Mine

private static Object lock = new Object();
	private static ConcurrentHashMap<String, ParamFileParser> paramFiles = new ConcurrentHashMap<String, ParamFileParser>();
	public static ParamFileParser getParamFileParser(File f)
	{
		ParamFileParser param = paramFiles.get(f.getAbsolutePath());
		
		if(param == null)
		{
			synchronized(lock)
			{
				param = paramFiles.get(f.getAbsolutePath());
				
				if(param == null)
				{
					param = new ParamFileParser(f);
				}
				return paramFiles.putIfAbsent(f.getAbsolutePath(), param);
			}
		} else
		{
			return param;
		}
		
	}