Why is BufferedReader read() much slower than readLine()?

Question

I need to read a file one character at a time and I\'m using the read() method from BufferedReader. *

I found that read() is a

Answer 1

Java JIT optimizes away empty loop bodies, so your loops actually look like this:

while((c = fa.read()) != -1);

and

while((line = fa.readLine()) != null);

I suggest you read up on benchmarking here and the optimization of the loops here.

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As to why the time taken differs:

• Reason one (This only applies if the bodies of the loops contain code): In the first example, you're doing one operation per line, in the second, you're doing one per character. This this adds up the more lines/characters you have.

  while((c = fa.read()) != -1){
      //One operation per character.
  }
  
  while((line = fa.readLine()) != null){
      //One operation per line.
  }
  

• Reason two: In the class BufferedReader, the method readLine() doesn't use read() behind the scenes - it uses its own code. The method readLine() does less operations per character to read a line, than it would take to read a line with the read() method - this is why readLine() is faster at reading an entire file.

• Reason three: It takes more iterations to read each character, than it does to read each line (unless each character is on a new line); read() is called more times than readLine().