Repository: logging-log4j2 Updated Branches: refs/heads/master 57169eb88 -> dea6d414c
LOG4J2-1802: Convert javastyle page to asciidoc Project: http://git-wip-us.apache.org/repos/asf/logging-log4j2/repo Commit: http://git-wip-us.apache.org/repos/asf/logging-log4j2/commit/dea6d414 Tree: http://git-wip-us.apache.org/repos/asf/logging-log4j2/tree/dea6d414 Diff: http://git-wip-us.apache.org/repos/asf/logging-log4j2/diff/dea6d414 Branch: refs/heads/master Commit: dea6d414c06f2740f4f57e9211be8e771ad4ecd6 Parents: 57169eb Author: Matt Sicker <boa...@gmail.com> Authored: Fri Apr 6 14:39:35 2018 -0500 Committer: Matt Sicker <boa...@gmail.com> Committed: Fri Apr 6 14:39:35 2018 -0500 ---------------------------------------------------------------------- src/site/asciidoc/javastyle.adoc | 1033 +++++++++++++++++++++++++++++++++ src/site/xdoc/javastyle.xml | 806 ------------------------- 2 files changed, 1033 insertions(+), 806 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/logging-log4j2/blob/dea6d414/src/site/asciidoc/javastyle.adoc ---------------------------------------------------------------------- diff --git a/src/site/asciidoc/javastyle.adoc b/src/site/asciidoc/javastyle.adoc new file mode 100644 index 0000000..f123ce7 --- /dev/null +++ b/src/site/asciidoc/javastyle.adoc @@ -0,0 +1,1033 @@ +//// + 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 + + https://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. +//// += Java Style Guidelines + +[#intro] +== Introduction + +This document serves as the *complete* 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. + +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 +*hard-and-fast rules* that we follow universally, and avoids giving +_advice_ that isn't clearly enforceable (whether by human or tool). + +[#terminology] +=== Terminology notes + +In this document, unless otherwise clarified: + +1. The term _class_ is used inclusively to mean an "ordinary" class, +enum class, interface or annotation type (`@interface`). +2. The term _comment_ always refers to _implementation_ comments. We do +not use the phrase "documentation comments", instead using the common +term "Javadoc." + +Other "terminology notes" will appear occasionally throughout the +document. + +[#guide-notes] +=== Guide notes + +Example code in this document is *non-normative*. That is, while the +examples are in Log4j Style, they may not illustrate the _only_ stylish +way to represent the code. Optional formatting choices made in examples +should not be enforced as rules. + +[#source-file-basics] +== Source File Basics + +[#file-name] +=== File name + +The source file name consists of the case-sensitive name of the +top-level class it contains, plus the `.java` extension. + +[#file-encoding] +=== File encoding: UTF-8 + +Source files are encoded in *UTF-8*. + +[#special-characters] +=== Special characters + +[#whitespace-characters] +==== Whitespace characters + +Aside from the line terminator sequence, the *ASCII horizontal space +character* (*0x20*) is the only whitespace character that appears +anywhere in a source file. This implies that: + +1. All other whitespace characters in string and character literals are +escaped. +2. Tab characters are *not* used for indentation. + +[#special-escape-sequences] +==== Special escape sequences + +For any character that has a special escape sequence (`\b`, `\t`, `\n`, +`\f`, `\r`, `\"`, `\'` and `\\`), that sequence is used rather than the +corresponding octal (e.g. `\012`) or Unicode (e.g. `\u000a`) escape. + +[#non-ascii-characters] +==== Non-ASCII characters + +For the remaining non-ASCII characters, either the actual Unicode +character (e.g. `â`) or the equivalent Unicode escape (e.g. `\u221e`) is +used, depending only on which makes the code *easier to read and +understand*. + +TIP: In the Unicode escape case, and occasionally even when actual +Unicode characters are used, an explanatory comment can be very helpful. + +Examples: + +[cols=",",options="header",] +|======================================================================= +|Example |Discussion +|`String unitAbbrev = "μs";` |Best: perfectly clear even without a +comment. + +|`String unitAbbrev = "\u03bcs"; // "μs"` |Allowed, but there's no +reason to do this. + +|`String unitAbbrev = "\u03bcs"; // Greek letter mu, "s"` |Allowed, but +awkward and prone to mistakes. + +|`String unitAbbrev = "\u03bcs";` |Poor: the reader has no idea what +this is. + +|`return '\ufeff' + content; // byte order mark` |Good: use escapes for +non-printable characters, and comment if necessary. +|======================================================================= + +TIP: 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 *broken* and they must be *fixed*. + +[#source-file-structure] +== Source File Structure + +[[filestructure]] +A source file consists of, *in order*: + +1. Apache license +2. Package statement +3. Import statements +4. Exactly one top-level class + +*Exactly one blank line* separates each section that is present. + +[#license] +=== Apache License + +The Apache license belongs here. No other license should appear. Other +licenses that apply should be referenced in a NOTICE file + +[#package-statement] +=== Package statement + +The package statement is *not line-wrapped*. The column limit +(<<column-limit>>) does not apply to package statements. + +[#import-statements] +=== Import statements + +[[imports]] + +[#wildcard-imports] +==== No wildcard imports in the main tree + +*Wildcard imports*, static or otherwise, *are not used*. + +[#static-wildcart-imports] +==== Static wildcard imports in the test tree + +*Wildcard static imports* are encouraged for test imports like JUnit, +EasyMock, and Hamcrest. + +[#import-line-wrapping] +==== No line-wrapping + +Import statements are *not line-wrapped*. The column limit +(<<column-limit>>) does not apply to import +statements. + +[#import-ordering-and-spacing] +==== Ordering and spacing + +Import statements are divided into the following groups, in this order, +with each group separated by a single blank line: + +1. java +2. javax +3. org +4. com +5. All static imports in a single group + +Within a group there are no blank lines, and the imported names appear +in ASCII sort order. (NOTE: this is not the same as the import +_statements_ being in ASCII sort order; the presence of semicolons warps +the result.) + +IDE settings for ordering imports automatically can be found in the +source distributions under `src/ide`. For example: + +* Eclipse: `src/ide/eclipse/4.3.2/organize-imports.importorder` +* IntelliJ: `src/ide/Intellij/13/IntellijSettings.jar` + +[#class-declaration] +=== Class declaration + +[#one-top-level-class] +==== Exactly one top-level class declaration + +[[oneclassperfile]] +Each top-level class resides in a source file of its own. + +[#class-member-ordering] +==== Class member ordering + +Class members should be grouped in the following order>. + +. static variables grouped in the order shown below. Within a group +variables may appear in any order. +.. public +.. protected +.. package +.. private +. instance variables grouped in the order shown below. Within a group +variables may appear in any order +.. public +.. protected +.. package +.. private +.. constructors +. methods may be specified in the following order but may appear in +another order if it improves the clarity of the program. +.. public +.. protected +.. package +.. private + +[[overloads]] [[never-split]] +Overloads: never split + +When a class has multiple constructors, or multiple methods with the +same name, these appear sequentially, with no intervening members. + +[#formatting] +== Formatting + +[NOTE] +==== +_block-like construct_ refers to the body of a +class, method or constructor. Note that, by +link:#array-initializers[array initializers], any array initializer _may_ +optionally be treated as if it were a block-like construct. +==== + +[#braces] +=== Braces + +[#braces-always-used] +==== Braces are used where optional + +Braces are used with `if`, `else`, `for`, `do` and `while` statements, +even when the body is empty or contains only a single statement. + +[#blocks-k-r-style] +==== Nonempty blocks: K & R style + +Braces follow the Kernighan and Ritchie style +("http://www.codinghorror.com/blog/2012/07/new-programming-jargon.html[Egyptian +brackets]") for _nonempty_ blocks and block-like constructs: + +* No line break before the opening brace. +* Line break after the opening brace. +* Line break before the closing brace. +* Line break after the closing brace _if_ that brace terminates a +statement or the body of a method, constructor or _named_ class. For +example, there is _no_ line break after the brace if it is followed by +`else` or a comma. + +Example: + +[source,java] +---- +return new MyClass() { + @Override public void method() { + if (condition()) { + try { + something(); + } catch (ProblemException e) { + recover(); + } + } + } +}; +---- + +A few exceptions for enum classes are given in <<enum-classes>>. + + +[#braces-empty-blocks] +==== Empty blocks: may be concise + +[[emptyblocks]] +An empty block or block-like construct _may_ be closed immediately after +it is opened, with no characters or line break in between (`{}`), +*unless* it is part of a _multi-block statement_ (one that directly +contains multiple blocks: `if/else-if/else` or `try/catch/finally`). + +Example: + +[source,java] +---- +void doNothing() {} +---- + +[#block-indentation] +=== Block indentation: +4 spaces + +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 <<blocks-k-r-style>>.) + +[#one-statement-per-line] +=== One statement per line + +Each statement is followed by a line-break. + + +[#column-limit] +=== Column limit: 120 + +[[columnlimit]] +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 +<<line-wrapping>>. + +*Exceptions:* + +1. Lines where obeying the column limit is not possible (for example, a +long URL in Javadoc, or a long JSNI method reference). +2. `package` and `import` statements (see +link:#package-statement[Package statement] and +link:#import-statements[Import statements]). +3. Command lines in a comment that may be cut-and-pasted into a shell. + +[#line-wrapping] +=== Line-wrapping + +*Terminology Note:* 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 _line-wrapping_. + +There is no comprehensive, deterministic formula showing _exactly_ how +to line-wrap in every situation. Very often there are several valid ways +to line-wrap the same piece of code. + +TIP: Extracting a method or local variable may solve the problem +without the need to line-wrap. + +[#line-wrapping-where-to-break] +==== Where to break + +The prime directive of line-wrapping is: prefer to break at a *higher +syntactic level*. Also: + +1. When a line is broken at a _non-assignment_ operator the break comes +_before_ the symbol. (Note that this is not the same practice used in +Google style for other languages, such as C++ and JavaScript.) +* This also applies to the following "operator-like" symbols: the dot +separator (`.`), the ampersand in type bounds (`<T extends Foo & Bar>`), +and the pipe in catch blocks (`catch (FooException | BarException e)`). +2. When a line is broken at an _assignment_ operator the break +typically comes _after_ the symbol, but either way is acceptable. +* This also applies to the "assignment-operator-like" colon in an +enhanced `for` ("foreach") statement. +3. A method or constructor name stays attached to the open parenthesis +(`(`) that follows it. +4. A comma (`,`) stays attached to the token that precedes it. + + +[#line-wrapping-indent] +==== Indent continuation lines at least +8 spaces + +[[indentation]] +When line-wrapping, each line after the first (each _continuation line_) +is indented at least +8 from the original line. + +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. + +The section on link:#horizontal-alignment[Horizontal alignment] +addresses the discouraged practice of using a variable number of spaces +to align certain tokens with previous lines. + +[#whitespace] +=== Whitespace + +[#vertical-whitespace] +==== Vertical Whitespace + +A single blank line appears: + +1. _Between_ consecutive members (or initializers) of a class: fields, +constructors, methods, nested classes, static initializers, instance +initializers. +* *Exception:* A blank line between two consecutive fields (having no +other code between them) is optional. Such blank lines are used as +needed to create _logical groupings_ of fields. +2. Within method bodies, as needed to create _logical groupings_ of +statements. +3. _Optionally_ before the first member or after the last member of the +class (neither encouraged nor discouraged). +4. As required by other sections of this document (such as +<<import-statements>>). + +_Multiple_ consecutive blank lines are permitted, but never required (or +encouraged). + +[#horizontal-whitespace] +==== Horizontal whitespace + +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 *only*. + +1. Separating any reserved word, such as `if`, `for` or `catch`, from +an open parenthesis (`(`) that follows it on that line +2. Separating any reserved word, such as `else` or `catch`, from a +closing curly brace (`}`) that precedes it on that line +3. Before any open curly brace (`{`), with two exceptions: +* `String[][] x = {{"foo"}};` (no space is required between `{{`, by +item 8 below) +4. On both sides of any binary or ternary operator. This also applies +to the following "operator-like" symbols: +* the ampersand in a conjunctive type bound: `<T extends Foo & Bar>` +* the pipe for a catch block that handles multiple exceptions: +`catch (FooException | BarException e)` +* the colon (`:`) in an enhanced `for` ("foreach") statement +5. After `,:;` or the closing parenthesis (`)`) of a cast +6. On both sides of the double slash (`//`) that begins an end-of-line +comment. Here, multiple spaces are allowed, but not required. +7. Between the type and variable of a declaration: `List<String> list` +8. _Optional_ just inside both braces of an array initializer +* `new int[] {5, 6}` and `new int[] { 5, 6 }` are both valid + +NOTE: This rule never requires or forbids additional space at the +start or end of a line, only _interior_ space. + +[#horizontal-alignment] +==== Horizontal alignment: never required + +*Terminology Note:* _Horizontal alignment_ is the practice of adding a +variable number of additional spaces in your code with the goal of +making certain tokens appear directly below certain other tokens on +previous lines. + +This practice is permitted, but is *never required* by Google Style. It +is not even required to _maintain_ horizontal alignment in places where +it was already used. + +Here is an example without alignment, then using alignment: + +[source,java] +---- +private int x; // this is fine +private Color color; // this too + +private int x; // permitted, but future edits +private Color color; // may leave it unaligned +---- + +TIP: 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 *allowed*. 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. + +[#grouping-parentheses] +=== Grouping parentheses: recommended + +[[parentheses]] +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 +_not_ reasonable to assume that every reader has the entire Java +operator precedence table memorized. + +[#specific-constructs] +=== Specific constructs + +[#enum-classes] +==== Enum classes + +After each comma that follows an enum constant, a line-break is +optional. + +An enum class with no methods and no documentation on its constants may +optionally be formatted as if it were an array initializer (see +link:array-initializers[array initializers]). + +[source,java] +---- +private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS } +---- + +Since enum classes _are classes_, all other rules for formatting classes +apply. + +[#variable-declarations] +==== Variable declarations + +[[localvariables]] +[[variables-per-declaration]] +One variable per declaration + +Every variable declaration (field or local) declares only one variable: +declarations such as `int a, b;` are not used. + +[[variables-limited-scope]] +Declared when needed, initialized as soon as possible + +Local variables are *not* 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. + +[#s4.8.3-arrays] +==== Arrays + +[[array-initializers]] +Array initializers: can be "block-like" + +Any array initializer may _optionally_ be formatted as if it were a +"block-like construct." For example, the following are all valid (*not* +an exhaustive list): + +[source,java] +---- +new int[] { new int[] { + 0, 1, 2, 3 0, +} 1, + 2, +new int[] { 3, + 0, 1, } + 2, 3 +} new int[] + {0, 1, 2, 3} +---- + +[[array-declarations]] +No C-style array declarations + +The square brackets form a part of the _type_, not the variable: +`String[] args`, not `String args[]`. + +[#switch] +==== Switch statements + +*Terminology Note:* Inside the braces of a _switch block_ are one or +more _statement groups_. Each statement group consists of one or more +_switch labels_ (either `case FOO:` or `default:`), followed by one or +more statements. + +[[switch-indentation]] +===== Indentation + +As with any other block, the contents of a switch block are indented +2. + +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. + +[#switch-fall-through] +===== Fall-through: commented + +[[fallthrough]] +Within a switch block, each statement group either terminates abruptly +(with a `break`, `continue`, `return` or thrown exception), or is marked +with a comment to indicate that execution will or _might_ continue into +the next statement group. Any comment that communicates the idea of +fall-through is sufficient (typically `// fall through`). This special +comment is not required in the last statement group of the switch block. +Example: + +[source,java] +---- +switch (input) { + case 1: + case 2: + prepareOneOrTwo(); + // fall through + case 3: + handleOneTwoOrThree(); + break; +default: + handleLargeNumber(input); +} +---- + +[[switch-default]] +The default case is present. + +Each switch statement includes a `default` statement group, even if it +contains no code. + +[#annotations] +==== Annotations + +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, +link:#line-wrapping[Line-wrapping]), so the indentation level is not +increased. Example: + +[source,java] +---- +@Override +@Nullable +public String getNameIfPresent() { ... } +---- + +*Exception:* A _single_ parameterless annotation _may_ instead appear +together with the first line of the signature, for example: + +[source,java] +---- +@Override public int hashCode() { ... } +---- + +Annotations applying to a field also appear immediately after the +documentation block, but in this case, _multiple_ annotations (possibly +parameterized) may be listed on the same line; for example: + +[source,java] +---- + @Partial @Mock DataLoader loader; +---- + +There are no specific rules for formatting parameter and local variable +annotations. + +[#comments] +==== Comments + +[#block-comment-style] +===== Block comment style + +Block comments are indented at the same level as the surrounding code. +They may be in `/* ... */` style or `// ...` style. For multi-line +`/* ... */` comments, subsequent lines must start with `*` aligned with +the `*` on the previous line. + +[source,java] +---- +/* + * This is // And so /* Or you can + * okay. // is this. * even do this. */ + */ +---- + +Comments are not enclosed in boxes drawn with asterisks or other +characters. + +TIP: When writing multi-line comments, use the `/* ... */` style if +you want automatic code formatters to re-wrap the lines when necessary +(paragraph-style). Most formatters don't re-wrap lines in `// ...` style +comment blocks. + +[#modifiers] +==== Modifiers + +Class and member modifiers, when present, appear in the order +recommended by the Java Language Specification: + +[source,java] +---- +public protected private abstract static final transient volatile synchronized native strictfp +---- + +[#numeric-literals] +==== Numeric Literals + +`long`-valued integer literals use an uppercase `L` suffix, never +lowercase (to avoid confusion with the digit `1`). For example, +`3000000000L` rather than `3000000000l`. + +[#naming] +== Naming + +[#identifier-names] +=== Rules common to all identifiers + +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 `\w+` . + +In Google Style special prefixes or suffixes, like those seen in the +examples `name_`, `mName`, `s_name` and `kName`, are *not* used. + +[#specific-identifier-names] +=== Rules by identifier type + +[#package-names] +==== Package names + +Package names are all lowercase, with consecutive words simply +concatenated together (no underscores). For example, +`com.example.deepspace`, not `com.example.deepSpace` or +`com.example.deep_space`. + +[#class-names] +==== Class names + +Class names are written in link:#camel-case[UpperCamelCase]. + +Class names are typically nouns or noun phrases. For example, +`Character` or `ImmutableList`. Interface names may also be nouns or +noun phrases (for example, `List`), but may sometimes be adjectives or +adjective phrases instead (for example, `Readable`). + +There are no specific rules or even well-established conventions for +naming annotation types. + +_Test_ classes are named starting with the name of the class they are +testing, and ending with `Test`. For example, `HashTest` or +`HashIntegrationTest`. + +[#method-names] +==== Method names + +Method names are written in link:#s5.3-camel-case[lowerCamelCase]. + +Method names are typically verbs or verb phrases. For example, +`sendMessage` or `stop`. + +Underscores may appear in JUnit _test_ method names to separate logical +components of the name. One typical pattern is +`test<MethodUnderTest>_<state>`, for example `testPop_emptyStack`. There +is no One Correct Way to name test methods. + +[#constant-names] +==== Constant names + +[[constants]] +Constant names use `CONSTANT_CASE`: all uppercase letters, with words +separated by underscores. But what _is_ a constant, exactly? + +Every constant is a static final field, but not all static final fields +are constants. Before choosing constant case, consider whether the field +really _feels like_ a constant. For example, if any of that instance's +observable state can change, it is almost certainly not a constant. +Merely _intending_ to never mutate the object is generally not enough. +Examples: + +[source,java] +---- +// Constants +static final int NUMBER = 5; +static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann"); +static final Joiner COMMA_JOINER = Joiner.on(','); // because Joiner is immutable +static final SomeMutableType[] EMPTY_ARRAY = {}; +enum SomeEnum { ENUM_CONSTANT } + +// Not constants +static String nonFinal = "non-final"; +final String nonStatic = "non-static"; +static final Set<String> mutableCollection = new HashSet<String>(); +static final ImmutableSet<SomeMutableType> mutableElements = ImmutableSet.of(mutable); +static final Logger logger = Logger.getLogger(MyClass.getName()); +static final String[] nonEmptyArray = {"these", "can", "change"}; +---- + +These names are typically nouns or noun phrases. + +[#non-constant-field-names] +==== Non-constant field names + +Non-constant field names (static or otherwise) are written in +link:#camel-case[lowerCamelCase]. + +These names are typically nouns or noun phrases. For example, +`computedValues` or `index`. + +[#parameter-names] +==== Parameter names + +Parameter names are written in link:#camel-case[lowerCamelCase]. + +One-character parameter names should be avoided. + +[#local-variable-names] +==== Local variable names + +Local variable names are written in link:#camel-case[lowerCamelCase], +and can be abbreviated more liberally than other types of names. + +However, one-character names should be avoided, except for temporary and +looping variables. + +Even when final and immutable, local variables are not considered to be +constants, and should not be styled as constants. + +[#type-variable-names] +==== Type variable names + +Each type variable is named in one of two styles: + +* A single capital letter, optionally followed by a single numeral (such +as `E`, `T`, `X`, `T2`) +* A name in the form used for classes (see link:#class-names[Class +names]), followed by the capital letter `T` (examples: `RequestT`, +`FooBarT`). + +[#camel-case] +=== Camel case: defined + +[[acronyms]] +[[camelcase]] +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. + +Beginning with the prose form of the name: + +1. Convert the phrase to plain ASCII and remove any apostrophes. For +example, "Müller's algorithm" might become "Muellers algorithm". +2. Divide this result into words, splitting on spaces and any remaining +punctuation (typically hyphens). +* _Recommended:_ 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 _per se_; it defies _any_ convention, so this +recommendation does not apply. +3. Now lowercase _everything_ (including acronyms), then uppercase only +the first character of: +* ... each word, to yield _upper camel case_, or +* ... each word except the first, to yield _lower camel case_ +4. Finally, join all the words into a single identifier. + +Note that the casing of the original words is almost entirely +disregarded. Examples: + +[cols=",,",options="header",] +|================================================================= +|Prose form |Correct |Incorrect +|"XML HTTP request" |`XmlHttpRequest` |`XMLHTTPRequest` +|"new customer ID" |`newCustomerId` |`newCustomerID` +|"inner stopwatch" |`innerStopwatch` |`innerStopWatch` +|"supports IPv6 on iOS?" |`supportsIpv6OnIos` |`supportsIPv6OnIOS` +|"YouTube importer" |`YouTubeImporter` + +`YoutubeImporter`* | +|================================================================= + +*Acceptable, but not recommended. + +NOTE: Some words are ambiguously hyphenated in the English language: +for example "nonempty" and "non-empty" are both correct, so the method +names `checkNonempty` and `checkNonEmpty` are likewise both correct. + +[#programming-practices] +== Programming Practices + +[#override-annotation] +=== @Override: always used + +A method is marked with the `@Override` 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. + +**Exception:** `@Override` may be omitted when the parent method is +`@Deprecated`. + +[#caught-exceptions] +=== Caught exceptions: not ignored + +[[caughtexceptions]] +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 `AssertionError`.) + +When it truly is appropriate to take no action whatsoever in a catch +block, the reason this is justified is explained in a comment. + +[source,java] +---- +try { + int i = Integer.parseInt(response); + return handleNumericResponse(i); +} catch (NumberFormatException ok) { + // it's not numeric; that's fine, just continue +} +return handleTextResponse(response); +---- + +*Exception:* In tests, a caught exception may be ignored without comment +_if_ it is named `expected`. The following is a very common idiom for +ensuring that the method under test _does_ throw an exception of the +expected type, so a comment is unnecessary here. + +[source,java] +---- +try { + emptyStack.pop(); + fail(); +} catch (NoSuchElementException expected) { +} +---- + +[#static-members] +=== Static members: qualified using class + +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. + +[source,java] +---- +Foo aFoo = ...; +Foo.aStaticMethod(); // good +aFoo.aStaticMethod(); // bad +somethingThatYieldsAFoo().aStaticMethod(); // very bad +---- + +[#finalizers] +=== Finalizers: not used + +It is *extremely rare* to override `Object.finalize`. + +TIP: Don't do it. If you absolutely must, first read and understand +http://books.google.com/books?isbn=8131726592[_Effective Java_] Item 7, +"Avoid Finalizers," very carefully, and _then_ don't do it. + +[#javadoc] +== Javadoc + +[#javadoc-formatting] +=== Formatting + +[#javadoc-multi-line] +==== General form + +The _basic_ formatting of Javadoc blocks is as seen in this example: + +[source,java] +---- +/** + * Multiple lines of Javadoc text are written here, + * wrapped normally... + */ +public int method(String p1) { ... } +---- + +... or in this single-line example: + +[source,java] +---- +/** An especially short bit of Javadoc. */ +---- + +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. + +[#javadoc-paragraphs] +==== Paragraphs + +One blank lineâthat is, a line containing only the aligned leading +asterisk (`*`)âappears between paragraphs, and before the group of +"at-clauses" if present. Each paragraph but the first has `<p>` +immediately before the first word, with no space after. + +[#javadoc-at-clauses] +==== At-clauses + +Any of the standard "at-clauses" that are used appear in the order +`@param`, `@return`, `@throws`, `@deprecated`, 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 `@`. + +[#summary-fragment] +=== The summary fragment + +The Javadoc for each class and member begins with a brief *summary +fragment*. This fragment is very important: it is the only part of the +text that appears in certain contexts such as class and method indexes. + +This is a fragmentâa noun phrase or verb phrase, not a complete +sentence. It does *not* begin with `A {@code Foo} is a...`, or +`This method returns...`, nor does it form a complete imperative +sentence like `Save the record.`. However, the fragment is capitalized +and punctuated as if it were a complete sentence. + +TIP: A common mistake is to write simple Javadoc in the form +`/** @return the customer ID */`. This is incorrect, and should be +changed to `/** Returns the customer ID. */`. + +[#javadoc-where-required] +=== Where Javadoc is used + +[[javadoc-optional]] +At the _minimum_, Javadoc is present for every `public` class, and every +`public` or `protected` member of such a class, with a few exceptions +noted below. + +Other classes and members still have Javadoc _as needed_. 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.) + +[#javadoc-exception-self-explanatory] +==== Exception: self-explanatory methods + +Javadoc is optional for "simple, obvious" methods like `getFoo`, in +cases where there _really and truly_ is nothing else worthwhile to say +but "Returns the foo". + +IMPORTANT: 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 `getCanonicalName`, don't omit its +documentation (with the rationale that it would say only +`/** Returns the canonical name. */`) if a typical reader may have no +idea what the term "canonical name" means! + +[#javadoc-exception-overrides] +==== Exception: overrides + +Javadoc is not always present on a method that overrides a supertype +method. http://git-wip-us.apache.org/repos/asf/logging-log4j2/blob/dea6d414/src/site/xdoc/javastyle.xml ---------------------------------------------------------------------- diff --git a/src/site/xdoc/javastyle.xml b/src/site/xdoc/javastyle.xml deleted file mode 100644 index f09f7ea..0000000 --- a/src/site/xdoc/javastyle.xml +++ /dev/null @@ -1,806 +0,0 @@ -<?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
