Repository: logging-log4j-audit Updated Branches: refs/heads/master ace89fa5b -> 34383867c
http://git-wip-us.apache.org/repos/asf/logging-log4j-audit/blob/4fe17cae/src/site/xdoc/javastyle.xml ---------------------------------------------------------------------- diff --git a/src/site/xdoc/javastyle.xml b/src/site/xdoc/javastyle.xml new file mode 100644 index 0000000..f09f7ea --- /dev/null +++ b/src/site/xdoc/javastyle.xml @@ -0,0 +1,806 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> +<document xmlns="http://maven.apache.org/XDOC/2.0"; xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; + xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd";> + + <properties> + <title>Java Style Guidelines</title> + </properties> + + <body> + <section name="Apache Log4j Code Style Guidelines"> + <a name="intro"/> + <subsection name="Introduction"> + <p>This document serves as the <strong>complete</strong> definition of the Log4j project's coding standards for + source code in the Java⢠Programming Language. It originated from the Google coding standards but incorporates + modifications that reflect the desires of the Log4j community.</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="terminology"/> + <h3>Terminology notes</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>@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="guide-notes"/> + <h3>Guide notes</h3> + <p>Example code in this document is <strong>non-normative</strong>. That is, while the examples + are in Log4j 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> + </subsection> + <a name="source-file-basics"/> + <subsection name="Source File Basics"> + <a name="file-name"/> + <h3>File name</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="file-encoding"/> + <h3>2.2 File encoding: UTF-8</h3> + <p>Source files are encoded in <strong>UTF-8</strong>.</p> + <a name="special-characters"/> + <h3>Special characters</h3> + <a name="whitespace-characters"/> + <h4>Whitespace characters</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="special-escape-sequences"/> + <h4>Special escape sequences</h4> + <p>For any character that has a special escape sequence + (<code>\b</code>, + <code>\t</code>, + <code>\n</code>, + <code>\f</code>, + <code>\r</code>, + <code>\"</code>, + <code>\'</code> and + <code>\\</code>), that sequence is used rather than the corresponding octal + (e.g. <code>\012</code>) or Unicode (e.g. <code>\u000a</code>) escape.</p> + <a name="non-ascii-characters"/> + <h4>Non-ASCII characters</h4> + <p>For the remaining non-ASCII characters, either the actual Unicode character + (e.g. <code>â</code>) or the equivalent Unicode escape (e.g. <code>\u221e</code>) is used, depending only on which + makes the code <strong>easier to read and understand</strong>.</p> + <p><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>String unitAbbrev = "μs";</code></td><td>Best: perfectly clear even without a comment.</td></tr> + <tr><td><code>String unitAbbrev = "\u03bcs"; // "μs"</code></td><td>Allowed, but there's no reason to do this.</td></tr> + <tr><td><code>String unitAbbrev = "\u03bcs"; // Greek letter mu, "s"</code></td><td>Allowed, but awkward and prone to mistakes.</td></tr> + <tr><td><code>String unitAbbrev = "\u03bcs";</code></td><td>Poor: the reader has no idea what this is.</td></tr> + <tr><td><code>return '\ufeff' + content; // byte order mark</code></td><td>Good: use escapes for non-printable characters, and comment if necessary.</td></tr> + </table> + <p><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> + </subsection> + <a name="filestructure"/> + <a name="source-file-structure"/> + <subsection name="Source file structure"> + <p>A source file consists of, <strong>in order</strong>:</p> + <ol> + <li>Apache license</li> + <li>Package statement</li> + <li>Import statements</li> + <li>Exactly one top-level class</li> + </ol> + <p><strong>Exactly one blank line</strong> separates each section that is present.</p> + <a name="license"/> + <h3>Apache License</h3> + <p>The Apache license belongs here. No other license should appear. Other licenses that apply should be referenced in + a NOTICE file</p> + <a name="package-statement"/> + <h3>Package statement</h3> + <p>The package statement is <strong>not line-wrapped</strong>. The column limit + (<a href="#column-limit">Column limit: 120</a>) does not apply to package statements.</p> + <a name="imports"/> + <a name="import-statements"/> + <h3>Import statements</h3> + <a name="wildcard-imports"/> + <h4>No wildcard imports in the main tree</h4> + <p><strong>Wildcard imports</strong>, static or otherwise, <strong>are not used</strong>.</p> + <h4>Static wildcard imports in the test tree</h4> + <p><strong>Wildcard static imports</strong> are encouraged for test imports like JUnit, EasyMock, and Hamcrest.</p> + <a name="import-line-wrapping"/> + <h4>No line-wrapping</h4> + <p>Import statements are <strong>not line-wrapped</strong>. The column limit + (<a href="#column-limit">Column limit: 120</a>) does not apply to import statements.</p> + <a name="import-ordering-and-spacing"/> + <h4>Ordering and spacing</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>java</li> + <li>javax</li> + <li>org</li> + <li>com</li> + <li>All static imports in a single group</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> + <p>IDE settings for ordering imports automatically can be found in the source distributions under + <code>src/ide</code>. For example:</p> + <ul> + <li>Eclipse: <code>src/ide/eclipse/4.3.2/organize-imports.importorder</code></li> + <li>IntelliJ: <code>src/ide/Intellij/13/IntellijSettings.jar</code></li> + </ul> + <a name="class-declaration"/> + <h3>Class declaration</h3> + <a name="oneclassperfile"/> + <a name="one-top-level-class"/> + <h4>Exactly one top-level class declaration</h4> + <p>Each top-level class resides in a source file of its own.</p> + <a name="class-member-ordering"/> + <h4>Class member ordering</h4> + <p>Class members should be grouped in the following order>.</p> + <ol> + <li>static variables grouped in the order shown below. Within a group variables may appear in any order.</li> + <li> + <ol> + <li>public</li> + <li>protected</li> + <li>package</li> + <li>private</li> + </ol> + </li> + <li>instance variables grouped in the order shown below. Within a group variables may appear in any order</li> + <li> + <ol> + <li>public</li> + <li>protected</li> + <li>package</li> + <li>private</li> + </ol> + </li> + <li>constructors</li> + <li>methods may be specified in the following order but may appear in another order if it improves the + clarity of the program.</li> + <li> + <ol> + <li>public</li> + <li>protected</li> + <li>package</li> + <li>private</li> + </ol> + </li> + </ol> + <a name="overloads"/> + <a name="never-split"/> + <h5>Overloads: never split</h5> + <p>When a class has multiple constructors, or multiple methods with the same name, these appear + sequentially, with no intervening members.</p> + </subsection> + <a name="formatting"/> + <subsection name="Formatting"> + <p><strong>Terminology Note:</strong> <em>block-like construct</em> refers to + the body of a class, method or constructor. Note that, by + <a href="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"/> + <h3>Braces</h3> + <a name="braces-always-used"/> + <h4>Braces are used where optional</h4> + <p>Braces are used with + <code>if</code>, + <code>else</code>, + <code>for</code>, + <code>do</code> and + <code>while</code> statements, even when the + body is empty or contains only a single statement.</p> + <a name="blocks-k-r-style"/> + <h4>Nonempty blocks: K & R style</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>else</code> or a + comma.</li></ul><p>Example:</p> +<pre> + 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="enum-classes">Enum classes</a>.</p> + <a name="emptyblocks"/> + <a name="braces-empty-blocks"/> + <h4>Empty blocks: may be concise</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>{}</code>), <strong>unless</strong> it is part of a + <em>multi-block statement</em> (one that directly contains multiple blocks: + <code>if/else-if/else</code> or + <code>try/catch/finally</code>).</p> + <p>Example:</p><pre> + void doNothing() {} + </pre><a name="block-indentation"/> + <h3>Block indentation: +4 spaces</h3> + <p>Each time a new block or block-like construct is opened, the indent increases by four + 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="#blocks-k-r-style">Nonempty blocks: K & R Style</a>.)</p> + <a name="one-statement-per-line"/> + <h3>One statement per line</h3> + <p>Each statement is followed by a line-break.</p> + <a name="columnlimit"/> + <a name="column-limit"/> + <h3>Column limit: 120</h3> + <p> + The column limit for Log4j is 120 characters. + + Except as noted below, any line that would exceed this limit must be line-wrapped, as explained in + <a href="#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>package</code> and <code>import</code> statements (see <a href="#package-statement">Package statement</a> and + <a href="#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="line-wrapping"/> + <h3>Line-wrapping</h3> + <p class="terminology"><strong>Terminology Note:</strong> When code that might otherwise legally + occupy a single line is divided into multiple lines, 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="line-wrapping-where-to-break"/> + <h4>Where to break</h4> + <p>The prime directive of line-wrapping is: prefer to break at a + <strong>higher syntactic level</strong>. Also:</p> + <ol> + <li>When a line is broken at a <em>non-assignment</em> operator the break comes <em>before</em> + 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>.</code>), the ampersand in type bounds + (<code><T extends Foo & Bar></code>), and the pipe in + catch blocks + (<code>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>for</code> ("foreach") statement.</li> + </ul> + </li> + <li>A method or constructor name stays attached to the open parenthesis + (<code>(</code>) that follows it.</li> + <li>A comma (<code>,</code>) stays attached to the token that + precedes it.</li> + </ol> + <a name="indentation"/> + <a name="line-wrapping-indent"/> + <h4>Indent continuation lines at least +8 spaces</h4> + <p>When line-wrapping, each line after the first (each <em>continuation line</em>) is indented + at least +8 from the original line.</p> + <p>When there are multiple continuation lines, indentation may be varied beyond +8 as + desired. In general, two continuation lines use the same indentation level if and only if they + begin with syntactically parallel elements.</p> + <p>The section on <a href="#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="whitespace"/> + <h3>Whitespace</h3> + <a name="vertical-whitespace"/> + <h4>Vertical Whitespace</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 + <a href="#import-statements">Import statements</a>).</li> + </ol> + <p><em>Multiple</em> consecutive blank lines are permitted, but never required (or encouraged).</p> + <a name="horizontal-whitespace"/> + <h4>Horizontal whitespace</h4> + <p>Beyond where required by the language or other style rules, and apart from literals, comments and + Javadoc, a single ASCII space also appears in the following places <strong>only</strong>.</p> + <ol> + <li>Separating any reserved word, such as + <code>if</code>, + <code>for</code> or + <code>catch</code>, from an open parenthesis + (<code>(</code>) + that follows it on that line</li> + <li>Separating any reserved word, such as + <code>else</code> or + <code>catch</code>, from a closing curly brace + (<code>}</code>) that precedes it on that line</li> + <li>Before any open curly brace + (<code>{</code>), with two exceptions: + <ul> + <li><code>String[][] x = {{"foo"}};</code> (no space is required + between <code>{{</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><T extends Foo & Bar></code></li> + <li>the pipe for a catch block that handles multiple exceptions: + <code>catch (FooException | BarException e)</code></li> + <li>the colon (<code>:</code>) in an enhanced + <code>for</code> ("foreach") statement</li> + </ul> + </li> + <li>After <code>,:;</code> or the closing parenthesis + (<code>)</code>) of a cast</li> + <li>On both sides of the double slash (<code>//</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>List<String> list</code></li> + <li><em>Optional</em> just inside both braces of an array initializer + <ul> + <li><code>new int[] {5, 6}</code> and + <code>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 + start or end of a line, only <em>interior</em> space.</p> + <a name="horizontal-alignment"/> + <h4>Horizontal alignment: never required</h4> + <p class="terminology"><strong>Terminology Note:</strong> <em>Horizontal alignment</em> 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> + 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"><strong>Tip:</strong> 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="grouping-parentheses"/> + <h3>Grouping parentheses: recommended</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="specific-constructs"/> + <h3>Specific constructs</h3> + <a name="enum-classes"/> + <h4>Enum classes</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 (see + <a href="array-initializers">array initializers</a>).</p><pre> + 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="variable-declarations"/> + <h4>Variable declarations</h4> + <a name="variables-per-declaration"/> + <h5>One variable per declaration</h5> + <p>Every variable declaration (field or local) declares only one variable: declarations such as + <code>int a, b;</code> are not used.</p> + <a name="variables-limited-scope"/> + <h5>Declared when needed, initialized as soon as possible</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>Arrays</h4> + <a name="array-initializers"/> + <h5>Array initializers: can be "block-like"</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> + 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="array-declarations"/> + <h5>No C-style array declarations</h5> + <p>The square brackets form a part of the <em>type</em>, not the variable: + <code>String[] args</code>, not + <code>String args[]</code>.</p> + <a name="switch"/> + <h4>Switch statements</h4> + <p class="terminology"><strong>Terminology Note:</strong> 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>case FOO:</code> or + <code>default:</code>), followed by one or more statements.</p> + <a name="switch-indentation"/> + <h5>Indentation</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="switch-fall-through"/> + <h5>Fall-through: commented</h5> + <p>Within a switch block, each statement group either terminates abruptly (with a + <code>break</code>, + <code>continue</code>, + <code>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>// fall through</code>). This special comment is not required in + the last statement group of the switch block. Example:</p><pre> + switch (input) { + case 1: + case 2: + prepareOneOrTwo(); + // fall through + case 3: + handleOneTwoOrThree(); + break; + default: + handleLargeNumber(input); + } + </pre><a name="switch-default"/> + <h5>The default case is present</h5> + <p>Each switch statement includes a <code>default</code> statement + group, even if it contains no code.</p> + <a name="annotations"/> + <h4>Annotations</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="#line-wrapping">Line-wrapping</a>), so the indentation level is not + increased. Example:</p><pre> + @Override + @Nullable + public String getNameIfPresent() { ... } + </pre><p class="exception"><strong>Exception:</strong> A <em>single</em> parameterless annotation + <em>may</em> instead appear together with the first line of the signature, for example:</p><pre> + @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> + @Partial @Mock DataLoader loader; + </pre><p>There are no specific rules for formatting parameter and local variable annotations.</p> + <a name="comments"/> + <h4>Comments</h4> + <a name="block-comment-style"/> + <h5>Block comment style</h5> + <p>Block comments are indented at the same level as the surrounding code. They may be in + <code>/* ... */</code> style or + <code>// ...</code> style. For multi-line + <code>/* ... */</code> comments, subsequent lines must start with + <code>*</code> aligned with the <code>*</code> on the previous line.</p><pre> + /* + * 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><strong>Tip:</strong> When writing multi-line comments, use the + <code>/* ... */</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>// ...</code> style comment blocks.</p> + <a name="modifiers"/> + <h4>Modifiers</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="numeric-literals"/> + <h4>Numeric Literals</h4> + <p><code>long</code>-valued integer literals use an uppercase <code>L</code> suffix, never + lowercase (to avoid confusion with the digit <code>1</code>). For example, <code>3000000000L</code> + rather than <code>3000000000l</code>.</p> + </subsection> + <a name="naming"/> + <subsection name="Naming"> + <a name="identifier-names"/> + <h3>Rules common to all identifiers</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>name_</code>, + <code>mName</code>, <code>s_name</code> and + <code>kName</code>, are <strong>not</strong> used.</p> + <a name="specific-identifier-names"/> + <h3>Rules by identifier type</h3> + <a name="package-names"/> + <h4>Package names</h4> + <p>Package names are all lowercase, with consecutive words simply concatenated together (no + underscores). For example, <code>com.example.deepspace</code>, not + <code>com.example.deepSpace</code> or + <code>com.example.deep_space</code>.</p> + <a name="class-names"/> + <h4>Class names</h4> + <p>Class names are written in <a href="#camel-case">UpperCamelCase</a>.</p> + <p>Class names are typically nouns or noun phrases. For example, + <code>Character</code> or + <code>ImmutableList</code>. Interface names may also be nouns or + noun phrases (for example, <code>List</code>), but may sometimes be + adjectives or adjective phrases instead (for example, + <code>Readable</code>).</p><p>There are no specific rules or even well-established conventions for naming annotation types.</p><p><em>Test</em> classes are named starting with the name of the class they are testing, and ending + with <code>Test</code>. For example, + <code>HashTest</code> or + <code>HashIntegrationTest</code>.</p> + <a name="method-names"/> + <h4>Method names</h4> + <p>Method names are written in <a href="#s5.3-camel-case">lowerCamelCase</a>.</p> + <p>Method names are typically verbs or verb phrases. For example, + <code>sendMessage</code> or + <code>stop</code>.</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>testPop_emptyStack</code>. There is no One Correct + Way to name test methods.</p> + <a name="constants"/> + <a name="constant-names"/> + <h4>Constant names</h4> + <p>Constant names use <code>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> + // 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="non-constant-field-names"/> + <h4>Non-constant field names</h4> + <p>Non-constant field names (static or otherwise) are written + in <a href="#camel-case">lowerCamelCase</a>.</p> + <p>These names are typically nouns or noun phrases. For example, + <code>computedValues</code> or + <code>index</code>.</p> + <a name="parameter-names"/> + <h4>Parameter names</h4> + <p>Parameter names are written in <a href="#camel-case">lowerCamelCase</a>.</p> + <p>One-character parameter names should be avoided.</p> + <a name="local-variable-names"/> + <h4>Local variable names</h4> + <p>Local variable names are written in <a href="#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="type-variable-names"/> + <h4>Type variable names</h4> + <p>Each type variable is named in one of two styles:</p><ul><li>A single capital letter, optionally followed by a single numeral (such as + <code>E</code>, <code>T</code>, + <code>X</code>, <code>T2</code>) + </li><li>A name in the form used for classes (see + <a href="#class-names">Class names</a>), followed by the capital letter + <code>T</code> (examples: + <code>RequestT</code>, + <code>FooBarT</code>).</li></ul><a name="acronyms"/> + <a name="camelcase"/> + <a name="camel-case"/> + <h3>Camel case: defined</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>XmlHttpRequest</code></td><td><code>XMLHTTPRequest</code></td></tr> + <tr><td>"new customer ID"</td><td><code>newCustomerId</code></td><td><code>newCustomerID</code></td></tr> + <tr><td>"inner stopwatch"</td><td><code>innerStopwatch</code></td><td><code>innerStopWatch</code></td></tr> + <tr><td>"supports IPv6 on iOS?"</td><td><code>supportsIpv6OnIos</code></td><td><code>supportsIPv6OnIOS</code></td></tr> + <tr><td>"YouTube importer"</td><td><code>YouTubeImporter</code><br/><code>YoutubeImporter</code>*</td><td/></tr> + </table> + <p>*Acceptable, but not recommended.</p> + <p><strong>Note:</strong> Some words are ambiguously hyphenated in the English + language: for example "nonempty" and "non-empty" are both correct, so the method names + <code>checkNonempty</code> and + <code>checkNonEmpty</code> are likewise both correct.</p> + </subsection> + <subsection name="Programming Practices"> + <a name="programming-practices"/> + <a name="override-annotation"/> + <h3>@Override: always used</h3> + <p>A method is marked with the <code>@Override</code> annotation + 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 + method.</p> + <p class="exception"><strong>Exception:</strong><code>@Override</code> may be omitted when the parent method is + <code>@Deprecated</code>.</p> + <a name="caughtexceptions"/> + <a name="caught-exceptions"/> + <h3>Caught exceptions: not ignored</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>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> + 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><strong>Exception:</strong> In tests, a caught exception may be ignored + without comment <em>if</em> it is named <code>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> + try { + emptyStack.pop(); + fail(); + } catch (NoSuchElementException expected) { + } + </pre><a name="static-members"/> + <h3>Static members: qualified using class</h3> + <p>When a reference to a static class member must be qualified, it is qualified with that class's + name, not with a reference or expression of that class's type.</p><pre> + Foo aFoo = ...; + Foo.aStaticMethod(); // good + <span>aFoo.aStaticMethod();</span> // bad + <span>somethingThatYieldsAFoo().aStaticMethod();</span> // very bad + </pre> + <a name="finalizers"/> + <h3>Finalizers: not used</h3> + <p>It is <strong>extremely rare</strong> to override <code>Object.finalize</code>.</p> + <p><strong>Tip:</strong> Don't do it. If you absolutely must, first read and understand + <a href="http://books.google.com/books?isbn=8131726592";><em>Effective Java</em></a> + Item 7, "Avoid Finalizers," very carefully, and <em>then</em> don't do it.</p> + </subsection> + <a name="javadoc"/> + <subsection name="Javadoc"> + <a name="javadoc-formatting"/> + <h3>Formatting</h3> + <a name="javadoc-multi-line"/> + <h4>General form</h4> + <p>The <em>basic</em> formatting of Javadoc blocks is as seen in this example:</p><pre> + /** + * 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> + /** An especially short bit of Javadoc. */ + </pre><p>The basic form is always acceptable. The single-line form may be substituted when there are no + at-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on a + single line.</p> + <a name="javadoc-paragraphs"/> + <h4>Paragraphs</h4> + <p>One blank lineâthat is, a line containing only the aligned leading asterisk + (<code>*</code>)âappears 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="javadoc-at-clauses"/> + <h4>At-clauses</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="summary-fragment"/> + <h3>The summary fragment</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 fragmentâa noun phrase or verb phrase, not a complete sentence. It does + <strong>not</strong> begin with <code>A {@code Foo} is a...</code>, or + <code>This method returns...</code>, nor does it form a complete imperative sentence + like <code>Save the record.</code>. However, the fragment is capitalized and + 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>/** @return the customer ID */</code>. This is incorrect, and should be + changed to <code>/** Returns the customer ID. */</code>.</p> + <a name="javadoc-optional"/> + <a name="javadoc-where-required"/> + <h3>Where Javadoc is used</h3> + <p>At the <em>minimum</em>, Javadoc is present for every + <code>public</code> class, and every + <code>public</code> or + <code>protected</code> member of such a class, with a few exceptions + 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="javadoc-exception-self-explanatory"/> + <h4>Exception: self-explanatory methods</h4> + <p>Javadoc is optional for "simple, obvious" methods like + <code>getFoo</code>, in cases where there <em>really and truly</em> is + 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 + omitting relevant information that a typical reader might need to know. For example, for a method + named <code>getCanonicalName</code>, don't omit its documentation + (with the rationale that it would say only + <code>/** Returns the canonical name. */</code>) if a typical reader may have no idea + what the term "canonical name" means!</p> + <a name="javadoc-exception-overrides"/> + <h4>Exception: overrides</h4> + <p>Javadoc is not always present on a method that overrides a supertype method. + </p> + </subsection> + </section> + </body> +</document> \ No newline at end of file
