...
Coding
...
standards
...
Guidelines
...
Summary
...
This
...
style
...
guide
...
is
...
intended
...
to
...
help
...
the
...
computer
...
professional
...
produce
...
better
...
Java
...
programs.
...
It
...
presents
...
a
...
set
...
of
...
specific
...
guidelines
...
for
...
using
...
the
...
features
...
of
...
Java
...
in
...
a
...
disciplined
...
manner.
...
The
...
goal
...
is
...
to
...
develop
...
high
...
quality,
...
reliable,
...
reusable,
...
portable
...
software.
...
For
...
a
...
number
...
of
...
reasons,
...
no
...
programming
...
language
...
can
...
ensure
...
the
...
achievements
...
of
...
these
...
desirable
...
objectives
...
on
...
its
...
own.
...
Programming
...
must
...
be
...
embedded
...
in
...
a
...
disciplined
...
development
...
process
...
that
...
addresses
...
a
...
number
...
of
...
topics
...
in
...
a
...
well
...
managed
...
way.
...
The
...
use
...
of
...
Java
...
is
...
one
...
of
...
those.
...
It
...
must
...
conform
...
to
...
good
...
programming
...
practices
...
be
...
based
...
on
...
well
...
established
...
software
...
engineering
...
principles.
...
This
...
style
...
guide
...
is
...
intended
...
to
...
bridge
...
the
...
gap
...
between
...
these
...
principles
...
and
...
the
...
actual
...
practice
...
of
...
programming
...
in
...
Java.
...
Clear,
...
readable,
...
understandable
...
source
...
text
...
eases
...
program
...
evolution,
...
adaptation
...
and
...
maintenance.
...
First,
...
such
...
source
...
text
...
is
...
more
...
likely
...
to
...
be
...
correct
...
and
...
reliable.
...
Second,
...
effective
...
code
...
adaptation
...
is
...
a
...
prerequisite
...
to
...
code
...
reuse,
...
a
...
technique
...
that
...
has
...
the
...
potential
...
for
...
drastic
...
reductions
...
in
...
system
...
development
...
costs.
...
Easy
...
adaptation
...
requires
...
thorough
...
understanding
...
of
...
the
...
software,
...
and
...
that
...
is
...
facilitated
...
considerably
...
by
...
clarity.
...
Finally,
...
since
...
maintenance
...
(really
...
evolution)
...
is
...
a
...
costly
...
process
...
that
...
continues
...
throughout
...
the
...
life
...
of
...
a
...
system,
...
clarity
...
plays
...
a
...
major
...
role
...
in
...
keeping
...
maintenance
...
costs
...
down.
...
Over
...
the
...
entire
...
life
...
cycle,
...
code
...
has
...
to
...
be
...
read
...
and
...
understood
...
far
...
more
...
often
...
than
...
it
...
is
...
written;
...
the
...
investment
...
of
...
effort
...
in
...
writing
...
readable,
...
understandable
...
code
...
is
...
thus
...
well
...
worthwhile.
...
Many
...
of
...
the
...
guidelines
...
in
...
this
...
style
...
guide
...
are
...
designed
...
to
...
promote
...
clarity
...
of
...
the
...
source
...
text.
...
This
...
style
...
guide
...
is
...
intended
...
for
...
those
...
involved
...
in
...
the
...
development
...
of
...
real
...
software
...
systems
...
written
...
in
...
Java.
...
Different
...
roles
...
in
...
a
...
software
...
project
...
can
...
exploit
...
the
...
style
...
guide
...
in
...
different
...
ways.
...
The
...
programmer
...
can
...
use
...
it
...
as
...
a
...
reference
...
on
...
good
...
Java
...
style.
...
It
...
can
...
be
...
used
...
in
...
code
...
reviews
...
as
...
a
...
common
...
reference.
...
Finally,
...
lessons
...
learned
...
in
...
real
...
projects
...
can
...
be
...
captured
...
by
...
extending
...
the
...
style guide.
Class layout and comments
Files and filenames
Files longer than 2000 lines are cumbersome and should be avoided.
File names
The file must be named after the class it represents. As for most cases each file contains only one class, this is an easy naming convention. For nested or inner classes the name of the main class must be the name of the file. As names in Java are case-sensitive, the filename is case-sensitive also.
File organization
Each Java source file contains a single class or interface. Of course, this excludes inner classes as these must be defined without an (outer) class, and thus in the same file.
Java source files have the following ordering:
- Beginning comments
- Package and import statements
- Class and interface declarations
Beginning comments
All source files must begin with the comments shown in the following code sample.
Code Block |
---|
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
|
Note that this comment part is not according to the JavaDoc style (See: How to write doc comments for JavaDoc - Sun Microsystems, Inc.) as this is file specific information that is not relevant in generated API documentation.
Package and import Statements
The first non-comment line of most Java source files is a package statement. After an empty line import statements can follow. For example:
Code Block |
---|
package org.apache.felix.whatever.this.is; import java.awt.Frame; import java. guide. h2. CLASS LAYOUT AND COMMENTS h3. Files and filenames Files longer than 2000 lines are cumbersome and should be avoided. h4. File suffixes File Type Suffix Java source .java Java bytecode .class h4. File names The file must be named after the class it represents. As for most cases each file contains only one class, this is an easy naming convention. For nested or inner classes the name of the main class must be the name of the file. As names in Java are case-sensitive the filename is case-sensitive also. h4. File organization Each Java source file contains a single class or interface. Of course, this excludes inner classes as these must be defined without an (outer) class, and thus in the same file. Java source files have the following ordering: - Beginning comments (see 2.1.3.1 Beginning Comments) - Package and Import statements (see 2.1.3.2 Package and Import Statements) - Class and interface declarations (see 2.1.3.3 Class and Interface Declarations) h4. Beginning Comments All source files must begin with the comments shown in the following code sample. {code} /* * $RCSfile$ * Last modified: $Date$ by $Author$ * Copyright 2006 luminis B.V. All rights reserved. * Copyright 2006 luminis B.V. Tous droits réservés. */ {code} Note that this comment part is not according to the JavaDoc style ([REF2] How to Write Doc Comments for JavaDoc - Sun Microsystems, Inc.) as this is file specific information that is not relevant in generated API documentation. The names that start with a '$' are source integrity keywords. The used source integrity tool must support these keywords and will expand them to the correct version, date etc., and after each change they will be automatically updated. h5. Package and Import Statements The first non-comment line of most Java source files is a package statement. After an empty line import statements can follow. For example: package net.luminis.atlas.whatever.this.is; import java.awt.Frame; import java.io.InputStream; import java.util.Vector; |
A
...
few
...
notes
...
must
...
be
...
made
...
here:
...
- Package
...
- rules.
...
When
...
- not
...
- using
...
- an
...
- explicit
...
- package
...
- statement
...
- in
...
- your
...
- code
...
- the
...
- code
...
- still
...
- is
...
- in
...
- a
...
- package,
...
- the
...
- default
...
- package.
...
- This
...
- easily
...
- results
...
- in
...
- name
...
- clashes
...
- and
...
- as
...
- package
...
- naming
...
- should
...
- be
...
- a
...
- part
...
- of
...
- the
...
- design,
...
- always
...
- use
...
- an
...
- explicit
...
- package
...
- name.
...
- For
...
- naming
...
- rules
...
- of
...
- packages
...
- see
...
- 3.4
...
- Naming
...
- conventions.
...
- Import
...
- statements
...
- need
...
- to
...
- be
...
- explicit
...
- in
...
- order
...
- to
...
- overcome
...
- name
...
- clashes.
...
They
...
- should
...
- be
...
- grouped
...
- by
...
- name.
...
- When
...
- the
...
- number
...
- of
...
- import
...
- statements
...
- of
...
- the
...
- same
...
- package
...
- exceeds
...
- the
...
- 'readability'
...
- limit
...
- (please
...
- use
...
- common
...
- sense),
...
- then
...
- import
...
- the
...
- complete
...
- package
...
- by
...
- adding
...
- '.*'.
...
- Import
...
- order.
...
First
...
- in
...
- this
...
- section
...
- should
...
- be
...
- the
...
- standard
...
- Java
...
- imports
...
- like:
...
- java.lang.Throwable.
...
- Second
...
- should
...
- be
...
- the
...
- Java
...
- extensions
...
- (i.e.
...
- javax),
...
- third,
...
- the
...
- third
...
- party
...
- stuff.
...
- Finally
...
- the
...
- project-specific
...
- imports
...
- should
...
- be added.
Class and interface Declarations
The following comment block is an example for the comment that belongs to the declaration of a class or an interface. The combination of JavaDoc syntax and keywords that are expanded by the source integrity tool result in the following block:
Code Block |
---|
added. See 5.1 Java Source File Example for a complete source file example. h5. Class and Interface Declarations The following comment block is an example for the comment that belongs to the declaration of a class or an interface. The combination of JavaDoc syntax and keywords that are expanded by the source integrity tool result in the following block: {code} /** * This class is not really a class, because this file is just * a template that shows how the file header and class header * should look like. * @version $Revision$ ($Name$) * @author Andre Linoge* @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> */ {code} (Using CVS, the $Name$ is replaced by the label for labeled versions.) The following table describes the parts of a class or interface declaration, in the order that they should appear. || Part of Class/Interface Declaration || Notes || |Class/Interface documentation|According to comment block as shown above.| |Class or interface statement| | |Class (static) variables|These should be grouped by functionality rather than by scope.| |Instance variables|These should be grouped by functionality rather than by scope.| |Constructors|Start with the default constructor if any.| |Methods that belong to the class (see also |
The following table describes the parts of a class or interface declaration, in the order that they should appear.
Part of Class/Interface Declaration | Notes |
---|---|
Class/Interface documentation | According to comment block as shown above. |
Class or interface statement |
|
Class (static) variables | These should be grouped by functionality rather than by scope. |
Instance variables | These should be grouped by functionality rather than by scope. |
Constructors | Start with the default constructor if any. |
Methods that belong to the class (see also 2.1.3.4 |
...
Class |
...
methods |
...
versus |
...
specific |
...
interface |
...
methods |
...
and |
...
event |
...
methods) |
...
These |
...
methods |
...
should |
...
also |
...
be |
...
grouped |
...
by |
...
functionality |
...
rather |
...
than |
...
by |
...
scope |
...
or |
...
accessibility. |
...
E.g. |
...
a |
...
private |
...
class |
...
method |
...
can |
...
be |
...
in |
...
between |
...
two |
...
public |
...
instance |
...
methods. |
...
The |
...
goal |
...
is |
...
to |
...
make |
...
reading |
...
and |
...
understanding |
...
the |
...
code |
...
easier. |
...
When |
...
implementing |
...
an |
...
interface, |
...
group |
...
the |
...
methods |
...
that |
...
are |
...
part |
...
of |
...
the |
...
interface. |
...
Methods |
...
of |
...
interfaces |
...
that |
...
are |
...
implemented |
...
by |
...
the |
...
class. |
...
Automatically |
...
grouped |
...
by |
...
functionality |
...
if |
...
grouped |
...
by |
...
interface. |
...
Inner |
...
classes |
...
As |
...
they |
...
are |
...
only |
...
visible |
...
within |
...
their |
...
top-level |
...
class, |
...
they |
...
are |
...
placed |
...
at |
...
the |
...
bottom |
...
of |
...
the file. |
Indentation
Four spaces should be used as unit of indentation. Use spaces or let your editor convert tabs to spaces as some editors might show the tabs different than they were intended! Tabs must be set exactly every 4 spaces.
Line length
There is no explicit limit for the length of a line. Make sure that the flow of the code is clear and that, when printing the file, it is well formed when using a reasonable font. A reasonable length would be around 80 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 after the assignment;
- if the above rules lead to confusing code or to code that's squished up against the right margin, please use common sense.
Some examples breaking an arithmetic expression. The first is preferred, since the break occurs outside the parenthesised expression:
Code Block |
---|
file.| h5. Class methods versus specific interface methods and event methods As already described methods should be grouped by functionality. A class can implement multiple interfaces and can have also its own methods. Start always with the own methods and after that any interface can follow: {code} /*************************** * interface FrameTreeNode */ {code} Special cases are for example methods that handle (GUI) events. When we take the example of a button we must register ourselves as a listener in order to be notified whenever a specific event occurs. This can result in an inner (listener) class that is placed at the bottom of the file. When from within an inner listener class a top-level method is called and this method is only addressed by the inner class, place the method under the inner class. h5. Event methods There are several ways to handle events that occur on a user interface component. When using an IDE that is able to generate code for GUI components, the event code will have the look-and-feel of the IDE vendor. It often will happen that some code is generated and that new methods are called from within the generated code. Let's give as an example a Dialog with an OK and a Cancel button that must be handled: {code} class QuestionDialog extends JDialog { QuestionDialog() { m_buttonListener = new ButtonListener(); m_cancelButton = new JButton("Cancel"); m_okButton = new JButton("OK"); m_okButton.addActionListener(m_buttonListener); getContentPane().add(m_okButton); getContentPane().add(m_cancelButton); } private void okAction() { m_okButtonPressed = true; setVisible(false); } private void cancelAction() { m_okButtonPressed = false; setVisible(false); } /***************** * Inner Classes */ class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent action) { if (action.getSource() == m_okButton) okAction(); else if (action.getSource() == m_cancelButton) cancelAction(); } } } {code} As shown in the example, one ActionListener class is defined for all the buttons that are on the dialog. This could also be done for a different kind of action on another control type, e.g. a DocumentEvent on a JTextBox. Within the action class is checked what the source object is of the occurred event. This source object is compared to the button instance of interest. When the two instances are equal, a method in the top-level class is called. By putting this method in the top-level class the functionality is available to the entire class. A drawback is that we get if-then-else code or a switch statement to determine what method to call. This can be changed by putting each event for a control in a separate inner class. In OO terms this would be a better solution but on the other hand, the code in an inner class is not available to other classes and it does hardly contain any reusable code. h3. Indentation Four spaces should be used as unit of indentation. Use spaces or let your editor convert tabs to spaces as some editors might show the tabs different than they were intended! Tabs must be set exactly every 4 spaces. When using Eclipse this can be set in the Tools menu: Window â–º Preferences â–º General â–º Editors â–º Text Editors â–º Displayed tab width Set the tab width to 4 spaces. When using TogetherJ this can be set in the Options menu: Default â–º Text Editor tab Set the Tab size to 4 spaces. h4. Line length There is no explicit limit for the length of a line. Make sure that the flow of the code is clear and that, when printing the file, it is well formed when using a reasonable font. A reasonable length would be around 80 characters. h4. 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 after the assignment - if the above rules lead to confusing code or to code that's squished up against the right margin, please use common sense. Some examples breaking an arithmetic expression. The first is preferred, since the break occurs outside the parenthesised expression: {code} longName1 = longName2 * (longName3 + longName4 - longName5) + 4; //Preferred preferred longName1 = longName2 * (longName3 + longName4 - longName5) + 4; {code} h3. Comment h4. Comment styles The Java language supports three different kinds of |
Comment
Comment styles
The Java language supports three different kinds of comments:
Code Block |
---|
comments: {code} // text {code} |
The
...
compiler
...
ignores
...
everything
...
from
...
//
...
to
...
the
...
end
...
of
...
the
...
line.
...
Use
...
this
...
style
...
when
...
adding
...
a
...
description
...
or
...
some
...
kind
...
of
...
explanation
...
at
...
the
...
same
...
line
...
of
...
code.
Code Block |
---|
{code} /* text */ {code} |
The
...
compiler
...
ignores
...
everything
...
from
...
/*
...
to
...
*/.
...
The
...
next
...
documentation
...
style
...
is
...
preferred.
Code Block |
---|
} /** documentationDocumentation. */ {code} |
This
...
indicates
...
a
...
documentation
...
comment
...
(doc
...
comment,
...
for
...
short).
...
The
...
compiler
...
ignores
...
this
...
kind
...
of
...
comment,
...
just
...
like
...
it
...
ignores
...
comments
...
that
...
use
...
/*
...
and
...
*/.
...
The
...
JDK
...
JavaDoc
...
tool
...
uses
...
doc
...
comments
...
when
...
preparing
...
automatically
...
generated
...
documentation
...
(See: JavaDoc keywords and HTML tags).
...
But
...
JavaDoc
...
only
...
uses
...
this
...
documentation
...
when
...
it
...
occurs
...
at
...
an
...
expected
...
position
...
in
...
the
...
file
...
like
...
the
...
class
...
definition
...
or
...
a
...
member
...
declaration.
...
Block comments
Block comments are used to provide English descriptions of the contents of files, the task of methods and the description of data structures and algorithms. Block comments should be used at the beginning of each file and before each method. They can also be used in other places, such as within methods.
For a description of class comment see 2.1.3.3
...
Class
...
and
...
Interface
...
Declarations.
...
A
...
method
...
block
...
comment
...
looks
...
as
...
follows:
Code Block |
---|
} /** * Position the splitter location at a specified position. * This method can for instance be used when the last position * is stored as a preference setting for the user. * @param position New position of divider, defined in pixels * @param position New position of divider, defined in pixels * from the left of the containing window * @see com.sun.java.swing.JSplitPane * @exception net.luminis.atlas.gui.event org.apache.felix.player.PositionException * Whenever an invalid position is passed. */ public void setSplitterLocation(int position) {code} h4. JavaDoc keywords and HTML tags For class headers, method headers and member variables JavaDoc is used in order to generate API documentation from the source later on ([REF3] JavaDoc homepage - Sun Microsystems, Inc.). A few specific JavaDoc keywords are: ||Keyword||Short description|| |@version|Can be used to label a specific version of a package or application so the documentation shows this version number also.| |@author|The name entered here is shown as the author.| |@param|Used to define one parameter and describe this parameter.| |@see|When there are similarities with another class this tag is used to offer the reader a hyperlink to the mentioned class.| |@exception or @throws|Offered as hyperlink to the exception that can be thrown by a method.| |@return|Return value of a method| Some HTML-tags that can be used in order to make the comment blocks more readable: ||Tag||Short description|| |<p>|New paragraph.| |<br>|Break, a carriage return. For separation of two paragraphs, usage of <p> is preferred.| |<ul><li></li></ul>|Unordered list of items; each item should start with a <li> tag. By most browsers, this is formatted as a bulleted list.| |<code></code>|Code samples; use this when refering to class names, method names, parameter names, etc.| |<pre></pre>|Preformatted text. Use these tags to protect figures and schemas "drawn" in Ascii, against formatting by the browser (which normally ignores whitespace and line breaks)| |<dl><dt></dt><dd></dd></dl>|Definition lists; <dt> specifies the term that is defined and <dd> the definition of this term. Not frequently used.| Note: there is no need to embed the parameter name in the @param tag in <code> tags; this is done by javadoc automatically. The same holds for the exception name in the @exception or @throws tag. In the clarifying text however, use the <code> tags when refering to parameter names etc. The example below shows the <code> tag being used for the array parameter in the throws PositionException |
JavaDoc keywords and HTML tags
For class headers, method headers and member variables JavaDoc is used in order to generate API documentation from the source later on (See: JavaDoc homepage - Sun Microsystems, Inc.).
A few specific JavaDoc keywords are:
Keyword | Short description |
---|---|
@version | Can be used to label a specific version of a package or application so the documentation shows this version number also. |
@author | The name entered here is shown as the author. |
@param | Used to define one parameter and describe this parameter. |
@see | When there are similarities with another class this tag is used to offer the reader a hyperlink to the mentioned class. |
@exception or @throws | Offered as hyperlink to the exception that can be thrown by a method. |
@return | Return value of a method |
Some HTML-tags that can be used in order to make the comment blocks more readable:
Tag | Short description |
---|---|
<p> | New paragraph. |
<br> | Break, a carriage return. For separation of two paragraphs, usage of <p> is preferred. |
<ul><li></li></ul> | Unordered list of items; each item should start with a <li> tag. By most browsers, this is formatted as a bulleted list. |
<code></code> | Code samples; use this when refering to class names, method names, parameter names, etc. |
<pre></pre> | Preformatted text. Use these tags to protect figures and schemas "drawn" in Ascii, against formatting by the browser (which normally ignores whitespace and line breaks) |
<dl><dt></dt><dd></dd></dl> | Definition lists; <dt> specifies the term that is defined and <dd> the definition of this term. Not frequently used. |
Note: there is no need to embed the parameter name in the @param tag in <code> tags; this is done by javadoc automatically. The same holds for the exception name in the @exception or @throws tag. In the clarifying text however, use the <code> tags when refering to parameter names etc. The example below shows the <code> tag being used for the array parameter in the text, but not in its definition.
Example:
Code Block |
---|
text, but not in its definition. Example: {code} /** * Prints a range from an object array. The range * is specified by the first element to print, and * ranges to the last element of the array. * * @param array contains the objects to print * @param first index of first element in * the <code>array</code> to print */ public void printRange(Object[] array, int first) {code} h2. JAVA SYNTAX AND ITS LAYOUT h3. Declarations When declaring a variable or method make the accessibility as restrictive as possible. When using multiple keywords use the following ordering of keywords: # accessibility Start with the accessibility as it makes clear if the method or variable is reachable at all. # static (if applicable) # final (if applicable) # return type (methods only) or type (for variables) The type is for readability as close as possible to the name. This order is also compatible with the order that is used in Java for the main() method. This results in following sequence: {code} |
Java syntax and its layout
Declarations
When declaring a variable or method make the accessibility as restrictive as possible. When using multiple keywords use the following ordering of keywords:
- accessibility
Start with the accessibility as it makes clear if the method or variable is reachable at all. - static (if applicable)
- final (if applicable)
- return type (methods only) or type (for variables)
The type is for readability as close as possible to the name.
This order is also compatible with the order that is used in Java for the main() method. This results in following sequence:
Code Block |
---|
// A familiar one: public static void main(String[] args) {} private static String m_lastCreated = null; private static final int RED = 4711; |
Number per line
One declaration per line is recommended since it encourages commenting and it does not lead to confusing code. It also is more clear about the explicit initialization of variables as discussed in Initialization.
Example:
Code Block |
---|
{code} h4. Number per line One declaration per line is recommended since it encourages commenting and it does not lead to confusing code. It also is more clear about the explicit initialization of variables as discussed in 3.1.3 Initialization. Example: {code} int level = 0; // level where user enters the system int horizontalSize = 0; // horizontal size of current level layer {code} |
is
...
preferred
...
over:
Code Block |
---|
} int level, horizontalSize; // level and size of current level layer {code} h4. Placement In a method, declare local variables just before they are needed. This overcomes the problem of a big list of parameters at the beginning of a method and the use of a variable becomes more clearly in the context of the code, |
Placement
In a method, declare local variables just before they are needed. This overcomes the problem of a big list of parameters at the beginning of a method and the use of a variable becomes more clearly in the context of the code, .e.g.
...
its
...
initialization.
Initialization
The initialization of class variables is strictly not necessary because of the default initialization that takes place for these kinds of members. For some types, e.g. Booleans, this requires detailed knowledge of all the default values so it is more clear and explicit to initialize each member.
Variables that are used and declared within methods must always be initialized explicitly (the compiler will generate an error when you forget this).
Class and Interface Declarations
When coding Java classes and interfaces, the following formatting rules should be followed:
- no space between a method and its parameter list
- "{" is on a line by itself indented to match its corresponding opening statetment, except when it is a null statement, in which case the "{" should appear on the same line as the opening statement
- "}" starts a line by itself indented to match its corresponding opening statement, except when it is a null statement, in which the case the "}" should appear immediately after the "{".
Example:
Code Block |
---|
h4. Initialization The initialization of class variables is strictly not necessary because of the default initialization that takes place for these kinds of members. For some types, e.g. Booleans, this requires detailed knowledge of all the default values so it is more clear and explicit to initialize each member. Variables that are used and declared within methods must always be initialized explicitly (the compiler will generate an error when you forget this). h4. Class and Interface Declarations When coding Java classes and interfaces, the following formatting rules should be followed: - no space between a method and its parameter list - "{" appears at the end of the same line as the declaration - "}" starts a line by itself indented to match its corresponding opening statement, except when it is a null statement, in which the case the "}" should appear immediately after the "{". Example: {code} class ShipmoTrial extends Trial { int m_index = 0; ShipmoTrial(int index) { { m_index = index; } void emptyMethod() {} } {code} h3. Statements h4. Simple statements Each line should contain at most one statement. Example: { |
Statements
Simple statements
Each line should contain at most one statement.
Example:
Code Block |
---|
code} // Do not use this argv++; argc++; {code} h4. Compound statements Compound statements are statements that contain lists of statements enclosed in braces |
Compound statements
Compound statements are statements that contain lists of statements enclosed in braces ("{...}"):
...
- 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.
...
if,
...
if-else,
...
if
...
else-if
...
else
...
statements
...
There
...
are
...
a
...
lot
...
of
...
nested
...
possibilities
...
for
...
if-else
...
constructions.
...
All
...
these
...
variations
...
can
...
be
...
programmed
...
in
...
very
...
cryptic
...
ways
...
that
...
easily
...
and
...
often
...
will
...
lead
...
to
...
buggy
...
code.
...
By
...
being
...
more
...
explicit
...
in
...
the
...
used
...
coding
...
style
...
a
...
lot
...
of
...
confusion
...
can
...
be
...
taken
...
away.
...
Note:
...
When
...
using
...
only
...
one
...
statement
...
in
...
a
...
compound
...
block
...
brackets
...
are
...
optional.
...
It
...
can
...
be
...
a
...
good
...
practice
...
to
...
use
...
always
...
brackets
...
because
...
mistakes
...
can
...
be
...
made
...
easily
...
when
...
adding
...
a
...
second
...
statement
...
and
...
brackets
...
are
...
forgotten.
...
The
...
following
...
example
...
illustrates
...
the
...
correct
...
use
...
of
...
brackets
...
in
...
a
...
few
...
different
...
if-then-else
...
constructions:
Code Block |
---|
} if (condition) { statement1; statement2; } else { statement3; } if (condition) { statement1; statement2; } else if (condition1) { statement3; statement4; } else { statement5; statement6; } {code} |
Note
...
that
...
in
...
the
...
example
...
the
...
else
...
if
...
construction
...
is
...
started
...
at
...
a
...
new
...
line
...
so
...
the
...
statement
...
can
...
not
...
be
...
overlooked.
switch
When using a switch statement use following guidelines:
- 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.
- The so-called fall-through construction should be avoided. Only when there are good reasons to use it, make sure that it is very clear that a fall-through is used (comment it).
The next example shows the sample code that uses the guidelines for a switch statement:
Code Block |
---|
h4. switch When using a switch statement use following guidelines: - 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. - The so-called fall-through construction should be avoided. Only when there are good reasons to use it, make sure that it is very clear that a fall-through is used (comment it). The next example shows the sample code that uses the guidelines for a switch statement: {code} switch (condition) { case A: statements; // falls through here!! case B: statements; statements; break; default: statements; break; } {code} h4. try - catch A try - catch statement should have the following format: {code} try { |
try - catch
A try - catch statement should have the following format:
Code Block |
---|
try { statements; } catch (ExceptionClass eex) { statements; } {code} |
When
...
using
...
finally
...
to
...
add
...
code
...
that
...
always
...
will
...
be
...
executed
...
this
...
will
...
look
...
like:
Code Block |
---|
try {code} try { statements; } catch (ExceptionClass eex) { statements; } finally { statements; } {code} |
Note
...
that
...
the
...
catch
...
and
...
the
...
finally
...
start
...
at
...
a
...
new
...
line
...
in
...
order to be compliant to the guidelines for if-then-else statements.
White Space
Blank lines
Blank lines improve readability by setting of sections of code that are logically related.
Two blank lines should always be used in the following circumstances:
- between class and interface definitions;
- between a group of methods that belong together (by its functionality or because they are part of the same interface).
One blank line should always be used in the following circumstances:
- between methods;
- before a block or single line comment;
- between logical sections inside a method to improve readability.
Blank spaces
Blank spaces should be used in the following circumstances:
- A keyword followed by a parenthesis should be separated by a space.
Code Block while (ready == false)
...
{ ... }
...
Note
...
- that
...
- blanks
...
- should
...
- not
...
- be
...
- used
...
- between
...
- a
...
- method
...
- call
...
- and
...
- its
...
- opening
...
- parenthesis.
...
- This
...
- helps
...
- to
...
- distinguish
...
- keywords
...
- from
...
- function
...
- calls.
...
- Blanks
...
- should
...
- appear
...
- after
...
- commas
...
- in
...
- argument
...
- lists.
...
- All
...
- binary
...
- operators
...
- except
...
- "."
...
- should
...
- be
...
- separated
...
- from
...
- their
...
- operands
...
- by
...
- spaces.
...
- Blanks
...
- should
...
- never
...
- separate
...
- unary
...
- operators
...
- such
...
- as
...
- unary
...
- minus,
...
- increment("++")
...
- and
...
- decrement("--")
...
- from
...
- their
...
- operands.
...
Code Block
...
a += c + d; a = (a + b) / (c * d); xCoord++;
...
- The expressions in a for statement should be separated by blanks.
Code Block for (expr1; cond1; expr2)
...
- Casts should be followed by a blank.
Code Block myInstance.doIt((TreeFrame) frame);
...
Naming conventions
Naming conventions make programs more understandable by making them easier to read. They can also give information about the function of the identifier.
Identifier Type | Rules for Naming | Examples |
---|---|---|
Classes or inner classes | Class names should be nouns, in mixed case with the first letter of each word capitalised. Try to keep your class names simple and descriptive. Use whole words and avoid acronyms and abbreviations. | class Raster; |
Interfaces | Interface names should be capitalized like class names. | interface Enumeration; |
Methods | Methods should be verbs in mixed case with the first letter lowercase. Within each method name capital letters separate words. Property methods or get-set methods are used as follows: | run(); |
Variables (except for (constant) static final variables and member variables) | All variables are in mixed case with a lowercase first letter. Words are separated by capital letters. | int index; |
Member variables | The same capitalisation as for normal variables prefixed with 'm_'. | int m_index; |
Constant (static final) variables | Names should be all uppercase with words separated by underscores ("_"). | public static final int BLACK = 99; |
Exceptions | Like class names; always ending in "Exception" | InputException |
Packages | Lowercase only; avoid lengthy package names; always start with org.apache.felix. | org.apache.felix.demo.bundle |
...
Note:
...
All
...
Java
...
identifiers
...
are
...
case
...
sensitive.
...
References
- Java Code Conventions - Sun Microsystems, Inc.
No ref. number, only hyperlink: http://java.sun.com/docs/codeconv/
...
- How
...
- to
...
- Write
...
- Doc
...
- Comments
...
- for
...
- JavaDoc
...
- -
...
- Sun
...
- Microsystems,
...
- Inc.
...
...
- JavaDoc
...
- homepage
...
- -
...
- Sun
...
- Microsystems,
...
- Inc.
...
...