I will create another output file to save them (but my question is only to know how to parse this text file).
I tried using Scanner and I am NOT able to get beyond the first inetger:
Scanner s = new Scanner (new File ("a.txt")).useDelimiter("");
while (s.hasNext()){
System.out.print(s.nextInt());}
and the output is
1231
How can I also get other integers from both the lines?
My desired outout is:
1231
2134
143
-89
8
3
123
The delimiter should be something else like at least one whitespace or more
Scanner s = new Scanner (new File ("a.txt")).useDelimiter("\\s+");
while (s.hasNext()) {
if (s.hasNextInt()) { // check if next token is an int
System.out.print(s.nextInt()); // display the found integer
} else {
s.next(); // else read the next token
}
}
and i have to admit that the solution from gotuskar is the better one in this simple case.
When reading data from file, read all as string types. Then test whether it is number by parsing it using Integer.parseInt(). If it throws an exception then it is a string, otherwise it is a number.
while (s.hasNext()) {
String str = s.next();
try {
b = Integer.parseInt(str);
} catch (NumberFormatException e) { // only catch specific exception
// its a string, do what you need to do with it here
continue;
}
// its a number
}

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