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<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>Google Java Style Guide</title>
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<link rel="stylesheet" type="text/css" href="javaguide.css"/>
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<script language="javascript" src="include/styleguide.js"></script>
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<link href="https://www.google.com/favicon.ico" type="image/x-icon" rel="shortcut icon" />
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<script src="https://cdn.rawgit.com/google/code-prettify/master/loader/run_prettify.js" type="text/javascript"></script></head>
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<body onload="initStyleGuide();">
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<div id="content">
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<h1>Google Java Style Guide</h1>
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<div class="vertical_toc" id="tocDiv"></div>
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<div class="main_body">
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<h2 id="s1-introduction">1 Introduction</h2>
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<p>This document serves as the <strong>complete</strong> definition of Google's coding standards for
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source code in the Java™ Programming Language. A Java source file is described as being <em>in
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Google Style</em> if and only if it adheres to the rules herein.</p>
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<p>Like other programming style guides, the issues covered span not only aesthetic issues of
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formatting, but other types of conventions or coding standards as well. However, this document
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focuses primarily on the <strong>hard-and-fast rules</strong> that we follow universally, and
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avoids giving <em>advice</em> that isn't clearly enforceable (whether by human or tool).
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</p>
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<h3 id="s1.1-terminology">1.1 Terminology notes</h3>
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<p>In this document, unless otherwise clarified:</p>
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<ol>
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<li>The term <em>class</em> is used inclusively to mean an "ordinary" class, enum class,
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interface or annotation type (<code class="prettyprint lang-java">@interface</code>).</li>
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<li>The term <em>comment</em> always refers to <em>implementation</em> comments. We do not
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use the phrase "documentation comments", instead using the common term "Javadoc."</li>
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</ol>
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<p>Other "terminology notes" will appear occasionally throughout the document.</p>
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<h3 id="s1.2-guide-notes">1.2 Guide notes</h3>
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<p>Example code in this document is <strong>non-normative</strong>. That is, while the examples
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are in Google Style, they may not illustrate the <em>only</em> stylish way to represent the
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code. Optional formatting choices made in examples should not be enforced as rules.</p>
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<h2 id="s2-source-file-basics">2 Source file basics</h2>
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<h3 id="s2.1-file-name">2.1 File name</h3>
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<p>The source file name consists of the case-sensitive name of the top-level class it contains
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(of which there is <a href="#s3.4.1-one-top-level-class">exactly one</a>), plus the
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<code>.java</code> extension.</p>
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<h3 id="s2.2-file-encoding">2.2 File encoding: UTF-8</h3>
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<p>Source files are encoded in <strong>UTF-8</strong>.</p>
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<h3 id="s2.3-special-characters">2.3 Special characters</h3>
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<h4 id="s2.3.1-whitespace-characters">2.3.1 Whitespace characters</h4>
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<p>Aside from the line terminator sequence, the <strong>ASCII horizontal space
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character</strong> (<strong>0x20</strong>) is the only whitespace character that appears
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anywhere in a source file. This implies that:</p>
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<ol>
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<li>All other whitespace characters in string and character literals are escaped.</li>
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<li>Tab characters are <strong>not</strong> used for indentation.</li>
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</ol>
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<h4 id="s2.3.2-special-escape-sequences">2.3.2 Special escape sequences</h4>
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<p>For any character that has a
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<a href="http://docs.oracle.com/javase/tutorial/java/data/characters.html">
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special escape sequence</a>
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(<code class="prettyprint lang-java">\b</code>,
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<code class="prettyprint lang-java">\t</code>,
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<code class="prettyprint lang-java">\n</code>,
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<code class="prettyprint lang-java">\f</code>,
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<code class="prettyprint lang-java">\r</code>,
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<code class="prettyprint lang-java">\"</code>,
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<code class="prettyprint lang-java">\'</code> and
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<code class="prettyprint lang-java">\\</code>), that sequence
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is used rather than the corresponding octal
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(e.g. <code class="badcode">\012</code>) or Unicode
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(e.g. <code class="badcode">\u000a</code>) escape.</p>
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<h4 id="s2.3.3-non-ascii-characters">2.3.3 Non-ASCII characters</h4>
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<p>For the remaining non-ASCII characters, either the actual Unicode character
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(e.g. <code class="prettyprint lang-java">∞</code>) or the equivalent Unicode escape
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(e.g. <code class="prettyprint lang-java">\u221e</code>) is used. The choice depends only on
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which makes the code <strong>easier to read and understand</strong>, although Unicode escapes
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outside string literals and comments are strongly discouraged.</p>
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<p class="tip"><strong>Tip:</strong> In the Unicode escape case, and occasionally even when actual
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Unicode characters are used, an explanatory comment can be very helpful.</p>
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<p>Examples:</p>
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<table>
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<tbody><tr>
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<th>Example</th>
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<th>Discussion</th>
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</tr>
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<tr>
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<td><code class="prettyprint lang-java">String unitAbbrev = "μs";</code></td>
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<td>Best: perfectly clear even without a comment.</td>
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</tr>
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<tr>
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<td><code class="prettyprint lang-java">String unitAbbrev = "\u03bcs"; // "μs"</code></td>
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<td>Allowed, but there's no reason to do this.</td>
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</tr>
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<tr>
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<td><code class="prettyprint lang-java">String unitAbbrev = "\u03bcs";
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// Greek letter mu, "s"</code></td>
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<td>Allowed, but awkward and prone to mistakes.</td>
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</tr>
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<tr>
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<td><code class="badcode">String unitAbbrev = "\u03bcs";</code></td>
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<td>Poor: the reader has no idea what this is.</td>
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</tr>
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<tr>
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<td><code class="prettyprint lang-java">return '\ufeff' + content;
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// byte order mark</code></td>
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<td>Good: use escapes for non-printable characters, and comment if necessary.</td>
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</tr>
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</tbody></table>
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<p class="tip"><strong>Tip:</strong> Never make your code less readable simply out of fear that
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some programs might not handle non-ASCII characters properly. If that should happen, those
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programs are <strong>broken</strong> and they must be <strong>fixed</strong>.</p>
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<a name="filestructure"></a>
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<h2 id="s3-source-file-structure">3 Source file structure</h2>
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<div>
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<p>A source file consists of, <strong>in order</strong>:</p>
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<ol>
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<li>License or copyright information, if present</li>
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<li>Package statement</li>
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<li>Import statements</li>
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<li>Exactly one top-level class</li>
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</ol>
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</div>
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<p><strong>Exactly one blank line</strong> separates each section that is present.</p>
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<h3 id="s3.1-copyright-statement">3.1 License or copyright information, if present</h3>
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<p>If license or copyright information belongs in a file, it belongs here.</p>
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<h3 id="s3.2-package-statement">3.2 Package statement</h3>
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<p>The package statement is <strong>not line-wrapped</strong>. The column limit (Section 4.4,
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<a href="#s4.4-column-limit">Column limit: 100</a>) does not apply to package statements.</p>
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<a name="imports"></a>
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<h3 id="s3.3-import-statements">3.3 Import statements</h3>
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<h4 id="s3.3.1-wildcard-imports">3.3.1 No wildcard imports</h4>
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<p><strong>Wildcard imports</strong>, static or otherwise, <strong>are not used</strong>.</p>
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<h4 id="s3.3.2-import-line-wrapping">3.3.2 No line-wrapping</h4>
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<p>Import statements are <strong>not line-wrapped</strong>. The column limit (Section 4.4,
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<a href="#s4.4-column-limit">Column limit: 100</a>) does not apply to import
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statements.</p>
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<h4 id="s3.3.3-import-ordering-and-spacing">3.3.3 Ordering and spacing</h4>
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<p>Imports are ordered as follows:</p>
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<ol>
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<li>All static imports in a single block.</li>
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<li>All non-static imports in a single block.</li>
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</ol>
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<p>If there are both static and non-static imports, a single blank line separates the two
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blocks. There are no other blank lines between import statements.</p>
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<p>Within each block the imported names appear in ASCII sort order. (<strong>Note:</strong>
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this is not the same as the import <em>statements</em> being in ASCII sort order, since '.'
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sorts before ';'.)</p>
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<h3 id="s3.4-class-declaration">3.4 Class declaration</h3>
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<a name="oneclassperfile"></a>
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<h4 id="s3.4.1-one-top-level-class">3.4.1 Exactly one top-level class declaration</h4>
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<p>Each top-level class resides in a source file of its own.</p>
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<h4 id="s3.4.2-class-member-ordering">3.4.2 Class member ordering</h4>
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<p>The ordering of the members of a class can have a great effect on learnability, but there is
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no single correct recipe for how to do it. Different classes may order their members
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differently.</p>
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<p>What is important is that each class order its members in <strong><em>some</em> logical
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order</strong>, which its maintainer could explain if asked. For example, new methods are not
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just habitually added to the end of the class, as that would yield "chronological by date
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added" ordering, which is not a logical ordering.</p>
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<a name="overloads"></a>
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<h5 id="s3.4.2.1-overloads-never-split">3.4.2.1 Overloads: never split</h5>
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<p>When a class has multiple constructors, or multiple methods with the same name, these appear
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sequentially, with no intervening members (not even private ones).</p>
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<h2 id="s4-formatting">4 Formatting</h2>
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<p class="terminology"><strong>Terminology Note:</strong> <em>block-like construct</em> refers to
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the body of a class, method or constructor. Note that, by Section 4.8.3.1 on
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<a href="#s4.8.3.1-array-initializers">array initializers</a>, any array initializer
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<em>may</em> optionally be treated as if it were a block-like construct.</p>
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<a name="braces"></a>
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<h3 id="s4.1-braces">4.1 Braces</h3>
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<h4 id="s4.1.1-braces-always-used">4.1.1 Braces are used where optional</h4>
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<p>Braces are used with
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<code class="prettyprint lang-java">if</code>,
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<code class="prettyprint lang-java">else</code>,
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<code class="prettyprint lang-java">for</code>,
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<code class="prettyprint lang-java">do</code> and
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<code class="prettyprint lang-java">while</code> statements, even when the
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body is empty or contains only a single statement.</p>
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<h4 id="s4.1.2-blocks-k-r-style">4.1.2 Nonempty blocks: K & R style</h4>
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<p>Braces follow the Kernighan and Ritchie style
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("<a href="http://www.codinghorror.com/blog/2012/07/new-programming-jargon.html">Egyptian brackets</a>")
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for <em>nonempty</em> blocks and block-like constructs:</p>
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<ul>
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<li>No line break before the opening brace.</li>
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<li>Line break after the opening brace.</li>
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<li>Line break before the closing brace.</li>
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<li>Line break after the closing brace, <em>only if</em> that brace terminates a statement or
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terminates the body of a method, constructor, or <em>named</em> class.
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For example, there is <em>no</em> line break after the brace if it is followed by
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<code class="prettyprint lang-java">else</code> or a comma.</li>
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</ul>
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<p>Examples:</p>
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<pre class="prettyprint lang-java">return () -> {
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while (condition()) {
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method();
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}
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};
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return new MyClass() {
|
2013-12-18 06:56:22 +08:00
|
|
|
@Override public void method() {
|
|
|
|
|
if (condition()) {
|
|
|
|
|
try {
|
|
|
|
|
something();
|
|
|
|
|
} catch (ProblemException e) {
|
|
|
|
|
recover();
|
|
|
|
|
}
|
2016-06-30 07:36:05 +08:00
|
|
|
} else if (otherCondition()) {
|
|
|
|
|
somethingElse();
|
|
|
|
|
} else {
|
|
|
|
|
lastThing();
|
2013-12-18 06:56:22 +08:00
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
};
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>A few exceptions for enum classes are given in Section 4.8.1,
|
|
|
|
|
<a href="#s4.8.1-enum-classes">Enum classes</a>.</p>
|
|
|
|
|
|
|
|
|
|
<a name="emptyblocks"></a>
|
|
|
|
|
<h4 id="s4.1.3-braces-empty-blocks">4.1.3 Empty blocks: may be concise</h4>
|
|
|
|
|
|
|
|
|
|
<p>An empty block or block-like construct <em>may</em> be closed immediately after it is
|
2013-12-18 06:56:22 +08:00
|
|
|
opened, with no characters or line break in between
|
|
|
|
|
(<code class="prettyprint lang-java">{}</code>), <strong>unless</strong> it is part of a
|
|
|
|
|
<em>multi-block statement</em> (one that directly contains multiple blocks:
|
|
|
|
|
<code class="prettyprint lang-java">if/else-if/else</code> or
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">try/catch/finally</code>).</p>
|
|
|
|
|
|
|
|
|
|
<p>Example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java"> void doNothing() {}
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3 id="s4.2-block-indentation">4.2 Block indentation: +2 spaces</h3>
|
|
|
|
|
|
|
|
|
|
<p>Each time a new block or block-like construct is opened, the indent increases by two
|
2013-12-18 06:56:22 +08:00
|
|
|
spaces. When the block ends, the indent returns to the previous indent level. The indent level
|
|
|
|
|
applies to both code and comments throughout the block. (See the example in Section 4.1.2,
|
2016-06-30 07:36:05 +08:00
|
|
|
<a href="#s4.1.2-blocks-k-r-style">Nonempty blocks: K & R Style</a>.)</p>
|
|
|
|
|
|
|
|
|
|
<h3 id="s4.3-one-statement-per-line">4.3 One statement per line</h3>
|
2013-12-18 06:56:22 +08:00
|
|
|
|
2016-06-30 07:36:05 +08:00
|
|
|
<p>Each statement is followed by a line break.</p>
|
|
|
|
|
|
|
|
|
|
<a name="columnlimit"></a>
|
|
|
|
|
<h3 id="s4.4-column-limit">4.4 Column limit: 100</h3>
|
|
|
|
|
|
|
|
|
|
<p>Java code has a column limit of 100 characters.
|
2013-12-18 06:56:22 +08:00
|
|
|
Except as noted below, any line that would exceed this limit must be line-wrapped, as explained in
|
|
|
|
|
Section 4.5, <a href="#s4.5-line-wrapping">Line-wrapping</a>.
|
2016-06-30 07:36:05 +08:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p><strong>Exceptions:</strong></p>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>Lines where obeying the column limit is not possible (for example, a long URL in Javadoc,
|
|
|
|
|
or a long JSNI method reference).</li>
|
|
|
|
|
|
|
|
|
|
<li><code class="prettyprint lang-java">package</code> and
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">import</code> statements (see Sections
|
|
|
|
|
3.2 <a href="#s3.2-package-statement">Package statement</a> and
|
2016-06-30 07:36:05 +08:00
|
|
|
3.3 <a href="#s3.3-import-statements">Import statements</a>).</li>
|
|
|
|
|
|
|
|
|
|
<li>Command lines in a comment that may be cut-and-pasted into a shell.</li>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
<h3 id="s4.5-line-wrapping">4.5 Line-wrapping</h3>
|
|
|
|
|
|
|
|
|
|
<p class="terminology"><strong>Terminology Note:</strong> When code that might otherwise legally
|
|
|
|
|
occupy a single line is divided into multiple lines, this activity is called
|
|
|
|
|
<em>line-wrapping</em>.</p>
|
|
|
|
|
|
|
|
|
|
<p>There is no comprehensive, deterministic formula showing <em>exactly</em> how to line-wrap in
|
|
|
|
|
every situation. Very often there are several valid ways to line-wrap the same piece of code.</p>
|
|
|
|
|
|
|
|
|
|
<p class="note"><strong>Note:</strong> While the typical reason for line-wrapping is to avoid
|
|
|
|
|
overflowing the column limit, even code that would in fact fit within the column limit <em>may</em>
|
|
|
|
|
be line-wrapped at the author's discretion.</p>
|
|
|
|
|
|
|
|
|
|
<p class="tip"><strong>Tip:</strong> Extracting a method or local variable may solve the problem
|
|
|
|
|
without the need to line-wrap.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s4.5.1-line-wrapping-where-to-break">4.5.1 Where to break</h4>
|
|
|
|
|
|
|
|
|
|
<p>The prime directive of line-wrapping is: prefer to break at a
|
|
|
|
|
<strong>higher syntactic level</strong>. Also:</p>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>When a line is broken at a <em>non-assignment</em> operator the break comes <em>before</em>
|
2013-12-18 06:56:22 +08:00
|
|
|
the symbol. (Note that this is not the same practice used in Google style for other languages,
|
|
|
|
|
such as C++ and JavaScript.)
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li>This also applies to the following "operator-like" symbols: the dot separator
|
2016-07-13 03:08:12 +08:00
|
|
|
(<code class="prettyprint lang-java">.</code>), the two colons of a method reference
|
|
|
|
|
(<code class="prettyprint lang-java">::</code>), the ampersand in type bounds
|
2013-12-18 06:56:22 +08:00
|
|
|
(<code class="prettyprint lang-java"><T extends Foo & Bar></code>), and the pipe in
|
|
|
|
|
catch blocks
|
2016-06-30 07:36:05 +08:00
|
|
|
(<code class="prettyprint lang-java">catch (FooException | BarException e)</code>).</li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>When a line is broken at an <em>assignment</em> operator the break typically comes
|
2013-12-18 06:56:22 +08:00
|
|
|
<em>after</em> the symbol, but either way is acceptable.
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li>This also applies to the "assignment-operator-like" colon in an enhanced
|
|
|
|
|
<code class="prettyprint lang-java">for</code> ("foreach") statement.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>A method or constructor name stays attached to the open parenthesis
|
|
|
|
|
(<code class="prettyprint lang-java">(</code>) that follows it.</li>
|
|
|
|
|
|
|
|
|
|
<li>A comma (<code class="prettyprint lang-java">,</code>) stays attached to the token that
|
|
|
|
|
precedes it.</li>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
<p class="note"><strong>Note:</strong> The primary goal for line wrapping is to have clear
|
|
|
|
|
code, <em>not necessarily</em> code that fits in the smallest number of lines.</p>
|
|
|
|
|
|
|
|
|
|
<a name="indentation"></a>
|
|
|
|
|
<h4 id="s4.5.2-line-wrapping-indent">4.5.2 Indent continuation lines at least +4 spaces</h4>
|
|
|
|
|
|
|
|
|
|
<p>When line-wrapping, each line after the first (each <em>continuation line</em>) is indented
|
|
|
|
|
at least +4 from the original line.</p>
|
|
|
|
|
|
|
|
|
|
<p>When there are multiple continuation lines, indentation may be varied beyond +4 as
|
2013-12-18 06:56:22 +08:00
|
|
|
desired. In general, two continuation lines use the same indentation level if and only if they
|
2016-06-30 07:36:05 +08:00
|
|
|
begin with syntactically parallel elements.</p>
|
|
|
|
|
|
|
|
|
|
<p>Section 4.6.3 on <a href="#s4.6.3-horizontal-alignment">Horizontal alignment</a> addresses
|
2013-12-18 06:56:22 +08:00
|
|
|
the discouraged practice of using a variable number of spaces to align certain tokens with
|
2016-06-30 07:36:05 +08:00
|
|
|
previous lines.</p>
|
|
|
|
|
|
|
|
|
|
<h3 id="s4.6-whitespace">4.6 Whitespace</h3>
|
|
|
|
|
|
|
|
|
|
<h4 id="s4.6.1-vertical-whitespace">4.6.1 Vertical Whitespace</h4>
|
|
|
|
|
|
|
|
|
|
<p>A single blank line appears:</p>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li><em>Between</em> consecutive members (or initializers) of a class: fields, constructors,
|
2013-12-18 06:56:22 +08:00
|
|
|
methods, nested classes, static initializers, instance initializers.
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li><span class="exception"><strong>Exception:</strong> A blank line between two consecutive
|
2014-03-22 02:23:56 +08:00
|
|
|
fields (having no other code between them) is optional. Such blank lines are used as needed to
|
2016-06-30 07:36:05 +08:00
|
|
|
create <em>logical groupings</em> of fields.</span></li>
|
|
|
|
|
<li><span class="exception"><strong>Exception:</strong> Blank lines between enum constants are
|
|
|
|
|
covered in <a href="#s4.8.1-enum-classes">Section 4.8.1</a>.</span></li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>Between statements, <em>as needed</em> to organize the code into logical subsections.
|
|
|
|
|
|
|
|
|
|
</li><li><em>Optionally</em> before the first member or after the last member of the class (neither
|
|
|
|
|
encouraged nor discouraged).</li>
|
|
|
|
|
|
2016-07-13 03:08:12 +08:00
|
|
|
<li>As required by other sections of this document (such as Section 3,
|
|
|
|
|
<a href="#s3-source-file-structure">Source file structure</a>, and Section 3.3,
|
2016-06-30 07:36:05 +08:00
|
|
|
<a href="#s3.3-import-statements">Import statements</a>).</li>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
<p><em>Multiple</em> consecutive blank lines are permitted, but never required (or encouraged).</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s4.6.2-horizontal-whitespace">4.6.2 Horizontal whitespace</h4>
|
|
|
|
|
|
|
|
|
|
<p>Beyond where required by the language or other style rules, and apart from literals, comments and
|
|
|
|
|
Javadoc, a single ASCII space also appears in the following places <strong>only</strong>.</p>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>Separating any reserved word, such as
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">if</code>,
|
|
|
|
|
<code class="prettyprint lang-java">for</code> or
|
|
|
|
|
<code class="prettyprint lang-java">catch</code>, from an open parenthesis
|
|
|
|
|
(<code class="prettyprint lang-java">(</code>)
|
2016-06-30 07:36:05 +08:00
|
|
|
that follows it on that line</li>
|
|
|
|
|
|
|
|
|
|
<li>Separating any reserved word, such as
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">else</code> or
|
|
|
|
|
<code class="prettyprint lang-java">catch</code>, from a closing curly brace
|
2016-06-30 07:36:05 +08:00
|
|
|
(<code class="prettyprint lang-java">}</code>) that precedes it on that line</li>
|
|
|
|
|
|
|
|
|
|
<li>Before any open curly brace
|
2013-12-18 06:56:22 +08:00
|
|
|
(<code class="prettyprint lang-java">{</code>), with two exceptions:
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li><code class="prettyprint lang-java">@SomeAnnotation({a, b})</code> (no space is used)</li>
|
|
|
|
|
|
|
|
|
|
<li><code class="prettyprint lang-java">String[][] x = {{"foo"}};</code> (no space is required
|
|
|
|
|
between <code class="prettyprint lang-java">{{</code>, by item 8 below)</li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>On both sides of any binary or ternary operator. This also applies to the following
|
2013-12-18 06:56:22 +08:00
|
|
|
"operator-like" symbols:
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li>the ampersand in a conjunctive type bound:
|
|
|
|
|
<code class="prettyprint lang-java"><T extends Foo & Bar></code></li>
|
|
|
|
|
|
|
|
|
|
<li>the pipe for a catch block that handles multiple exceptions:
|
|
|
|
|
<code class="prettyprint lang-java">catch (FooException | BarException e)</code></li>
|
|
|
|
|
|
|
|
|
|
<li>the colon (<code class="prettyprint lang-java">:</code>) in an enhanced
|
|
|
|
|
<code class="prettyprint lang-java">for</code> ("foreach") statement</li>
|
2016-07-13 03:08:12 +08:00
|
|
|
|
|
|
|
|
<li>the arrow in a lambda expression:
|
|
|
|
|
<code class="prettyprint lang-java">(String str) -> str.length()</code></li>
|
|
|
|
|
</ul>
|
|
|
|
|
but not
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>the two colons (<code class="prettyprint lang-java">::</code>) of a method reference, which
|
|
|
|
|
is written like <code class="prettyprint lang-java">Object::toString</code></li>
|
|
|
|
|
<li>the dot separator (<code class="prettyprint lang-java">.</code>), which is written like
|
|
|
|
|
<code class="prettyprint lang-java">object.toString()</code></li>
|
2016-06-30 07:36:05 +08:00
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>After <code class="prettyprint lang-java">,:;</code> or the closing parenthesis
|
|
|
|
|
(<code class="prettyprint lang-java">)</code>) of a cast</li>
|
|
|
|
|
|
|
|
|
|
<li>On both sides of the double slash (<code class="prettyprint lang-java">//</code>) that
|
|
|
|
|
begins an end-of-line comment. Here, multiple spaces are allowed, but not required.</li>
|
|
|
|
|
|
|
|
|
|
<li>Between the type and variable of a declaration:
|
|
|
|
|
<code class="prettyprint lang-java">List<String> list</code></li>
|
|
|
|
|
|
|
|
|
|
<li><em>Optional</em> just inside both braces of an array initializer
|
|
|
|
|
<ul>
|
|
|
|
|
<li><code class="prettyprint lang-java">new int[] {5, 6}</code> and
|
|
|
|
|
<code class="prettyprint lang-java">new int[] { 5, 6 }</code> are both valid</li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
This rule is never interpreted as requiring or forbidding additional space at the start or
|
|
|
|
|
end of a line; it addresses only <em>interior</em> space.<p></p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s4.6.3-horizontal-alignment">4.6.3 Horizontal alignment: never required</h4>
|
|
|
|
|
|
|
|
|
|
<p class="terminology"><strong>Terminology Note:</strong> <em>Horizontal alignment</em> is the
|
2014-03-22 02:23:56 +08:00
|
|
|
practice of adding a variable number of additional spaces in your code with the goal of making
|
2016-06-30 07:36:05 +08:00
|
|
|
certain tokens appear directly below certain other tokens on previous lines.</p>
|
|
|
|
|
|
|
|
|
|
<p>This practice is permitted, but is <strong>never required</strong> by Google Style. It is not
|
|
|
|
|
even required to <em>maintain</em> horizontal alignment in places where it was already used.</p>
|
|
|
|
|
|
|
|
|
|
<p>Here is an example without alignment, then using alignment:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">private int x; // this is fine
|
2013-12-18 06:56:22 +08:00
|
|
|
private Color color; // this too
|
|
|
|
|
|
|
|
|
|
private int x; // permitted, but future edits
|
|
|
|
|
private Color color; // may leave it unaligned
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p class="tip"><strong>Tip:</strong> Alignment can aid readability, but it creates problems for
|
2014-03-22 02:23:56 +08:00
|
|
|
future maintenance. Consider a future change that needs to touch just one line. This change may
|
|
|
|
|
leave the formerly-pleasing formatting mangled, and that is <strong>allowed</strong>. More often
|
|
|
|
|
it prompts the coder (perhaps you) to adjust whitespace on nearby lines as well, possibly
|
|
|
|
|
triggering a cascading series of reformattings. That one-line change now has a "blast radius."
|
|
|
|
|
This can at worst result in pointless busywork, but at best it still corrupts version history
|
2016-06-30 07:36:05 +08:00
|
|
|
information, slows down reviewers and exacerbates merge conflicts.</p>
|
|
|
|
|
|
|
|
|
|
<a name="parentheses"></a>
|
|
|
|
|
<h3 id="s4.7-grouping-parentheses">4.7 Grouping parentheses: recommended</h3>
|
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|
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|
|
<p>Optional grouping parentheses are omitted only when author and reviewer agree that there is no
|
2013-12-18 06:56:22 +08:00
|
|
|
reasonable chance the code will be misinterpreted without them, nor would they have made the code
|
|
|
|
|
easier to read. It is <em>not</em> reasonable to assume that every reader has the entire Java
|
2016-06-30 07:36:05 +08:00
|
|
|
operator precedence table memorized.</p>
|
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|
|
<h3 id="s4.8-specific-constructs">4.8 Specific constructs</h3>
|
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|
<h4 id="s4.8.1-enum-classes">4.8.1 Enum classes</h4>
|
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|
|
<p>After each comma that follows an enum constant, a line break is optional. Additional blank
|
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|
|
lines (usually just one) are also allowed. This is one possibility:
|
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</p><pre class="prettyprint lang-java">private enum Answer {
|
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|
|
YES {
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|
|
@Override public String toString() {
|
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|
|
return "yes";
|
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|
|
}
|
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},
|
|
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NO,
|
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|
MAYBE
|
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|
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}
|
|
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|
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</pre>
|
|
|
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|
|
<p>An enum class with no methods and no documentation on its constants may optionally be formatted
|
2014-03-22 02:23:56 +08:00
|
|
|
as if it were an array initializer (see Section 4.8.3.1 on
|
2016-06-30 07:36:05 +08:00
|
|
|
<a href="#s4.8.3.1-array-initializers">array initializers</a>).</p>
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<pre class="prettyprint lang-java">private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS }
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</pre>
|
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<p>Since enum classes <em>are classes</em>, all other rules for formatting classes apply.</p>
|
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|
<a name="localvariables"></a>
|
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<h4 id="s4.8.2-variable-declarations">4.8.2 Variable declarations</h4>
|
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<h5 id="s4.8.2.1-variables-per-declaration">4.8.2.1 One variable per declaration</h5>
|
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<p>Every variable declaration (field or local) declares only one variable: declarations such as
|
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<code class="badcode">int a, b;</code> are not used.</p>
|
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<h5 id="s4.8.2.2-variables-limited-scope">4.8.2.2 Declared when needed</h5>
|
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|
|
<p>Local variables are <strong>not</strong> habitually declared at the start of their containing
|
2013-12-18 06:56:22 +08:00
|
|
|
block or block-like construct. Instead, local variables are declared close to the point they are
|
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|
|
first used (within reason), to minimize their scope. Local variable declarations typically have
|
2016-06-30 07:36:05 +08:00
|
|
|
initializers, or are initialized immediately after declaration.</p>
|
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|
<h4 id="s4.8.3-arrays">4.8.3 Arrays</h4>
|
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|
|
<h5 id="s4.8.3.1-array-initializers">4.8.3.1 Array initializers: can be "block-like"</h5>
|
|
|
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|
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|
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|
|
<p>Any array initializer may <em>optionally</em> be formatted as if it were a "block-like
|
2013-12-18 06:56:22 +08:00
|
|
|
construct." For example, the following are all valid (<strong>not</strong> an exhaustive
|
2016-06-30 07:36:05 +08:00
|
|
|
list):</p>
|
|
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|
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|
|
<pre class="prettyprint lang-java">new int[] { new int[] {
|
2013-12-18 06:56:22 +08:00
|
|
|
0, 1, 2, 3 0,
|
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|
|
} 1,
|
|
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|
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2,
|
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|
|
new int[] { 3,
|
|
|
|
|
0, 1, }
|
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|
|
2, 3
|
|
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|
|
} new int[]
|
|
|
|
|
{0, 1, 2, 3}
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
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|
|
|
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|
|
<h5 id="s4.8.3.2-array-declarations">4.8.3.2 No C-style array declarations</h5>
|
|
|
|
|
|
|
|
|
|
<p>The square brackets form a part of the <em>type</em>, not the variable:
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">String[] args</code>, not
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="badcode">String args[]</code>.</p>
|
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|
|
<h4 id="s4.8.4-switch">4.8.4 Switch statements</h4>
|
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|
|
<p class="terminology"><strong>Terminology Note:</strong> Inside the braces of a
|
2014-03-22 02:23:56 +08:00
|
|
|
<em>switch block</em> are one or more <em>statement groups</em>. Each statement group consists of
|
|
|
|
|
one or more <em>switch labels</em> (either <code class="prettyprint lang-java">case FOO:</code> or
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">default:</code>), followed by one or more statements.</p>
|
|
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|
|
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|
|
<h5 id="s4.8.4.1-switch-indentation">4.8.4.1 Indentation</h5>
|
|
|
|
|
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|
|
<p>As with any other block, the contents of a switch block are indented +2.</p>
|
|
|
|
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|
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|
|
<p>After a switch label, a newline appears, and the indentation level is increased +2, exactly as
|
2013-12-18 06:56:22 +08:00
|
|
|
if a block were being opened. The following switch label returns to the previous indentation
|
2016-06-30 07:36:05 +08:00
|
|
|
level, as if a block had been closed.</p>
|
|
|
|
|
|
|
|
|
|
<a name="fallthrough"></a>
|
|
|
|
|
<h5 id="s4.8.4.2-switch-fall-through">4.8.4.2 Fall-through: commented</h5>
|
|
|
|
|
|
|
|
|
|
<p>Within a switch block, each statement group either terminates abruptly (with a
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">break</code>,
|
|
|
|
|
<code class="prettyprint lang-java">continue</code>,
|
|
|
|
|
<code class="prettyprint lang-java">return</code> or thrown exception), or is marked with a comment
|
|
|
|
|
to indicate that execution will or <em>might</em> continue into the next statement group. Any
|
|
|
|
|
comment that communicates the idea of fall-through is sufficient (typically
|
|
|
|
|
<code class="prettyprint lang-java">// fall through</code>). This special comment is not required in
|
2016-06-30 07:36:05 +08:00
|
|
|
the last statement group of the switch block. Example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">switch (input) {
|
2013-12-18 06:56:22 +08:00
|
|
|
case 1:
|
|
|
|
|
case 2:
|
|
|
|
|
prepareOneOrTwo();
|
|
|
|
|
// fall through
|
|
|
|
|
case 3:
|
|
|
|
|
handleOneTwoOrThree();
|
|
|
|
|
break;
|
|
|
|
|
default:
|
|
|
|
|
handleLargeNumber(input);
|
|
|
|
|
}
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>Notice that no comment is needed after <code class="prettyprint lang-java">case 1:</code>, only
|
|
|
|
|
at the end of the statement group.</p>
|
|
|
|
|
|
|
|
|
|
<h5 id="s4.8.4.3-switch-default">4.8.4.3 The <code>default</code> case is present</h5>
|
|
|
|
|
|
|
|
|
|
<p>Each switch statement includes a <code class="prettyprint lang-java">default</code> statement
|
|
|
|
|
group, even if it contains no code.</p>
|
|
|
|
|
|
|
|
|
|
<a name="annotations"></a>
|
|
|
|
|
<h4 id="s4.8.5-annotations">4.8.5 Annotations</h4>
|
|
|
|
|
|
|
|
|
|
<p>Annotations applying to a class, method or constructor appear immediately after the
|
2013-12-18 06:56:22 +08:00
|
|
|
documentation block, and each annotation is listed on a line of its own (that is, one annotation
|
|
|
|
|
per line). These line breaks do not constitute line-wrapping (Section
|
|
|
|
|
4.5, <a href="#s4.5-line-wrapping">Line-wrapping</a>), so the indentation level is not
|
2016-06-30 07:36:05 +08:00
|
|
|
increased. Example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">@Override
|
2013-12-18 06:56:22 +08:00
|
|
|
@Nullable
|
|
|
|
|
public String getNameIfPresent() { ... }
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p class="exception"><strong>Exception:</strong> A <em>single</em> parameterless annotation
|
|
|
|
|
<em>may</em> instead appear together with the first line of the signature, for example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">@Override public int hashCode() { ... }
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>Annotations applying to a field also appear immediately after the documentation block, but in
|
2013-12-18 06:56:22 +08:00
|
|
|
this case, <em>multiple</em> annotations (possibly parameterized) may be listed on the same line;
|
2016-06-30 07:36:05 +08:00
|
|
|
for example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">@Partial @Mock DataLoader loader;
|
|
|
|
|
</pre>
|
|
|
|
|
|
2016-07-13 03:08:12 +08:00
|
|
|
<p>There are no specific rules for formatting annotations on parameters, local variables, or types.
|
|
|
|
|
</p>
|
2016-06-30 07:36:05 +08:00
|
|
|
|
|
|
|
|
<a name="comments"></a>
|
|
|
|
|
<h4 id="s4.8.6-comments">4.8.6 Comments</h4>
|
|
|
|
|
|
|
|
|
|
<p>This section addresses <em>implementation comments</em>. Javadoc is addressed separately in
|
|
|
|
|
Section 7, <a href="#s7-javadoc">Javadoc</a>.</p>
|
|
|
|
|
|
|
|
|
|
<h5 id="s4.8.6.1-block-comment-style">4.8.6.1 Block comment style</h5>
|
|
|
|
|
|
|
|
|
|
<p>Block comments are indented at the same level as the surrounding code. They may be in
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">/* ... */</code> style or
|
|
|
|
|
<code class="prettyprint lang-java">// ...</code> style. For multi-line
|
|
|
|
|
<code class="prettyprint lang-java">/* ... */</code> comments, subsequent lines must start with
|
2016-06-30 07:36:05 +08:00
|
|
|
<code>*</code> aligned with the <code>*</code> on the previous line.</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">/*
|
2013-12-18 06:56:22 +08:00
|
|
|
* This is // And so /* Or you can
|
|
|
|
|
* okay. // is this. * even do this. */
|
|
|
|
|
*/
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<p>Comments are not enclosed in boxes drawn with asterisks or other characters.</p>
|
|
|
|
|
|
|
|
|
|
<p class="tip"><strong>Tip:</strong> When writing multi-line comments, use the
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">/* ... */</code> style if you want automatic code formatters to
|
|
|
|
|
re-wrap the lines when necessary (paragraph-style). Most formatters don't re-wrap lines in
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">// ...</code> style comment blocks.</p>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<a name="modifiers"></a>
|
|
|
|
|
<h4 id="s4.8.7-modifiers">4.8.7 Modifiers</h4>
|
|
|
|
|
|
|
|
|
|
<p>Class and member modifiers, when present, appear in the order
|
2013-12-18 06:56:22 +08:00
|
|
|
recommended by the Java Language Specification:
|
2016-06-30 07:36:05 +08:00
|
|
|
</p>
|
|
|
|
|
|
2016-07-13 03:08:12 +08:00
|
|
|
<pre>public protected private abstract default static final transient volatile synchronized native strictfp
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h4 id="s4.8.8-numeric-literals">4.8.8 Numeric Literals</h4>
|
|
|
|
|
|
|
|
|
|
<p><code>long</code>-valued integer literals use an uppercase <code>L</code> suffix, never
|
2014-02-04 07:39:45 +08:00
|
|
|
lowercase (to avoid confusion with the digit <code>1</code>). For example, <code>3000000000L</code>
|
2016-06-30 07:36:05 +08:00
|
|
|
rather than <code class="badcode">3000000000l</code>.</p>
|
|
|
|
|
|
|
|
|
|
<a name="naming"></a>
|
|
|
|
|
<h2 id="s5-naming">5 Naming</h2>
|
|
|
|
|
|
|
|
|
|
<h3 id="s5.1-identifier-names">5.1 Rules common to all identifiers</h3>
|
|
|
|
|
|
|
|
|
|
<p>Identifiers use only ASCII letters and digits, and, in a small number of cases noted below,
|
|
|
|
|
underscores. Thus each valid identifier name is matched by the regular expression
|
|
|
|
|
<code>\w+</code> .</p>
|
|
|
|
|
|
|
|
|
|
<p>In Google Style special prefixes or
|
2014-03-22 02:23:56 +08:00
|
|
|
suffixes, like those seen in the examples <code class="badcode">name_</code>,
|
|
|
|
|
<code class="badcode">mName</code>, <code class="badcode">s_name</code> and
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="badcode">kName</code>, are <strong>not</strong> used.</p>
|
|
|
|
|
|
|
|
|
|
<h3 id="s5.2-specific-identifier-names">5.2 Rules by identifier type</h3>
|
|
|
|
|
|
|
|
|
|
<h4 id="s5.2.1-package-names">5.2.1 Package names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Package names are all lowercase, with consecutive words simply concatenated together (no
|
2014-02-04 07:39:45 +08:00
|
|
|
underscores). For example, <code>com.example.deepspace</code>, not
|
|
|
|
|
<code class="badcode">com.example.deepSpace</code> or
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="badcode">com.example.deep_space</code>.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s5.2.2-class-names">5.2.2 Class names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Class names are written in <a href="#s5.3-camel-case">UpperCamelCase</a>.</p>
|
|
|
|
|
|
|
|
|
|
<p>Class names are typically nouns or noun phrases. For example,
|
2014-02-04 07:39:45 +08:00
|
|
|
<code class="prettyprint lang-java">Character</code> or
|
|
|
|
|
<code class="prettyprint lang-java">ImmutableList</code>. Interface names may also be nouns or
|
|
|
|
|
noun phrases (for example, <code class="prettyprint lang-java">List</code>), but may sometimes be
|
|
|
|
|
adjectives or adjective phrases instead (for example,
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">Readable</code>).</p>
|
|
|
|
|
|
|
|
|
|
<p>There are no specific rules or even well-established conventions for naming annotation types.</p>
|
|
|
|
|
|
|
|
|
|
<p><em>Test</em> classes are named starting with the name of the class they are testing, and ending
|
2013-12-18 06:56:22 +08:00
|
|
|
with <code class="prettyprint lang-java">Test</code>. For example,
|
|
|
|
|
<code class="prettyprint lang-java">HashTest</code> or
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">HashIntegrationTest</code>.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s5.2.3-method-names">5.2.3 Method names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Method names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p>
|
|
|
|
|
|
|
|
|
|
<p>Method names are typically verbs or verb phrases. For example,
|
2014-02-04 07:39:45 +08:00
|
|
|
<code class="prettyprint lang-java">sendMessage</code> or
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">stop</code>.</p>
|
|
|
|
|
|
|
|
|
|
<p>Underscores may appear in JUnit <em>test</em> method names to separate logical components of the
|
2013-12-18 06:56:22 +08:00
|
|
|
name. One typical pattern is <code>test<i><MethodUnderTest></i>_<i><state></i></code>,
|
|
|
|
|
for example <code class="prettyprint lang-java">testPop_emptyStack</code>. There is no One Correct
|
2016-06-30 07:36:05 +08:00
|
|
|
Way to name test methods.</p>
|
|
|
|
|
|
|
|
|
|
<a name="constants"></a>
|
|
|
|
|
<h4 id="s5.2.4-constant-names">5.2.4 Constant names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Constant names use <code class="prettyprint lang-java">CONSTANT_CASE</code>: all uppercase
|
|
|
|
|
letters, with words separated by underscores. But what <em>is</em> a constant, exactly?</p>
|
|
|
|
|
|
|
|
|
|
<p>Every constant is a static final field, but not all static final fields are constants. Before
|
2013-12-18 06:56:22 +08:00
|
|
|
choosing constant case, consider whether the field really <em>feels like</em> a constant. For
|
|
|
|
|
example, if any of that instance's observable state can change, it is almost certainly not a
|
|
|
|
|
constant. Merely <em>intending</em> to never mutate the object is generally not
|
2016-06-30 07:36:05 +08:00
|
|
|
enough. Examples:</p>
|
|
|
|
|
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|
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|
|
<pre class="prettyprint lang-java">// Constants
|
2013-12-18 06:56:22 +08:00
|
|
|
static final int NUMBER = 5;
|
|
|
|
|
static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann");
|
2016-06-30 07:36:05 +08:00
|
|
|
static final Joiner COMMA_JOINER = Joiner.on(','); // because Joiner is immutable
|
2013-12-18 06:56:22 +08:00
|
|
|
static final SomeMutableType[] EMPTY_ARRAY = {};
|
|
|
|
|
enum SomeEnum { ENUM_CONSTANT }
|
|
|
|
|
|
|
|
|
|
// Not constants
|
|
|
|
|
static String nonFinal = "non-final";
|
|
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|
|
final String nonStatic = "non-static";
|
|
|
|
|
static final Set<String> mutableCollection = new HashSet<String>();
|
|
|
|
|
static final ImmutableSet<SomeMutableType> mutableElements = ImmutableSet.of(mutable);
|
|
|
|
|
static final Logger logger = Logger.getLogger(MyClass.getName());
|
|
|
|
|
static final String[] nonEmptyArray = {"these", "can", "change"};
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>These names are typically nouns or noun phrases.</p>
|
|
|
|
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|
|
|
<h4 id="s5.2.5-non-constant-field-names">5.2.5 Non-constant field names</h4>
|
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|
|
|
|
|
|
<p>Non-constant field names (static or otherwise) are written
|
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|
|
in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p>
|
|
|
|
|
|
|
|
|
|
<p>These names are typically nouns or noun phrases. For example,
|
2014-02-04 07:39:45 +08:00
|
|
|
<code class="prettyprint lang-java">computedValues</code> or
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">index</code>.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s5.2.6-parameter-names">5.2.6 Parameter names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Parameter names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p>
|
|
|
|
|
|
|
|
|
|
<p>One-character parameter names in public methods should be avoided.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s5.2.7-local-variable-names">5.2.7 Local variable names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Local variable names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p>
|
|
|
|
|
|
|
|
|
|
<p>Even when final and immutable, local variables are not considered to be constants, and should not
|
|
|
|
|
be styled as constants.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s5.2.8-type-variable-names">5.2.8 Type variable names</h4>
|
|
|
|
|
|
|
|
|
|
<p>Each type variable is named in one of two styles:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>A single capital letter, optionally followed by a single numeral (such as
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">E</code>, <code class="prettyprint lang-java">T</code>,
|
|
|
|
|
<code class="prettyprint lang-java">X</code>, <code class="prettyprint lang-java">T2</code>)
|
2016-06-30 07:36:05 +08:00
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>A name in the form used for classes (see Section 5.2.2,
|
2013-12-18 06:56:22 +08:00
|
|
|
<a href="#s5.2.2-class-names">Class names</a>), followed by the capital letter
|
|
|
|
|
<code class="prettyprint lang-java">T</code> (examples:
|
|
|
|
|
<code class="prettyprint lang-java">RequestT</code>,
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">FooBarT</code>).</li>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<a name="acronyms"></a>
|
|
|
|
|
<a name="camelcase"></a>
|
|
|
|
|
<h3 id="s5.3-camel-case">5.3 Camel case: defined</h3>
|
|
|
|
|
|
|
|
|
|
<p>Sometimes there is more than one reasonable way to convert an English phrase into camel case,
|
2013-12-18 06:56:22 +08:00
|
|
|
such as when acronyms or unusual constructs like "IPv6" or "iOS" are present. To improve
|
2016-06-30 07:36:05 +08:00
|
|
|
predictability, Google Style specifies the following (nearly) deterministic scheme.</p>
|
|
|
|
|
|
|
|
|
|
<p>Beginning with the prose form of the name:</p>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>Convert the phrase to plain ASCII and remove any apostrophes. For example, "Müller's
|
|
|
|
|
algorithm" might become "Muellers algorithm".</li>
|
|
|
|
|
|
|
|
|
|
<li>Divide this result into words, splitting on spaces and any remaining punctuation (typically
|
2013-12-18 06:56:22 +08:00
|
|
|
hyphens).
|
|
|
|
|
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li><em>Recommended:</em> if any word already has a conventional camel-case appearance in common
|
|
|
|
|
usage, split this into its constituent parts (e.g., "AdWords" becomes "ad words"). Note
|
2013-12-18 06:56:22 +08:00
|
|
|
that a word such as "iOS" is not really in camel case <em>per se</em>; it defies <em>any</em>
|
2016-06-30 07:36:05 +08:00
|
|
|
convention, so this recommendation does not apply.</li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>Now lowercase <em>everything</em> (including acronyms), then uppercase only the first
|
2013-12-18 06:56:22 +08:00
|
|
|
character of:
|
2016-06-30 07:36:05 +08:00
|
|
|
<ul>
|
|
|
|
|
<li>... each word, to yield <em>upper camel case</em>, or</li>
|
|
|
|
|
<li>... each word except the first, to yield <em>lower camel case</em></li>
|
|
|
|
|
</ul>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>Finally, join all the words into a single identifier.</li>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
<p>Note that the casing of the original words is almost entirely disregarded. Examples:</p>
|
|
|
|
|
|
|
|
|
|
<table>
|
|
|
|
|
<tbody><tr>
|
|
|
|
|
<th>Prose form</th>
|
|
|
|
|
<th>Correct</th>
|
|
|
|
|
<th>Incorrect</th>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td>"XML HTTP request"</td>
|
|
|
|
|
<td><code class="prettyprint lang-java">XmlHttpRequest</code></td>
|
|
|
|
|
<td><code class="badcode">XMLHTTPRequest</code></td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td>"new customer ID"</td>
|
|
|
|
|
<td><code class="prettyprint lang-java">newCustomerId</code></td>
|
|
|
|
|
<td><code class="badcode">newCustomerID</code></td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td>"inner stopwatch"</td>
|
|
|
|
|
<td><code class="prettyprint lang-java">innerStopwatch</code></td>
|
|
|
|
|
<td><code class="badcode">innerStopWatch</code></td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td>"supports IPv6 on iOS?"</td>
|
|
|
|
|
<td><code class="prettyprint lang-java">supportsIpv6OnIos</code></td>
|
|
|
|
|
<td><code class="badcode">supportsIPv6OnIOS</code></td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td>"YouTube importer"</td>
|
|
|
|
|
<td><code class="prettyprint lang-java">YouTubeImporter</code><br>
|
|
|
|
|
<code class="prettyprint lang-java">YoutubeImporter</code>*</td>
|
|
|
|
|
<td></td>
|
|
|
|
|
</tr>
|
|
|
|
|
</tbody></table>
|
|
|
|
|
|
|
|
|
|
<p>*Acceptable, but not recommended.</p>
|
|
|
|
|
|
|
|
|
|
<p class="note"><strong>Note:</strong> Some words are ambiguously hyphenated in the English
|
2014-03-22 02:23:56 +08:00
|
|
|
language: for example "nonempty" and "non-empty" are both correct, so the method names
|
2013-12-18 06:56:22 +08:00
|
|
|
<code class="prettyprint lang-java">checkNonempty</code> and
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">checkNonEmpty</code> are likewise both correct.</p>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<h2 id="s6-programming-practices">6 Programming Practices</h2>
|
|
|
|
|
|
|
|
|
|
<h3 id="s6.1-override-annotation">6.1 <code>@Override</code>: always used</h3>
|
|
|
|
|
|
|
|
|
|
<p>A method is marked with the <code class="prettyprint lang-java">@Override</code> annotation
|
2014-02-04 07:39:45 +08:00
|
|
|
whenever it is legal. This includes a class method overriding a superclass method, a class method
|
|
|
|
|
implementing an interface method, and an interface method respecifying a superinterface
|
2016-06-30 07:36:05 +08:00
|
|
|
method.</p>
|
|
|
|
|
|
|
|
|
|
<p class="exception"><strong>Exception:</strong>
|
|
|
|
|
<code class="prettyprint lang-java">@Override</code> may be omitted when the parent method is
|
|
|
|
|
<code class="prettyprint lang-java">@Deprecated</code>.</p>
|
|
|
|
|
|
|
|
|
|
<a name="caughtexceptions"></a>
|
|
|
|
|
<h3 id="s6.2-caught-exceptions">6.2 Caught exceptions: not ignored</h3>
|
|
|
|
|
|
|
|
|
|
<p>Except as noted below, it is very rarely correct to do nothing in response to a caught
|
2013-12-18 06:56:22 +08:00
|
|
|
exception. (Typical responses are to log it, or if it is considered "impossible", rethrow it as an
|
2016-06-30 07:36:05 +08:00
|
|
|
<code class="prettyprint lang-java">AssertionError</code>.)</p>
|
|
|
|
|
|
|
|
|
|
<p>When it truly is appropriate to take no action whatsoever in a catch block, the reason this is
|
|
|
|
|
justified is explained in a comment.</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">try {
|
2013-12-18 06:56:22 +08:00
|
|
|
int i = Integer.parseInt(response);
|
|
|
|
|
return handleNumericResponse(i);
|
|
|
|
|
} catch (NumberFormatException ok) {
|
|
|
|
|
// it's not numeric; that's fine, just continue
|
|
|
|
|
}
|
|
|
|
|
return handleTextResponse(response);
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p class="exception"><strong>Exception:</strong> In tests, a caught exception may be ignored
|
|
|
|
|
without comment <em>if</em> its name is or begins with <code class="prettyprint lang-java">expected</code>. The
|
|
|
|
|
following is a very common idiom for ensuring that the code under test <em>does</em> throw an
|
|
|
|
|
exception of the expected type, so a comment is unnecessary here.</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">try {
|
2013-12-18 06:56:22 +08:00
|
|
|
emptyStack.pop();
|
|
|
|
|
fail();
|
|
|
|
|
} catch (NoSuchElementException expected) {
|
|
|
|
|
}
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3 id="s6.3-static-members">6.3 Static members: qualified using class</h3>
|
|
|
|
|
|
|
|
|
|
<p>When a reference to a static class member must be qualified, it is qualified with that class's
|
|
|
|
|
name, not with a reference or expression of that class's type.</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">Foo aFoo = ...;
|
2013-12-18 06:56:22 +08:00
|
|
|
Foo.aStaticMethod(); // good
|
|
|
|
|
<span class="badcode">aFoo.aStaticMethod();</span> // bad
|
|
|
|
|
<span class="badcode">somethingThatYieldsAFoo().aStaticMethod();</span> // very bad
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<a name="finalizers"></a>
|
|
|
|
|
<h3 id="s6.4-finalizers">6.4 Finalizers: not used</h3>
|
|
|
|
|
|
|
|
|
|
<p>It is <strong>extremely rare</strong> to override <code class="prettyprint
|
|
|
|
|
lang-java">Object.finalize</code>.</p>
|
|
|
|
|
|
|
|
|
|
<p class="tip"><strong>Tip:</strong> Don't do it. If you absolutely must, first read and understand
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<a href="http://books.google.com/books?isbn=8131726592"><em>Effective Java</em></a>
|
|
|
|
|
|
|
|
|
|
Item 7, "Avoid Finalizers," very carefully, and <em>then</em> don't do it.</p>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<a name="javadoc"></a>
|
|
|
|
|
<h2 id="s7-javadoc">7 Javadoc</h2>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<h3 id="s7.1-javadoc-formatting">7.1 Formatting</h3>
|
|
|
|
|
|
|
|
|
|
<h4 id="s7.1.1-javadoc-multi-line">7.1.1 General form</h4>
|
|
|
|
|
|
|
|
|
|
<p>The <em>basic</em> formatting of Javadoc blocks is as seen in this example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">/**
|
2013-12-18 06:56:22 +08:00
|
|
|
* Multiple lines of Javadoc text are written here,
|
|
|
|
|
* wrapped normally...
|
|
|
|
|
*/
|
|
|
|
|
public int method(String p1) { ... }
|
2016-06-30 07:36:05 +08:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>... or in this single-line example:</p>
|
|
|
|
|
|
|
|
|
|
<pre class="prettyprint lang-java">/** An especially short bit of Javadoc. */
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>The basic form is always acceptable. The single-line form may be substituted when there are no
|
2013-12-18 06:56:22 +08:00
|
|
|
at-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on a
|
2016-06-30 07:36:05 +08:00
|
|
|
single line.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s7.1.2-javadoc-paragraphs">7.1.2 Paragraphs</h4>
|
|
|
|
|
|
|
|
|
|
<p>One blank line—that is, a line containing only the aligned leading asterisk
|
|
|
|
|
(<code>*</code>)—appears between paragraphs, and before the group of "at-clauses" if
|
2013-12-18 06:56:22 +08:00
|
|
|
present. Each paragraph but the first has <code><p></code> immediately before the first word,
|
2016-06-30 07:36:05 +08:00
|
|
|
with no space after.</p>
|
|
|
|
|
|
|
|
|
|
<h4 id="s7.1.3-javadoc-at-clauses">7.1.3 At-clauses</h4>
|
|
|
|
|
|
|
|
|
|
<p>Any of the standard "at-clauses" that are used appear in the order <code>@param</code>,
|
2013-12-18 06:56:22 +08:00
|
|
|
<code>@return</code>, <code>@throws</code>, <code>@deprecated</code>, and these four types never
|
|
|
|
|
appear with an empty description. When an at-clause doesn't fit on a single line, continuation lines
|
|
|
|
|
are indented four (or more) spaces from the position of the <code>@</code>.
|
2016-06-30 07:36:05 +08:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h3 id="s7.2-summary-fragment">7.2 The summary fragment</h3>
|
|
|
|
|
|
|
|
|
|
<p>The Javadoc for each class and member begins with a brief <strong>summary fragment</strong>. This
|
2013-12-18 06:56:22 +08:00
|
|
|
fragment is very important: it is the only part of the text that appears in certain contexts such as
|
2016-06-30 07:36:05 +08:00
|
|
|
class and method indexes.</p>
|
|
|
|
|
|
|
|
|
|
<p>This is a fragment—a noun phrase or verb phrase, not a complete sentence. It does
|
2013-12-18 06:56:22 +08:00
|
|
|
<strong>not</strong> begin with <code class="badcode">A {@code Foo} is a...</code>, or
|
|
|
|
|
<code class="badcode">This method returns...</code>, nor does it form a complete imperative sentence
|
|
|
|
|
like <code class="badcode">Save the record.</code>. However, the fragment is capitalized and
|
2016-06-30 07:36:05 +08:00
|
|
|
punctuated as if it were a complete sentence.</p>
|
|
|
|
|
|
|
|
|
|
<p class="tip"><strong>Tip:</strong> A common mistake is to write simple Javadoc in the form
|
2014-03-22 02:23:56 +08:00
|
|
|
<code class="badcode">/** @return the customer ID */</code>. This is incorrect, and should be
|
2016-06-30 07:36:05 +08:00
|
|
|
changed to <code class="prettyprint lang-java">/** Returns the customer ID. */</code>.</p>
|
|
|
|
|
|
|
|
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<a name="s7.3.3-javadoc-optional"></a>
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<h3 id="s7.3-javadoc-where-required">7.3 Where Javadoc is used</h3>
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<p>At the <em>minimum</em>, Javadoc is present for every
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<code class="prettyprint lang-java">public</code> class, and every
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<code class="prettyprint lang-java">public</code> or
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<code class="prettyprint lang-java">protected</code> member of such a class, with a few exceptions
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noted below.</p>
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<p>Additional Javadoc content may also be present, as explained in Section 7.3.4,
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<a href="#s7.3.4-javadoc-non-required">Non-required Javadoc</a>.</p>
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<h4 id="s7.3.1-javadoc-exception-self-explanatory">7.3.1 Exception: self-explanatory methods</h4>
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<p>Javadoc is optional for "simple, obvious" methods like
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<code class="prettyprint lang-java">getFoo</code>, in cases where there <em>really and truly</em> is
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nothing else worthwhile to say but "Returns the foo".</p>
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<p class="note"><strong>Important:</strong> it is not appropriate to cite this exception to justify
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omitting relevant information that a typical reader might need to know. For example, for a method
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named <code class="prettyprint lang-java">getCanonicalName</code>, don't omit its documentation
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(with the rationale that it would say only
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<code class="badcode">/** Returns the canonical name. */</code>) if a typical reader may have no idea
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what the term "canonical name" means!</p>
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<h4 id="s7.3.2-javadoc-exception-overrides">7.3.2 Exception: overrides</h4>
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<p>Javadoc is not always present on a method that overrides a supertype method.
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</p>
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<h4 id="s7.3.4-javadoc-non-required">7.3.4 Non-required Javadoc</h4>
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<p>Other classes and members have Javadoc <em>as needed or desired</em>.
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</p><p>Whenever an implementation comment would be used to define the overall purpose or behavior of a
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class or member, that comment is written as Javadoc instead (using <code>/**</code>).</p>
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<p>Non-required Javadoc is not strictly required to follow the formatting rules of Sections
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7.1.2, 7.1.3, and 7.2, though it is of course recommended.</p>
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</div>
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</div>
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</body>
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</html>
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