How to Read a File into an ArrayList in Java?

In Java, an ArrayList is a resizable array, which is implemented as part of the Java Collections Framework. It is a dynamic data structure that can hold any type of objects, including primitive types such as integers and characters.

As per the problem statement we have to read a file into an ArrayList. First and foremost we will take the path of the file as input and then we will apply different method to read the file.

Let's start!

For instance

Suppose the input file is “myfile.txt”.

After reading the content of the file, the result will be:

The contents of the file are: [Hello everyone, I am a coder.]

Algorithm

Step-1: Create the instance of ArrayList.

Step-2: Declare and initialize the file path.

Step-3: Read the content of the file.

Step-4: Print the result.

Multiple Approaches

We have provided the solution in different approaches.

• By Using FileReader and BufferReader

• By Using Scanner

Let's see the program along with its output one by one.

Note: This program will not work in any online Java compiler as it can not access local file paths from online compilers.

Approach-1: By Using FileReader and BufferReader

In this approach, path of file is taken as input by FileReader and then it is read line by line using BufferReader.

Example

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;

public class Main
{
   //main method
   public static void main(String[] args) 
   {
      //instance of ArrayList
      ArrayList<String> lines = new ArrayList<>();
      //try & catch block to handle exception
      try {
         //taking the file path as input using FileReader
         FileReader fileReader = new FileReader("C:/Users/ Desktop/ 
Program/myfile.txt");
         
         //reading the content of the file using BufferedReader
         BufferedReader bufferedReader = new BufferedReader(fileReader);
         String line;
         
         //storing the content of the file in String
         while ((line = bufferedReader.readLine()) != null) {
            lines.add(line);
         }
         bufferedReader.close();
         fileReader.close();
      } catch (IOException e) {
         System.out.println("An error occurred while reading the file.");
         e.printStackTrace();
      }
      //print the result
      System.out.println("The contents of the file are: " + lines);
   }
}

Output

The contents of the file are: [Hello everyone, I am a coder.] 

Approach-2: By Using User Defined Method

In this approach, path of file is taken as input by File and then it is read line by line using Scanner.

Example

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class Main
{
   //main method
   public static void main(String[] args) 
   {
      //instance of ArrayList
      ArrayList<String> lines = new ArrayList<>();
      try 
      {
         //taking the file path as input using File
         File file = new File("example.txt");
         
         //reading the content of the file using Scanner
         Scanner scanner = new Scanner(file);
         while (scanner.hasNextLine()) {
            
            //storing the content of the file in String
            String line = scanner.nextLine();
            lines.add(line);
         }
      
         scanner.close();
      }
      catch (FileNotFoundException e)
      {
         System.out.println("An error occurred while reading the file.");
         e.printStackTrace();
      }
      
      //print the result
      System.out.println("The contents of the file are: " + lines);
   }
}

Output

The contents of the file are: [Hello Users, Let's code.]

In this article, we explored different approaches to read a file into an ArrayList by using Java programming language.