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<!DOCTYPE html>
<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=
"https://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>
WPILib Java Style
</title>
</head>
<body>
<h1>
WPILib Java Style (Based on the <a href=
"http://google-styleguide.googlecode.com/svn/trunk/javaguide.html">Google
Java Style Guide</a>)
</h1>
<div class="change">
Last changed: June 19, 2015
</div>
<table border="0">
<tr>
<td>
<dl>
<dd>
<br>
</dd>
<dt class="toc1">
<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>
<dd>
<br>
</dd>
<dt class="toc1">
<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>
<dd class="toc3">
<a href="#s2.3.1-whitespace-characters">2.3.1 Whitespace
characters</a>
</dd>
<dd class="toc3">
<a href="#s2.3.2-special-escape-sequences">2.3.2 Special escape
sequences</a>
</dd>
<dd class="toc3">
<a href="#s2.3.3-non-ascii-characters">2.3.3 Non-ASCII
characters</a>
</dd>
<dd>
<br>
</dd>
<dt class="toc1">
<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 class="toc3">
<a href="#s3.3.1-wildcard-imports">3.3.1 No wildcard imports</a>
</dd>
<dd class="toc3">
<a href="#s3.3.2-import-line-wrapping">3.3.2 No line-wrapping</a>
</dd>
<dd class="toc3">
<a href="#s3.3.3-import-ordering-and-spacing">3.3.3 Ordering and
spacing</a>
</dd>
<dd>
<a href="#s3.4-class-declaration">3.4 Class declaration</a>
</dd>
<dd class="toc3">
<a href="#s3.4.1-one-top-level-class">3.4.1 Exactly one top-level
class declaration</a>
</dd>
<dd class="toc3">
<a href="#s3.4.2-class-member-ordering">3.4.2 Class member
ordering</a>
</dd>
</dl>
</td>
<td>
<dl>
<dd>
<br>
</dd>
<dt class="toc1">
<a href="#s4-formatting">4 Formatting</a>
</dt>
<dd>
<a href="#s4.1-braces">4.1 Braces</a>
</dd>
<dd class="toc3">
<a href="#s4.1.1-braces-always-used">4.1.1 Braces are used where
optional</a>
</dd>
<dd class="toc3">
<a href="#s4.1.2-blocks-k-r-style">4.1.2 Nonempty blocks: K & R
style</a>
</dd>
<dd class="toc3">
<a href="#s4.1.3-braces-empty-blocks">4.1.3 Empty blocks: may be
concise</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 class="toc3">
<a href="#s4.5.1-line-wrapping-where-to-break">4.5.1 Where to
break</a>
</dd>
<dd class="toc3">
<a href="#s4.5.2-line-wrapping-indent">4.5.2 Indent continuation
lines at least +4 spaces</a>
</dd>
<dd>
<a href="#s4.6-whitespace">4.6 Whitespace</a>
</dd>
<dd class="toc3">
<a href="#s4.6.1-vertical-whitespace">4.6.1 Vertical
Whitespace</a>
</dd>
<dd class="toc3">
<a href="#s4.6.2-horizontal-whitespace">4.6.2 Horizontal
whitespace</a>
</dd>
<dd class="toc3">
<a href="#s4.6.3-horizontal-alignment">4.6.3 Horizontal
alignment: never required</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>
<dd class="toc3">
<a href="#s4.8.1-enum-classes">4.8.1 Enum classes</a>
</dd>
<dd class="toc3">
<a href="#s4.8.2-variable-declarations">4.8.2 Variable
declarations</a>
</dd>
<dd class="toc3">
<a href="#s4.8.3-arrays">4.8.3 Arrays</a>
</dd>
<dd class="toc3">
<a href="#s4.8.4-switch">4.8.4 Switch statements</a>
</dd>
<dd class="toc3">
<a href="#s4.8.5-annotations">4.8.5 Annotations</a>
</dd>
<dd class="toc3">
<a href="#s4.8.6-comments">4.8.6 Comments</a>
</dd>
<dd class="toc3">
<a href="#s4.8.7-modifiers">4.8.7 Modifiers</a>
</dd>
<dd class="toc3">
<a href="#s4.8.8-numeric-literals">4.8.8 Numeric Literals</a>
</dd>
<dd class="toc3">
<a href="#s4.8.9-ternary-operator">4.8.9 Ternary Operator</a>
</dd>
</dl>
</td>
<td>
<dl>
<dd>
<br>
</dd>
<dt class="toc1">
<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 class="toc3">
<a href="#s5.2.1-package-names">5.2.1 Package names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.2-class-names">5.2.2 Class names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.3-method-names">5.2.3 Method names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.4-constant-names">5.2.4 Constant names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.5-non-constant-field-names">5.2.5 Non-constant
field names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.6-parameter-names">5.2.6 Parameter names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.7-local-variable-names">5.2.7 Local variable
names</a>
</dd>
<dd class="toc3">
<a href="#s5.2.8-type-variable-names">5.2.8 Type variable
names</a>
</dd>
<dd>
<a href="#s5.3-camel-case">5.3 Camel case: defined</a>
</dd>
<dd>
<br>
</dd>
<dt class="toc1">
<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>
<dd>
<a href="#s6.5-built-in-types">6.5 Built-in Types</a>
</dd>
<dd>
<a href="#s6.6-error-handling">6.6 Error Handling</a>
</dd>
<dd>
<a href="#s6.7-generated-files">6.7 Generated Files</a>
</dd>
<dd>
<br>
</dd>
<dt class="toc1">
<a href="#s7-javadoc">7 Javadoc</a>
</dt>
<dd>
<a href="#s7.1-javadoc-formatting">7.1 Formatting</a>
</dd>
<dd class="toc3">
<a href="#s7.1.1-javadoc-multi-line">7.1.1 General form</a>
</dd>
<dd class="toc3">
<a href="#s7.1.2-javadoc-paragraphs">7.1.2 Paragraphs</a>
</dd>
<dd class="toc3">
<a href="#s7.1.3-javadoc-at-clauses">7.1.3 At-clauses</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>
<dd class="toc3">
<a href="#s7.3.1-javadoc-exception-self-explanatory">7.3.1
Exception: self-explanatory methods</a>
</dd>
<dd class="toc3">
<a href="#s7.3.2-javadoc-exception-overrides">7.3.2 Exception:
overrides</a>
</dd>
</dl>
</td>
</tr>
</table>
<div>
<a name="s1-introduction" id="s1-introduction"></a>
<h2>
1 Introduction <a href="#s1-introduction"><img height="21" width=
"21" src="guidelink.png"></a>
</h2>
<p>
<strong>This guide is a work in progress.</strong> We are currently
working on getting this guide updated to a point where it is useful for
WPILib developers to use.
</p>
<p>
This document serves as the style guide for WPILib. It is
<em>heavily</em> based on the Google Java Style Guide and copies pretty
much word-for-word the formatting/style components of the guide while
cutting a couple of the programming practices. As this guide evolves,
we will likely introduce more suggested/mandated programming practices
specific to WPILib.
</p>
<p>
It is encouraged that anyone working on the Java WPILib also read the
corresponding C++ guide, as we generally try to develop the C++ and
Java components of the library in parallel and many programming
practices true in one language will be true in the other (although this
is not universally true).
</p><a name="s1.1-terminology" id="s1.1-terminology"></a>
<h3>
1.1 Terminology notes <a href="#s1.1-terminology"><img height="21"
width="21" src="guidelink.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" id="s1.2-guide-notes"></a>
<h3>
1.2 Guide notes <a href="#s1.2-guide-notes"><img height="21"
width="21" src="guidelink.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" id="s2-source-file-basics"></a>
<h2>
2 Source file basics <a href="#s2-source-file-basics"><img height=
"21" width="21" src="guidelink.png"></a>
</h2><a name="s2.1-file-name" id="s2.1-file-name"></a>
<h3>
2.1 File name <a href="#s2.1-file-name"><img height="21" width=
"21" src="guidelink.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.
</p><a name="s2.2-file-encoding" id="s2.2-file-encoding"></a>
<h3>
2.2 File encoding: UTF-8 <a href=
"#s2.2-file-encoding"><img height="21" width="21" src=
"guidelink.png"></a>
</h3>
<p>
Source files are encoded in <strong>UTF-8</strong>.
</p><a name="s2.3-special-characters" id="s2.3-special-characters"></a>
<h3>
2.3 Special characters <a href=
"#s2.3-special-characters"><img height="21" width="21" src=
"guidelink.png"></a>
</h3><a name="s2.3.1-whitespace-characters" id=
"s2.3.1-whitespace-characters"></a>
<h4>
2.3.1 Whitespace characters <a href=
"#s2.3.1-whitespace-characters"><img height="21" width="21" src=
"guidelink.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" id=
"s2.3.2-special-escape-sequences"></a>
<h4>
2.3.2 Special escape sequences <a href=
"#s2.3.2-special-escape-sequences"><img height="21" width="21" src=
"guidelink.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="badcode">\012</code>)
or Unicode (e.g. <code class="badcode">\u000a</code>) escape.
</p><a name="s2.3.3-non-ascii-characters" id=
"s2.3.3-non-ascii-characters"></a>
<h4>
2.3.3 Non-ASCII characters <a href=
"#s2.3.3-non-ascii-characters"><img height="21" width="21" src=
"guidelink.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">
<strong>Tip:</strong> 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="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">
<strong>Tip:</strong> 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" id="filestructure"></a><a name=
"s3-source-file-structure" id="s3-source-file-structure"></a>
<h2>
3 Source file structure <a href=
"#s3-source-file-structure"><img height="21" width="21" src=
"guidelink.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" id="s3.1-copyright-statement"></a>
<h3>
3.1 License or copyright information, if present <a href=
"#s3.1-copyright-statement"><img height="21" width="21" src=
"guidelink.png"></a>
</h3>
<p>
If license or copyright information belongs in a file, it belongs here.
</p><a name="s3.2-package-statement" id="s3.2-package-statement"></a>
<h3>
3.2 Package statement <a href=
"#s3.2-package-statement"><img height="21" width="21" src=
"guidelink.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</a>)
does not apply to package statements.
</p><a name="imports" id="imports"></a><a name="s3.3-import-statements"
id="s3.3-import-statements"></a>
<h3>
3.3 Import statements <a href=
"#s3.3-import-statements"><img height="21" width="21" src=
"guidelink.png"></a>
</h3><a name="s3.3.1-wildcard-imports" id="s3.3.1-wildcard-imports"></a>
<h4>
3.3.1 No wildcard imports <a href=
"#s3.3.1-wildcard-imports"><img height="21" width="21" src=
"guidelink.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" id=
"s3.3.2-import-line-wrapping"></a>
<h4>
3.3.2 No line-wrapping <a href=
"#s3.3.2-import-line-wrapping"><img height="21" width="21" src=
"guidelink.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</a>)
does not apply to import statements.
</p><a name="s3.3.3-import-ordering-and-spacing" id=
"s3.3.3-import-ordering-and-spacing"></a>
<h4>
3.3.3 Ordering and spacing <a href=
"#s3.3.3-import-ordering-and-spacing"><img height="21" width="21" src=
"guidelink.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" id="s3.4-class-declaration"></a>
<h3>
3.4 Class declaration <a href=
"#s3.4-class-declaration"><img height="21" width="21" src=
"guidelink.png"></a>
</h3><a name="oneclassperfile" id="oneclassperfile"></a><a name=
"s3.4.1-one-top-level-class" id="s3.4.1-one-top-level-class"></a>
<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=
"guidelink.png"></a>
</h4>
<p>
Each top-level class resides in a source file of its own.
</p><a name="s3.4.2-class-member-ordering" id=
"s3.4.2-class-member-ordering"></a>
<h4>
3.4.2 Class member ordering <a href=
"#s3.4.2-class-member-ordering"><img height="21" width="21" src=
"guidelink.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" id="overloads"></a><a name=
"s3.4.2.1-overloads-never-split" id="s3.4.2.1-overloads-never-split"></a>
<h5>
3.4.2.1 Overloads: never split <a href=
"#s3.4.2.1-overloads-never-split"><img height="21" width="21" src=
"guidelink.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" id="s4-formatting"></a>
<h2>
4 Formatting <a href="#s4-formatting"><img height="21" width="21"
src="guidelink.png"></a>
</h2>
<p class="terminology">
<strong>Terminology Note:</strong> <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" id="braces"></a><a name="s4.1-braces" id=
"s4.1-braces"></a>
<h3>
4.1 Braces <a href="#s4.1-braces"><img height="21" width="21" src=
"guidelink.png"></a>
</h3><a name="s4.1.1-braces-always-used" id=
"s4.1.1-braces-always-used"></a>
<h4>
4.1.1 Braces are used where optional <a href=
"#s4.1.1-braces-always-used"><img height="21" width="21" src=
"guidelink.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" id="s4.1.2-blocks-k-r-style"></a>
<h4>
4.1.2 Nonempty blocks: K & R style <a href=
"#s4.1.2-blocks-k-r-style"><img height="21" width="21" src=
"guidelink.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" id="emptyblocks"></a><a name=
"s4.1.3-braces-empty-blocks" id="s4.1.3-braces-empty-blocks"></a>
<h4>
4.1.3 Empty blocks: may be concise <a href=
"#s4.1.3-braces-empty-blocks"><img height="21" width="21" src=
"guidelink.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" id="s4.2-block-indentation"></a>
<h3>
4.2 Block indentation: +2 spaces <a href=
"#s4.2-block-indentation"><img height="21" width="21" src=
"guidelink.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" id=
"s4.3-one-statement-per-line"></a>
<h3>
4.3 One statement per line <a href=
"#s4.3-one-statement-per-line"><img height="21" width="21" src=
"guidelink.png"></a>
</h3>
<p>
Each statement is followed by a line-break.
</p><a name="columnlimit" id="columnlimit"></a><a name=
"s4.4-column-limit" id="s4.4-column-limit"></a>
<h3>
4.4 Column limit: 80 <a href="#s4.4-column-limit"><img height="21"
width="21" src="guidelink.png"></a>
</h3>
<p>
Projects should have a column limit of 80 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" id="s4.5-line-wrapping"></a>
<h3>
4.5 Line-wrapping <a href="#s4.5-line-wrapping"><img height="21"
width="21" src="guidelink.png"></a>
</h3>
<p class="terminology">
<strong>Terminology Note:</strong> 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">
<strong>Tip:</strong> 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" id=
"s4.5.1-line-wrapping-where-to-break"></a>
<h4>
4.5.1 Where to break <a href=
"#s4.5.1-line-wrapping-where-to-break"><img height="21" width="21" src=
"guidelink.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" id="indentation"></a><a name=
"s4.5.2-line-wrapping-indent" id="s4.5.2-line-wrapping-indent"></a>
<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=
"guidelink.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" id="s4.6-whitespace"></a>
<h3>
4.6 Whitespace <a href="#s4.6-whitespace"><img height="21" width=
"21" src="guidelink.png"></a>
</h3><a name="s4.6.1-vertical-whitespace" id=
"s4.6.1-vertical-whitespace"></a>
<h4>
4.6.1 Vertical Whitespace <a href=
"#s4.6.1-vertical-whitespace"><img height="21" width="21" src=
"guidelink.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"><strong>Exception:</strong> 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" id=
"s4.6.2-horizontal-whitespace"></a>
<h4>
4.6.2 Horizontal whitespace <a href=
"#s4.6.2-horizontal-whitespace"><img height="21" width="21" src=
"guidelink.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>