Implementation Comment Formats

Требования по форматированию исходного кода

Замечания: эти требования взяты из языка JAVA. Поэтому некоторые пункты могут не иметь аналогов в С++ (например, требования по наименованию файлов).

Introduction

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.

Acknowledgments

This document reflects the Java language coding standards presented in the Java Language Specification, from Sun Microsystems, Inc. Major contributions are from Peter King, Patrick Naughton, Mike DeMoney, Jonni Kanerva, Kathy Walrath, and Scott Hommel.

This document is maintained by Scott Hommel. Comments should be sent to [email protected]

File Names

This section lists commonly used file suffixes and names.

File Suffixes

Java Software uses the following file suffixes:

File Type	Suffix
Java source	.java
Java bytecode	.class

Common File Names

Frequently used file names include:

File Name	Use
GNUmakefile	The preferred name for makefiles. We use gnumake to build our software.
README	The preferred name for the file that summarizes the contents of a particular directory.

File Organization

A file consists of sections that should be separated by blank lines and an optional comment identifying each section.

Files longer than 2000 lines are cumbersome and should be avoided.

For an example of a Java program properly formatted, see "Java Source File Example" on page 19.

Java Source Files

Each Java source file contains a single public class or interface. When private classes and interfaces are associated with a public class, you can put them in the same source file as the public class. The public class should be the first class or interface in the file.

Java source files have the following ordering:

• Beginning comments (see "Beginning Comments" on page 4)
• Package and Import statements
• Class and interface declarations (see "Class and Interface Declarations" on page 4)

Beginning Comments

All source files should begin with a c-style comment that lists the class name, version information, date, and copyright notice:

/* * Classname * * Version information * * Date * * Copyright notice */

Package and Import Statements

The first non-comment line of most Java source files is a package statement. After that, import statements can follow. For example:

package java.awt; import java.awt.peer.CanvasPeer;

Note: The first component 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.

Class and Interface Declarations

The following table describes the parts of a class or interface declaration, in the order that they should appear. See "Java Source File Example" on page 19 for an example that includes comments.

	Part of Class/Interface Declaration	Notes
	Class/interface documentation comment (/**...*/)	See "Documentation Comments" on page 9 for information on what should be in this comment.
	class or interface statement
	Class/interface implementation comment (/*...*/), if necessary	This comment should contain any class-wide or interface-wide information that wasn't appropriate for the class/interface documentation comment.
	Class (static) variables	First the public class variables, then the protected, then package level (no access modifier), and then the private.
	Instance variables	First public, then protected, then package level (no access modifier), and then private.
	Constructors
	Methods	These methods should be grouped by functionality rather than by scope or accessibility. For example, a private class method can be in between two public instance methods. The goal is to make reading and understanding the code easier.

Indentation

Four spaces should be used as the unit of indentation. The exact construction of the indentation (spaces vs. tabs) is unspecified. Tabs must be set exactly every 8 spaces (not 4).

Line Length

Avoid lines longer than 80 characters, since they're not handled well by many terminals and tools.

Note: Examples for use in documentation should have a shorter line length-generally no more than 70 characters.

Wrapping Lines

When an expression will not fit on a single line, break it according to these general principles:

• 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 8 spaces instead.

Here are some examples of breaking method calls:

someMethod(longExpression1, longExpression2, longExpression3, longExpression4, longExpression5); var = someMethod1(longExpression1, someMethod2(longExpression2, longExpression3));

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.

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

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 INDENTATIONsomeMethod(int anArg, Object anotherArg, String yetAnotherArg, Object andStillAnother) { ...} //INDENT 8 SPACES TO AVOID VERY DEEP INDENTSprivate static synchronized horkingLongMethodName(int anArg, Object anotherArg, String yetAnotherArg, Object andStillAnother) { ...}

Line wrapping for if statements should generally use the 8-space rule, since conventional (4 space) indentation makes seeing the body difficult. For example:

//DON'T USE THIS INDENTATIONif ((condition1 && condition2) || (condition3 && condition4) ||!(condition5 && condition6)) { //BAD WRAPS doSomethingAboutIt(); //MAKE THIS LINE EASY TO MISS} //USE THIS INDENTATION INSTEADif ((condition1 && condition2) || (condition3 && condition4) ||!(condition5 && condition6)) { doSomethingAboutIt();} //OR USE THISif ((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;

Comments

Java programs can have two kinds of comments: implementation comments and documentation comments. Implementation comments are those found in C++, which are delimited by /*...*/, and //. Documentation comments (known as "doc comments") are Java-only, and are delimited by /**...*/. Doc comments can be extracted to HTML files using the javadoc tool.

Implementation comments are mean for commenting out code or for comments about the particular implementation. Doc comments are meant to describe the specification of the code, from an implementation-free perspective. to be read by developers who might not necessarily have the source code at hand.

Comments should be used to give overviews of code and provide additional information that is not readily available in the code itself. Comments should contain only information that is relevant to reading and understanding the program. For example, information about how the corresponding package is built or in what directory it resides should not be included as a comment.

Discussion of nontrivial or nonobvious design decisions is appropriate, but avoid duplicating information that is present in (and clear from) the code. It is too easy for redundant comments to get out of date. In general, avoid any comments that are likely to get out of date as the code evolves.

Note:The frequency of comments sometimes reflects poor quality of code. When you feel compelled to add a comment, consider rewriting the code to make it clearer.

Comments should not be enclosed in large boxes drawn with asterisks or other characters.
Comments should never include special characters such as form-feed and backspace.

Implementation Comment Formats

Programs can have four styles of implementation comments: block, single-line, trailing, and end-of-line.

Block Comments

Block comments are used to provide descriptions of files, methods, data structures and algorithms. Block comments may be used at the beginning of each file and before each method. They can also be used in other places, such as within methods. Block comments inside a function or method should be indented to the same level as the code they describe.

A block comment should be preceded by a blank line to set it apart from the rest of the code.

/* * Here is a block comment. */

Block comments can start with /*-, which is recognized by indent(1) as the beginning of a block comment that should not be reformatted. Example:

/*- * Here is a block comment with some very special * formatting that I want indent(1) to ignore. * * one * two * three */

Note: If you don't use indent(1), you don't have to use /*- in your code or make any other concessions to the possibility that someone else might run indent(1) on your code.

See also "Documentation Comments" on page 9.

Single-Line Comments

Short comments can appear on a single line indented to the level of the code that follows. If a comment can't be written in a single line, it should follow the block comment format (see section 5.1.1). A single-line comment should be preceded by a blank line. Here's an example of a single-line comment in Java code (also see "Documentation Comments" on page 9):

if (condition) { /* Handle the condition. */ ...}

Trailing Comments

Very short comments can appear on the same line as the code they describe, but should be shifted far enough to separate them from the statements. If more than one short comment appears in a chunk of code, they should all be indented to the same tab setting.

Here's an example of a trailing comment in Java code:

if (a == 2) { return TRUE; /* special case */} else { return isPrime(a); /* works only for odd a */}

End-Of-Line Comments

The // comment delimiter can comment out a complete line or only a partial line. It shouldn't be used on consecutive multiple lines for text comments; however, it can be used in consecutive multiple lines for commenting out sections of code. Examples of all three styles follow: