This document serves as the complete definition of Googleâs coding standards for source code in the Java⢠Programming Language. A Java source file is described as being in Google Style if and only if it adheres to the rules herein.
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 isnât clearly enforceable (whether by human or tool).
In this document, unless otherwise clarified:
@interface).Other âterminology notesâ will appear occasionally throughout the document.
Example code in this document is non-normative. That is, while the examples are in Google 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.
For a source file containing classes, the file name consists of the
case-sensitive name of the top-level class (of which there is
exactly one), plus the .java extension.
Source files are encoded in UTF-8.
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:
char and string literals
and in text blocks.For any character that has a
special escape sequence
(\b, \t, \n, \f, \r, \s, \", \' and \\ ), that sequence is
used rather than the corresponding octal (e.g. \012) or Unicode (e.g.
\u000a) escape.
For the remaining non-ASCII characters, either the actual Unicode character
(e.g. â) or the equivalent Unicode escape (e.g. \u221e) is used. The choice
depends only on which makes the code easier to read and understand, although
Unicode escapes outside string literals and comments are strongly discouraged.
Tip: In the Unicode escape case, and occasionally even when actual Unicode characters are used, an explanatory comment can be very helpful.
Examples:
| Example | Discussion |
|---|---|
String unitAbbrev = "Îźs"; |
Best: perfectly clear even without a comment. |
String unitAbbrev = "\u03bcs"; // "Îźs" |
Allowed, but thereâs 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.
An ordinary source file consists of these sections, in order:
Exactly one blank line separates each section that is present.
A package-info.java file is the same, but without the class declaration.
A module-info.java file does not contain a package declaration and replaces
the class declaration with a module declaration, but otherwise follows the same
structure.
If license or copyright information belongs in a file, it belongs here.
Every source file must have a package declaration.
Compact source files are not used. (This rule
obviously does not apply to module-info.java files, which have a different
syntax that does not include a package declaration.)
The package declaration is not line-wrapped. The column limit (Section 4.4, Column limit: 100) does not apply to package declarations.
Wildcard (âon-demandâ) imports, static or otherwise, are not used.
Module imports are not used.
Example:
import module java.base;
Imports are not line-wrapped. The column limit (Section 4.4, Column limit: 100) does not apply to imports.
Imports are ordered as follows:
If there are both static and non-static imports, a single blank line separates the two groups. There are no other blank lines between imports.
Within each group the imported names appear in ASCII sort order. (Note: this is not the same as the import lines being in ASCII sort order, since â.â sorts before â;â.)
Static import is not used for static nested classes. They are imported with normal imports.
Each top-level class resides in a source file of its own.
The order you choose for the members and initializers of your class can have a great effect on learnability. However, thereâs no single correct recipe for how to do it; different classes may order their contents in different ways.
What is important is that each class uses some logical order, which its maintainer could explain if asked. For example, new methods are not just habitually added to the end of the class, as that would yield âchronological by date addedâ ordering, which is not a logical ordering.
Methods of a class that share the same name appear in a single contiguous group
with no other members in between. The same applies to multiple constructors.
This rule applies even when modifiers such as static or private differ
between the methods or constructors.
Module directives are ordered as follows:
requires directives in a single block.exports directives in a single block.opens directives in a single block.uses directives in a single block.provides directives in a single block.A single blank line separates each block that is present.
Terminology Note: block-like construct refers to the body of a class, method, constructor, or switch. Note that, by Section 4.8.3.1 on array initializers, any array initializer may optionally be treated as if it were a block-like construct.
Braces are used with if, else, for, do and while statements, even when
the body is empty or contains only a single statement.
Other optional braces, such as those in a lambda expression, remain optional.
Braces follow the Kernighan and Ritchie style for nonempty blocks and block-like constructs:
else or a comma.Exception: In places where these rules allow a single statement ending with a
semicolon (;), a block of statements can appear, and the opening brace of this
block is preceded by a line break. Blocks like these are typically introduced to
limit the scope of local variables.
Examples:
return () -> {
while (condition()) {
method();
}
};
return new MyClass() {
@Override public void method() {
if (condition()) {
try {
something();
} catch (ProblemException e) {
recover();
}
} else if (otherCondition()) {
somethingElse();
} else {
lastThing();
}
{
int x = foo();
frob(x);
}
}
};
A few exceptions for enum classes are given in Section 4.8.1, Enum classes.
An empty block or block-like construct may be in K & R style (as described in
Section 4.1.2). Alternatively, it 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 or try/catch/finally).
Examples:
// This is acceptable
void doNothing() {}
// This is equally acceptable
void doNothingElse() {
}
// This is not acceptable: No concise empty blocks in a multi-block statement
try {
doSomething();
} catch (Exception e) {}
Each time a new block or block-like construct is opened, the indent increases by two spaces. When the block ends, the indent returns to the previous indent level. The indent level applies to both code and comments throughout the block. (See the example in Section 4.1.2, Nonempty blocks: K & R Style.)
Each statement is followed by a line break.
Java code has a column limit of 100 characters. A âcharacterâ means any Unicode code point. Except as noted below, any line that would exceed this limit must be line-wrapped, as explained in Section 4.5, Line-wrapping.
Tip: Each Unicode code point counts as one character, even if its display width is greater or less. For example, if using fullwidth characters, you may choose to wrap the line earlier than where this rule strictly requires.
Exceptions:
package declarations and imports (see Sections 3.2
Package declarations and 3.3
Imports).Terminology Note: When code that might otherwise occupy a single line is divided into multiple lines, 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.
Note: While the typical reason for line-wrapping is to avoid overflowing the column limit, even code that would in fact fit within the column limit may be line-wrapped at the authorâs discretion.
Tip: Extracting a method or local variable may solve the problem without the need to line-wrap.
The prime directive of line-wrapping is: prefer to break at a higher 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 âoperator-likeâ symbols:
.)::)<T extends Foo & Bar>)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.
for (âforeachâ)
statement.A method, constructor, or record-class name stays attached to the open
parenthesis (() that follows it.
A comma (,) stays attached to the token that precedes it.
A line is never broken adjacent to the arrow in a lambda or a switch rule, except that a break may come immediately after the arrow if the text following it consists of a single unbraced expression. Examples:
MyLambda<String, Long, Object> lambda =
(String label, Long value, Object obj) -> {
...
};
Predicate<String> predicate = str ->
longExpressionInvolving(str);
switch (x) {
case ColorPoint(Color color, Point(int x, int y)) ->
handleColorPoint(color, x, y);
...
}
Note: The primary goal for line wrapping is to have clear code, not necessarily code that fits in the smallest number of lines.
When line-wrapping, each line after the first (each continuation line) is indented at least +4 from the original line.
When there are multiple continuation lines, indentation may be varied beyond +4 as desired. In general, two continuation lines use the same indentation level if and only if they begin with syntactically parallel elements.
Section 4.6.3 on Horizontal alignment addresses the discouraged practice of using a variable number of spaces to align certain tokens with previous lines.
A single blank line always appears:
Between consecutive members or initializers of a class: fields, constructors, methods, nested classes, static initializers, and instance initializers.
As required by other sections of this document (such as Section 3, Source file structure, and Section 3.3, Imports).
A single blank line may also appear anywhere it improves readability, for example between statements to organize the code into logical subsections. A blank line before the first member or initializer, or after the last member or initializer of the class, is neither encouraged nor discouraged.
Multiple consecutive blank lines are permitted, but never required (or encouraged).
Beyond where required by the language or other style rules, and apart from within literals, comments and Javadoc, a single ASCII space also appears in the following places only.
Separating any keyword, such as if, for or catch, from an open
parenthesis (() that follows it on that line
Separating any keyword, 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
10 below)On both sides of any binary or ternary operator. This also applies to the following âoperator-likeâ symbols:
<T extends Foo & Bar>catch (FooException | BarException e):) in an enhanced for (âforeachâ) statement(String str) -> str.length() case "FOO" -> bar();but not
::) of a method reference, which is written like
Object::toString.), which is written like object.toString()After ,:; or the closing parenthesis ()) of a cast
Between any content and a double slash (//) which begins a comment.
Multiple spaces are allowed.
Between a double slash (//) which begins a comment and the commentâs text.
Multiple spaces are allowed.
Between the type and identifier 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 validBetween a type annotation and [] or ....
This rule is never interpreted as requiring or forbidding additional space at the start or end of a line; it addresses only interior space.
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:
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 attempting to preserve alignment for its own sake creates future problems. For example, consider a change that touches only one line. If that change disrupts the previous alignment, itâs important not to introduce additional changes on nearby lines simply to realign them. Introducing formatting changes on otherwise unaffected lines corrupts version history, slows down reviewers, and exacerbates merge conflicts. These practical concerns take priority over alignment.
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.
After the comma that follows an enum constant, a line break is optional. Additional blank lines (usually just one) are also allowed. This is one possibility:
private enum Answer {
YES {
@Override public String toString() {
return "yes";
}
},
NO,
MAYBE
}
An enum class with no methods and no documentation on its constants may optionally be formatted as if it were an array initializer (see Section 4.8.3.1 on array initializers).
private enum Suit { CLUBS, HEARTS, SPADES, DIAMONDS }
Since enum classes are classes, all other rules for formatting classes apply.
Every variable declaration (field or local) declares only one variable:
declarations such as int a, b; are not used.
Exception: Multiple variable declarations are acceptable in the header of a
for loop.
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.
Any array initializer may optionally be formatted as if it were a âblock-like construct.â For example, the following are all valid (not an exhaustive list):
new int[] { new int[] {
0, 1, 2, 3 0,
} 1,
2,
new int[] { 3,
0, 1, }
2, 3
} new int[]
{0, 1, 2, 3}
The square brackets form a part of the type, not the variable:
String[] args, not String args[].
For historical reasons, the Java language has two distinct syntaxes for
switch, which we can call old-style and new-style. New-style switches use
an arrow (->) after the switch labels, while old-style switches use a colon
(:).
Terminology Note: Inside the braces of a switch block are either one or
more switch rules (new-style); or one or more statement groups (old-style).
A switch rule consists of a switch label (case ... or default) followed
by -> and an expression, block, or throw. A statement group consists of one
or more switch labels each followed by a colon, then one or more statements, or,
for the last statement group, zero or more statements. (These definitions
match the Java Language Specification,
§14.11.)
As with any other block, the contents of a switch block are indented +2. Each switch label starts with this +2 indentation.
In a new-style switch, a switch rule can be written on a single line if it
otherwise follows Google style. (It must not exceed the column limit, and if it
contains a non-empty block then there must be a line break after {.) The
line-wrapping rules of Section 4.5 apply, including the
+4 indent for continuation lines. For a switch rule with a non-empty block after
the arrow, the same rules apply as for blocks elsewhere: lines between { and
} are indented a further +2 relative to the line with the switch label.
switch (number) {
case 0, 1 -> handleZeroOrOne();
case 2 ->
handleTwoWithAnExtremelyLongMethodCallThatWouldNotFitOnTheSameLine();
default -> {
logger.atInfo().log("Surprising number %s", number);
handleSurprisingNumber(number);
}
}
In an old-style switch, the colon of each switch label is followed by a line break. The statements within a statement group are indented a further +2.
Within an old-style 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:
switch (input) {
case 1:
case 2:
prepareOneOrTwo();
// fall through
case 3:
handleOneTwoOrThree();
break;
default:
handleLargeNumber(input);
}
Notice that no comment is needed after case 1:, only at the end of the
statement group.
There is no fall-through in new-style switches.
default labelThe Java language requires switch expressions and many kinds of switch
statements to be exhaustive. That effectively means that every possible value
that could be switched on will be matched by one of the switch labels. A switch
is exhaustive if it has a default label, but also for example if the value
being switched on is an enum and every value of the enum is matched by a switch
label. Google Style requires every switch to be exhaustive, even those where
the language itself does not require it. This may require adding a default
label, even if it contains no code.
Switch expressions must be new-style switches:
return switch (list.size()) {
case 0 -> "";
case 1 -> list.getFirst();
default -> String.join(", ", list);
};
Type-use annotations appear immediately before the annotated type. An annotation
is a type-use annotation if it is meta-annotated with
@Target(ElementType.TYPE_USE). Example:
final @Nullable String name;
public @Nullable Person getPersonByName(String name);
Annotations applying to a class, package, or module declaration 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, Line-wrapping), so the indentation level is not increased. Examples:
/// This is a class.
@Deprecated
@CheckReturnValue
public final class Frozzler { ... }
/// This is a package.
@Deprecated
@CheckReturnValue
package com.example.frozzler;
/// This is a module.
@Deprecated
@SuppressWarnings("CheckReturnValue") // TODO(b/123): Fix existing CRV violations.
module com.example.frozzler { ... }
The rules for annotations on method and constructor declarations are the same as the previous section. Example:
@Deprecated
@Override
public String getNameIfPresent() { ... }
Exception: If the method or constructor only has a single, parameterless annotation, it may 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 in this 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 annotations on parameters or local variables (except, of course, when the annotation is a type-use annotation).
This section addresses implementation comments. Javadoc is addressed separately in Section 7, Javadoc.
Any line break may be preceded by arbitrary whitespace followed by an implementation comment. Such a comment renders the line non-blank.
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 to re-wrap the lines when necessary (paragraph-style).
Most formatters donât re-wrap lines in // ... style comment blocks.
Use TODO comments for code that is temporary, a short-term solution, or
good-enough but not perfect.
A TODO comment begins with the word TODO in all caps, a following colon, and
a link to a resource that contains the context, ideally a bug reference. A bug
reference is preferable because bugs are tracked and have follow-up comments.
Follow this piece of context with an explanatory string introduced with a hyphen
-.
The purpose is to have a consistent TODO format that can be searched to find
out how to get more details.
// TODO: crbug.com/12345678 - Remove this after the 2047q4 compatibility window expires.
Avoid adding TODOs that refer to an individual or team as the context:
// TODO: @yourusername - File an issue and use a '*' for repetition.
If your TODO is of the form âAt a future date do somethingâ make sure that you
either include a very specific date (âFix by November 2005â) or a very specific
event (âRemove this code when all clients can handle XML responses.â).
Class and member modifiers, when present, appear in the order recommended by the Java Language Specification:
public protected private abstract default static final sealed non-sealed
transient volatile synchronized native strictfp
Modifiers on requires module directives, when present, appear in the following
order:
transitive static
long-valued integer literals use an uppercase L suffix, never lowercase (to
avoid confusion with the digit 1). For example, 3000000000L rather than
3000000000l.
The opening """ of a text block is always on a new line. That line may either
follow the same indentation rules as other constructs, or it may have no
indentation at all (so it starts at the left margin). The closing """ is on a
new line with the same indentation as the opening """, and may be followed on
the same line by further code. Each line of text in the text block is indented
at least as much as the opening and closing """. (If a line is indented
further, then the string literal defined by the text block will have space at
the start of that line.)
The contents of a text block may exceed the column limit.
Identifiers use only ASCII letters and digits, and, in a small number of cases
noted below, underscores. Thus each valid identifier name is matched by the
regular expression \w+ .
In Google Style, special prefixes or suffixes are not used. For example,
these names are not Google Style: name_, mName, s_name and kName.
Package and module names use only lowercase letters and digits (no underscores).
Consecutive words are simply concatenated together. For example,
com.example.deepspace, not com.example.deepSpace or
com.example.deep_space.
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 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.
A test class has a name that ends with Test, for example,
HashIntegrationTest. If it covers a single class, its name is the name of that
class plus Test, for example HashImplTest.
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 the name, with each component written in
lowerCamelCase, for example
transferMoney_deductsFromSource. There is no One Correct Way to name test
methods.
Constant names use UPPER_SNAKE_CASE: all uppercase letters, with each word
separated from the next by a single underscore. But what is a constant,
exactly?
Constants are static final fields whose contents are deeply immutable and whose
methods have no detectable side effects. Examples include primitives, strings,
immutable value classes, and anything set to null. If any of the instanceâs
observable state can change, it is not a constant. Merely intending to never
mutate the object is not enough. Examples:
// Constants
static final int NUMBER = 5;
static final ImmutableList<String> NAMES = ImmutableList.of("Ed", "Ann");
static final Map<String, Integer> AGES = ImmutableMap.of("Ed", 35, "Ann", 32);
static final Joiner COMMA_JOINER = Joiner.on(','); // because Joiner is immutable
static final SomeMutableType[] EMPTY_ARRAY = {};
// 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 ImmutableMap<String, SomeMutableType> mutableValues =
ImmutableMap.of("Ed", mutableInstance, "Ann", mutableInstance2);
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 (static or otherwise) are written in lowerCamelCase.
These names are typically nouns or noun phrases. For example, computedValues
or index.
Parameter names are written in lowerCamelCase.
One-character parameter names in public methods should be avoided.
Local variable names are written in lowerCamelCase.
Even when final and immutable, local variables are not considered to be constants, and should not be styled as constants.
Each type variable is named in one of two styles:
E, T, X, T2)T
(examples: RequestT, FooBarT).The _ syntax for unnamed variables and parameters is allowed wherever it is
applicable. For example:
Predicate<String> alwaysTrue = _ -> true;
Sometimes there is more than one reasonable way to convert an English phrase into camel case, such as when acronyms or unusual constructs like âIPv6â or âiOSâ are present. To improve predictability, 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, âMĂźllerâs algorithmâ might become âMuellers algorithmâ.
Divide this result into words, splitting on spaces and any remaining punctuation (typically hyphens).
Now lowercase everything (including acronyms), then uppercase only the first character of:
Finally, join all the words into a single identifier. Note that the casing of the original words is almost entirely disregarded.
In very rare circumstances (for example, multipart version numbers), you may need to use underscores to separate adjacent numbers, since numbers do not have upper and lower case variants.
Examples:
| Prose form | Correct | Incorrect |
|---|---|---|
| âXML HTTP requestâ | XmlHttpRequest |
XMLHTTPRequest |
| ânew customer IDâ | newCustomerId |
newCustomerID |
| âinner stopwatchâ | innerStopwatch |
innerStopWatch |
| âsupports IPv6 on iOS?â | supportsIpv6OnIos |
supportsIPv6OnIOS |
| âYouTube importerâ | YouTubeImporterYoutubeImporter* |
 |
| âTurn on 2SVâ | turnOn2sv |
turnOn2Sv |
| âGuava 33.4.6â | guava33_4_6 |
guava3346 |
*Acceptable, but not recommended.
Note: Some words are ambiguously hyphenated in the English language: for
example ânonemptyâ and ânon-emptyâ are both correct, so the method names
checkNonempty and checkNonEmpty are likewise both correct.
@Override: always usedA 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, an interface method respecifying a
superinterface method, and an explicitly declared accessor method for a record
component.
Exception: @Override may be omitted when the parent method is
@Deprecated.
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 âimpossibleâ, 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.
try {
int i = Integer.parseInt(response);
return handleNumericResponse(i);
} catch (NumberFormatException _) {
// it's not numeric; that's fine, just continue
}
return handleTextResponse(response);
When a reference to a static class member must be qualified, it is qualified with that classâs name, not with a reference or expression of that classâs type.
Foo aFoo = ...;
Foo.aStaticMethod(); // good
aFoo.aStaticMethod(); // bad
somethingThatYieldsAFoo().aStaticMethod(); // very bad
Do not override Object.finalize. Finalization support is
scheduled for removal.
Both Markdown Javadoc and Traditional Javadoc are acceptable. Markdown Javadoc looks like this example:
/// Javadoc text is written here,
/// wrapped normally...
public int method(String p1) { ... }
The basic formatting of Traditional 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 the entirety of the Javadoc block (including comment markers) can fit on a
single line. Note that this only applies when there are no block tags such as
@param.
With Traditional Javadoc, one blank lineâthat is, a line containing only the
aligned leading asterisk (*)âappears between paragraphs, and before the group
of block tags if present. Each paragraph except the first has <p> immediately
before the first word, with no space after it. HTML tags for other block-level
elements, such as <ul> or <table>, are not preceded with <p>.
With Markdown Javadoc, paragraphs are separated as usual for Markdown, by a line
that is blank apart from the leading ///. No <p> is needed.
Any of the standard âblock tagsâ that are used appear in the order @param,
@return, @throws, @deprecated, and these four types never appear with an
empty description. When a block tag doesnât fit on a single line, continuation
lines are indented four (or more) spaces from the position of the @ for
Traditional Javadoc, and exactly two spaces for Markdown Javadoc. (A four-space
indentation in Markdown is interpreted as an indented code block in some
contexts.)
Each Javadoc block 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 `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. or /// {@return the customer ID}.
At the minimum, Javadoc is present for every visible class, member, or
record component, with a few exceptions noted below. A top-level class is
visible if it is public; a member is visible if it is public or protected
and its containing class is visible; and a record component is visible if its
containing record is visible.
Additional Javadoc content may also be present, as explained in Section 7.3.4, Non-required Javadoc.
Javadoc is optional for âsimple, obviousâ members and record components, such as
a getFoo() method, if there really and truly is nothing else worthwhile to
say but âthe fooâ.
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 record component named canonicalName, donât omit its documentation (with the
rationale that it would say only @param canonicalName the canonical name) if a
typical reader may have no idea what the term âcanonical nameâ means!
Javadoc is not always present on a method that overrides a supertype method.
Other classes, members, and record components have Javadoc as needed or desired.
Whenever an implementation comment would be used to define the overall purpose
or behavior of a class or member, that comment is written as Javadoc instead
(using /// or /**).
Non-required Javadoc is not strictly required to follow the formatting rules of Sections 7.1.1, 7.1.2, 7.1.3, and 7.2, though it is of course recommended.