Java Style Guide

A mostly reasonable approach to Java!

1 Introduction
- 1.1 Why have code conventions
- 1.2 Guide notes
2 Source file basics
3 Source file structure
4 Formatting
5 Naming
6 Programming Practices
7 Javadoc

1 Introduction

1.1 Why have code conventions

Code conventions are important to programmers for a number of reasons:

80% of the lifetime cost of a piece of software goes to maintenance.
Hardly any software is maintained for its whole life by the original author.
Code conventions improve the readability of the software, allowing engineers to understand new code more quickly and thoroughly.
If you ship your source code as a product, you need to make sure it is as well packaged and clean as any other product you create.

For the conventions to work, every person writing software must conform to the code conventions. Everyone.

1.2 Guide notes

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

2 Source file basics

2.1 File suffixes

Use the following file suffixes:

File type	Suffix
Java source	`.java`
Java bytecode	`.class`

2.2 File name

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

2.3 File encoding

Source files are encoded in UTF-8.

2.4 Special characters

2.4.1 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:

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

2.4.2 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.

2.4.3 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 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.

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.

3 Source file structure

A source file consists of, in order:

License or copyright information (if present)
Package statement
Import statements
Exactly one top-level class

Exactly one blank line separates each section that is present.

3.1 License or copyright information

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

3.2 Package statement

The first non-comment line of most Java source files is a package statement.

3.2.1 No line-wrapping

The package statement is not line-wrapped. The section 4.2.1 Line length 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

The import statement is not line-wrapped. The section 4.2.1 Line length does not apply to import statements.

3.3.3 Ordering and spacing

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

com.shorky imports (only if this source file is in the com.shorky package space)
Third-party imports, one group per top-level package, in ASCII sort order
- for example: android, com, junit, org, sun
java imports
javax imports
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.)

Example:

package com.shorky.service.auth.adapter;

import com.shorky.service.AuthenticationService;
import com.shorky.service.auth.Authentication;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.easymock.EasyMock;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.net.ssl.SSLPeerUnverifiedException;

import static org.assertj.core.api.Assertions.assertThat;

3.4 Class and Interface declaration

3.4.1 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 is no single correct recipe for how to do it. Different classes may order their members differently.

What is important is that each class order its members in 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 "chronological by date added" ordering, which is not a logical ordering.

You can optionally adopt the following arrangement (which place public method before all other to separate API from implementation):

field public static
field protected static
field package static
field private static
field public
field protected
field package
field private
constructor
method public static
method public
method non-public static
method non-public
inner enum
inner interface
inner class static
inner class

3.4.3 Overloads: never split

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

Moreover keep getter and setter together.

4 Formatting

4.1 Indentation

Each time a new block or block-like construct is opened, the indent increases by tab. When the block ends, the indent returns to the previous indent level. The indent level applies to both code and comments throughout the block.

4.1.1 Alignement using 4 spaces

Use 4 spaces for expressing the indentation level and for alignment.

Example using indentation equals to four spaces:

int f(int x, int y) {
....return g(x, y);
}

4.1.2 Why not using tabs/smartab?

Tabs are evil.

4.2 Lines

4.2.1 Line length

Avoid lines longer than 120 characters. Except as noted below, any line that would exceed this limit must be line-wrapped, as explained in Section 4.2.2 Wrapping lines.

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 Section 3.2 Package statement and Section 3.3 Import statements).
Command lines in a comment that may be cut-and-pasted into a shell.

4.2.2 Wrapping lines

When line-wrapping, each line after the first (each continuation line) is indented at least +8 (2 times indentation) from the original line.

When there are multiple continuation lines, indentation may be varied beyond +8 (2 times indentation) as desired. In general, two continuation lines use the same indentation level if and only if they begin with syntactically parallel elements.

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.

General principles can be used:

Break after a comma.
Break before an operator.
Prefer higher-level breaks to lower-level breaks.
Align the new line with the beginning of the expression at the same level on the previous line.
If the above rules lead to confusing code or to code that's squished up against the right margin, just indent two times instead.

Tip: extracting a method or local variable may solve the problem without the need to line-wrap.

Here are some examples of breaking method calls:

// ALLOWED
someMethod(longExpression1, longExpression2, longExpression3,
        longExpression4, longExpression5);

// PREFERED
someMethod(longExpression1,
           longExpression2,
           longExpression3,
           longExpression4,
           longExpression5);

Following are two examples of breaking an arithmetic expression. The first is preferred, since the break occurs outside the parenthesized expression, which is at a higher level.

// AVOID
longName1 = longName2 * (longName3 + longName4
            - longName5) + 4 * longname6;

// INSTEAD
longName1 = longName2 * (longName3 + longName4 - longName5)
            + 4 * longname6;

Following are two examples of indenting method declarations. The first is the conventional case. The second would shift the second and third lines to the far right if it used conventional indentation, so instead it indents only 8 spaces.

// CONVENTIONAL INDENTATION
someMethod(int anArg, Object anotherArg, String yetAnotherArg,
           Object andStillAnother) {
    ...
}

// INDENT 2 TIME TO AVOID VERY DEEP INDENTS
private static synchronized horkingLongMethodName(int anArg,
        Object anotherArg, String yetAnotherArg,
        Object andStillAnother) {
    ...
}

Line wrapping for if statements should generally use the 2 tabs rule, since conventional (1 tab) indentation makes seeing the body difficult. For example:

// AVOID
if ((condition1 && condition2)
    || (condition3 && condition4)
    || !(condition5 && condition6)) {
    doSomethingAboutIt(); // IT MAKES THIS LINE EASY TO MISS
}

// USE THIS INDENTATION INSTEAD
if ((condition1 && condition2)
        || (condition3 && condition4)
        || !(condition5 && condition6)) {
    doSomethingAboutIt();
}

Here are three acceptable ways to format ternary expressions:

alpha = (aLongBooleanExpression) ? beta : gamma;

alpha = (aLongBooleanExpression) ? beta
                                 : gamma;

alpha = (aLongBooleanExpression)
        ? beta
        : gamma;

4.3 Braces

4.3.1 Nonempty blocks

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 () -> {
  while (condition()) {
    method();
  }
};

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

4.3.2 Empty blocks

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:

// AVOID
void doNothing() {

}

// AVOID
void doNothing()
{}

// ALLOWED
void doNothing() {
}

// PREFERED
void doNothing() {}

For multi-block statement:

// AVOID
if (test) {
    ...
} else {}

// AVOID
if (test) {}
else {
    ...
}

// ALLOWED
if (test) {
    ...
} else {

}

// PREFERED
if (test) {
    ...
} else {
    // Add comment to explain why the block is empty
}

4.4 Whitespace

4.4.1 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.
- Exception: Blank lines between enum constants are covered in Section 4.7.1 Enum classes.
Between statements, as needed to organize the code into logical subsections.
Between switch cases, see Section 4.6.8 switch 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).

4.4.2 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.

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 needed)
- String[][] x = {{"foo"}}; (no space is required between {{)
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
- the arrow in a lambda expression: (String str) -> str.length() but not
- the two colons (::) of a method reference, which is written like Object::toString
- the dot separator (.), which is written like object.toString()
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

This rule never requires or forbids additional space at the start or end of a line; it addresses only interior space.

4.4.3 Horizontal alignment

This practice is permitted, but is never required. 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 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.

4.5 Declarations

4.5.1 Variables

4.5.1.1 One variable per declaration

Every variable declaration (field or local) declares only one variable: declarations such as int a, b; are not used.

4.5.1.2 Initialization

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.

4.5.2 Classes and Interfaces

When coding Java classes and interfaces, the following formatting rules should be followed:

No space between a method name and the parenthesis (() starting its parameter list.
Open brace ({) appears at the end of the same line as the declaration statement.
Closing brace (}) starts a line by itself indented to match its corresponding opening statement, except when it is a null statement the (}) should appear immediately after the ({).
Methods are separated by a blank line.

class Sample extends Object {
    int ivar1;
    int ivar2;

    Sample(int i, int j) {
        ivar1 = i;
        ivar2 = j;
    }

    int emptyMethod() {}
    ...
}

4.6 Statements

4.6.1 Simple statements

Each line should contain at most one statement. Example:

// AVOID
argv++; argc--;

// INSTEAD
argv++;
argc++;

4.6.2 Compound statements

Compound statements are statements that contain lists of statements enclosed in braces ({ statements }). See the following sections for examples.

The enclosed statements should be indented one more level than the compound statement.
The opening brace should be at the end of the line that begins the compound statement; the closing brace should begin a line and be indented to the beginning of the compound statement.
Braces are used around all statements, even single statements, when they are part of a control structure, such as a if-else or for statement. This makes it easier to add statements without accidentally introducing bugs due to forgetting to add braces.

4.6.3 `return` statements

A returnstatement with a value should not use parentheses unless they make the return value more obvious in some way. Example:

return;
return myDisk.size();
return (size ? size : defaultSize);

4.6.4 `if`, `if-else`, `if else-if else` statements

The if-else class of statements should have the following form:

// if
if (condition) {
    statements;
}

// if-else
if (condition) {
    statements;
} else {
    statements;
}

//if else-if else
if (condition) {
    statements;
} else if (condition) {
    statements;
} else {
    statements;
}

Note: if statements always use braces {}. Avoid the following error-prone form:

//AVOID! THIS OMITS THE BRACES {}!
if (condition)
    statement;

4.6.5 `for` statements

A for statement should have the following forms:

// Standard
for (initialization; condition; update) {
    statements;
}

// For-each way
for (variable : collection) {
    statements;
}

When using the comma operator in the initialization or update clause of aforstatement, avoid the complexity of using more than three variables. If needed, use separate statements before the for loop (for the initialization clause) or at the end of the loop (for the update clause).

An empty for statement (one in which all the work is done in the initialization, condition, and update clauses) should have the following form:

for (initialization; condition; update);

4.6.6 `while` statements

A while statement should have the following form:

while (condition) {
    statements;
}

An empty while statement should have the following form:

while (condition);

4.6.7 `do-while` statements

A do-while statement should have the following form:

do {
    statements;
} while (condition);

4.6.8 `switch` statements

A switch statement should have the following form:

switch (condition) {
    case ABC:
        statements;
        // falls through
    case DEF:
        statements;
        break;
    case XYZ:
        statements;
        break;
    default:
        statements;
        break;
}

Vertical whitespaces are allowed:

switch (condition) {
    case ABC:
        statements;
        // falls through

    case DEF:
        statements;
        break;

    case XYZ:
        statements;
        break;

    default:
        statements;
        break;
}

4.6.8.1 Indentation

As with any other block, the contents of a switch block are indented +4.

After a switch label, a newline appears, and the indentation level is increased +4, 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.

4.6.8.2 Fall-through: commented

Every time a case falls through (doesn’t include a break statement), add a comment where the break statement would normally be. This is shown in the preceding code example with the for example: // falls through comment.

4.6.8.3 Default case

Every switch statement should include a default case. The break in the default case is redundant, but it prevents a fall-through error if later another case is added.

4.6.9 `try-catch` statements

A try-catch statement should have the following forms:

try {
    statements;
} catch (ExceptionClass e) {
    statements;
}

try (resource) {
    statements;
}

A try-catch statement may has multiple redundant catch clause:

// AVOID
try {
    statements;
} catch (ExceptionClass e) {
    logger.error(e.getMessage(), e);
} catch (OtherExceptionClass e) {
    logger.error(e.getMessage(), e);
}

// PREFERED
try {
    statements;
} catch (ExceptionClass | OtherExceptionClass e) {
    logger.error(e.getMessage(), e);
}

A try-catch statement may also be followed by finally, which executes regardless of whether or not the try block has completed successfully

try {
    statements;
} catch (ExceptionClass e) {
    statements;
} finally {
    statements;
}

4.7 Specific constructs

4.7.1 Enum classes

After each 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 4.7.3.1 Array initializers).

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

Since enum classes are classes, all other rules for formatting classes apply Section 4.5.2 Classes and Interfaces.

4.7.2 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). Example:

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

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

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

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

4.7.3 Arrays

4.7.3.1 Array initializers

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):

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

4.7.3.2 No C-style array declarations

The square brackets form a part of the type, not the variable: String[] args, not String args[].

4.7.4 Comments

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
 * okay.            // is 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.

4.8 Modifiers

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

public protected private abstract default static final transient volatile synchronized native strictfp

4.9 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.

4.10 Runtime Exception

RuntimeException or any unchecked exception should not declared on signature since it is misleading to the user of that API.

Declaring in javadoc is recommended if possible.

5 Naming

5.1 Common to all identifiers

Only ASCII letters and digits (and in two cases, noted below, underscores). Identifier name have to match with the regexp \w+.

Special prefixes or suffixes, like those seen in the examples name_, mName, s_name and kName, are not used

5.2 By indentifier type

5.2.1 Package names

The prefix of a unique package name is always written in all-lowercase ASCII letters and should be one of the top-level domain names, currently com, edu, gov, mil, net, org or one of the English two-letter codes identifying countries as specified in ISO Standard 3166, 1981.

Package names are all lowercase, with consecutive words simply concatenated together (no underscores). For example,

// AVOID
COM.shorky.Service
// INSTEAD
com.shorky.service

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 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

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 the name. One typical pattern is <UnitOfWork>_<StateUnderTest>_<ExpectedBehavior>, for example Sum_NegativeNumberAs1stParam_ExceptionThrown. There is no One Correct Way to name test methods.

5.2.4 Constant names

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

// 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 written in 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 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.

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 4.5.2 Classes and Interfaces), followed by the capital letter T (examples: RequestT, FooBarT).

5.3 Camel case

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 use the following (nearly) deterministic scheme.

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`*

* Can also accept YoutubeImporter 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.

6 Programming Practices

6.1 Avoid public class members

Don’t make any instance or class variable public without good reason. Often, instance variables don’t need to be explicitly set or gotten—often that happens as a side effect of method calls.

One example of appropriate public instance variables is the case where the class is essentially a data structure, with no behavior. In other words, if you would have used a struct instead of a class (if Java supported struct), then it’s appropriate to make the class’s instance variables public.

6.2 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.

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

6.3 Variable Assignments

Avoid assigning several variables to the same value in a single statement. It is hard to read. Example:

fooBar.fChar = barFoo.lchar = 'c'; // AVOID!

Do not use the assignment operator in a place where it can be easily confused with the equality operator. Example:

// AVOID
if (c++ = d++) {
    ...
}

should be written as

if ((c++ = d++) != 0) {
    ...
}

Do not use embedded assignments in an attempt to improve run-time performance. This is the job of the compiler. Example:

// AVOID
d = (a = b + c) + r;

should be written as

a = b + c;
d = a + r;

6.4 Grouping parentheses

It is generally a good idea to use parentheses liberally in expressions involving mixed operators to avoid operator precedence problems. Even if the operator precedence seems clear to you, it might not be to others—you shouldn’t assume that other programmers know precedence as well as you do.

// AVOID
if (a == b && c == d)

// PREFERED
if ((a == b) && (c == d))

6.5 Returning Values

Try to make the structure of your program match the intent. Example:

if (booleanExpression) {
    return true;
} else {
    return false;
}

should instead be written as

return booleanExpression;

Similarly,

if (condition) {
    return x;
}
return y;

should be written as

return (condition ? x : y);

6.6 Expressions before '?' in the Conditional Operator

If an expression containing a binary operator appears before the ? in the ternary ?: operator, it should be parenthesized. Example:

(x >= 0) ? x : -x;

6.7 @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.

6.8 Caught exceptions

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.

try {
    int i = Integer.parseInt(response);
    return handleNumericResponse(i);
} catch (NumberFormatException ok) {
    // it's not numeric; that's fine, just continue
}

return handleTextResponse(response);

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 no at-clauses present, and the entirety of the Javadoc block (including comment markers) can fit on a single 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" if present. 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 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 @.

7.2 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.

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 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.)

7.3.1 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".

7.3.2 Exception: overrides

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

License

#
# Copyright 2021 @SharkSV
# License Identifier: MIT
#

itzsharksv / java-style-guide Goto Github PK

java-style-guide's Introduction

Java Style Guide

Table of Contents

1 Introduction

1.1 Why have code conventions

1.2 Guide notes

2 Source file basics

2.1 File suffixes

2.2 File name

2.3 File encoding

2.4 Special characters

2.4.1 Whitespace characters

2.4.2 Special escape sequences

2.4.3 Non-ASCII characters

3 Source file structure

3.1 License or copyright information

3.2 Package statement

3.2.1 No line-wrapping

3.3 Import statements

3.3.1 No wildcard imports

3.3.2 No line-wrapping

3.3.3 Ordering and spacing

3.4 Class and Interface declaration

3.4.1 One top-level class declaration

3.4.2 Class member ordering

3.4.3 Overloads: never split

4 Formatting

4.1 Indentation

4.1.1 Alignement using 4 spaces

4.1.2 Why not using tabs/smartab?

4.2 Lines

4.2.1 Line length

4.2.2 Wrapping lines

4.3 Braces

4.3.1 Nonempty blocks

4.3.2 Empty blocks

4.4 Whitespace

4.4.1 Vertical Whitespace

4.4.2 Horizontal whitespace

4.4.3 Horizontal alignment

4.5 Declarations

4.5.1 Variables

4.5.1.1 One variable per declaration

4.5.1.2 Initialization

4.5.2 Classes and Interfaces

4.6 Statements

4.6.1 Simple statements

4.6.2 Compound statements

4.6.3 return statements

4.6.4 if, if-else, if else-if else statements

4.6.5 for statements

4.6.6 while statements

4.6.7 do-while statements

4.6.8 switch statements

4.6.8.1 Indentation

4.6.8.2 Fall-through: commented

4.6.8.3 Default case

4.6.9 try-catch statements

4.7 Specific constructs

4.7.1 Enum classes

4.7.2 Annotations

4.7.3 Arrays

4.7.3.1 Array initializers

4.7.3.2 No C-style array declarations

4.7.4 Comments

4.8 Modifiers

4.9 Numeric Literals

4.10 Runtime Exception

5 Naming

5.1 Common to all identifiers

5.2 By indentifier type

5.2.1 Package names

5.2.2 Class names

5.2.3 Method names

5.2.4 Constant names

5.2.5 Non-constant field names

5.2.6 Parameter names

5.2.7 Local variable names

5.2.8 Type variable names

4.6.3 `return` statements

4.6.4 `if`, `if-else`, `if else-if else` statements

4.6.5 `for` statements

4.6.6 `while` statements

4.6.7 `do-while` statements

4.6.8 `switch` statements

4.6.9 `try-catch` statements