This is documentation for the old, first-generation Kaa platform v0.x.
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Code style

This guide provides some important conventions on writing clear, readable code and API documentation. It is highly recommended that you refer to the guides mentioned at the bottom of the page to learn more about code style conventions used in Kaa.


Never spell “Kaa” as “KAA” (except for Jira tickets, e.g.: [KAA-1]).

Code formatting and naming

  • For indentation, use four spaces per indent level for most programming languages, and two spaces for markup languages (HTML, XML, etc.).
  • Set maximum line length in your IDE to 160 characters (in Eclipse, go to Java -> Code Style -> Formatter).
  • Enable removal of the trailing spaces on file saving in your IDE.
  • Always use LOG as a logger name in Java, for example:
    private static final Logger LOG = LoggerFactory.getLogger(DefaultBootstrapInitializationService.class);
  • Log exceptions as shown in the following code example (do not use .toString()).
    LOG.error("Exception caught!", e);
  • Log parameters using {}, for example:
    LOG.trace("Bootstrap server register in ZK: thriftHost {}; thriftPort {}; nettyHost {}; nettyPort {}" , thriftHost, thriftPort, nettyHost, nettyPort);

Code commenting

  • Place each comment on its own line and before the code that it’s describing.
  • Add a meaningful description before each class declaration. You may add author(s) full name(s) as in the following example.
      * DefaultBootstrapInitializationService Class.
      * Starts and stops all services in the Bootstrap service:
      * 1. CLI Thrift service
      * 2. ZooKeeper service
      * 3. Netty HTTP service
      * @author Andrey Panasenko
  • Observe standard rules of punctuation and grammar (use articles!).
  • Do not use the first person, that is, I or We. For example, do not write “Here we display a list of servers.” Use present tense and omit the subject in comments that describe a code block, and use imperative mood to describe the action within that code block or between code blocks.
    // Displays a list of servers with their addresses in the console.
    void printServers(List<Server> serverList) {
        // Display the name and address for each server.
        for (Server server : serverList) {
            System.out.printf("Server: %s, %s", server.getName(), server.getAddress());
    // Insert code for get and set accessors.

Log levels

Use the following log levels according to the log purpose.

Log Level Description
Info Use for important or interesting run time events that help understand what the program is doing at the moment
Error Use for run time errors or unexpected conditions that the program can gracefully recover from
Fatal Use for severe errors that cause premature program termination
Warning Use for unexpected or undesirable run time conditions that are not necessarily affecting the program
Debug Use to log detailed information according to the logical work flow of the system
Trace Use to log the most detailed information intended for development and debugging purposes only