public VCFReader(String _dataFile, String _sampleName) throws IOException {
		dataFile = _dataFile;
		sampleName = _sampleName;
				
		br = new BufferedReader(new FileReader(dataFile));
		String line = null;
		
		while ((line=br.readLine())!=null) {
			if (line.length()<=0) continue;
			
			// If it is not a meta-information line or a header line, stop. 
			// Usually, this condition will not be satisfied.
			// Because the header line should appear before that.
			if (line.charAt(0)!='#')
				break;
			
			if (line.charAt(0)=='#') {
				// the header line
				if ( line.length()>1 && line.charAt(1)!='#') {					
					String[] tmp = line.split(FS);
					for(int i=sampleOffset; i<tmp.length; ++i)
						if (tmp[i].equals(sampleName))
							sampleColumn=i;
					break;
				}
				// else the line is meta-infomation, skip
			}
		}
		
		if (sampleColumn<0)
			throw(new RuntimeException("Sample name not found in VCF file."));
	}