Perfomatix - Java Coding Standards

Best Practice Guidelines
For Java

www.perfomatix.com

Table of Content

1. Project Structure Practises
1.1 Introduction
1.2 Directory Layout
1.3 The Root Directory
1.4 The src/main Directory
1.5 The src/main Directory

2. Error Handling Practises
2.1 Clean Up Resources in a Finally Block or Use a Try-With-Resource
Statement
2.2 Use a Finally Block
2.3 Prefer Specific Exceptions
2.4 Document the Exceptions You Specify
2.5 Throw Exceptions With Descriptive Messages
2.6 Catch the Most Specific Exception First
2.7 Don’t Catch Throwable
2.8 Don’t Ignore Exceptions
2.9 Don’t Log and Throw
2.10 Wrap the Exception Without Consuming it
3. File Organization
4. Source code style guidelines
5. Implementation Comments
6. Declarations
7. Standards for Statements
8. Naming Conventions

9. Naming Convention standards
10. Variable Assignments
11. Best Practices

1. Project Structure Practises

1.1. Introduction
The worst large application pitfall is maintaining a huge code base with
hundreds of dependencies - such a monolith slows down developers as they
try to incorporate new features. Instead, partition your code into
components, each gets its own folder or a dedicated codebase, and ensure
that each unit is kept small and simple.
The ultimate solution is to develop small software: divide the whole stack
into self-contained components that don't share files with others, each
constitutes very few files (e.g. API, service, data access, test, etc.) so that it's
very easy to reason about it.
So promoting a uniform directory structure across projects is also one of its
important aspects. Here we’ll be following standard directory layout of a
typical Maven project.
1.2. Directory Layout
A typical Maven project has a pom.xml file and a directory structure based on
defined conventions:
└───maven-project
├───pom.xml
├───README.txt
├───NOTICE.txt
├───LICENSE.txt
└───src
├───main
│ ├───java
│ ├───resources
│ ├───filters
│ └───webapp

├───test
│ ├───java
│ ├───resources
│ └───filters
├───it
├───site
└───assembly
The default directory layout can be overridden using project descriptors, but
this is uncommon and discouraged.
1.3. The Root Directory
This directory serves as the root of every Maven project.
Following are the standard files and subdirectories that are typically found at
root:
● maven-project/pom.xml – defines dependencies and modules needed
during the build lifecycle of a Maven project
● maven-project/LICENSE.txt – licensing information of the project
● maven-project/README.txt – summary of the project
● maven-project/NOTICE.txt – information about third-party libraries
used in the project
● maven-project/src/main – contains source code and resources that
become part of the artifact
● maven-project/src/test – holds all the test code and resources
● maven-project/src/it – usually reserved for integration tests used by
the Maven Failsafe Plugin
● maven-project/src/site – site documentation created using the Maven
Site Plugin
● maven-project/src/assembly – assembly configuration for packaging
binaries

1.4. The src/main Directory
src/main is the most important directory of a Maven project. Anything that is
supposed to be part of an artifact, be it a jar or war, should be present here.
Its subdirectories are:
● src/main/java – Java source code for the artifact
● src/main/resources – configuration files and others such as i18n files,
per-environment configuration files, and XML configurations
● src/main/webapp – for web applications, contains resources like
JavaScript, CSS, HTML files, view templates, and images
● src/main/filters – contains files that inject values into configuration
properties in the resources folder during the build phase

1.5. The src/test Directory
The directory src/test is the place where tests of each component in the
application reside.
Note that none of these directories or files will become part of the artifact.
Let's see its subdirectories:
● src/test/java – Java source code for tests
● src/test/resources – configuration files and others used by tests
● src/test/filters – contains files that inject values into configuration
properties in the resources folder during the test phase

2. Error Handling Practises
2.1 Clean Up Resources in a Finally Block or Use a
Try-With-Resource Statement
It happens quite often that you use a resource in your try block, like an
InputStream, which you need to close afterwards. A common mistake in
these situations is to close the resource at the end of the try block.
public void doNotCloseResourceInTry() {
FileInputStream inputStream = null;
try {
File file = new File("./tmp.txt");

inputStream = new
FileInputStream(file);
// use the inputStream to read a file
// do NOT do this
inputStream.close();
} catch (FileNotFoundException e) {
log.error(e);
} catch (IOException e) {
log.error(e);
}
}
The problem is that this approach seems to work perfectly fine as long as no
exception gets thrown. All statements within the try block will get executed,
and the resource gets closed.
But you added the try block for a reason. You call one or more methods
which might throw an exception, or maybe you throw the exception yourself.
That means you might not reach the end of the try block. And as a result, you
will not close the resources.
You should, therefore, put all your clean up code into the finally block or use
a try-with-resource statement.
2.2 Use a Finally Block
In contrast to the last few lines of your try block, the finally block gets always
executed. That happens either after the successful execution of the try block
or after you handled an exception in a catch block. Due to this, you can be
sure that you clean up all the opened resources.
public void closeResourceInFinally() {
FileInputStream inputStream = null;
try {
File file = new File("./tmp.txt");
inputStream = new FileInputStream(file);
// use the inputStream to read a file
} catch (FileNotFoundException e) {
log.error(e);
} finally {

if (inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
log.error(e);
}
}
}
}

2.3 Prefer Specific Exceptions
The more specific the exception is that you throw, the better. Always keep in
mind that a coworker who doesn’t know your code, or maybe you in a few
months, need to call your method and handle the exception.
Therefore make sure to provide them as much information as possible. That
makes your API easier to understand. And as a result, the caller of your
method will be able to handle the exception better or avoid it with an
additional check.
So, always try to find the class that fits best to your exceptional event, e.g.
throw a NumberFormatException instead of an IllegalArgumentException.
And avoid throwing an unspecific Exception.
public void doNotDoThis() throws Exception {
...
}
public void doThis() throws NumberFormatException {
...
}

2.4 Document the Exceptions You Specify
Whenever you specify an exception in your method signature, you should
also document it in your Javadoc. That has the same goal as the previous
best practice: Provide the caller as much information as possible so that he
can avoid or handle the exception.

So, make sure to add a @throws declaration to your Javadoc
and to describe the situations that can cause the exception.
/**
* This method does something extremely useful ...
*
* @param input
* @throws MyBusinessException if ... happens
*/
public void doSomething(String input) throws MyBusinessException {
...
}

2.5 Throw Exceptions With Descriptive Messages
The idea behind this best practice is similar to the two previous ones. But this
time, you don’t provide the information to the caller of your method. The
exception’s message gets read by everyone who has to understand what had
happened when the exception was reported in the log file or your monitoring
tool.
It should, therefore, describe the problem as precisely as possible and
provide the most relevant information to understand the exceptional event.
Don’t get me wrong; you shouldn’t write a paragraph of text. But you should
explain the reason for the exception in 1-2 short sentences. That helps your
operations team to understand the severity of the problem, and it also
makes it easier for you to analyze any service incidents.
If you throw a specific exception, it's class name will most likely already
describe the kind of error. So, you don’t need to provide a lot of additional
information. A good example of that is the NumberFormatException. It gets
thrown by the constructor of the class java.lang.Long when you provide a
String in the wrong format.

try {
new Long("xyz");
} catch (NumberFormatException e) {

log.error(e);
}

The name of the NumberFormatException class already tells you the kind of
problem. Its message only needs to provide the input string that caused the
problem. If the name of the exception class isn’t that expressive, you need to
provide the required information in the message.

17:17:26,386 ERROR Test Exception Handling:52-java.lang.Number Format
Exception: For input string: "xyz"

2.6 Catch the Most Specific Exception First
Most IDEs help you with this best practice. They report an unreachable code
block when you try to catch the less specific exception first.
The problem is that only the first catch block that matches the exception gets
executed. So, if you catch an IllegalArgumentException first, you will never
reach the catch block that should handle the more specific
NumberFormatException because it’s a subclass of the Illegal Argument
Exception.
Always catch the most specific exception class first and add the less specific
catch blocks to the end of your list.
You can see an example of such a try-catch statement in the following code
snippet. The first catch block handles all NumberFormatExceptions and the
second one all IllegalArgumentExceptions which are not a
NumberFormatException.
public void catchMostSpecificExceptionFirst() {
try {
doSomething("A message");
log.error(e);
} catch (IllegalArgumentException e) {
log.error(e)
}

}

2.7 Don’t Catch Throwable
Throwable is the superclass of all exceptions and errors. You can use it in a
catch clause, but you should never do it!
If you use Throwable in a catch clause, it will not only catch all exceptions; it
will also catch all errors. Errors are thrown by the JVM to indicate serious
problems that are not intended to be handled by an application. Typical
examples for that are the OutOfMemoryError or the StackOverflowError.
Both are caused by situations that are outside of the control of the
application and can’t be handled.
So, better don’t catch a Throwable unless you’re absolutely sure that you’re in
an exceptional situation in which you’re able or required to handle an error.
public void doNotCatchThrowable() {
try {
// do something
} catch (Throwable t) {
// don't do this!
}
}

2.8 Don’t Ignore Exceptions
The developer was probably pretty sure that it would never be thrown and
added a catch block that doesn’t handle or logs it. And when you find this
block, you most likely even find one of the famous “This will never happen”
comments.
public void doNotIgnoreExceptions() {
try {
// do something
// this will never happen
}

}

Well, you might be analyzing a problem in which the impossible happened.
So, please, never ignore an exception. You don’t know how the code will
change in the future. Someone might remove the validation that prevented
the exceptional event without recognizing that this creates a problem. Or the
code that throws the exception gets changed and now throws multiple
exceptions of the same class, and the calling code doesn’t prevent all of
them.
You should at least write a log message telling everyone that the unthinkable
just had happened and that someone needs to check it.
public void logAnException() {
try {
// do something
log.error("This should never happen: " + e);
}
}

2.9 Don’t Log and Throw
That is probably the most often ignored best practice in this list. You can find
lots of code snippets and even libraries in which an exception gets caught,
logged and rethrown.
try {
new Long("xyz");
log.error(e);
throw e;
}

It might feel intuitive to log an exception when it occurred and
then rethrow it so that the caller can handle it appropriately. But it will write
multiple error messages for the same exception.
17:44:28,945 ERROR TestExceptionHandling:65 -
java.lang.NumberFormatException: For input string: "xyz"
Exception in thread "main" java.lang.NumberFormatException: For input
string: "xyz"
at
java.lang.NumberFormatException.forInputString(NumberFormatException.j
ava:65)
at java.lang.Long.parseLong(Long.java:589)
at java.lang.Long.(Long.java:965)
at
com.stackify.example.TestExceptionHandling.logAndThrowException(TestExc
eptionHandling.java:63)
at
com.stackify.example.TestExceptionHandling.main(TestExceptionHandling.ja
va:58)

The additional messages also don’t add any information. As explained in best
practice #4, the exception message should describe the exceptional event.
And the stack trace tells you in which class, method, and line the exception
was thrown.
If you need to add additional information, you should catch the exception
and wrap it in a custom one. But make sure to follow best practice number 9.
public void wrapException(String input) throws MyBusinessException {
try {
// do something
throw new MyBusinessException("A message that describes the error.", e);
}
}

So, only catch an exception if you want to handle it. Otherwise,
specify it in the method signature and let the caller take care of it.
2.10 Wrap the Exception Without Consuming it
It’s sometimes better to catch a standard exception and to wrap it into a
custom one. A typical example of such an exception is an application or
framework-specific business exception. That allows you to add additional
information and you can also implement special handling for your exception
class.
When you do that, make sure to set the original exception as the cause. The
Exception class provides specific constructor methods that accept a
Throwable as a parameter. Otherwise, you lose the stack trace and message
of the original exception which will make it difficult to analyze the exceptional
event that caused your exception.
public void wrapException(String input) throws MyBusinessException {
try {
// do something
throw new MyBusinessException("A message that describes the error.", e);
}
}

3. File Organization
Java source are named as *. java while the compiled Java byte code is named as
*.class file. Each Java source file contains a single public class or interface. Each
class must be placed in a separate file. This also applies to non-public classes too.
If a file consists of sections, they should be separated by blank lines and an optional
comment, identifying each section. Files longer than 2000 lines should be avoided.
Java classes should be packaged in a new java package for each self-contained
project or group of related functionality. Preferably there should be an HTML
document file in each directory briefly outlining the purpose and structure of the
package. Java Source files should have the following ordering: Package and Import
statements, beginning comments, Class and Interface Declarations. There should

not be any duplicate import statements. There should not be any
hardcoded values in code. Max. No of Parameters in any class should be 12.
4. Source code style guidelines

Beginning Comments
All source files should begin with a c-style header as follows carrying the Title,
Version, Date in mm/dd/yy format and the copyright information.

The header should be followed the package and import statements and then
the documentation comments exactly in the following sequence and
indented to the same level.

The tags see, since and deprecated are not mandatory and may be used
when required.
Indentation
Four spaces should be used as the unit of indentation. The indentation
pattern should be consistently followed throughout.

Left and Right braces
The starting brace should be at the end of the conditional and the ending
brace must be on a separate line and aligned with the conditional. It is
strongly recommended that all conditional constructs define a block of code
for single lines of code.

Wrapping Lines
Lines longer than 80 characters should be avoided. When an expression will
not fit on a single line, it should be broken according to these general
principles:
● Break after a comma.
● Break after 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 4 spaces instead.
Example

White Space
Blank Lines
Blank lines improve readability by the setting of sections of code that are
logically related.
Two blank lines should be used in the following circumstances:
● Between sections of a source file
● Between class and interface definitions

One blank line should always be used in the following
circumstances:
● Between methods.
● Between the local variables in a method and its first statement.
● Before a block or single-line comment.
● Between logical sections inside a method to improve readability.
● Before and after comments.
Blank Spaces
Blank spaces should be used in the following circumstances:
● A keyword followed by a parenthesis should be separated by a space.
Example: while (true)
● A blank space should appear after commas in argument lists.
● All binary operators except a period ‘.’ should be separated from their
operands by spaces. Blank spaces should never separate unary
operators such as unary minus, increment (“++”), and decrement (“--”)
from their operands.
● The expressions in a for statement should be separated by blank
spaces.
Example:

● Casts should be followed by a blank space.

However blank space should not be used between a method name and its
opening
parenthesis. This helps to distinguish keywords from method calls.

5. Implementation Comments
Java codes should have implementation comments delimited by /*...*/ or //. For
commenting out code a double slash i.e. // is recommended, while for multiple or
single-line comments given as an overview of code, the c-style comments i.e. /* */
should be used. For clarity in code, comments should be followed by a blank line.
Code should have four styles of implementation comments as follows and anything
that goes against a standard should always be documented.
Block Comments
Block comments are used to provide descriptions of files, methods, data
structures and algorithms. Block comments should be used at the beginning
of each file and in places where code is to be explained. They can be used in
places such as before or within methods. Block comments inside a 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. Block comments should be delimited by /*...*/.
During the process of development, the developer may need to leave some
portions of the code to be reviewed and enhanced later. These portions
should be specifically commented with a /* FIX ME */ tag specifying clearly
the modifications to be made and the date of
marking. This construct should, however, be sparingly used.
Single-Line & Trailing Comments
Short comments can appear on a single line indented to the level of the code
that follows. A single-line comment may be preceded by a blank line if it gives
clarity to code. It is recommended that single-line comments also be
delimited by /*...*/.
Very short comments may appear on the same line as the code they describe
but should be shifted far enough to separate them from the statements.
They may be used for explaining the use of a variable or any statement and
should also be delimited by /*...*/.
Commenting Codes
The // comment delimiter can comment out a complete line or only a partial
line. It should not be used on consecutive multiple lines for text comments,

however, it may be used in single or consecutive multiple lines
for commenting out sections of code.
Documentation Comment
Java codes should have documentation comments delimited by /**...*/.
Documentation 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.
Simple Documentation comments should add to the clarity of code and
should be followed by a blank line.
Classes and Interfaces
All comments using Javadoc conventions should be shown. Each class should
be documented describing the purpose of the class, guaranteed invariants,
usage instructions, and/or usage examples.
Variables
First, the static variables should be declared in the sequence public also all
the static variables defined before the methods in the classes, then
protected, then package level and then the private followed by instance
variables in the same sequence. Nature, purpose, constraints, and usage of
static and instances variables should be documented using Javadoc
conventions.
A blank line should follow the declarations.

Operators

The parenthesis should be effectively used to avoid operator precedence.

Methods

Each method should declare the Javadoc tags exactly in the
sequence as given below. Each line item begins with an asterisk. All
subsequent lines in the multiline component are to be indented so that they
line up vertically with the previous line. For reference, the Javadoc tags are
explained in detail in Annexure.

Example

Description

Every method should include a header at the top of the source code that
documents all of the information that is critical to understanding it.
A detailed description of the method may include the intent of method i.e. what
and why the method does, what a method should be passed as parameters and
what it returns, any Known bugs, exceptions that the method throws, information
on visibility decisions., how a method changes the object, pre and post conditions,
side effects, dependencies, implementation notes, who should be calling this
method, whether the method should or should not be overridden, were to invoke
super when overriding, control flow or state dependencies that need to exist before
calling this method.

PARAMETER SECTION

Describes the type, class, or protocol of all the methods or routine arguments.
Should describe the parameters intended use and constraints. Every function
parameter value should be checked before being used (Usually check for nulls and
Data Validation).

EXAMPLE:

RETURNS SECTION

This section is used to describe the method return type. Specifically, it needs to
detail the actual data type returned, the range of possible return values, and where
applicable, error information returned by the method. Every function should return
the correct value at every function return point or throw correct Exceptions in case
of Errors.
Example:
* @return Possible values are 1..n.

EXCEPTION SECTION

The purpose section is a complete description of all the non-system exceptions that
this method throws. A description of whether the exception is recoverable or not
should also be included. If applicable, a recovery strategy for the exception can be
described here.

In addition to the method documentation, it is also required to include comments
within the methods to make it easier to understand, maintain, and enhance.
● The control structures i.e. what each control structure, such as loop,
does should be documented.
● Any assumptions or calculations should be documented.
● Each local variable should have an end line comment describing its
use.
● Any complex code in a method should be documented if it is not
obvious.
● If there are statements that must be executed in a defined order then
this fact should be documented.

6. Declarations

One declaration per line is recommended since it encourages
commenting and enhances the clarity of code. The order and position of
declaration should be as follows:
First, the static/class variables should be placed in the sequence: First public class
variables, protected, package/default level i.e. with no access modifier and then the
private. As far as possible static or class fields should be explicitly instantiated by
the use of static initializers because instances of a class may sometimes not be
created before a static field is accessed.
● Instance variables should be placed in the sequence: First public instance
variables, protected,
● package level with no access modifier and then private.
● Next, class constructors should be declared.
● This should be followed by the inner classes, if applicable
● Class methods should be grouped by functionality rather than by scope or
accessibility to make
● reading and understanding the code easier.
● Declarations for local variables should be only at the beginning of blocks e.g.
at the beginning of a try-catch construct.
● Local declarations that hide declarations at higher levels should be avoided.
For example, the same variable name in an inner block.
● Numerical constants should not be coded directly except 1, 0, -1.

7. Standards for Statements
Each line should contain at most one statement. While 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 should be used
around all statements, even single statements, when they are part of a control
structure, such as an if-else or for statement. A boolean expression/function should
only be compared to a boolean constant. goto statements should be avoided. Try to
move invariable computation outside the loop.
E.g. D += 9*24*pie *x
Where pie is a constant then 9*24*pie can be moved out and assigned to a local
variable and used inside a loop where x changes in the loop

● return Statements
A return statement with a value should not use parentheses unless they make the
return value more
obvious in some way.

Example:

● if, if-else Statements
The ‘if’ keyword and conditional expression must be placed on the same line.
The if statements must
always use braces {}
Example:

● for Statements
A for statement should have the following form:

When using the comma operator in the initialization or update clause of a for
statement, avoid the complexity of using more than three variables. If
needed, separate statements before the for loop (for the initialization clause)
or at the end of the loop (for the update clause) may be used. The keyword
‘for’ and the parenthesis should be separated by a space and the expressions
in a for statement should be separated by blank space. The statement block
is placed on the next line. The closing curly brace starts in a new line,
indented to match its corresponding opening statement.

● while Statements
The ‘while’ construct uses the same layout format as the ‘if’ construct. The
‘while’ keyword should appear on its own line, immediately followed by the
conditional expression. The keyword ‘while’ and the parenthesis should be
separated by a space. The statement block is placed on the next line. The
closing curly brace starts in a new line, indented to match its corresponding
opening statement.
Example:

● do-while Statements
The DO..WHILE form of the while construct should appear as shown below:
Examples:

The statement block is placed on the next line. The closing curly brace starts
in a new line, indented to match its corresponding opening statement.

● switch Statements
The ‘switch’ construct should use the same layout format as the ‘if’ construct.
The ‘switch’ keyword should appear on its own line, immediately followed by
its test expression. The keyword ‘switch’ and the parenthesis should be
separated by a space.
The statement block should be placed on the next line. The closing curly
brace starts in a new line, indented to match its corresponding opening
statement. Every time a case falls through i.e. does not include a break
statement, a comment should be added where the break statement would
normally be. Every switch statement must include a default case. A break in
the default case is redundant, but it prevents an error if another case is
added later and therefore may be added. All missing switch case break
statements should be correct and marked with a comment.
Examples:

● try-catch Statements
In the try/catch construct the ‘try’ keyword should be followed by the open
brace in its own line. This is followed by the statement body and the close
brace on its own line. This may follow any number of ‘catch’ phrases -
consisting of the ‘catch’ keyword and the exception expression on its own
line with the ‘catch’ body; followed by the close brace on its own line.
Try-catch should be accomplished with finally block to destroys all Objects
not required. There should not be any empty try-catch blocks.

Example:

8. Naming Conventions

Naming conventions make programs more understandable by
making them easier to read. Following conventions should be followed while
naming a class or a member:
● Use full English descriptors that accurately describe the variable, method or
class. For example, the use of names like totalSales, currentDate instead of
names like x1, y1, or fn.
● Terminology applicable to the domain should be used. Implying that if user
refers to clients as customers, then the term Customer should be used for
the class, not Client.
● The mixed-case should be used to make names readable with lower case
letters, in general, capitalizing the first letter of class names and interface
names.
● Abbreviations should not be used as far as possible, but if used, should be
documented and consistently used.
● Very long or similar names for classes or methods should be avoided.
● Standard acronyms such as SQL should also be represented in the mixed
case as sqlDatabase().

Standards for Methods
Naming Methods

Methods should be named using a full English description, using mixed case with
the first letter of any non-initial word capitalized. It is also common practice for the
first word of a method name to be a strong, active verbs. e.g. getValue(), printData(),
save() ,delete(). This convention results in methods whose purpose can often be
determined just by looking at its name. It is recommended that accessor methods
be used to improve the maintainability of classes.

Getters

Getters are methods that return the value of a field. The word ‘get’ should be
prefixed to the name of the field, unless it is a boolean field where ‘is’ should be
prefixed to the name of the field . e.g. getTotalSales(), isPersistent(). Alternately the
prefix ‘has’ or ‘can’ instead of ‘is’ for boolean getters may be used. For example,
getter names such as hasDependents() and canPrint() can be created. Getters
should always be made protected, so that only subclasses can access the fields
except when an ‘outside class’ needs to access the field when the getter

method may be made public and the setter protected.

Setters

Setters, also known as mutators, are methods that modify the values of a field. The
word ‘set’ should be prefixed to the name of the field for such methods type.
Example: setTotalSales(),setPersistent(boolean isPersistent)

Getters for Constants

Constant values may need to be changed over a period of time. Therefore
constants should be implemented as getter methods. By using accessors for
constants there is only one source to retrieve the value. This increases the
maintainability of the system.

Accessors for Collections

The main purpose of accessors is to encapsulate the access to fields. Collections,
such as arrays and vectors need to have getter and setter method and as it is
possible to add and remove to and from collections, accessor methods need to be
included to do so. The advantage of this approach is that the collection is fully
encapsulated, allowing changes later like replacing it with another structure, like a
linked list.
Examples: getOrderItems(), setOrderItems(), insertOrderItem(), deleteOrderItem(),
newOrderItem()

Method Visibility

For a good design, the rule is to be as restrictive as possible when setting the
visibility of a method. If a method doesn’t have to be private then it should have
default access modifier, if it doesn’ t have to be
default then it should be made protected and if it doesn’ t have to protected only
then it should be made public. Wherever a method is made more visible it should
be documented why.
Access modifiers for methods should be explicitly mentioned in cases like interfaces
where the default permissible access modifier is public.

Standards for Parameters (Arguments) To Methods

Parameters should be named following the same conventions as for
local variables. Parameters to a method are documented in the header
documentation for the method using the javadoc@param tag.
However:
● Cascading method calls like method1().method2() should be avoided.
● Overloading methods on argument type should be avoided.
● It should be declared when a class or method is thread-safe.
● Synchronized methods should be preferred over synchronized blocks.
● The fact that a method invokes wait should always be documented
● Abstract methods should be preferred in base classes over those with
default no-op implementations.
● All possible overflow or underflow conditions should be checked for a
computation.
There should be no space between a method/constructor name and the
parenthesis but there should be a blank space after commas in argument lists.

9. Naming Convention standards
Naming Variables

Use a full English descriptor for variable names to make it obvious what the field
represents. Fields, that are collections, such as arrays or vectors, should be given
names that are plural to indicate that they represent multiple values. Variable
names should not start with an
underscore _ or dollar sign $ characters and should be short and meaningful. The
choice of a variable name should be mnemonic i.e., designed to indicate to the
casual observer the intent of its use. Single character variable names should be
avoided except for temporary
“throwaway” variables.

Naming Components

For names of components, full English descriptor should be used, postfixed by the
Component type. This makes it easy to identify the purpose of the component as
well as its type, making it easier to find each component in a list. Therefore names
like NewHelpMenuItem, CloseButton should be preferred over Button1, Button2,

etc.

Naming Constants

Constants, whose values that do not change, are typically implemented as static
final fields of classes. They should be represented with full English words, all in
uppercase, with underscores between the words like FINAL_VALUE.

Naming Collections

A collection, such as an array or a vector, should be given a pluralized name
representing the types of objects stored by the array. The name should be a full
English descriptor with the first letter of all non-initial words capitalized like
customers, orderItems, aliases

Naming Local Variables

In general, local variables are named following the same conventions as used for
fields, in other words use of full English descriptors with the first letter of any
non-initial word in uppercase. For the sake of convenience, however, this naming
convention is relaxed for several specific types of local variable like Streams, Loop
counters, Exceptions.Name hiding or data hiding refers to the practice of naming a
local variable, argument, or methods the same or similar as that of another one of
greater scope in same or super class. This may lead to confusion and should be
avoided.

Naming Streams

When there is a single input and/or output stream being opened, used, and then
closed within a method the common convention is to use ‘in’ and ‘out’ for the
names of these streams, respectively.

Naming Loop Counters

Loop counters are a very common use for local variables therefore the use of i, j, or
k, is acceptable for loop counters where they are obvious. However, if these names
are used for loop counters, they should be used consistently. For complex nested
loops the counters should be given full meaningful English descriptors.

10. Variable Assignments
Assigning several variables to the same value in a single statement should be
avoided, i.e., we should avoid constructs like var1 = var2 = var3 = 0;
Assignment operator should not be used in a place where it can be easily confused
with the equality operator.
Embedded assignments in an attempt to improve run-time performance should be
avoided

Variable Visibility

For reasons of encapsulation, fields should not be declared public. All fields should
be declared private unless necessary otherwise. Fields should never be accessed
directly, instead accessor methods should be used i.e. private members should be
accessed through methods. All fields should be declared private and accessed by
getter and setter methods also called accessors.

Documenting & Declaring a Variable

Every field should be documented well enough so that other developers can
understand it. There is a need to document description, all applicable invariants,
visibility decisions. Wherever a field is made more visible it should be documented
why. There are some conventions regarding the declaration and documentation of
local variable. These conventions are:
● Declare one local variable per line of code.
● Document local variables with an end line comment.
● Declare local variables at the top of the block of code.
● Use local variables for one thing only at a time.
● However the following should be taken into consideration while using
variables:
● Instance variables should not be declared public.
● Implicit initializers for static or instance variables should not be relied and
initialization should be explicit.
● Use of static should be minimized as they act like globals. They make
methods more context dependent, hide possible side effects, sometimes
present synchronized access problems and are the source of fragile,

non-extensible constructions. Also, neither static variables nor
methods are overridable in any useful sense in subclasses.
● Generally prefer double to float and use int for compatibility with standard
Java constructs and classes.
● Use final and/or comment conventions to indicate whether instance
variables that never have their values changed after construction are
intended to be constant (immutable) for the lifetime of the object.
● Declare and initialize a new local variable rather than reusing/reassigning an
existing one whose value happens to no longer be used at that program
point.
● Assign null to any reference variable that is no longer being used to enable
garbage collection.
● Same names of variables or methods should be avoided in methods and
subclasses

11. Best Practices

Efficient String Concatenation:- For making a long string by adding different small
strings always use append method of java.lang.StringBuffer and never use ordinary
‘+’ operator for adding up strings.

Optimal Use Of Garbage Collector:- For easing out the work of java Garbage
Collector always set all referenced variables used to ‘null’ explicitly thus
de-referencing the object which is no more required by the application and allowing
Garbage Collector to swap away that variable thus realizing memory.

Writing Oracle Stored Procedures Optimally:- Avoid using ‘IN’ and ‘NOT IN’ clause
and rather try to use ‘OR’ operator for increasing the response time for the Oracle
Stored Procedures.

Using variables in any Code Optimally:- Try to make minimum number of
variables in JSP/Java class and try to use already made variables in different
algorithms shared in the same JSP/Java class by setting already populated variable
to ‘null’ and then again populating that variable with new value and then reusing
them.

Perfomatix - Java Coding Standards

More Related Content

What's hot (20)

Similar to Perfomatix - Java Coding Standards (20)

Recently uploaded (20)

Perfomatix - Java Coding Standards