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- +665 −0 javaguide.html
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javaguide.css
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| +table { | ||
| + border-collapse: collapse; | ||
| +} | ||
| + | ||
| +td, th { | ||
| + border: 1px solid #ccc; | ||
| + padding: 2px 12px; | ||
| + font-size: 10pt; | ||
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| +pre { | ||
| + font-size: 10pt; | ||
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| + border-style: solid; | ||
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| + border-left-width: 5px; | ||
| + padding-left: 12px; | ||
| + padding-right: 12px; | ||
| + padding-top: 4px; | ||
| + padding-bottom: 4px; | ||
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| + | ||
| +hr { | ||
| + margin-top: 3.5em; | ||
| + border-width: 1px; | ||
| + color: #fff; | ||
| +} | ||
| + | ||
| +html { | ||
| + margin-top:2em; | ||
| + margin-left:10%; | ||
| + margin-right:10%; | ||
| + padding:0; | ||
| +} | ||
| + | ||
| +.bp-reset-element, | ||
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| + font-size:100%; | ||
| + font-family:inherit; | ||
| + vertical-align:baseline; | ||
| +} | ||
| + | ||
| +body { | ||
| + font-family:'Arial', sans-serif; | ||
| + font-size:81.25%; | ||
| + color:#222; | ||
| + background-color:#fff; | ||
| + line-height:1.67; | ||
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| +h4, | ||
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| +h6 { | ||
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| + | ||
| +h1 img, | ||
| +h2 img, | ||
| +h3 img, | ||
| +h4 img, | ||
| +h5 img, | ||
| +h6 img { | ||
| + margin:0; | ||
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| + | ||
| +a img { | ||
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| + | ||
| +pre { | ||
| + margin:1.5em 0; | ||
| + white-space:pre; | ||
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| + | ||
| +pre, | ||
| +code, | ||
| +kbd, | ||
| +tt { | ||
| + font:1em 'Droid Sans Mono', monospace; | ||
| + line-height:1.5; | ||
| +} | ||
| + | ||
| +dl { | ||
| + margin:0 0 1.5em 0; | ||
| +} | ||
| + | ||
| +dl dt { | ||
| + font-weight:bold; | ||
| +} | ||
| + | ||
| +dd { | ||
| + margin-left:1.5em; | ||
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| + | ||
| +hr { | ||
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| + border-top:1px solid #ccc; | ||
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| +} | ||
| + | ||
| +table { | ||
| + border:1px solid #bbb; | ||
| + border-spacing:0; | ||
| + border-collapse:collapse; | ||
| + margin:0 0 1.5em; | ||
| + vertical-align:middle; | ||
| + width:100%; | ||
| +} | ||
| + | ||
| +table.unlined, | ||
| +table.unlined th, | ||
| +table.unlined tr, | ||
| +table.unlined td { | ||
| + border:0; | ||
| +} | ||
| + | ||
| +th, | ||
| +td, | ||
| +caption { | ||
| + float:none !important; | ||
| + text-align:left; | ||
| + font-weight:normal; | ||
| + vertical-align:middle; | ||
| + padding:4px; | ||
| +} | ||
| + | ||
| +caption { | ||
| + padding:0; | ||
| +} | ||
| + | ||
| +td { | ||
| + border:1px solid #bbb; | ||
| + vertical-align:top; | ||
| +} | ||
| + | ||
| +th { | ||
| + border:0; | ||
| + border-bottom:1px solid black; | ||
| + font-weight:bold; | ||
| + background:rgb(229, 236, 249); | ||
| +} | ||
| + | ||
| +table th code { | ||
| + background-color:inherit; | ||
| + color:inherit; | ||
| +} | ||
| + | ||
| +table tfoot th { | ||
| + border:1px solid #bbb; | ||
| +} | ||
| + | ||
| +tfoot { | ||
| + font-style:italic; | ||
| +} | ||
| + | ||
| +caption { | ||
| + background:#eee; | ||
| +} | ||
| + | ||
| +table[border='0'] { | ||
| + border:none; | ||
| +} | ||
| + | ||
| +table[border='0']>tbody>tr>td, | ||
| +table[border='0']>tr>td { | ||
| + border:none; | ||
| +} | ||
| + | ||
| +tr.alt td, | ||
| +td.alt { | ||
| + background-color:#efefef; | ||
| +} | ||
| + | ||
| +table.striped tr:nth-child(even) td, | ||
| +table tr.even td { | ||
| + background:#efefef; | ||
| +} | ||
| + | ||
| +table.columns { | ||
| + border:none; | ||
| +} | ||
| + | ||
| +table.columns>tbody>tr>td, | ||
| +table.columns>tr>td { | ||
| + border:none; | ||
| + padding:0 3em 0 0; | ||
| +} | ||
| + | ||
| +table.columns>tbody>tr>td:last-child, | ||
| +table.columns>tr>td:last-child { | ||
| + border:none; | ||
| + padding:0; | ||
| +} | ||
| + | ||
| +ul, | ||
| +ol { | ||
| + margin:0 1.5em 1.5em 0; | ||
| + padding-left:2em; | ||
| +} | ||
| + | ||
| +li ul, | ||
| +li ol { | ||
| + margin:0; | ||
| +} | ||
| + | ||
| +ul { | ||
| + list-style-type:disc; | ||
| +} | ||
| + | ||
| +ol { | ||
| + list-style-type:decimal; | ||
| +} | ||
| + | ||
| +ul { | ||
| + list-style-type:disc; | ||
| +} | ||
| + | ||
| +ul ul { | ||
| + list-style-type:circle; | ||
| +} | ||
| + | ||
| +ul ul ul { | ||
| + list-style-type:square; | ||
| +} | ||
| + | ||
| +ul.disc { | ||
| + list-style-type:disc; | ||
| +} | ||
| + | ||
| +ul.circle { | ||
| + list-style-type:circle; | ||
| +} | ||
| + | ||
| +ul.square { | ||
| + list-style-type:square; | ||
| +} | ||
| + | ||
| +ol { | ||
| + list-style-type:decimal; | ||
| +} | ||
| + | ||
| +ol ol { | ||
| + list-style-type:lower-alpha; | ||
| +} | ||
| + | ||
| +ol ol ol { | ||
| + list-style-type:lower-roman; | ||
| +} | ||
| + | ||
| +ol ul { | ||
| + list-style-type:circle; | ||
| +} | ||
| + | ||
| +ol.decimal { | ||
| + list-style-type:decimal; | ||
| +} | ||
| + | ||
| +ol.upper-alpha { | ||
| + list-style-type:upper-alpha; | ||
| +} | ||
| + | ||
| +ol.lower-alpha { | ||
| + list-style-type:lower-alpha; | ||
| +} | ||
| + | ||
| +ol.upper-roman { | ||
| + list-style-type:upper-roman; | ||
| +} | ||
| + | ||
| +ol.lower-roman { | ||
| + list-style-type:lower-roman; | ||
| +} | ||
| + | ||
| +ol.nolist, | ||
| +ul.nolist { | ||
| + padding-left:0; | ||
| + list-style-image:none; | ||
| + list-style-type:none; | ||
| + margin-left:0; | ||
| +} | ||
| + | ||
| +.center { | ||
| + text-align:center; | ||
| +} | ||
| + | ||
| +code, | ||
| +kbd, | ||
| +pre { | ||
| + color:#007000; | ||
| +} | ||
| + | ||
| +kbd { | ||
| + font-weight: bold; | ||
| +} | ||
| + | ||
| +table.striped code { | ||
| + background-color:inherit; | ||
| +} | ||
| + | ||
| +pre { | ||
| + padding:6px 10px; | ||
| + background-color:#FAFAFA; | ||
| + border:1px solid #bbb; | ||
| + overflow:auto; | ||
| +} | ||
| + | ||
| +pre.prettyprint { | ||
| + padding:6px 10px !important; | ||
| + border:1px solid #bbb !important; | ||
| +} | ||
| + | ||
| +code.bad, code.badcode { | ||
| + background-color:#fcc; | ||
| +} | ||
| +pre.bad, pre.badcode { | ||
| + background-color:#fcc; | ||
| + border-top:1px inset #a03; | ||
| + border-left:1px inset #a03; | ||
| +} | ||
| + | ||
| +.tip { | ||
| + background-color:#fffbd9; | ||
| + padding:6px 8px 6px 10px; | ||
| + border-left:6px solid #ffef70; | ||
| +} | ||
| + | ||
| +.note { | ||
| + background-color:#e5ecf9; | ||
| + padding:6px 8px 6px 10px; | ||
| + border-left:6px solid #36c; | ||
| +} | ||
| + | ||
| +@media print { | ||
| + | ||
| + .str { | ||
| + color:#060; | ||
| + } | ||
| + | ||
| + .kwd { | ||
| + color:#006; | ||
| + font-weight:bold; | ||
| + } | ||
| + | ||
| + .com { | ||
| + color:#600; | ||
| + font-style:italic; | ||
| + } | ||
| + | ||
| + .typ { | ||
| + color:#404; | ||
| + font-weight:bold; | ||
| + } | ||
| + | ||
| + .lit { | ||
| + color:#044; | ||
| + } | ||
| + | ||
| + .pun, | ||
| + .opn, | ||
| + .clo { | ||
| + color:#440; | ||
| + } | ||
| + | ||
| + .pln { | ||
| + color:#000; | ||
| + } | ||
| + | ||
| + .tag { | ||
| + color:#006; | ||
| + font-weight:bold; | ||
| + } | ||
| + | ||
| + .atn { | ||
| + color:#404; | ||
| + } | ||
| + | ||
| + .atv { | ||
| + color:#060; | ||
| + } | ||
| + | ||
| + h1 { | ||
| + font-style:italic; | ||
| + } | ||
| +} | ||
| + | ||
| +ol.linenums { | ||
| + margin-top:0; | ||
| + margin-bottom:0; | ||
| +} | ||
| + | ||
| +code { | ||
| + background-color:#FAFAFA; | ||
| + padding: 0.25em 0.5em; | ||
| + white-space: nowrap | ||
| +} |
665
javaguide.html
| @@ -0,0 +1,665 @@ | ||
| +<html lang="en"> | ||
| +<head> | ||
| + <meta http-equiv="content-type" content="text/html; charset=UTF-8" /> | ||
| + <link rel="stylesheet" type="text/css" href="javaguide.css"/> | ||
| + <script src="http://google-code-prettify.googlecode.com/svn/loader/run_prettify.js" | ||
| + type="text/javascript"></script> | ||
| + <link href="http://www.google.com/favicon.ico" | ||
| + type="image/x-icon" rel="shortcut icon" /> | ||
| + <title>Google Java Style</title> | ||
| +</head> | ||
| +<body> | ||
| + <h1>Google Java Style</h1> | ||
| + <div class="change">Last changed: December 17, 2013</div> | ||
| +<table border="0"> | ||
| +<tr> | ||
| +<td> | ||
| +<dl> | ||
| +<dt> | ||
| +<a href="#s1-introduction">1 Introduction</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s1.1-terminology">1.1 Terminology notes</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s1.2-guide-notes">1.2 Guide notes</a> | ||
| +</dd> | ||
| +<dt> | ||
| +<a href="#s2-source-file-basics">2 Source file basics</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s2.1-file-name">2.1 File name</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s2.2-file-encoding">2.2 File encoding: UTF-8</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s2.3-special-characters">2.3 Special characters</a> | ||
| +</dd> | ||
| +<dt> | ||
| +<a href="#s3-source-file-structure">3 Source file structure</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s3.1-copyright-statement">3.1 License or copyright information, if present</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s3.2-package-statement">3.2 Package statement</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s3.3-import-statements">3.3 Import statements</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s3.4-class-declaration">3.4 Class declaration</a> | ||
| +</dd> | ||
| +</dl> | ||
| +</td><td> | ||
| +<dl> | ||
| +<dt> | ||
| +<a href="#s4-formatting">4 Formatting</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s4.1-braces">4.1 Braces</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.2-block-indentation">4.2 Block indentation: +2 spaces</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.3-one-statement-per-line">4.3 One statement per line</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.4-column-limit">4.4 Column limit: 80 or 100</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.5-line-wrapping">4.5 Line-wrapping</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.6-whitespace">4.6 Whitespace</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.7-grouping-parentheses">4.7 Grouping parentheses: recommended</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s4.8-specific-constructs">4.8 Specific constructs</a> | ||
| +</dd> | ||
| +<dt> | ||
| +<a href="#s5-naming">5 Naming</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s5.1-identifier-names">5.1 Rules common to all identifiers</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s5.2-specific-identifier-names">5.2 Rules by identifier type</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s5.3-camel-case">5.3 Camel case: defined</a> | ||
| +</dd> | ||
| +</dl> | ||
| +</td><td> | ||
| +<dl> | ||
| +<dt> | ||
| +<a href="#s6-programming-practices">6 Programming Practices</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s6.1-override-annotation">6.1 @Override: always used</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s6.2-caught-exceptions">6.2 Caught exceptions: not ignored</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s6.3-static-members">6.3 Static members: qualified using class</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s6.4-finalizers">6.4 Finalizers: not used</a> | ||
| +</dd> | ||
| +<dt> | ||
| +<a href="#s7-javadoc">7 Javadoc</a> | ||
| +</dt> | ||
| +<dd> | ||
| +<a href="#s7.1-javadoc-formatting">7.1 Formatting</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s7.2-summary-fragment">7.2 The summary fragment</a> | ||
| +</dd> | ||
| +<dd> | ||
| +<a href="#s7.3-javadoc-where-required">7.3 Where Javadoc is used</a> | ||
| +</dd> | ||
| +</dl> | ||
| +</td> | ||
| +</tr> | ||
| +</table> | ||
| +<div><div id="with-header-links"><a name="s1-introduction"/> | ||
| + <h2>1 Introduction <a href="#s1-introduction"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <p>This document serves as the <strong>complete</strong> definition of Google's coding standards for | ||
| +source code in the Java™ Programming Language. A Java source file is described as being <em>in | ||
| +Google Style</em> if and only if it adheres to the rules herein.</p><p>Like other programming style guides, the issues covered span not only aesthetic issues of | ||
| +formatting, but other types of conventions or coding standards as well. However, this document | ||
| +focuses primarily on the <strong>hard-and-fast rules</strong> that we follow universally, and | ||
| +avoids giving <em>advice</em> that isn't clearly enforceable (whether by human or tool). | ||
| +</p><a name="s1.1-terminology"/> | ||
| + <h3>1.1 Terminology notes <a href="#s1.1-terminology"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>In this document, unless otherwise clarified:</p><ol><li>The term <em>class</em> is used inclusively to mean an "ordinary" class, enum class, | ||
| + interface or annotation type (<code class="prettyprint lang-java">@interface</code>).</li><li>The term <em>comment</em> always refers to <em>implementation</em> comments. We do not | ||
| + use the phrase "documentation comments", instead using the common term "Javadoc."</li></ol><p>Other "terminology notes" will appear occasionally throughout the document.</p><a name="s1.2-guide-notes"/> | ||
| + <h3>1.2 Guide notes <a href="#s1.2-guide-notes"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Example code in this document is <strong>non-normative</strong>. That is, while the examples | ||
| +are in Google Style, they may not illustrate the <em>only</em> stylish way to represent the | ||
| +code. Optional formatting choices made in examples should not be enforced as rules.</p><a name="s2-source-file-basics"/> | ||
| + <h2>2 Source file basics <a href="#s2-source-file-basics"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <a name="s2.1-file-name"/> | ||
| + <h3>2.1 File name <a href="#s2.1-file-name"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>The source file name consists of the case-sensitive name of the top-level class it contains, | ||
| +plus the <code>.java</code> extension (aside from <code>package-info.java</code> files).</p><a name="s2.2-file-encoding"/> | ||
| + <h3>2.2 File encoding: UTF-8 <a href="#s2.2-file-encoding"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Source files are encoded in <strong>UTF-8</strong>.</p><a name="s2.3-special-characters"/> | ||
| + <h3>2.3 Special characters <a href="#s2.3-special-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s2.3.1-whitespace-characters"/> | ||
| + <h4>2.3.1 Whitespace characters <a href="#s2.3.1-whitespace-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Aside from the line terminator sequence, the <strong>ASCII horizontal space | ||
| +character</strong> (<strong>0x20</strong>) is the only whitespace character that appears | ||
| +anywhere in a source file. This implies that:</p><ol><li>All other whitespace characters in string and character literals are escaped.</li><li>Tab characters are <strong>not</strong> used for indentation.</li></ol><a name="s2.3.2-special-escape-sequences"/> | ||
| + <h4>2.3.2 Special escape sequences <a href="#s2.3.2-special-escape-sequences"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>For any character that has a special escape sequence | ||
| +(<code class="prettyprint lang-java">\b</code>, | ||
| +<code class="prettyprint lang-java">\t</code>, | ||
| +<code class="prettyprint lang-java">\n</code>, | ||
| +<code class="prettyprint lang-java">\f</code>, | ||
| +<code class="prettyprint lang-java">\r</code>, | ||
| +<code class="prettyprint lang-java">\"</code>, | ||
| +<code class="prettyprint lang-java">\'</code> and | ||
| +<code class="prettyprint lang-java">\\</code>), that sequence | ||
| +is used rather than the corresponding octal | ||
| +(e.g. <code class="prettyprint lang-java badcode">\012</code>) or Unicode | ||
| +(e.g. <code class="prettyprint lang-java badcode">\u000a</code>) escape.</p><a name="s2.3.3-non-ascii-characters"/> | ||
| + <h4>2.3.3 Non-ASCII characters <a href="#s2.3.3-non-ascii-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>For the remaining non-ASCII characters, either the actual Unicode character | ||
| +(e.g. <code class="prettyprint lang-java">∞</code>) or the equivalent Unicode escape | ||
| +(e.g. <code class="prettyprint lang-java">\u221e</code>) is used, depending only on which | ||
| +makes the code <strong>easier to read and understand</strong>.</p><p class="tip"><b>Tip:</b> in the Unicode escape case, and occasionally even when actual Unicode characters | ||
| +are used, an explanatory comment can be very helpful.</p><p>Examples:</p><table><tr><th>Example</th><th>Discussion</th></tr><tr><td><code class="prettyprint lang-java">String unitAbbrev = "μs";</code></td><td>Best: perfectly clear even without a comment.</td></tr><tr><td><code class="prettyprint lang-java">String unitAbbrev = "\u03bcs"; // "μs"</code></td><td>Allowed, but there's no reason to do this.</td></tr><tr><td><code class="prettyprint lang-java">String unitAbbrev = "\u03bcs"; | ||
| + // Greek letter mu, "s"</code></td><td>Allowed, but awkward and prone to mistakes.</td></tr><tr><td><code class="prettyprint lang-java badcode">String unitAbbrev = "\u03bcs";</code></td><td>Poor: the reader has no idea what this is.</td></tr><tr><td><code class="prettyprint lang-java">return '\ufeff' + content; | ||
| + // byte order mark</code></td><td>Good: use escapes for non-printable characters, and comment if necessary.</td></tr></table><p class="tip"><b>Tip:</b> Never make your code less readable simply out of fear that some programs might | ||
| +not handle non-ASCII characters properly. If that should happen, those programs | ||
| +are <strong>broken</strong> and they must be <strong>fixed</strong>.</p><a name="filestructure"/><a name="s3-source-file-structure"/> | ||
| + <h2>3 Source file structure <a href="#s3-source-file-structure"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <div><p>A source file consists of, <strong>in order</strong>:</p><ol><li>License or copyright information, if present</li><li>Package statement</li><li>Import statements</li><li>Exactly one top-level class</li></ol></div><p><strong>Exactly one blank line</strong> separates each section that is present.</p><a name="s3.1-copyright-statement"/> | ||
| + <h3>3.1 License or copyright information, if present <a href="#s3.1-copyright-statement"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>If license or copyright information belongs in a file, it belongs here.</p><a name="s3.2-package-statement"/> | ||
| + <h3>3.2 Package statement <a href="#s3.2-package-statement"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>The package statement is <strong>not line-wrapped</strong>. The column limit (Section 4.4, | ||
| +<a href="#s4.4-column-limit">Column limit: 80 or 100</a>) does not apply to package statements.</p><a name="imports"/><a name="s3.3-import-statements"/> | ||
| + <h3>3.3 Import statements <a href="#s3.3-import-statements"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s3.3.1-wildcard-imports"/> | ||
| + <h4>3.3.1 No wildcard imports <a href="#s3.3.1-wildcard-imports"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p><strong>Wildcard imports</strong>, static or otherwise, <strong>are not used</strong>.</p><a name="s3.3.2-import-line-wrapping"/> | ||
| + <h4>3.3.2 No line-wrapping <a href="#s3.3.2-import-line-wrapping"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Import statements are <strong>not line-wrapped</strong>. The column limit (Section 4.4, | ||
| +<a href="#s4.4-column-limit">Column limit: 80 or 100</a>) does not apply to import | ||
| +statements.</p><a name="s3.3.3-import-ordering-and-spacing"/> | ||
| + <h4>3.3.3 Ordering and spacing <a href="#s3.3.3-import-ordering-and-spacing"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Import statements are divided into the following groups, in this order, with each group | ||
| +separated by a single blank line:</p><ol><li>All static imports in a single group</li><li><code>com.google</code> imports | ||
| + (only if this source file is in the <code>com.google</code> package | ||
| + space)</li><li>Third-party imports, one group per top-level package, in ASCII sort order | ||
| + <ul><li>for example: <code>android</code>, <code>com</code>, <code>junit</code>, <code>org</code>, | ||
| + <code>sun</code></li></ul></li><li><code>java</code> imports</li><li><code>javax</code> imports</li></ol><p>Within a group there are no blank lines, and the imported names appear in ASCII sort | ||
| +order. (<strong>Note:</strong> this is not the same as the import <em>statements</em> being in | ||
| +ASCII sort order; the presence of semicolons warps the result.)</p><a name="s3.4-class-declaration"/> | ||
| + <h3>3.4 Class declaration <a href="#s3.4-class-declaration"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="oneclassperfile"/><a name="s3.4.1-one-top-level-class"/> | ||
| + <h4>3.4.1 Exactly one top-level class declaration <a href="#s3.4.1-one-top-level-class"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Each top-level class resides in a source file of its own.</p><p class="exception"><b>Exception:</b> of course, no such class appears in <code>package-info.java</code> | ||
| +files.</p><a name="s3.4.2-class-member-ordering"/> | ||
| + <h4>3.4.2 Class member ordering <a href="#s3.4.2-class-member-ordering"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>The ordering of the members of a class can have a great effect on learnability, but there is | ||
| +no single correct recipe for how to do it. Different classes may order their members | ||
| +differently.</p><p>What is important is that each class order its members in <strong><em>some</em> logical | ||
| +order</strong>, which its maintainer could explain if asked. For example, new methods are not | ||
| +just habitually added to the end of the class, as that would yield "chronological by date | ||
| +added" ordering, which is not a logical ordering.</p><a name="overloads"/><a name="s3.4.2.1-overloads-never-split"/> | ||
| + <h5>3.4.2.1 Overloads: never split <a href="#s3.4.2.1-overloads-never-split"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>When a class has multiple constructors, or multiple methods with the same name, these appear | ||
| +sequentially, with no intervening members.</p><a name="s4-formatting"/> | ||
| + <h2>4 Formatting <a href="#s4-formatting"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <p class="terminology"><b>Terminology Note:</b> <em>block-like construct</em> refers to the body of a class, method or | ||
| +constructor. Note that, by Section 4.8.3.1 on | ||
| +<a href="#s4.8.3.1-array-initializers">array initializers</a>, any array initializer | ||
| +<em>may</em> optionally be treated as if it were a block-like construct.</p><a name="braces"/><a name="s4.1-braces"/> | ||
| + <h3>4.1 Braces <a href="#s4.1-braces"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s4.1.1-braces-always-used"/> | ||
| + <h4>4.1.1 Braces are used where optional <a href="#s4.1.1-braces-always-used"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Braces are used with | ||
| +<code class="prettyprint lang-java">if</code>, | ||
| +<code class="prettyprint lang-java">else</code>, | ||
| +<code class="prettyprint lang-java">for</code>, | ||
| +<code class="prettyprint lang-java">do</code> and | ||
| +<code class="prettyprint lang-java">while</code> statements, even when the | ||
| +body is empty or contains only a single statement.</p><a name="s4.1.2-blocks-k-r-style"/> | ||
| + <h4>4.1.2 Nonempty blocks: K & R style <a href="#s4.1.2-blocks-k-r-style"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Braces follow the Kernighan and Ritchie style | ||
| +("<a href="http://www.codinghorror.com/blog/2012/07/new-programming-jargon.html">Egyptian brackets</a>") | ||
| +for <em>nonempty</em> blocks and block-like constructs:</p><ul><li>No line break before the opening brace.</li><li>Line break after the opening brace.</li><li>Line break before the closing brace.</li><li>Line break after the closing brace <em>if</em> that brace terminates a statement or the body | ||
| + of a method, constructor or <em>named</em> class. For example, there is <em>no</em> line break | ||
| + after the brace if it is followed by <code class="prettyprint lang-java">else</code> or a | ||
| + comma.</li></ul><p>Example:</p><pre class="prettyprint lang-java"> | ||
| +return new MyClass() { | ||
| + @Override public void method() { | ||
| + if (condition()) { | ||
| + try { | ||
| + something(); | ||
| + } catch (ProblemException e) { | ||
| + recover(); | ||
| + } | ||
| + } | ||
| + } | ||
| +}; | ||
| +</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 name="s4.1.3-braces-empty-blocks"/> | ||
| + <h4>4.1.3 Empty blocks: may be concise <a href="#s4.1.3-braces-empty-blocks"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>An empty block or block-like construct <em>may</em> be closed immediately after it is | ||
| +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 | ||
| +<code class="prettyprint lang-java">try/catch/finally</code>).</p><p>Example:</p><pre class="prettyprint lang-java"> | ||
| + void doNothing() {} | ||
| +</pre><a name="s4.2-block-indentation"/> | ||
| + <h3>4.2 Block indentation: +2 spaces <a href="#s4.2-block-indentation"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Each time a new block or block-like construct is opened, the indent increases by two | ||
| +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, | ||
| +<a href="#s4.1.2-blocks-k-r-style">Nonempty blocks: K & R Style</a>.)</p><a name="s4.3-one-statement-per-line"/> | ||
| + <h3>4.3 One statement per line <a href="#s4.3-one-statement-per-line"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Each statement is followed by a line-break.</p><a name="columnlimit"/><a name="s4.4-column-limit"/> | ||
| + <h3>4.4 Column limit: 80 or 100 <a href="#s4.4-column-limit"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p> | ||
| + Projects are free to choose a column limit of either 80 or 100 characters. | ||
| + | ||
| +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>. | ||
| +</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 | ||
| + <code class="prettyprint lang-java">import</code> statements (see Sections | ||
| + 3.2 <a href="#s3.2-package-statement">Package statement</a> and | ||
| + 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><a name="s4.5-line-wrapping"/> | ||
| + <h3>4.5 Line-wrapping <a href="#s4.5-line-wrapping"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p class="terminology"><b>Terminology Note:</b> When code that might otherwise legally occupy a single line is divided into | ||
| +multiple lines, typically to avoid overflowing the column limit, 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="tip"><b>Tip:</b> extracting a method or local variable may solve the problem without the need to | ||
| +line-wrap.</p><a name="s4.5.1-line-wrapping-where-to-break"/> | ||
| + <h4>4.5.1 Where to break <a href="#s4.5.1-line-wrapping-where-to-break"><img height="21" width="21" src="javaguidelink.png"/></a></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> | ||
| + the symbol. (Note that this is not the same practice used in Google style for other languages, | ||
| + such as C++ and JavaScript.) | ||
| + <ul><li>This also applies to the following "operator-like" symbols: the dot separator | ||
| + (<code class="prettyprint lang-java">.</code>), the ampersand in type bounds | ||
| + (<code class="prettyprint lang-java"><T extends Foo & Bar></code>), and the pipe in | ||
| + catch blocks | ||
| + (<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 | ||
| + <em>after</em> the symbol, but either way is acceptable. | ||
| + <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><a name="indentation"/><a name="s4.5.2-line-wrapping-indent"/> | ||
| + <h4>4.5.2 Indent continuation lines at least +4 spaces <a href="#s4.5.2-line-wrapping-indent"><img height="21" width="21" src="javaguidelink.png"/></a></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 | ||
| +desired. In general, two continuation lines use the same indentation level if and only if they | ||
| +begin with syntactically parallel elements.</p><p>Section 4.6.3 on <a href="#s4.6.3-horizontal-alignment">Horizontal alignment</a> addresses | ||
| +the discouraged practice of using a variable number of spaces to align certain tokens with | ||
| +previous lines.</p><a name="s4.6-whitespace"/> | ||
| + <h3>4.6 Whitespace <a href="#s4.6-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s4.6.1-vertical-whitespace"/> | ||
| + <h4>4.6.1 Vertical Whitespace <a href="#s4.6.1-vertical-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>A single blank line appears:</p><ol><li><em>Between</em> consecutive members (or initializers) of a class: fields, constructors, | ||
| + methods, nested classes, static initializers, instance initializers. | ||
| + <ul><li><span class="exception"><b>Exception:</b> a blank line between two consecutive fields (having no other code | ||
| + between them) is optional. Such blank lines are used as needed to create <em>logical | ||
| + groupings</em> of fields.</span></li></ul></li><li>Within method bodies, as needed to create <em>logical groupings</em> of statements.</li><li><em>Optionally</em> before the first member or after the last member of the class (neither | ||
| + encouraged nor discouraged).</li><li>As required by other sections of this document (such as Section 3.3, | ||
| + <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><a name="s4.6.2-horizontal-whitespace"/> | ||
| + <h4>4.6.2 Horizontal whitespace <a href="#s4.6.2-horizontal-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></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 | ||
| + <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>) | ||
| + that follows it on that line</li><li>Separating any reserved word, such as | ||
| + <code class="prettyprint lang-java">else</code> or | ||
| + <code class="prettyprint lang-java">catch</code>, from a closing curly brace | ||
| + (<code class="prettyprint lang-java">}</code>) that precedes it on that line</li><li>Before any open curly brace | ||
| + (<code class="prettyprint lang-java">{</code>), with two exceptions: | ||
| + <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 | ||
| + "operator-like" symbols: | ||
| + <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></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><p class="note"><b>Note:</b> this rule never requires or forbids additional space at the start or end of a | ||
| +line, only <em>interior</em> space.</p><a name="s4.6.3-horizontal-alignment"/> | ||
| + <h4>4.6.3 Horizontal alignment: never required <a href="#s4.6.3-horizontal-alignment"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p class="terminology"><b>Terminology Note:</b> Horizontal alignment is the practice of adding a variable number of | ||
| +additional spaces in your code with the goal of making 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 | ||
| +private Color color; // this too | ||
| + | ||
| +private int x; // permitted, but future edits | ||
| +private Color color; // may leave it unaligned | ||
| +</pre><p class="tip"><b>Tip:</b> Alignment can aid readability, but it creates problems for 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 information, slows down | ||
| +reviewers and exacerbates merge conflicts.</p><a name="parentheses"/><a name="s4.7-grouping-parentheses"/> | ||
| + <h3>4.7 Grouping parentheses: recommended <a href="#s4.7-grouping-parentheses"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Optional grouping parentheses are omitted only when author and reviewer agree that there is no | ||
| +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 | ||
| +operator precedence table memorized.</p><a name="s4.8-specific-constructs"/> | ||
| + <h3>4.8 Specific constructs <a href="#s4.8-specific-constructs"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s4.8.1-enum-classes"/> | ||
| + <h4>4.8.1 Enum classes <a href="#s4.8.1-enum-classes"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>After each comma that follows an enum constant, a line-break is optional.</p><p>An enum class with no methods and no documentation on its constants may optionally be formatted | ||
| +as if it were an array initializer:</p><pre class="prettyprint lang-java"> | ||
| +private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS } | ||
| +</pre><p>Since enum classes <em>are classes</em>, all other rules for formatting classes apply.</p><a name="localvariables"/><a name="s4.8.2-variable-declarations"/> | ||
| + <h4>4.8.2 Variable declarations <a href="#s4.8.2-variable-declarations"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <a name="s4.8.2.1-variables-per-declaration"/> | ||
| + <h5>4.8.2.1 One variable per declaration <a href="#s4.8.2.1-variables-per-declaration"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>Combined declarations such as <code class="prettyprint lang-java badcode">int a, b;</code> are | ||
| +<strong>not</strong> used.</p><a name="s4.8.2.2-variables-limited-scope"/> | ||
| + <h5>4.8.2.2 Declared when needed, initialized as soon as | ||
| +possible <a href="#s4.8.2.2-variables-limited-scope"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>Local variables are <strong>not</strong> habitually declared at the start of their containing | ||
| +block or block-like construct. Instead, local variables are declared close to the point they are | ||
| +first used (within reason), to minimize their scope. Local variable declarations typically have | ||
| +initializers, or are initialized immediately after declaration.</p><a name="s4.8.3-arrays"/> | ||
| + <h4>4.8.3 Arrays <a href="#s4.8.3-arrays"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <a name="s4.8.3.1-array-initializers"/> | ||
| + <h5>4.8.3.1 Array initializers: can be "block-like" <a href="#s4.8.3.1-array-initializers"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>Any array initializer may <em>optionally</em> be formatted as if it were a "block-like | ||
| +construct." For example, the following are all valid (<strong>not</strong> an exhaustive | ||
| +list):</p><pre class="prettyprint lang-java"> | ||
| +new int[] { new int[] { | ||
| + 0, 1, 2, 3 0, | ||
| +} 1, | ||
| + 2, | ||
| +new int[] { 3, | ||
| + 0, 1, } | ||
| + 2, 3 | ||
| +} new int[] | ||
| + {0, 1, 2, 3} | ||
| +</pre><a name="s4.8.3.2-array-declarations"/> | ||
| + <h5>4.8.3.2 No C-style array declarations <a href="#s4.8.3.2-array-declarations"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>The square brackets form a part of the <em>type</em>, not the variable: | ||
| +<code class="prettyprint lang-java">String[] args</code>, not | ||
| +<code class="prettyprint lang-java badcode">String args[]</code>.</p><a name="s4.8.4-switch"/> | ||
| + <h4>4.8.4 Switch statements <a href="#s4.8.4-switch"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p class="terminology"><b>Terminology Note:</b> Inside the braces of a <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 | ||
| +<code class="prettyprint lang-java">default:</code>), followed by one or more statements.</p><a name="s4.8.4.1-switch-indentation"/> | ||
| + <h5>4.8.4.1 Indentation <a href="#s4.8.4.1-switch-indentation"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>As with any other block, the contents of a switch block are indented +2.</p><p>After a switch label, a newline appears, and the indentation level is increased +2, exactly as | ||
| +if a block were being opened. The following switch label returns to the previous indentation | ||
| +level, as if a block had been closed.</p><a name="fallthrough"/><a name="s4.8.4.2-switch-fall-through"/> | ||
| + <h5>4.8.4.2 Fall-through: commented <a href="#s4.8.4.2-switch-fall-through"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>Within a switch block, each statement group either terminates abruptly (with a | ||
| +<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 | ||
| +the last statement group of the switch block. Example:</p><pre class="prettyprint lang-java"> | ||
| +switch (input) { | ||
| + case 1: | ||
| + case 2: | ||
| + prepareOneOrTwo(); | ||
| + // fall through | ||
| + case 3: | ||
| + handleOneTwoOrThree(); | ||
| + break; | ||
| + default: | ||
| + handleLargeNumber(input); | ||
| +} | ||
| +</pre><a name="s4.8.4.3-switch-default"/> | ||
| + <h5>4.8.4.3 The default case is present <a href="#s4.8.4.3-switch-default"><img height="21" width="21" src="javaguidelink.png"/></a></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 name="s4.8.5-annotations"/> | ||
| + <h4>4.8.5 Annotations <a href="#s4.8.5-annotations"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Annotations applying to a class, method or constructor appear immediately after the | ||
| +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 | ||
| +increased. Example:</p><pre class="prettyprint lang-java"> | ||
| +@Override | ||
| +@Nullable | ||
| +public String getNameIfPresent() { ... } | ||
| +</pre><p class="exception"><b>Exception:</b> 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 | ||
| +this case, <em>multiple</em> annotations (possibly parameterized) may be listed on the same line; | ||
| +for example:</p><pre class="prettyprint lang-java"> | ||
| +@Partial @Mock DataLoader loader; | ||
| +</pre><p>There are no specific rules for formatting parameter and local variable annotations.</p><a name="comments"/><a name="s4.8.6-comments"/> | ||
| + <h4>4.8.6 Comments <a href="#s4.8.6-comments"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <a name="s4.8.6.1-block-comment-style"/> | ||
| + <h5>4.8.6.1 Block comment style <a href="#s4.8.6.1-block-comment-style"><img height="21" width="21" src="javaguidelink.png"/></a></h5> | ||
| + <p>Block comments are indented at the same level as the surrounding code. They may be in | ||
| +<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 | ||
| +<code>*</code> aligned with the <code>*</code> on the previous line.</p><pre class="prettyprint lang-java"> | ||
| +/* | ||
| + * This is // And so /* Or you can | ||
| + * okay. // is this. * even do this. */ | ||
| + */ | ||
| +</pre><p>Comments are not enclosed in boxes drawn with asterisks or other characters.</p><p class="tip"><b>Tip:</b> When writing multi-line comments, use the | ||
| +<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 | ||
| +<code class="prettyprint lang-java">// ...</code> style comment blocks.</p><a name="modifiers"/><a name="s4.8.7-modifiers"/> | ||
| + <h4>4.8.7 Modifiers <a href="#s4.8.7-modifiers"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Class and member modifiers, when present, appear in the order | ||
| +recommended by the Java Language Specification: | ||
| +</p><pre> | ||
| +public protected private abstract static final transient volatile synchronized native strictfp | ||
| +</pre><a name="naming"/><a name="s5-naming"/> | ||
| + <h2>5 Naming <a href="#s5-naming"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <a name="s5.1-identifier-names"/> | ||
| + <h3>5.1 Rules common to all identifiers <a href="#s5.1-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Identifiers use only ASCII letters and digits, and in two 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 | ||
| +suffixes, like those seen in the examples <code class="prettyprint lang-java badcode">name_</code>, | ||
| +<code class="prettyprint lang-java badcode">mName</code>, | ||
| +<code class="prettyprint lang-java badcode">s_name</code> and | ||
| +<code class="prettyprint lang-java badcode">kName</code>, are <strong>not</strong> used.</p><a name="s5.2-specific-identifier-names"/> | ||
| + <h3>5.2 Rules by identifier type <a href="#s5.2-specific-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s5.2.1-package-names"/> | ||
| + <h4>5.2.1 Package names <a href="#s5.2.1-package-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Package names are all lowercase, with consecutive words simply concatenated together (no | ||
| +underscores).</p><a name="s5.2.2-class-names"/> | ||
| + <h4>5.2.2 Class names <a href="#s5.2.2-class-names"><img height="21" width="21" src="javaguidelink.png"/></a></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. Interface names may sometimes be adjectives or | ||
| +adjective phrases instead. 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 | ||
| +with <code class="prettyprint lang-java">Test</code>. For example, | ||
| +<code class="prettyprint lang-java">HashTest</code> or | ||
| +<code class="prettyprint lang-java">HashIntegrationTest</code>.</p><a name="s5.2.3-method-names"/> | ||
| + <h4>5.2.3 Method names <a href="#s5.2.3-method-names"><img height="21" width="21" src="javaguidelink.png"/></a></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.</p><p>Underscores may appear in JUnit <em>test</em> method names to separate logical components of the | ||
| +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 | ||
| +Way to name test methods.</p><a name="constants"/><a name="s5.2.4-constant-names"/> | ||
| + <h4>5.2.4 Constant names <a href="#s5.2.4-constant-names"><img height="21" width="21" src="javaguidelink.png"/></a></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 | ||
| +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 | ||
| +enough. Examples:</p><pre class="prettyprint lang-java"> | ||
| +// Constants | ||
| +static final int NUMBER = 5; | ||
| +static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann"); | ||
| +static final Joiner COMMA_JOINER = Joiner.on(','); // because Joiner is immutable | ||
| +static final SomeMutableType[] EMPTY_ARRAY = {}; | ||
| +enum SomeEnum { ENUM_CONSTANT } | ||
| + | ||
| +// Not constants | ||
| +static String nonFinal = "non-final"; | ||
| +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"}; | ||
| +</pre><p>These names are typically nouns or noun phrases.</p><a name="s5.2.5-non-constant-field-names"/> | ||
| + <h4>5.2.5 Non-constant field names <a href="#s5.2.5-non-constant-field-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Non-constant field names (static or otherwise) are written | ||
| +in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p><p>These names are typically nouns or noun phrases.</p><a name="s5.2.6-parameter-names"/> | ||
| + <h4>5.2.6 Parameter names <a href="#s5.2.6-parameter-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Parameter names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p><p>One-character parameter names should be avoided.</p><a name="s5.2.7-local-variable-names"/> | ||
| + <h4>5.2.7 Local variable names <a href="#s5.2.7-local-variable-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Local variable names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>, and can be | ||
| +abbreviated more liberally than other types of names.</p><p>However, one-character names should be avoided, except for temporary and looping variables.</p><p>Even when final and immutable, local variables are not considered to be constants, and should not | ||
| +be styled as constants.</p><a name="s5.2.8-type-variable-names"/> | ||
| + <h4>5.2.8 Type variable names <a href="#s5.2.8-type-variable-names"><img height="21" width="21" src="javaguidelink.png"/></a></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 | ||
| + <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>) | ||
| + </li><li>A name in the form used for classes (see Section 5.2.2, | ||
| + <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>, | ||
| + <code class="prettyprint lang-java">FooBarT</code>).</li></ul><a name="acronyms"/><a name="camelcase"/><a name="s5.3-camel-case"/> | ||
| + <h3>5.3 Camel case: defined <a href="#s5.3-camel-case"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Sometimes there is more than one reasonable way to convert an English phrase into camel case, | ||
| +such as when acronyms or unusual constructs like "IPv6" or "iOS" are present. To improve | ||
| +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 | ||
| + hyphens). | ||
| + | ||
| + <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 | ||
| + that a word such as "iOS" is not really in camel case <em>per se</em>; it defies <em>any</em> | ||
| + convention, so this recommendation does not apply.</li></ul></li><li>Now lowercase <em>everything</em> (including acronyms), then uppercase only the first | ||
| + character of: | ||
| + <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><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="prettyprint lang-java badcode">XMLHTTPRequest</code></td></tr><tr><td>"new customer ID"</td><td><code class="prettyprint lang-java">newCustomerId</code></td><td><code class="prettyprint lang-java badcode">newCustomerID</code></td></tr><tr><td>"inner stopwatch"</td><td><code class="prettyprint lang-java">innerStopwatch</code></td><td><code class="prettyprint lang-java badcode">innerStopWatch</code></td></tr><tr><td>"supports IPv6 on iOS?"</td><td><code class="prettyprint lang-java">supportsIpv6OnIos</code></td><td><code class="prettyprint lang-java 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/></tr></table><p>*Acceptable, but not recommended.</p><p class="note"><b>Note:</b> Some words are ambiguously hyphenated in the English language: for example | ||
| +"nonempty" and "non-empty" are both correct, so the method names | ||
| +<code class="prettyprint lang-java">checkNonempty</code> and | ||
| +<code class="prettyprint lang-java">checkNonEmpty</code> are likewise both correct.</p><a name="s6-programming-practices"/> | ||
| + <h2>6 Programming Practices <a href="#s6-programming-practices"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <a name="s6.1-override-annotation"/> | ||
| + <h3>6.1 @Override: always used <a href="#s6.1-override-annotation"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>The <code class="prettyprint lang-java">@Override</code> annotation is used in any context in | ||
| +which it is legal.</p><a name="caughtexceptions"/><a name="s6.2-caught-exceptions"/> | ||
| + <h3>6.2 Caught exceptions: not ignored <a href="#s6.2-caught-exceptions"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>Except as noted below, it is very rarely correct to do nothing in response to a caught | ||
| +exception. (Typical responses are to log it, or if it is considered "impossible", rethrow it as an | ||
| +<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 { | ||
| + int i = Integer.parseInt(response); | ||
| + return handleNumericResponse(i); | ||
| +} catch (NumberFormatException ok) { | ||
| + // it's not numeric; that's fine, just continue | ||
| +} | ||
| +return handleTextResponse(response); | ||
| +</pre><p class="exception"><b>Exception:</b> in tests, a caught exception may be ignored without comment <em>if</em> it is | ||
| +named <code class="prettyprint lang-java">expected</code>. The following is a very common idiom | ||
| +for ensuring that the method 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 { | ||
| + emptyStack.pop(); | ||
| + fail(); | ||
| +} catch (NoSuchElementException expected) { | ||
| +} | ||
| +</pre><a name="s6.3-static-members"/> | ||
| + <h3>6.3 Static members: qualified using class <a href="#s6.3-static-members"><img height="21" width="21" src="javaguidelink.png"/></a></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 = ...; | ||
| +Foo.aStaticMethod(); // good | ||
| +<span class="badcode">aFoo.aStaticMethod();</span> // bad | ||
| +<span class="badcode">somethingThatYieldsAFoo().aStaticMethod();</span> // very bad | ||
| +</pre><a name="finalizers"/><a name="s6.4-finalizers"/> | ||
| + <h3>6.4 Finalizers: not used <a href="#s6.4-finalizers"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>It is <strong>extremely rare</strong> to override <code class="prettyprint lang-java">Object.finalize</code>.</p><p class="tip"><b>Tip:</b> 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 name="s7-javadoc"/> | ||
| + <h2>7 Javadoc <a href="#s7-javadoc"><img height="21" width="21" src="javaguidelink.png"/></a></h2> | ||
| + <a name="s7.1-javadoc-formatting"/> | ||
| + <h3>7.1 Formatting <a href="#s7.1-javadoc-formatting"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <a name="s7.1.1-javadoc-multi-line"/> | ||
| + <h4>7.1.1 General form <a href="#s7.1.1-javadoc-multi-line"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>The <em>basic</em> formatting of Javadoc blocks is as seen in this general example:</p><pre class="prettyprint lang-java"> | ||
| +/** | ||
| + * Multiple lines of Javadoc text are written here, | ||
| + * wrapped normally... | ||
| + */ | ||
| +public int method(String p1) { ... } | ||
| +</pre><p>... or in this single-line example:</p><pre class="prettyprint lang-java"> | ||
| +/** An especially short bit of Javadoc. */ | ||
| +</pre><p>The general form is always acceptable. The single-line form may be substituted when there are no | ||
| +at-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on a | ||
| +single line.</p><a name="s7.1.2-javadoc-paragraphs"/> | ||
| + <h4>7.1.2 Paragraphs <a href="#s7.1.2-javadoc-paragraphs"><img height="21" width="21" src="javaguidelink.png"/></a></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 | ||
| +present. Each paragraph but the first has <code><p></code> immediately before the first word, | ||
| +with no space after.</p><a name="s7.1.3-javadoc-at-clauses"/> | ||
| + <h4>7.1.3 At-clauses <a href="#s7.1.3-javadoc-at-clauses"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Any of the standard "at-clauses" that are used appear in the order <code>@param</code>, | ||
| +<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>. | ||
| +</p><a name="s7.2-summary-fragment"/> | ||
| + <h3>7.2 The summary fragment <a href="#s7.2-summary-fragment"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>The Javadoc for each class and member begins with a brief <strong>summary fragment</strong>. This | ||
| +fragment is very important: it is the only part of the text that appears in certain contexts such as | ||
| +class and method indexes.</p><p>This is a fragment—a noun phrase or verb phrase, not a complete sentence. It does | ||
| +<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 | ||
| +punctuated as if it were a complete sentence.</p><p class="tip"><b>Tip:</b> A common mistake is to write simple Javadoc in the form | ||
| +<code class="prettyprint lang-java badcode">/** @return the customer ID */</code>. This is | ||
| +incorrect, and should be changed to | ||
| +<code class="prettyprint lang-java">/** Returns the customer ID. */</code>.</p><a name="s7.3-javadoc-where-required"/> | ||
| + <h3>7.3 Where Javadoc is used <a href="#s7.3-javadoc-where-required"><img height="21" width="21" src="javaguidelink.png"/></a></h3> | ||
| + <p>At the <em>minimum</em>, Javadoc is present for every | ||
| +<code class="prettyprint lang-java">public</code> class, and every | ||
| +<code class="prettyprint lang-java">public</code> or | ||
| +<code class="prettyprint lang-java">protected</code> member of such a class, with a few exceptions | ||
| +noted below.</p><a name="s7.3.1-javadoc-exception-self-explanatory"/> | ||
| + <h4>7.3.1 Exception: self-explanatory methods <a href="#s7.3.1-javadoc-exception-self-explanatory"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Javadoc is optional for "simple, obvious" methods like | ||
| +<code class="prettyprint lang-java">getFoo</code>, in cases where there <em>really and truly</em> is | ||
| +nothing else worthwhile to say but "Returns the foo".</p><p>The test methods of a unit test class are perhaps the most common example of this exemption. | ||
| +These methods can <em>usually</em> be named descriptively enough that no additional documentation is | ||
| +needed.</p><p class="tip"><b>Tip:</b> <strong>Important:</strong> it is not appropriate to cite this exception to justify | ||
| +omitting relevant information that a typical reader might need to know. For example, for a method | ||
| +named <code class="prettyprint lang-java">getCanonicalName</code>, don't omit its documentation | ||
| +(with the rationale that it would say only <code class="prettyprint lang-java badcode">/** Returns | ||
| +the canonical name. */</code>) if a typical reader may have no idea what the term "canonical name" | ||
| +means!</p><a name="s7.3.2-javadoc-exception-overrides"/> | ||
| + <h4>7.3.2 Exception: overrides <a href="#s7.3.2-javadoc-exception-overrides"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Javadoc is not always present on a method that overrides a supertype method. | ||
| +</p><a name="s7.3.3-javadoc-optional"/> | ||
| + <h4>7.3.3 Optional javadoc <a href="#s7.3.3-javadoc-optional"><img height="21" width="21" src="javaguidelink.png"/></a></h4> | ||
| + <p>Classes and members that are not visible outside their package still have Javadoc <em>as | ||
| +needed</em>. Whenever an implementation comment would be used to define the overall purpose or | ||
| +behavior of a class, method or field, that comment is written as Javadoc instead. (It's more | ||
| +uniform, and more tool-friendly.)</p></div></div> <hr/> | ||
| + <div class="change">Last changed: December 17, 2013</div> | ||
| +</body> | ||
| +</html> |
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