Java - read text file with specific jvm size

Question

I have created a .txt test file containing only character 'a'. The file size is about 20 MB. I tried to read the file in three ways

Using BufferedReader

String fileName = "C:\\testFile.txt";
        FileReader fileReader = new FileReader(fileName);

        try (BufferedReader bufferedReader = new BufferedReader(fileReader)) {
            String line;

            while ((line = bufferedReader.readLine()) != null) {
                System.out.println(line);
            }
        }

Using Scanner

 Scanner sc = null;

    try {

        sc = new Scanner(new File("C:\\testFile2.txt"), "UTF-8");
        while (sc.hasNextLine()) {
            String line = sc.nextLine();
            System.out.println(line);
        }

        if (sc.ioException() != null) {
            throw sc.ioException();
        }
    } finally {

        if (sc != null) {
            sc.close();
        }
    }

And, using Java8 stream

try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
        stream.forEach(System.out::println);
}

I set my jvm heap size using eclipse run configuration as shown here http://www.planetofbits.com/eclipse/increase-jvm-heap-size-in-eclipse/

In all three cases my value is : -Xms5M -Xmx100M.

Even though the file size is 20MB, it is always giving java.lang.OutOfMemoryError. When I set the heap size to -Xmx200M, it runs fine for all. I wonder what is eating up the memory and whether there is another more memory efficient way to read the file.

Any help is appreciated.

EDIT Profiling

Thanks Rann and Adam. I did use Jprofiler for the Scanner code. The memory usage is shown in the char[] array takes a lot and OverAll memory usage

It is interesting to see that char[] array taking up this much. No idea why!

Side note: Now I have changed my test file to contain integer and newline, so each line contains a random integer. With that in place, I can read the file ( even size of 100MB) easily with Scanner, as it will only read one line at a time. Previously, there was only character 'a' in the file and no new line.

Answer 1

The best way (imo) to answer your question would be to inspect you application with a memory profiling tool such as Java VisualVM or JProfiler . These applications will allow you to inspect how your program's memory is allocated and perhaps allow you to see where excessive memory is being used.