Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "The NumWorker configuration or TOPOLOGY_WORKERS configuration defined in Storm."

A block of code is set as follows:

// instantiates the new builder object
TopologyBuilder builder = new TopologyBuilder();
// Adds a new spout of type "RandomSentenceSpout" with a  parallelism hint of 5
builder.setSpout("spout", new RandomSentenceSpout(), 5);

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are highlighted:

  public void execute(Tuple tuple) {
      String sentence = tuple.getString(0);
      for(String word: sentence.split(" ")) {
          _collector.emit(tuple, new Values(word)); //1
      }
      _collector.ack(tuple); //2
  }
  public void declareOutputFields(OutputFieldsDeclarer  declarer) {
      declarer.declare(new Fields("word")); //3
  }
}

Any command-line input or output is written as follows:

sudo apt-get -qy install rabbitmq-server

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: " Go to the Admin tab and select Policies and click on Add policy".