public class Start {
    public static void main(String[] args) {
        try {
            BigFile file = new BigFile("C://test.txt", 10);
            for (char c : file)
                System.out.println(c + " (" + BigFile.IoReads + "th read)");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}


import java.util.*;
import java.io.*;

public class BigFile implements Iterable<Character> {
    BufferedReader _reader;
    int _bufferSize;

    public static long IoReads = 0;

    public BigFile(String filePath, int bufferSize) throws Exception {
        _reader = new BufferedReader(new FileReader(filePath));
        _bufferSize = bufferSize;
        if (_bufferSize < 1)
            throw new Exception("buffer too small");
    }

    public void Close() {
        try {
            _reader.close();
        } catch (Exception ex) {
        }
    }

    public Iterator<Character> iterator() {
        return new FileIterator(_bufferSize);
    }

    private class FileIterator implements Iterator<Character> {
        char[] _buffer;
        long _gindex;
        int _lastRead;

        public FileIterator(int bufferSize) {
            _buffer = new char[bufferSize];
            _gindex = -1;
            _lastRead = bufferSize;
        }

        public boolean hasNext() {
            try {
                _gindex++;
                if (_gindex % _buffer.length == 0) {
                    if (_lastRead == _buffer.length) {
                        _lastRead = _reader.read(_buffer, 0, _buffer.length);
                        BigFile.IoReads++;
                    }
                }
            } catch (Exception ex) {
                _buffer = null;
                ex.printStackTrace();
            }

            return _buffer != null && (int) (_gindex % _bufferSize) < _lastRead;
        }

        public Character next() {
            int bufferIndex = (int) (_gindex % _buffer.length);
            return _buffer[bufferIndex];
        }

        public void remove() {
        }
    }
}