OutOfMemoryError: Java heap space when trying to read large file

Question

I'm trying to read large file(approximately 516mb), and it has 18 lines of text. I tried to write down the code myself and got an error in the first line of code while trying to read the file:

 try(BufferedReader br = new BufferedReader(new FileReader("test.txt"))) {
        String line;
        while ((line = br.readLine()) != null) {
            String fileContent = line;
        }
 }

Note: File exists and it's size is approximately 516mb. If there is another safer and faster method of reading from please tell me(Even if it will linebreaks). Edit: Here I tried by using Scanner, but it lasts a bit longer and then gives the same error

try(BufferedReader br = new BufferedReader(new FileReader("test.txt"))) {
    Scanner scanner = new Scanner(br);
    while(scanner.hasNext()){
        int index = Integer.parseInt(scanner.next());
        // and here do something with index
    }
}

I even splitted file into 1800 lines, but nothing got fixed

Answer 1

Using BufferedReader already help you to avoid loading the whole file into the memory. So, for further improvement, as you mentioned each number is separated by space, so instead of this:

line = br.readLine();

We can wrap the reader with a scanner,

Scanner scanner = new Scanner(br);

And extract each number in the file using scanner.next(); and store it into an integer array will also help to reduce memory usage:

int val = Integer.parseInt(scanner.next());

This will help you avoiding reading the whole sentence.

And you can also limit your buffer size for BufferedReader

BufferedReader br = new BufferedReader(new FileReader("test.txt") , 8*1024);

More information Does the Scanner class load the entire file into memory at once?