Google Java Style

转自：http://google.github.io/styleguide/javaguide.html

Google Java Style

Last changed: March 21, 2014

1 Introduction1.1 Terminology notes1.2 Guide notes 2 Source file basics2.1 File name2.2 File encoding: UTF-82.3 Special characters2.3.1 Whitespace characters2.3.2 Special escape sequences2.3.3 Non-ASCII characters 3 Source file structure3.1 License or copyright information, if present3.2 Package statement3.3 Import statements3.3.1 No wildcard imports3.3.2 No line-wrapping3.3.3 Ordering and spacing3.4 Class declaration3.4.1 Exactly one top-level class declaration3.4.2 Class member ordering

4 Formatting4.1 Braces4.1.1 Braces are used where optional4.1.2 Nonempty blocks: K & R style4.1.3 Empty blocks: may be concise4.2 Block indentation: +2 spaces4.3 One statement per line4.4 Column limit: 80 or 1004.5 Line-wrapping4.5.1 Where to break4.5.2 Indent continuation lines at least +4 spaces4.6 Whitespace4.6.1 Vertical Whitespace4.6.2 Horizontal whitespace4.6.3 Horizontal alignment: never required4.7 Grouping parentheses: recommended4.8 Specific constructs4.8.1 Enum classes4.8.2 Variable declarations4.8.3 Arrays4.8.4 Switch statements4.8.5 Annotations4.8.6 Comments4.8.7 Modifiers4.8.8 Numeric Literals

5 Naming5.1 Rules common to all identifiers5.2 Rules by identifier type5.2.1 Package names5.2.2 Class names5.2.3 Method names5.2.4 Constant names5.2.5 Non-constant field names5.2.6 Parameter names5.2.7 Local variable names5.2.8 Type variable names5.3 Camel case: defined 6 Programming Practices6.1 @Override: always used6.2 Caught exceptions: not ignored6.3 Static members: qualified using class6.4 Finalizers: not used 7 Javadoc7.1 Formatting7.1.1 General form7.1.2 Paragraphs7.1.3 At-clauses7.2 The summary fragment7.3 Where Javadoc is used7.3.1 Exception: self-explanatory methods7.3.2 Exception: overrides

1 Introduction

This document serves as the complete definition of Google's coding standards forsource code in the Java™ Programming Language. A Java source file is described as being
inGoogle Style if and only if it adheres to the rules herein.

Like other programming style guides, the issues covered span not only aesthetic issues offormatting, but other types of conventions or coding standards as well. However, this documentfocuses primarily on the
hard-and-fast rules that we follow universally, andavoids giving
advice that isn't clearly enforceable (whether by human or tool).

1.1 Terminology notes

In this document, unless otherwise clarified:The term class is used inclusively to mean an "ordinary" class, enum class, interface or annotation type (

@interface

).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.

1.2 Guide notes

Example code in this document is non-normative. That is, while the examplesare in Google Style, they may not illustrate the
only stylish way to represent thecode. Optional formatting choices made in examples should not be enforced as rules.

2 Source file basics

2.1 File name

The source file name consists of the case-sensitive name of the top-level class it contains,plus the

.java

extension.

2.2 File encoding: UTF-8

Source files are encoded in UTF-8.

2.3 Special characters

2.3.1 Whitespace characters

Aside from the line terminator sequence, the ASCII horizontal spacecharacter (0x20) is the only whitespace character that appearsanywhere in a source file. This implies that:

All other whitespace characters in string and character literals are escaped.Tab characters are not used for indentation.

2.3.2 Special escape sequences

For any character that has a special escape sequence(

\b

,

\t

,

\n

,

\f

,

\r

,

\"

,

\'

and

\\

), that sequenceis used rather than the corresponding octal(e.g.

\012

) or Unicode(e.g.

\u000a

) escape.

2.3.3 Non-ASCII characters

For the remaining non-ASCII characters, either the actual Unicode character(e.g.

∞

) or the equivalent Unicode escape(e.g.

\u221e

)
is used, depending only on whichmakes the code easier to read and understand.

Tip: In the Unicode escape case, and occasionally even when actualUnicode characters are used, an explanatory comment can be very helpful.Examples:

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 thatsome programs might not handle non-ASCII characters properly. If that should happen, thoseprograms are
broken and they must be fixed.

3 Source file structure

A source file consists of, in order:

License or copyright information, if present
Package statement
Import statementsExactly one top-level class

Exactly one blank line separates each section that is present.

3.1 License or copyright information, if present

If license or copyright information belongs in a file, it belongs here.

3.2 Package statement

The package statement is not line-wrapped. The column limit (Section 4.4,Column limit: 80 or 100) does not apply to package statements.

3.3 Import statements

3.3.1 No wildcard imports

Wildcard imports, static or otherwise, are not used.

3.3.2 No line-wrapping

Import statements are not line-wrapped. The column limit (Section 4.4,Column limit: 80 or 100) does not apply to importstatements.

3.3.3 Ordering and spacing

Import statements are divided into the following groups, in this order, with each groupseparated by a single blank line:

All static imports in a single group

com.google

imports (only if this source file is in the

com.google

package space)Third-party imports, one group per top-level package, in ASCII sort orderfor example:

android

,

com

,

junit

,

org

,

sun

java

imports

javax

imports

Within a group there are no blank lines, and the imported names appear in ASCII sortorder. (Note: this is not the same as the import
statements being inASCII sort order; the presence of semicolons warps the result.)

3.4 Class declaration

3.4.1 Exactly one top-level class declaration

Each top-level class resides in a source file of its own.

3.4.2 Class member ordering

The ordering of the members of a class can have a great effect on learnability, but there isno single correct recipe for how to do it. Different classes may order their membersdifferently.

What is important is that each class order its members in some logicalorder, which its maintainer could explain if asked. For example, new methods are notjust habitually added to the end of the class, as that would yield "chronological
by dateadded" ordering, which is not a logical ordering.

3.4.2.1 Overloads: never split


When a class has multiple constructors, or multiple methods with the same name, these appearsequentially, with no intervening members.

4 Formatting

Terminology Note: block-like construct refers tothe body of a class, method or constructor. Note that, by Section 4.8.3.1 onarray
initializers, any array initializermay optionally be treated as if it were a block-like construct.

4.1 Braces

4.1.1 Braces are used where optional

Braces are used with

if

,

else

,

for

,

do

and

while

statements, even when thebody is empty or contains only a single statement.

4.1.2 Nonempty blocks: K & R style

Braces follow the Kernighan and Ritchie style("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:

return new MyClass() {
  @Override public void method() {
    if (condition()) {
      try {
        something();
      } catch (ProblemException e) {
        recover();
      }
    }
  }
};

A few exceptions for enum classes are given in Section 4.8.1,Enum classes.

4.1.3 Empty blocks: may be concise

An empty block or block-like construct may be closed immediately after it isopened, with no characters or line break in between(

{}

),
unless it is part of amulti-block statement (one that directly contains multiple blocks:

if/else-if/else

or

try/catch/finally

).
Example:

void doNothing() {}

4.2 Block indentation: +2 spaces

Each time a new block or block-like construct is opened, the indent increases by twospaces. When the block ends, the indent returns to the previous indent level. The indent levelapplies to both code and comments throughout the block. (See the example in
Section 4.1.2,Nonempty blocks: K & R Style.)

4.3 One statement per line

Each statement is followed by a line-break.

4.4 Column limit: 80 or 100

Projects are free to choose a column limit of either 80 or 100 characters.Except as noted below, any line that would exceed this limit must be line-wrapped, as explained inSection 4.5,

Line-wrapping.

Exceptions:

Lines where obeying the column limit is not possible (for example, a long URL in Javadoc, or a long JSNI method reference).

package

and

import

statements (see Sections 3.2

Package statement and 3.3
Import statements).
Command lines in a comment that may be cut-and-pasted into a shell.

4.5 Line-wrapping

Terminology Note: When code that might otherwise legallyoccupy a single line is divided into multiple lines, typically to avoid overflowing the columnlimit, this activity is calledline-wrapping.There is no comprehensive, deterministic formula showing exactly how to line-wrap inevery 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 problemwithout the need to line-wrap.

4.5.1 Where to break

The prime directive of line-wrapping is: prefer to break at ahigher syntactic level. Also:

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)

).

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.

A method or constructor name stays attached to the open parenthesis (

(

) that follows it.
A comma (

,

) stays attached to the token that precedes it.

4.5.2 Indent continuation lines at least +4 spaces

When line-wrapping, each line after the first (each continuation line) is indentedat least +4 from the original line.

When there are multiple continuation lines, indentation may be varied beyond +4 asdesired. In general, two continuation lines use the same indentation level if and only if theybegin with syntactically parallel elements.

Section 4.6.3 on
Horizontal alignment addressesthe discouraged practice of using a variable number of spaces to align certain tokens withprevious lines.

4.6 Whitespace

4.6.1 Vertical Whitespace

A single blank line appears:

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.

Within method bodies, as needed to create logical groupings of statements.
Optionally before the first member or after the last member of the class (neither encouraged nor discouraged).
As required by other sections of this document (such as Section 3.3,
Import statements).

Multiple consecutive blank lines are permitted, but never required (or encouraged).

4.6.2 Horizontal whitespace

Beyond where required by the language or other style rules, and apart from literals, comments andJavadoc, a single ASCII space also appears in the following places
only.

Separating any reserved word, such as

if

,

for

or

catch

, from an open parenthesis (

(

) that follows it on that line
Separating any reserved word, such as

else

or

catch

, from a closing curly brace (

}

) that precedes it on that line
Before any open curly brace (

{

), with two exceptions:

@SomeAnnotation({a, b})

(no space is
used)

String[][] x
= {{"foo"}};

(no space is required between

{{

, by item 8 below)

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

After

,:;

or the closing parenthesis (

)

) of a cast
On both sides of the double slash (

//

) that begins an end-of-line comment. Here, multiple spaces are allowed, but not required.
Between the type and variable of a declaration:

List<String> list

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 thestart or end of a line, only
interior space.

4.6.3 Horizontal alignment: never required

Terminology Note: Horizontal alignment is thepractice of adding a variable number of additional spaces in your code with the goal of makingcertain tokens appear directly below certain other tokens on previous
lines.This practice is permitted, but is never required by Google Style. It is noteven required to
maintain horizontal alignment in places where it was already used.

Here is an example without alignment, then using alignment:

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 forfuture maintenance. Consider a future change that needs to touch just one line. This change mayleave the formerly-pleasing formatting mangled, and that is
allowed. More oftenit prompts the coder (perhaps you) to adjust whitespace on nearby lines as well, possiblytriggering 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 historyinformation, slows down reviewers and exacerbates merge conflicts.

4.7 Grouping parentheses: recommended

Optional grouping parentheses are omitted only when author and reviewer agree that there is noreasonable chance the code will be misinterpreted without them, nor would they have made the codeeasier to read. It is
not reasonable to assume that every reader has the entire Javaoperator precedence table memorized.

4.8 Specific constructs

4.8.1 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 formattedas if it were an array initializer (see Section 4.8.3.1 onarray
initializers).

private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS }

Since enum classes are classes, all other rules for formatting classes apply.

4.8.2 Variable declarations

4.8.2.1 One variable per declaration

Every variable declaration (field or local) declares only one variable: declarations such as

int a, b;

are not used.

4.8.2.2 Declared when needed, initialized as soon aspossible


Local variables are not habitually declared at the start of their containingblock or block-like construct. Instead, local variables are declared close to the point they arefirst used (within reason), to minimize their scope. Local variable
declarations typically haveinitializers, or are initialized immediately after declaration.

4.8.3 Arrays

4.8.3.1 Array initializers: can be "block-like"


Any array initializer may optionally be formatted as if it were a "block-likeconstruct." For example, the following are all valid (not an exhaustivelist):

new int[] {           new int[] {
  0, 1, 2, 3            0,
}                       1,
                        2,
new int[] {             3,
  0, 1,               }
  2, 3
}                     new int[]
                          {0, 1, 2, 3}

4.8.3.2 No C-style array declarations

The square brackets form a part of the type, not the variable:

String[] args

, not

String
 args[]

.

4.8.4 Switch statements

Terminology Note: Inside the braces of aswitch block are one or more
statement groups. Each statement group consists ofone or more switch labels (either

case FOO:

or

default:

),
followed by one or more statements.

4.8.4.1 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 asif a block were being opened. The following switch label returns to the previous indentationlevel, as if a block had been closed.

4.8.4.2 Fall-through: commented


Within a switch block, each statement group either terminates abruptly (with a

break

,

continue

,

return

or thrown exception), or is marked with a commentto indicate that execution will or
might continue into the next statement group. Anycomment that communicates the idea of fall-through is sufficient (typically

// fall through

). This special comment
is not required inthe last statement group of the switch block. Example:

switch (input) {
  case 1:
  case 2:
    prepareOneOrTwo();
    // fall through
  case 3:
    handleOneTwoOrThree();
    break;
  default:
    handleLargeNumber(input);
}

4.8.4.3 The default case is present

Each switch statement includes a

default

statementgroup, even if it contains no code.

4.8.5 Annotations

Annotations applying to a class, method or constructor appear immediately after thedocumentation block, and each annotation is listed on a line of its own (that is, one annotationper line). These line breaks do not constitute line-wrapping (Section4.5,

Line-wrapping), so the indentation level is notincreased. Example:

@Override
@Nullable
public String getNameIfPresent() { ... }

Exception: A single parameterless annotationmay instead appear together with the first line of the signature, for example:

@Override public int hashCode() { ... }

Annotations applying to a field also appear immediately after the documentation block, but inthis case,
multiple annotations (possibly parameterized) may be listed on the same line;for example:

@Partial @Mock DataLoader loader;

There are no specific rules for formatting parameter and local variable annotations.

4.8.6 Comments

4.8.6.1 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.

/*
 * 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 tore-wrap the lines when necessary
(paragraph-style). Most formatters don't re-wrap lines in

// ...

style comment blocks.

4.8.7 Modifiers

Class and member modifiers, when present, appear in the orderrecommended by the Java Language Specification:

public protected private abstract static final transient volatile synchronized native strictfp

4.8.8 Numeric Literals

long

-valued integer literals use an uppercase

L

suffix, neverlowercase (to avoid confusion with the digit

1

). For example,

3000000000L

rather than

3000000000l

.

5 Naming

5.1 Rules common to all identifiers

Identifiers use only ASCII letters and digits, and in two cases noted below, underscores. Thuseach valid identifier name is matched by the regular expression

\w+

.

In Google Style special prefixes orsuffixes, like those seen in the examples

name_

,

mName

,

s_name

and

kName

, are
not used.

5.2 Rules by identifier type

5.2.1 Package names

Package names are all lowercase, with consecutive words simply concatenated together (nounderscores). For example,

com.example.deepspace

, not

com.example.deepSpace

or

com.example.deep_space

.

5.2.2 Class names

Class names are written in
UpperCamelCase.

Class names are typically nouns or noun phrases. For example,

Character

or

ImmutableList

.
Interface names may also be nouns ornoun phrases (for example,

List

), but may sometimes beadjectives 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 endingwith

Test

. For example,

HashTest

or

HashIntegrationTest

.

5.2.3 Method names

Method names are written in
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 thename. One typical pattern is

test<MethodUnderTest>_<state>

,for example

testPop_emptyStack

. There is no One CorrectWay to name test methods.

5.2.4 Constant names

Constant names use

CONSTANT_CASE

: all uppercaseletters, 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. Beforechoosing constant case, consider whether the field really
feels like a constant. Forexample, if any of that instance's observable state can change, it is almost certainly not aconstant. Merely
intending to never mutate the object is generally notenough. Examples:

// 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.

5.2.5 Non-constant field names

Non-constant field names (static or otherwise) are writtenin
lowerCamelCase.These names are typically nouns or noun phrases. For example,

computedValues

or

index

.

5.2.6 Parameter names

Parameter names are written in
lowerCamelCase.

One-character parameter names should be avoided.

5.2.7 Local variable names

Local variable names are written in
lowerCamelCase, and can beabbreviated 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 notbe styled as constants.

5.2.8 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 Section 5.2.2,
Class names), followed by the capital letter

T

(examples:

RequestT

,

FooBarT

).

5.3 Camel case: defined

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 improvepredictability, Google Style specifies the following (nearly) deterministic
scheme.

Beginning with the prose form of the name:

Convert the phrase to plain ASCII and remove any apostrophes. For example, "Müller's algorithm" might become "Muellers algorithm".
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.

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

Finally, join all the words into a single identifier.

Note that the casing of the original words is almost entirely disregarded. Examples:

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 Englishlanguage: for example "nonempty" and "non-empty" are both correct, so the method names

checkNonempty

and

checkNonEmpty

are likewise both correct.

6 Programming Practices

6.1 @Override: always used

A method is marked with the

@Override

annotationwhenever it is legal. This includes a class method overriding a superclass method, a class methodimplementing an interface method, and an interface method respecifying a superinterfacemethod.

Exception:

@Override

may be omitted when the parent method is

@Deprecated

.

6.2 Caught exceptions: not ignored

Except as noted below, it is very rarely correct to do nothing in response to a caughtexception. (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 isjustified is explained in a comment.

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 ignoredwithout commentif it is named

expected

. Thefollowing is a very common idiom for ensuring that the method under test
does throw anexception of the expected type, so a comment is unnecessary here.

try {
  emptyStack.pop();
  fail();
} catch (NoSuchElementException expected) {
}

6.3 Static members: qualified using class

When a reference to a static class member must be qualified, it is qualified with that class'sname, not with a reference or expression of that class's type.

Foo aFoo = ...;
Foo.aStaticMethod(); // good
aFoo.aStaticMethod(); // bad
somethingThatYieldsAFoo().aStaticMethod(); // very bad

6.4 Finalizers: not used

It is extremely rare to override

Object.finalize

.

Tip: Don't do it. If you absolutely must, first read and understandEffective JavaItem 7, "Avoid Finalizers," very carefully, and
then don't do it.

7 Javadoc

7.1 Formatting

7.1.1 General form

The basic formatting of Javadoc blocks is as seen in this example:

/**
 * Multiple lines of Javadoc text are written here,
 * wrapped normally...
 */
public int method(String p1) { ... }

... or in this single-line example:

/** An especially short bit of Javadoc. */

The basic form is always acceptable. The single-line form may be substituted when there are noat-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on asingle line.

7.1.2 Paragraphs

One blank line—that is, a line containing only the aligned leading asterisk(

*

)—appears between paragraphs, and before the group of "at-clauses" ifpresent. Each paragraph but the first has

<p>

immediately before the first word,with no space after.

7.1.3 At-clauses

Any of the standard "at-clauses" that are used appear in the order

@param

,

@return

,

@throws

,

@deprecated

, and these four types neverappear with an empty description. When an at-clause doesn't fit on a single line, continuation linesare indented four (or more) spaces from the position of the

@

.

7.2 The summary fragment

The Javadoc for each class and member begins with a brief summary fragment. Thisfragment is very important: it is the only part of the text that appears in certain contexts such asclass and method indexes.This is a fragment—a noun phrase or verb phrase, not a complete sentence. It doesnot begin with

A {@code Foo} is a...

, or

This method returns...

, nor does it form a complete imperative sentencelike

Save the record.

. However, the fragment is capitalized andpunctuated 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 bechanged to

/** Returns the customer ID. */

.

7.3 Where Javadoc is used

At the minimum, Javadoc is present for every

public

class, and every

public

or

protected

member of such a class, with a few exceptionsnoted below.

Other classes and members still have Javadoc as needed. Whenever an implementationcomment would be used to define the overall purpose or behavior of a class, method or field, thatcomment is written as Javadoc instead. (It's more uniform, and more
tool-friendly.)

7.3.1 Exception: self-explanatory methods

Javadoc is optional for "simple, obvious" methods like

getFoo

, in cases where there
really and truly isnothing else worthwhile to say but "Returns the foo".

Important: it is not appropriate to cite this exception to justifyomitting relevant information that a typical reader might need to know. For example, for a methodnamed

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 ideawhat the term "canonical name" means!

7.3.2 Exception: overrides

Javadoc is not always present on a method that overrides a supertype method.

Last changed: March 21, 2014