How to Open a Txt File and Read Numbers in Java

How to open a txt file and read numbers in Java

Read file, parse each line into an integer and store into a list:

List<Integer> list = new ArrayList<Integer>();
File file = new File("file.txt");
BufferedReader reader = null;

try {
    reader = new BufferedReader(new FileReader(file));
    String text = null;

    while ((text = reader.readLine()) != null) {
        list.add(Integer.parseInt(text));
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
} finally {
    try {
        if (reader != null) {
            reader.close();
        }
    } catch (IOException e) {
    }
}

//print out the list
System.out.println(list);

How to read integer values from text file

You might want to do something like this (if you're using java 5 and more)

Scanner scanner = new Scanner(new File("tall.txt"));
int [] tall = new int [100];
int i = 0;
while(scanner.hasNextInt())
{
     tall[i++] = scanner.nextInt();
}

Via Julian Grenier from Reading Integers From A File In An Array

Find Integers and float numbers in txt file

You can do it with the following easy steps:

1. When you read a line, split it on whitespace and get an array of tokens.
2. While processing each token,
   
   • Trim any leading and trailing whitespace and then replace , with .
   • First check if the token can be parsed into an int. If yes, write it into outInt (the writer for integers). Otherwise, check if the token can be parsed into float. If yes, write it into outFloat (the writer for floats). Otherwise, ignore it.

Demo:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws FileNotFoundException, IOException {
        BufferedReader in = new BufferedReader(new FileReader("t.txt"));
        BufferedWriter outInt = new BufferedWriter(new FileWriter("t2.txt"));
        BufferedWriter outFloat = new BufferedWriter(new FileWriter("t3.txt"));
        String line = "";

        while ((line = in.readLine()) != null) {// Read until EOF is reached
            // Split the line on whitespace and get an array of tokens
            String[] tokens = line.split("\\s+");

            // Process each token
            for (String s : tokens) {
                // Trim any leading and trailing whitespace and then replace , with .
                s = s.trim().replace(',', '.');

                // First check if the token can be parsed into an int
                try {
                    Integer.parseInt(s);
                    // If yes, write it into outInt
                    outInt.write(s + " ");
                } catch (NumberFormatException e) {
                    // Otherwise, check if token can be parsed into float
                    try {
                        Float.parseFloat(s);
                        // If yes, write it into outFloat
                        outFloat.write(s + " ");
                    } catch (NumberFormatException ex) {
                        // Otherwise, ignore it
                    }
                }
            }
        }

        in.close();
        outInt.close();
        outFloat.close();
    }
}

Read Data From Text File And Sum Numbers

You are calling textfile.nextInt() twice in the loop. Try:

static void filereader(Scanner textfile)     
{         
    int i = 0;         
    int sum = 0;          
    while(i <= 19)         
    {       
        int nextInt = textfile.nextInt();          

        System.out.println(nextInt);             
        sum = sum + nextInt;
        i++;         
    }     
}

Read one number per line from file Java

Here is a simple example of how to read the coordinates from a file called input.txt and parse them into integer variables x and y:

    Stream<String> lines = Files.lines(Paths.get("input.txt"));
    lines.forEach(
            line -> {
                String[] split = line.split(" ");

                int x = Integer.parseInt(split[0]);
                int y = Integer.parseInt(split[1]);

                System.out.println("x = " + x);
                System.out.println("y = " + y);
            }
    );

Or without using Files.lines():

    BufferedReader reader = new BufferedReader(new FileReader("input.txt"));
    String line = reader.readLine();
    while (line != null) {

        String[] split = line.split(" ");

        int x = Integer.parseInt(split[0]);
        int y = Integer.parseInt(split[1]);

        System.out.println("x = " + x);
        System.out.println("y = " + y);

        // read next line
        line = reader.readLine();
    }
    reader.close();

Reading only integers from text file and adding them

You are almost there. Make a sum to add up the numbers, and add continue to skip to the next line on error:

int sum = 0;
boolean isGood = true;
for(String str : words) {
    try {
        sum += Integer.parseInt(str);
    } catch (NumberFormatException nfe) {
        // If any of the items fails to parse, skip the entire line
        isGood = false;
        continue;
    };
}
if (isGood) {
    // If everything parsed, print the sum
    System.out.println(sum);
}

Java - How to read a text file with Int's and Strings in the same line

Try something like this:

String line = "";
String[] tokens;
int number;
String name;

while((line = reader.readLine()) != null)
{
    tokens = line.split(" ");

    // Use the following if you would rather split on whitespace for tab separated data
    // tokens = line.split("\\s+");

    number = Integer.parseInt(tokens[0]);
    name = tokens[1];

    System.out.println("Fruit number " + number + " is a " + name + "."
}

Read up on the String.split() method.

Reading a plain text file in Java

ASCII is a TEXT file so you would use Readers for reading. Java also supports reading from a binary file using InputStreams. If the files being read are huge then you would want to use a BufferedReader on top of a FileReader to improve read performance.

Go through this article on how to use a Reader

I'd also recommend you download and read this wonderful (yet free) book called Thinking In Java

In Java 7:

new String(Files.readAllBytes(...))

(docs)
or

Files.readAllLines(...)

(docs)

In Java 8:

Files.lines(..).forEach(...)

(docs)

---

Related Topics