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java style guide update: presentation

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10
javaguide.css
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@ -128,6 +128,10 @@ body {
margin-bottom:1em; margin-bottom:1em;
} }
em {
font-style: italic
}
h1, h1,
h2, h2,
h3, h3,
@ -402,7 +406,7 @@ ul.nolist {
code, code,
kbd, kbd,
pre { pre {
color:#007000; color:#009900;
} }
kbd { kbd {
@ -426,10 +430,10 @@ pre.prettyprint {
} }
code.bad, code.badcode { code.bad, code.badcode {
background-color:#fcc; color: magenta;
} }
pre.bad, pre.badcode { pre.bad, pre.badcode {
background-color:#fcc; background-color:#ffe6d8;
border-top:1px inset #a03; border-top:1px inset #a03;
border-left:1px inset #a03; border-left:1px inset #a03;
} }

141
javaguide.html
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@ -2,7 +2,7 @@
<head> <head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8" /> <meta http-equiv="content-type" content="text/html; charset=UTF-8" />
<link rel="stylesheet" type="text/css" href="javaguide.css"/> <link rel="stylesheet" type="text/css" href="javaguide.css"/>
<script src="http://google-code-prettify.googlecode.com/svn/loader/run_prettify.js" <script src="https://google-code-prettify.googlecode.com/svn/loader/run_prettify.js"
type="text/javascript"></script> type="text/javascript"></script>
<link href="http://www.google.com/favicon.ico" <link href="http://www.google.com/favicon.ico"
type="image/x-icon" rel="shortcut icon" /> type="image/x-icon" rel="shortcut icon" />
@ -10,7 +10,7 @@
</head> </head>
<body> <body>
<h1>Google Java Style</h1> <h1>Google Java Style</h1>
<div class="change">Last changed: February 03, 2014</div> <div class="change">Last changed: March 21, 2014</div>
<table border="0"> <table border="0">
<tr> <tr>
<td> <td>
@ -241,14 +241,11 @@
<dd class="toc3"> <dd class="toc3">
<a href="#s7.3.2-javadoc-exception-overrides">7.3.2 Exception: overrides</a> <a href="#s7.3.2-javadoc-exception-overrides">7.3.2 Exception: overrides</a>
</dd> </dd>
<dd class="toc3">
<a href="#s7.3.3-javadoc-optional">7.3.3 Optional javadoc</a>
</dd>
</dl> </dl>
</td> </td>
</tr> </tr>
</table> </table>
<div><div id="with-header-links"><a name="s1-introduction"/> <div><a name="s1-introduction"/>
<h2>1 Introduction&nbsp;<a href="#s1-introduction"><img height="21" width="21" src="javaguidelink.png"/></a></h2> <h2>1 Introduction&nbsp;<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 <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 source code in the Java™ Programming Language. A Java source file is described as being <em>in
@ -289,18 +286,18 @@ anywhere in a source file. This implies that:</p><ol><li>All other whitespace ch
<code class="prettyprint lang-java">\'</code> and <code class="prettyprint lang-java">\'</code> and
<code class="prettyprint lang-java">\\</code>), that sequence <code class="prettyprint lang-java">\\</code>), that sequence
is used rather than the corresponding octal is used rather than the corresponding octal
(e.g. <code class="prettyprint lang-java badcode">\012</code>) or Unicode (e.g. <code class="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"/> (e.g. <code class="badcode">\u000a</code>) escape.</p><a name="s2.3.3-non-ascii-characters"/>
<h4>2.3.3 Non-ASCII characters&nbsp;<a href="#s2.3.3-non-ascii-characters"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>2.3.3 Non-ASCII characters&nbsp;<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 <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">∞</code>) or the equivalent Unicode escape
(e.g. <code class="prettyprint lang-java">\u221e</code>) is used, depending only on which (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>&nbsp;in the Unicode escape case, and occasionally even when actual Unicode characters makes the code <strong>easier to read and understand</strong>.</p><p class="tip"><strong>Tip:</strong> In the Unicode escape case, and occasionally even when actual
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"; 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; // Greek letter mu, "s"</code></td><td>Allowed, but awkward and prone to mistakes.</td></tr><tr><td><code class="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>&nbsp; Never make your code less readable simply out of fear that some programs might // byte order mark</code></td><td>Good: use escapes for non-printable characters, and comment if necessary.</td></tr></table><p class="tip"><strong>Tip:</strong> Never make your code less readable simply out of fear that
not handle non-ASCII characters properly. If that should happen, those programs some programs might not handle non-ASCII characters properly. If that should happen, those
are <strong>broken</strong> and they must be <strong>fixed</strong>.</p><a name="filestructure"/><a name="s3-source-file-structure"/> 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&nbsp;<a href="#s3-source-file-structure"><img height="21" width="21" src="javaguidelink.png"/></a></h2> <h2>3 Source file structure&nbsp;<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"/> <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&nbsp;<a href="#s3.1-copyright-statement"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>3.1 License or copyright information, if present&nbsp;<a href="#s3.1-copyright-statement"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
@ -340,8 +337,8 @@ added" ordering, which is not a logical ordering.</p><a name="overloads"/><a nam
<p>When a class has multiple constructors, or multiple methods with the same name, these appear <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"/> sequentially, with no intervening members.</p><a name="s4-formatting"/>
<h2>4 Formatting&nbsp;<a href="#s4-formatting"><img height="21" width="21" src="javaguidelink.png"/></a></h2> <h2>4 Formatting&nbsp;<a href="#s4-formatting"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
<p class="terminology"><b>Terminology Note:</b>&nbsp;<em>block-like construct</em> refers to the body of a class, method or <p class="terminology"><strong>Terminology Note:</strong> <em>block-like construct</em> refers to
constructor. Note that, by Section 4.8.3.1 on 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 <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"/> <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&nbsp;<a href="#s4.1-braces"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>4.1 Braces&nbsp;<a href="#s4.1-braces"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
@ -402,11 +399,12 @@ Section 4.5, <a href="#s4.5-line-wrapping">Line-wrapping</a>.
3.2 <a href="#s3.2-package-statement">Package statement</a> and 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"/> 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&nbsp;<a href="#s4.5-line-wrapping"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>4.5 Line-wrapping&nbsp;<a href="#s4.5-line-wrapping"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
<p class="terminology"><b>Terminology Note:</b>&nbsp;When code that might otherwise legally occupy a single line is divided into <p class="terminology"><strong>Terminology Note:</strong> When code that might otherwise legally
multiple lines, typically to avoid overflowing the column limit, this activity is called 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 <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>&nbsp;extracting a method or local variable may solve the problem without the need to every situation. Very often there are several valid ways to line-wrap the same piece of code.</p><p class="tip"><strong>Tip:</strong> Extracting a method or local variable may solve the problem
line-wrap.</p><a name="s4.5.1-line-wrapping-where-to-break"/> without the need to line-wrap.</p><a name="s4.5.1-line-wrapping-where-to-break"/>
<h4>4.5.1 Where to break&nbsp;<a href="#s4.5.1-line-wrapping-where-to-break"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.5.1 Where to break&nbsp;<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 <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> <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>
@ -434,9 +432,9 @@ previous lines.</p><a name="s4.6-whitespace"/>
<h4>4.6.1 Vertical Whitespace&nbsp;<a href="#s4.6.1-vertical-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.6.1 Vertical Whitespace&nbsp;<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, <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. methods, nested classes, static initializers, instance initializers.
<ul><li><span class="exception"><b>Exception:</b>&nbsp;a blank line between two consecutive fields (having no other code <ul><li><span class="exception"><strong>Exception:</strong> A blank line between two consecutive
between them) is optional. Such blank lines are used as needed to create <em>logical fields (having no other code between them) is optional. Such blank lines are used as needed to
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 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, 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"/> <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&nbsp;<a href="#s4.6.2-horizontal-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.6.2 Horizontal whitespace&nbsp;<a href="#s4.6.2-horizontal-whitespace"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
@ -462,25 +460,25 @@ Javadoc, a single ASCII space also appears in the following places <strong>only<
begins an end-of-line comment. Here, multiple spaces are allowed, but not required.</li><li>Between the type and variable of a declaration: 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&lt;String&gt; list</code></li><li><em>Optional</em> just inside both braces of an array initializer <code class="prettyprint lang-java">List&lt;String&gt; 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 <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>&nbsp;this rule never requires or forbids additional space at the start or end of a <code class="prettyprint lang-java">new int[] { 5, 6 }</code> are both valid</li></ul></li></ol><p class="note"><strong>Note:</strong> This rule never requires or forbids additional space at the
line, only <em>interior</em> space.</p><a name="s4.6.3-horizontal-alignment"/> 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&nbsp;<a href="#s4.6.3-horizontal-alignment"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.6.3 Horizontal alignment: never required&nbsp;<a href="#s4.6.3-horizontal-alignment"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
<p class="terminology"><b>Terminology Note:</b>&nbsp;Horizontal alignment is the practice of adding a variable number of <p class="terminology"><strong>Terminology Note:</strong> <em>Horizontal alignment</em> is the
additional spaces in your code with the goal of making certain tokens appear directly below certain practice of adding a variable number of additional spaces in your code with the goal of making
other tokens on previous lines.</p><p>This practice is permitted, but is <strong>never required</strong> by Google Style. It is not 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"> 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 int x; // this is fine
private Color color; // this too private Color color; // this too
private int x; // permitted, but future edits private int x; // permitted, but future edits
private Color color; // may leave it unaligned private Color color; // may leave it unaligned
</pre><p class="tip"><b>Tip:</b>&nbsp;Alignment can aid readability, but it creates problems for future maintenance. </pre><p class="tip"><strong>Tip:</strong> Alignment can aid readability, but it creates problems for
Consider a future change that needs to touch just one line. This change may leave the future maintenance. Consider a future change that needs to touch just one line. This change may
formerly-pleasing formatting mangled, and that is <strong>allowed</strong>. More often it prompts leave the formerly-pleasing formatting mangled, and that is <strong>allowed</strong>. More often
the coder (perhaps you) to adjust whitespace on nearby lines as well, possibly triggering a it prompts the coder (perhaps you) to adjust whitespace on nearby lines as well, possibly
cascading series of reformattings. That one-line change now has a "blast radius." This can at worst triggering a cascading series of reformattings. That one-line change now has a "blast radius."
result in pointless busywork, but at best it still corrupts version history information, slows down This can at worst result in pointless busywork, but at best it still corrupts version history
reviewers and exacerbates merge conflicts.</p><a name="parentheses"/><a name="s4.7-grouping-parentheses"/> information, slows down reviewers and exacerbates merge conflicts.</p><a name="parentheses"/><a name="s4.7-grouping-parentheses"/>
<h3>4.7 Grouping parentheses: recommended&nbsp;<a href="#s4.7-grouping-parentheses"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>4.7 Grouping parentheses: recommended&nbsp;<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 <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 reasonable chance the code will be misinterpreted without them, nor would they have made the code
@ -490,14 +488,15 @@ operator precedence table memorized.</p><a name="s4.8-specific-constructs"/>
<a name="s4.8.1-enum-classes"/> <a name="s4.8.1-enum-classes"/>
<h4>4.8.1 Enum classes&nbsp;<a href="#s4.8.1-enum-classes"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.8.1 Enum classes&nbsp;<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 <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"> as if it were an array initializer (see Section 4.8.3.1 on
<a href="#s4.8.3.1-array-initializers">array initializers</a>).</p><pre class="prettyprint lang-java">
private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS } 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"/> </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&nbsp;<a href="#s4.8.2-variable-declarations"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.8.2 Variable declarations&nbsp;<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"/> <a name="s4.8.2.1-variables-per-declaration"/>
<h5>4.8.2.1 One variable per declaration&nbsp;<a href="#s4.8.2.1-variables-per-declaration"><img height="21" width="21" src="javaguidelink.png"/></a></h5> <h5>4.8.2.1 One variable per declaration&nbsp;<a href="#s4.8.2.1-variables-per-declaration"><img height="21" width="21" src="javaguidelink.png"/></a></h5>
<p>Every variable declaration (field or local) declares only one variable: declarations such as <p>Every variable declaration (field or local) declares only one variable: declarations such as
<code class="prettyprint lang-java badcode">int a, b;</code> are not used.</p><a name="s4.8.2.2-variables-limited-scope"/> <code class="badcode">int a, b;</code> are not used.</p><a name="s4.8.2.2-variables-limited-scope"/>
<h5>4.8.2.2 Declared when needed, initialized as soon as <h5>4.8.2.2 Declared when needed, initialized as soon as
possible&nbsp;<a href="#s4.8.2.2-variables-limited-scope"><img height="21" width="21" src="javaguidelink.png"/></a></h5> possible&nbsp;<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 <p>Local variables are <strong>not</strong> habitually declared at the start of their containing
@ -523,11 +522,11 @@ new int[] { 3,
<h5>4.8.3.2 No C-style array declarations&nbsp;<a href="#s4.8.3.2-array-declarations"><img height="21" width="21" src="javaguidelink.png"/></a></h5> <h5>4.8.3.2 No C-style array declarations&nbsp;<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: <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">String[] args</code>, not
<code class="prettyprint lang-java badcode">String args[]</code>.</p><a name="s4.8.4-switch"/> <code class="badcode">String args[]</code>.</p><a name="s4.8.4-switch"/>
<h4>4.8.4 Switch statements&nbsp;<a href="#s4.8.4-switch"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>4.8.4 Switch statements&nbsp;<a href="#s4.8.4-switch"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
<p class="terminology"><b>Terminology Note:</b>&nbsp;Inside the braces of a <em>switch block</em> are one or more <p class="terminology"><strong>Terminology Note:</strong> Inside the braces of a
<em>statement groups</em>. Each statement group consists of one or more <em>switch labels</em> <em>switch block</em> are one or more <em>statement groups</em>. Each statement group consists of
(either <code class="prettyprint lang-java">case FOO:</code> or 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"/> <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&nbsp;<a href="#s4.8.4.1-switch-indentation"><img height="21" width="21" src="javaguidelink.png"/></a></h5> <h5>4.8.4.1 Indentation&nbsp;<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 <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
@ -566,8 +565,8 @@ increased. Example:</p><pre class="prettyprint lang-java">
@Override @Override
@Nullable @Nullable
public String getNameIfPresent() { ... } public String getNameIfPresent() { ... }
</pre><p class="exception"><b>Exception:</b>&nbsp;a <em>single</em> parameterless annotation <em>may</em> instead appear </pre><p class="exception"><strong>Exception:</strong> A <em>single</em> parameterless annotation
together with the first line of the signature, for example:</p><pre class="prettyprint lang-java"> <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() { ... } @Override public int hashCode() { ... }
</pre><p>Annotations applying to a field also appear immediately after the documentation block, but in </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; this case, <em>multiple</em> annotations (possibly parameterized) may be listed on the same line;
@ -586,7 +585,7 @@ for example:</p><pre class="prettyprint lang-java">
* This is // And so /* Or you can * This is // And so /* Or you can
* okay. // is this. * even do this. */ * 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>&nbsp;When writing multi-line comments, use the </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
<code class="prettyprint lang-java">/* ... */</code> style if you want automatic code formatters to <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 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"/> <code class="prettyprint lang-java">// ...</code> style comment blocks.</p><a name="modifiers"/><a name="s4.8.7-modifiers"/>
@ -605,10 +604,9 @@ rather than <code class="badcode">3000000000l</code>.</p><a name="naming"/><a na
<h3>5.1 Rules common to all identifiers&nbsp;<a href="#s5.1-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>5.1 Rules common to all identifiers&nbsp;<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 <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 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>, suffixes, like those seen in the examples <code class="badcode">name_</code>,
<code class="prettyprint lang-java badcode">mName</code>, <code class="badcode">mName</code>, <code class="badcode">s_name</code> and
<code class="prettyprint lang-java badcode">s_name</code> and <code class="badcode">kName</code>, are <strong>not</strong> used.</p><a name="s5.2-specific-identifier-names"/>
<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&nbsp;<a href="#s5.2-specific-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>5.2 Rules by identifier type&nbsp;<a href="#s5.2-specific-identifier-names"><img height="21" width="21" src="javaguidelink.png"/></a></h3>
<a name="s5.2.1-package-names"/> <a name="s5.2.1-package-names"/>
<h4>5.2.1 Package names&nbsp;<a href="#s5.2.1-package-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>5.2.1 Package names&nbsp;<a href="#s5.2.1-package-names"><img height="21" width="21" src="javaguidelink.png"/></a></h4>
@ -687,8 +685,8 @@ predictability, Google Style specifies the following (nearly) deterministic sche
that a word such as "iOS" is not really in camel case <em>per se</em>; it defies <em>any</em> 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 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: 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>&nbsp;Some words are ambiguously hyphenated in the English language: for example <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="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/></tr></table><p>*Acceptable, but not recommended.</p><p class="note"><strong>Note:</strong> Some words are ambiguously hyphenated in the English
"nonempty" and "non-empty" are both correct, so the method names 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> and
<code class="prettyprint lang-java">checkNonEmpty</code> are likewise both correct.</p><a name="s6-programming-practices"/> <code class="prettyprint lang-java">checkNonEmpty</code> are likewise both correct.</p><a name="s6-programming-practices"/>
<h2>6 Programming Practices&nbsp;<a href="#s6-programming-practices"><img height="21" width="21" src="javaguidelink.png"/></a></h2> <h2>6 Programming Practices&nbsp;<a href="#s6-programming-practices"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
@ -697,7 +695,8 @@ predictability, Google Style specifies the following (nearly) deterministic sche
<p>A method is marked with the <code class="prettyprint lang-java">@Override</code> annotation <p>A method is marked with the <code class="prettyprint lang-java">@Override</code> annotation
whenever it is legal. This includes a class method overriding a superclass method, a class method 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 implementing an interface method, and an interface method respecifying a superinterface
method.</p><a name="caughtexceptions"/><a name="s6.2-caught-exceptions"/> 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 name="s6.2-caught-exceptions"/>
<h3>6.2 Caught exceptions: not ignored&nbsp;<a href="#s6.2-caught-exceptions"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>6.2 Caught exceptions: not ignored&nbsp;<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 <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 exception. (Typical responses are to log it, or if it is considered "impossible", rethrow it as an
@ -710,10 +709,10 @@ try {
// it's not numeric; that's fine, just continue // it's not numeric; that's fine, just continue
} }
return handleTextResponse(response); return handleTextResponse(response);
</pre><p class="exception"><b>Exception:</b>&nbsp;in tests, a caught exception may be ignored without comment <em>if</em> it is </pre><p class="exception"><strong>Exception:</strong> In tests, a caught exception may be ignored
named <code class="prettyprint lang-java">expected</code>. The following is a very common idiom without comment <em>if</em> it is named <code class="prettyprint lang-java">expected</code>. The
for ensuring that the method under test <em>does</em> throw an exception of the expected type, so following is a very common idiom for ensuring that the method under test <em>does</em> throw an
a comment is unnecessary here.</p><pre class="prettyprint lang-java"> exception of the expected type, so a comment is unnecessary here.</p><pre class="prettyprint lang-java">
try { try {
emptyStack.pop(); emptyStack.pop();
fail(); fail();
@ -729,7 +728,7 @@ Foo.aStaticMethod(); // good
<span class="badcode">somethingThatYieldsAFoo().aStaticMethod();</span> // very bad <span class="badcode">somethingThatYieldsAFoo().aStaticMethod();</span> // very bad
</pre><a name="finalizers"/><a name="s6.4-finalizers"/> </pre><a name="finalizers"/><a name="s6.4-finalizers"/>
<h3>6.4 Finalizers: not used&nbsp;<a href="#s6.4-finalizers"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>6.4 Finalizers: not used&nbsp;<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>&nbsp;Don't do it. If you absolutely must, first read and understand <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> <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"/> 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&nbsp;<a href="#s7-javadoc"><img height="21" width="21" src="javaguidelink.png"/></a></h2> <h2>7 Javadoc&nbsp;<a href="#s7-javadoc"><img height="21" width="21" src="javaguidelink.png"/></a></h2>
@ -766,35 +765,29 @@ class and method indexes.</p><p>This is a fragment—a noun phrase or verb phras
<strong>not</strong> begin with <code class="badcode">A {@code Foo} is a...</code>, or <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 <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 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>&nbsp;A common mistake is to write simple Javadoc in the form 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
<code class="prettyprint lang-java badcode">/** @return the customer ID */</code>. This is <code class="badcode">/** @return the customer ID */</code>. This is incorrect, and should be
incorrect, and should be changed to changed to <code class="prettyprint lang-java">/** Returns the customer ID. */</code>.</p><a name="s7.3.3-javadoc-optional"/><a name="s7.3-javadoc-where-required"/>
<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&nbsp;<a href="#s7.3-javadoc-where-required"><img height="21" width="21" src="javaguidelink.png"/></a></h3> <h3>7.3 Where Javadoc is used&nbsp;<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 <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> class, and every
<code class="prettyprint lang-java">public</code> or <code class="prettyprint lang-java">public</code> or
<code class="prettyprint lang-java">protected</code> member of such a class, with a few exceptions <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"/> noted below.</p><p>Other classes and members 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><a name="s7.3.1-javadoc-exception-self-explanatory"/>
<h4>7.3.1 Exception: self-explanatory methods&nbsp;<a href="#s7.3.1-javadoc-exception-self-explanatory"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>7.3.1 Exception: self-explanatory methods&nbsp;<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 <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 <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. nothing else worthwhile to say but "Returns the foo".</p><p class="note"><strong>Important:</strong> it is not appropriate to cite this exception to justify
These methods can <em>usually</em> be named descriptively enough that no additional documentation is
needed.</p><p class="tip"><b>Tip:</b>&nbsp;<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 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 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 (with the rationale that it would say only
the canonical name. */</code>) if a typical reader may have no idea what the term "canonical name" <code class="badcode">/** Returns the canonical name. */</code>) if a typical reader may have no idea
means!</p><a name="s7.3.2-javadoc-exception-overrides"/> what the term "canonical name" means!</p><a name="s7.3.2-javadoc-exception-overrides"/>
<h4>7.3.2 Exception: overrides&nbsp;<a href="#s7.3.2-javadoc-exception-overrides"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <h4>7.3.2 Exception: overrides&nbsp;<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>Javadoc is not always present on a method that overrides a supertype method.
</p><a name="s7.3.3-javadoc-optional"/> </p></div> <hr/>
<h4>7.3.3 Optional javadoc&nbsp;<a href="#s7.3.3-javadoc-optional"><img height="21" width="21" src="javaguidelink.png"/></a></h4> <div class="change">Last changed: March 21, 2014</div>
<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: February 03, 2014</div>
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