How to Convert Space-Separated Integers from a Text File into an ArrayList in Java?

Java Text File Reading: Converting Space-Separated Values into an ArrayList

Reading data from text files and organizing it into an efficient format is often essential in programming. Let's explore how to read a text file containing space-separated integers and store them in an ArrayList using Java.

Step 1: Reading the File

To read the text file, you can employ the Files.readAllLines() method, which returns a list of string lines. Each line of the text file will be represented as a string in this list.

Step 2: Splitting the Lines

To extract the integer values from each line, we can use the split() method on each string. This method splits the string into an array of substrings based on a delimiter. For space-separated values, we would use "\s " as the delimiter, which matches one or more whitespace characters.

Step 3: Converting Strings to Integers

Each substring resulting from the split() call represents an integer. We can use the Integer.valueOf() method to convert these substrings into integer values.

Step 4: Adding Integers to the ArrayList

Finally, we can iterate over the array of integers and add each one to an ArrayList using the add() method.

Putting it All Together

Combining these steps, we arrive at the following Java code snippet:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class TextFileReader {

    public static void main(String[] args) {
        String pathToFile = "/path/to/test.txt";

        try {
            // Read the file into a list of strings
            List<string> lines = Files.readAllLines(Paths.get(pathToFile));

            // Initialize an empty ArrayList to store the integers
            List<integer> numbers = new ArrayList();

            // Iterate over each line
            for (String line : lines) {
                // Split the line into substrings
                String[] parts = line.split("\s+");

                // Convert each substring to an integer and add it to the ArrayList
                for (String part : parts) {
                    int i = Integer.valueOf(part);
                    numbers.add(i);
                }
            }

            // Print the ArrayList to demonstrate it has been populated
            System.out.println(numbers);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}</integer></string>

Note: For Java 8 and above, there is a simpler and more concise approach using the Stream API. You can find the Java 8 version in the provided answer section.

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