---
layout: docpage

title: "Documentation"

is_homepage: false
is_sphinx_doc: true

doc-parent: "Contributing to Cassandra"

doc-title: "Code Style"
doc-header-links: '
  <link rel="top" title="Apache Cassandra Documentation v4.0-alpha4" href="../index.html"/>
      <link rel="up" title="Contributing to Cassandra" href="index.html"/>
      <link rel="next" title="Review Checklist" href="how_to_review.html"/>
      <link rel="prev" title="Contributing Code Changes" href="patches.html"/>
'
doc-search-path: "../search.html"

extra-footer: '
<script type="text/javascript">
    var DOCUMENTATION_OPTIONS = {
      URL_ROOT:    "",
      VERSION:     "",
      COLLAPSE_INDEX: false,
      FILE_SUFFIX: ".html",
      HAS_SOURCE:  false,
      SOURCELINK_SUFFIX: ".txt"
    };
</script>
'

---
<div class="container-fluid">
  <div class="row">
    <div class="col-md-3">
      <div class="doc-navigation">
        <div class="doc-menu" role="navigation">
          <div class="navbar-header">
            <button type="button" class="pull-left navbar-toggle" data-toggle="collapse" data-target=".sidebar-navbar-collapse">
              <span class="sr-only">Toggle navigation</span>
              <span class="icon-bar"></span>
              <span class="icon-bar"></span>
              <span class="icon-bar"></span>
            </button>
          </div>
          <div class="navbar-collapse collapse sidebar-navbar-collapse">
            <form id="doc-search-form" class="navbar-form" action="../search.html" method="get" role="search">
              <div class="form-group">
                <input type="text" size="30" class="form-control input-sm" name="q" placeholder="Search docs">
                <input type="hidden" name="check_keywords" value="yes" />
                <input type="hidden" name="area" value="default" />
              </div>
            </form>
            
            
            <ul class="current">
<li class="toctree-l1"><a class="reference internal" href="../getting_started/index.html">Getting Started</a></li>
<li class="toctree-l1"><a class="reference internal" href="../new/index.html">New Features in Apache Cassandra 4.0</a></li>
<li class="toctree-l1"><a class="reference internal" href="../architecture/index.html">Architecture</a></li>
<li class="toctree-l1"><a class="reference internal" href="../cql/index.html">The Cassandra Query Language (CQL)</a></li>
<li class="toctree-l1"><a class="reference internal" href="../data_modeling/index.html">Data Modeling</a></li>
<li class="toctree-l1"><a class="reference internal" href="../configuration/index.html">Configuring Cassandra</a></li>
<li class="toctree-l1"><a class="reference internal" href="../operating/index.html">Operating Cassandra</a></li>
<li class="toctree-l1"><a class="reference internal" href="../tools/index.html">Cassandra Tools</a></li>
<li class="toctree-l1"><a class="reference internal" href="../troubleshooting/index.html">Troubleshooting</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="index.html">Contributing to Cassandra</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="gettingstarted.html">Getting Started</a></li>
<li class="toctree-l2"><a class="reference internal" href="ide.html">Building and IDE Integration</a></li>
<li class="toctree-l2"><a class="reference internal" href="testing.html">Testing</a></li>
<li class="toctree-l2"><a class="reference internal" href="patches.html">Contributing Code Changes</a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#">Code Style</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#general-code-conventions">General Code Conventions</a></li>
<li class="toctree-l3"><a class="reference internal" href="#exception-handling">Exception handling</a></li>
<li class="toctree-l3"><a class="reference internal" href="#boilerplate">Boilerplate</a></li>
<li class="toctree-l3"><a class="reference internal" href="#multiline-statements">Multiline statements</a></li>
<li class="toctree-l3"><a class="reference internal" href="#whitespace">Whitespace</a></li>
<li class="toctree-l3"><a class="reference internal" href="#imports">Imports</a></li>
<li class="toctree-l3"><a class="reference internal" href="#format-files-for-ides">Format files for IDEs</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="how_to_review.html">Review Checklist</a></li>
<li class="toctree-l2"><a class="reference internal" href="how_to_commit.html">How-to Commit</a></li>
<li class="toctree-l2"><a class="reference internal" href="documentation.html">Working on Documentation</a></li>
<li class="toctree-l2"><a class="reference internal" href="ci.html">Jenkins CI Environment</a></li>
<li class="toctree-l2"><a class="reference internal" href="dependencies.html">Dependency Management</a></li>
<li class="toctree-l2"><a class="reference internal" href="release_process.html">Release Process</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../faq/index.html">Frequently Asked Questions</a></li>
<li class="toctree-l1"><a class="reference internal" href="../plugins/index.html">Third-Party Plugins</a></li>
<li class="toctree-l1"><a class="reference internal" href="../bugs.html">Reporting Bugs</a></li>
<li class="toctree-l1"><a class="reference internal" href="../contactus.html">Contact us</a></li>
</ul>

            
          </div><!--/.nav-collapse -->
        </div>
      </div>
    </div>
    <div class="col-md-8">
      <div class="content doc-content">
        <div class="content-container">
          
  <div class="section" id="code-style">
<h1>Code Style<a class="headerlink" href="#code-style" title="Permalink to this headline">¶</a></h1>
<div class="section" id="general-code-conventions">
<h2>General Code Conventions<a class="headerlink" href="#general-code-conventions" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li>The Cassandra project follows <a class="reference external" href="http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html">Sun’s Java coding conventions</a> with an important exception: <code class="docutils literal notranslate"><span class="pre">{</span></code> and <code class="docutils literal notranslate"><span class="pre">}</span></code> are always placed on a new line</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="exception-handling">
<h2>Exception handling<a class="headerlink" href="#exception-handling" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li>Never ever write <code class="docutils literal notranslate"><span class="pre">catch</span> <span class="pre">(...)</span> <span class="pre">{}</span></code> or <code class="docutils literal notranslate"><span class="pre">catch</span> <span class="pre">(...)</span> <span class="pre">{</span> <span class="pre">logger.error()</span> <span class="pre">}</span></code> merely to satisfy Java’s compile-time exception checking. Always propagate the exception up or throw <code class="docutils literal notranslate"><span class="pre">RuntimeException</span></code> (or, if it “can’t happen,” <code class="docutils literal notranslate"><span class="pre">AssertionError</span></code>). This makes the exceptions visible to automated tests.</li>
<li>Avoid propagating up checked exceptions that no caller handles. Rethrow as <code class="docutils literal notranslate"><span class="pre">RuntimeException</span></code> (or <code class="docutils literal notranslate"><span class="pre">IOError</span></code>, if that is more applicable).</li>
<li>Similarly, logger.warn() is often a cop-out: is this an error or not? If it is don’t hide it behind a warn; if it isn’t, no need for the warning.</li>
<li>If you genuinely know an exception indicates an expected condition, it’s okay to ignore it BUT this must be explicitly explained in a comment.</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="boilerplate">
<h2>Boilerplate<a class="headerlink" href="#boilerplate" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li>Avoid redundant <code class="docutils literal notranslate"><span class="pre">&#64;Override</span></code> annotations when implementing abstract or interface methods.</li>
<li>Do not implement equals or hashcode methods unless they are actually needed.</li>
<li>Prefer public final fields to private fields with getters. (But prefer encapsulating behavior in “real” methods to either.)</li>
<li>Prefer requiring initialization in the constructor to setters.</li>
<li>Avoid redundant <code class="docutils literal notranslate"><span class="pre">this</span></code> references to member fields or methods.</li>
<li>Do not extract interfaces (or abstract classes) unless you actually need multiple implementations of it.</li>
<li>Always include braces for nested levels of conditionals and loops. Only avoid braces for single level.</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="multiline-statements">
<h2>Multiline statements<a class="headerlink" href="#multiline-statements" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li>Try to keep lines under 120 characters, but use good judgement – it’s better to exceed 120 by a little, than split a line that has no natural splitting points.</li>
<li>When splitting inside a method call, use one line per parameter and align them, like this:</li>
</ul>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>SSTableWriter writer = new SSTableWriter(cfs.getTempSSTablePath(),
                                         columnFamilies.size(),
                                         StorageService.getPartitioner());
</pre></div>
</div>
<ul class="simple">
<li>When splitting a ternary, use one line per clause, carry the operator, and align like this:</li>
</ul>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>var = bar == null
    ? doFoo()
    : doBar();
</pre></div>
</div>
</div></blockquote>
</div>
<div class="section" id="whitespace">
<h2>Whitespace<a class="headerlink" href="#whitespace" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li>Please make sure to use 4 spaces instead of the tab character for all your indentation.</li>
<li>Many lines in many files have a bunch of trailing whitespace… Please either clean these up in a separate patch, or leave them alone, so that reviewers now and anyone reading code history later doesn’t have to pay attention to whitespace diffs.</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="imports">
<h2>Imports<a class="headerlink" href="#imports" title="Permalink to this headline">¶</a></h2>
<p>Please observe the following order for your imports:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>java
[blank line]
com.google.common
org.apache.commons
org.junit
org.slf4j
[blank line]
everything else alphabetically
</pre></div>
</div>
</div>
<div class="section" id="format-files-for-ides">
<h2>Format files for IDEs<a class="headerlink" href="#format-files-for-ides" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li>IntelliJ: <a class="reference external" href="https://wiki.apache.org/cassandra/CodeStyle?action=AttachFile&amp;do=view&amp;target=intellij-codestyle.jar">intellij-codestyle.jar</a></li>
<li>IntelliJ 13: <a class="reference external" href="https://gist.github.com/jdsumsion/9ab750a05c2a567c6afc">gist for IntelliJ 13</a> (this is a work in progress, still working on javadoc, ternary style, line continuations, etc)</li>
<li>Eclipse (<a class="reference external" href="https://github.com/tjake/cassandra-style-eclipse">https://github.com/tjake/cassandra-style-eclipse</a>)</li>
</ul>
</div></blockquote>
</div>
</div>


          <div class="doc-prev-next-links" role="navigation" aria-label="footer navigation">
            
            <a href="how_to_review.html" class="btn btn-default pull-right " role="button" title="Review Checklist" accesskey="n">Next <span class="glyphicon glyphicon-circle-arrow-right" aria-hidden="true"></span></a>
            
            
            <a href="patches.html" class="btn btn-default" role="button" title="Contributing Code Changes" accesskey="p"><span class="glyphicon glyphicon-circle-arrow-left" aria-hidden="true"></span> Previous</a>
            
          </div>
          
        </div>
      </div>
    </div>
  </div>
</div>