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 18.

3.1 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 3)
• 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 3)

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
 *
 * Copyright notice
 */

3.1.2 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;

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 18 for an example that includes comments.

	Part of Class/Interface Declaration	Notes
1	Class/interface documentation comment (/**...*/)	See "Documentation Comments" on page 8 for information on what should be in this comment.
2	class or interface statement
3	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.
4	Class (static) variables	First the public class variables, then the protected, and then the private.
5	Instance variables	First public, then protected, and then private.
6	Constructors
7	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.