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Java

Code Conventions

September 12, 1997ii

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Copyright Information

 1997, SunMicrosystems, Inc. All rights reserved.

2550 Garcia Avenue,Mountain View, California 94043-1100 U.S.A.

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Sun, SunMicrosystems, SunMicroelectronics, the Sun Logo, SunXTL, JavaSoft, JavaOS, the

JavaSoft Logo, Java,

HotJava Views,HotJJavaChips, picoJava,microJava, UltraJava, JDBC, the Java Cup and

SteamLogo, “WriteOnce,

Run Anywhere” and Solaris are trademarks or registered trademarks of SunMicrosystems, Inc. in

the United States

and other countries.

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through X/Open

IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF

MERCHANTABILITY,

FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.

THIS DOCUMENT COULD INCLUDE TECHNICAL INACCURACIES OR

TYPOGRAPHICAL ERRORS.

CHANGES ARE PERIODICALLY ADDED TO THE INFORMATION HEREIN; THESE

CHANGES WILL BE

INCORPORATED IN NEW EDITIONS OF THE DOCUMENT. SUN MICROSYSTEMS, INC.

MAY MAKE

IMPROVEMENTSAND/OR CHANGES INTHE PRODUCT(S)AND/OR THE

1.1 Why Have Code Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 File Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.1 File Suffixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.2 Common File Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 File Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3.1 Java Source Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3.1.1 Beginning Comments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

5.1 Implementation Comment Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5.1.1 Block Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5.1.2 Single-Line Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.1.3 Trailing Comments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.1.4 End-Of-Line Comments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.2 Documentation Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6 Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6.1 Number Per Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6.2 Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6.3 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

7.5 for Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7.6 while Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7.7 do-while Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7.8 switch Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7.9 try-catch Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8 White Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8.1 Blank Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8.2 Blank Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

9 Naming Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

10 Programming Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

10.4 Variable Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

10.5 Miscellaneous Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

10.5.1 Parentheses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

10.5.2 Returning Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

10.5.3 Expressions before ‘?’ in the Conditional Operator. . . . . . . . . . . 17

10.5.4 Special Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

11 Code Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

11.1 Java Source File Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 - File Names

• 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.

1.2 Acknowledgments

This document reflects the Java language coding standards presented in the Java Language

Specification, from Sun Microsystems. Major contributions are from Peter King, Patrick

Naughton, Mike DeMoney, Jonni Kanerva, Kathy Walrath, and Scott Hommel.

For questions concerning adaptation, modification, or redistribution of this document, please

3

2.1 File Suffixes

JavaSoft uses the following file suffixes:

2.2 Common File Names

Frequently used file names include:

3 - 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

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; for example:

import java.applet.Applet;

import java.awt.*;

import java.net.*;

• Class and interface declarations (see “Class and Interface Declarations” on page 4)

README The preferred name for the file that summarizes the

contents of a particular directory.3 - File Organization

4

3.1.1 Beginning Comments

All source files should begin with a c-style comment that lists the programmer(s), the date, a

copyright notice, and also a brief description of the purpose of the program. For example:

/*

* Classname

*

* Version info

package java.awt;

import java.awt.peer.CanvasPeer;

3.1.3 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

1 Class/interface documentation

comment (/**...*/)