java - What does it really mean by reading file into memory all at once?

Question

I am confused with the term "Do not read file into memory all at once". For the below code, will it be correct to say that I not reading file into memory all at once but line by line?

File file = new File("C:\Users\Desktop\test.txt"); 
  
  BufferedReader br = new BufferedReader(new FileReader(file)); 
  
  String st; 
  while ((st = br.readLine()) != null) 
    System.out.println(st); 
  } 
} 

question from:https://stackoverflow.com/questions/65837816/what-does-it-really-mean-by-reading-file-into-memory-all-at-once

Answer 1

For the below code, will it be correct to say that I not reading file into memory all at once but line by line?

You cannot make any such assumptions. Since you are using a BufferedReader, all you can say with assuredness is that you are reading some of the file into a memory buffer, perhaps all of the file, but the buffer is in control, not you. And when the buffer's data has been depleted, then more of the file will be read into it, if there is still data remaining to be read.