Code Conventions for the Java

Code Conventions for the Java

Why Have Code Conventions

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.

Common File Names

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

Package and Import statements

Class and interface declarations

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

Class and Interface Declarations

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.

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

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.

Declarations

Number Per Line

One declaration per line is recommended since it encourages commenting. In other words,

int level; // indentation levelint size; // size of table is preferred over

int level, size;

Placement

Put declarations only at the beginning of blocks. (A block is any code surrounded by curly braces "{" and "}".) Don't wait to declare variables until their first use; it can confuse the unwary programmer and hamper code portability within the scope.

void myMethod() { int int1 = 0; // beginning of method block if (condition) { int int2 = 0; // beginning of "if" block ... }}

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 "{"

class Sample extends Object {

int ivar1;

int ivar2;

Sample(int i, int j) {

ivar1 = i; ivar2 = j;

}

int emptyMethod() {

}

...}

Methods are separated by a blank line

Java Servlet tutorial 1

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