Question

I have a log file that I am reading to a string

public static String read (String path) throws IOException {
   StringBuilder sb = new StringBuilder();
   FileInputStream fs = new FileInputStream(path);
   InputStream in = new BufferedInputStream(fs);

   int r;
   while ((r = in.read()) != -1) {
       sb.append((char)r);
   }

   fs.close();
   in.close();

   return sb.toString();
}

Then I have a parser that iterates over the entire string once

void parse () {
   String con = read("log.txt");
   for (int i = 0; i < con.length; i++) {
       /* parsing action */
   }
}

This is hugely a waste of cpu cycles. I loop over all the content in Read. Then I loop over all the content in Parse. I could just place the /* parsing action */ under the while loop in the Read method, which would be find but I don’t want to copy the same code all over the place.

How can I parse the file in one iteration over the contents and still have separate methods for parsing and reading?

In C# I understand there is some sort of yield return thing, but I’m locked with Java.

What are my options in Java?

Answer 1

This is hugely a waste of cpu cycles. I loop over all the content in Read. Then I loop over all the content in Parse. I could just place the /* parsing action */ under the while loop in the Read method, which would be find but I don’t want to copy the same code all over the place.

It’s worse than just a huge waste of cpu cycles. It’s a huge waste of memory to read the entire file into a string, if you’re only going to use it once and the use is looking at one character at a time moving forward, as your code indicates. And if your file is large, you’ll exhaust memory.

You should parse as you read, and never have the entire file loaded into memory at once.

If the parsing action needs to be called from more than one place, make it a function and call it rather than copying the same code all over the place. Copying a single-line function call is fine.