Question

In every Java implementation I see of reading from a file, I almost always see a file reader used to read line by line. My thought would be that this would be terribly inefficient because it requires a system call per line.

What I’d been doing instead is to use an input stream and grab the bytes directly. In my experiments, this is significantly faster. My test was a 1MB file.

    //Stream method
    try {
        Long startTime = new Date().getTime();

        InputStream is = new FileInputStream("test");
        byte[] b = new byte[is.available()];
        is.read(b);
        String text = new String(b);
        //System.out.println(text);

        Long endTime = new Date().getTime();
        System.out.println("Text length: " + text.length() + ", Total time: " + (endTime - startTime));

    }
    catch (Exception e) {
        e.printStackTrace();
    }

    //Reader method
    try {
        Long startTime = new Date().getTime();

        BufferedReader br = new BufferedReader(new FileReader("test"));
        String line = null;
        StringBuilder sb = new StringBuilder();
        while ((line = br.readLine()) != null) {
            sb.append(line);
            sb.append("\n");
        }
        String text = sb.toString();

        Long endTime = new Date().getTime();
        System.out.println("Text length: " + text.length() + ", Total time: " + (endTime - startTime));

    }
    catch (Exception e) {
        e.printStackTrace();
    }

This gives a result of:

Text length: 1054631, Total time: 9
Text length: 1034099, Total time: 22

So, why do people use readers instead of streams?

If I have a method that takes a text file and returns a String that contains all of the text, is it necessarily better to do it using a stream?

Answer 1

You are comparing apples to bananas. Reading one line at a time is going to be less efficient even with a bufferedReader than grabbing data as fast as possible. Note that use of available is discouraged, as it is not accurate in all situations. I found this out myself when I started using cipher streams.