Revision as of 15:35, 31 January 2011

Introduction

This document lists Java coding recommendations common in the Java development community. This text is a copy of http://geosoft.no/development/javastyle.html and slightly adopted for the code recommenders project. The recommendations described here are based on established standards collected from a number of sources, individual experience, local requirements/needs, as well as suggestions given in.

Layout of the Recommendation.

The recommendations are grouped by topic and each recommendation is numbered to make it easier to refer to during reviews.

Layout for the recommendations is as follows:

n. Guideline short description
Example if applicable
Motivation, background and additional information.

The motivation section is important. Coding standards and guidelines tend to start "religious wars", and it is important to state the background for the recommendation.

Recommendation Importance

In the guideline sections the terms must, should and can have special meaning. A must requirement must be followed, a should is a strong recommendation, and a can is a general guideline.

Automatic Style Checking

Many tools provide automatic code style checking and automated code formatting. Checkstyle by Oliver Burn is probably one of the most popular of such tools. An Eclipse integration for Checkstyle can be found here http://eclipse-cs.sourceforge.net.

To use Checkstyle with Code Recommenders guidelines please use this xml configuration file: <TODO>

General Recommendation

Any violation to the guide is allowed if it enhances readability.

The main goal of the recommendation is to improve readability and thereby the understanding and the maintainability and general quality of the code. It is impossible to cover all the specific cases in a general guide and the programmer should be flexible.

No code without license header!

At Eclipse every java source code file (at least) needs an EPL license header BEFORE it is checked in. The typical license header looks like this:

/**
 * Copyright (c) 2010 Darmstadt University of Technology.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Marcel Bruch - initial API and implementation.
 */
package org.eclipse.recommenders.internal.rcp.codecompletion;

import ...
public class CompilerAstCompletionNodeFinder extends ASTVisitor {
  ...
}

Adopt the copyright header and Contributors section according to your affiliation and name. Inform your build master if you are using a new license. Otherwise it may break the build.

No check-in without running mvn clean install locally.

$ pwd
/Users/Marcel/Workspaces/code-recommenders/public/org.eclipse.recommenders.parent
$ mvn clean install
... wait a few minutes and check the build results

The one who breaks the build... you already know what happens, right?

Naming Conventions

General Naming Conventions

Names representing packages should be in all lower case.

 mypackage, com.company.application.ui

Package naming convention used by Sun for the Java core packages. The initial package name representing the domain name must be in lower case.

Eclipse Package Naming Conventions

At Eclipse there are a set of naming conventions described in great detail here:

A bief summary of this discussion for code recommenders is:

All packages start with:

org.eclipse.recommenders.*

Internal packages always start with

org.eclipse.recommenders.internal.* // NOT org.eclipse.recommenders.other.package.internal;
  // NOT org.eclipse.recommenders.other.internal.package;

Test packages start with

org.eclipse.recommenders.tests.* // NOT org.eclipse.recommenders.other.package.tests;
  // NOT org.eclipse.recommenders.other.tests.package;

Example packages start with

org.eclipse.recommenders.examples.* // NOT org.eclipse.recommenders.other.package.examples;
  // NOT org.eclipse.recommenders.other.examples.package;

Names representing types must be nouns and written in mixed case starting with upper case.

Line, AudioSystem

Common practice in the Java development community and also the type naming convention used by Sun for the Java core packages.

Interfaces follow the Eclipse Style I[TypeName] convention

public interface IVariableUsageResolver // NOT just VariableUsageResolver
{
 ...
}

The I[TypeName] convention allows developers to quickly assess the relevant interfaces in a package. Like it or not - this is an Eclipse convention we have to obey.

Variable names must be in mixed case starting with lower case.

line, audioSystem

Common practice in the Java development community and also the naming convention for variables used by Sun for the Java core packages. Makes variables easy to distinguish from types, and effectively resolves potential naming collision as in the declaration Line line;

Names representing constants (final variables) must be all uppercase using underscore to separate words.

MAX_ITERATIONS, COLOR_RED

Common practice in the Java development community and also the naming convention used by Sun for the Java core packages.

TODO :Add section about enums

Names representing methods must be verbs and written in mixed case starting with lower case.

getName(), computeTotalWidth()

Common practice in the Java development community and also the naming convention used by Sun for the Java core packages. This is identical to variable names, but methods in Java are already distinguishable from variables by their specific form.

Abbreviations and acronyms should not be uppercase when used as name.

exportHtmlSource(); // NOT: exportHTMLSource();
openDvdPlayer(); // NOT: openDVDPlayer();

Using all uppercase for the base name will give conflicts with the naming conventions given above. A variable of this type whould have to be named dVD, hTML etc. which obviously is not very readable. Another problem is illustrated in the examples above; When the name is connected to another, the readability is seriously reduced; The word following the acronym does not stand out as it should.

TODO

liste der Standard abkürzungen:

ast -> jdt.deom rec -> recommenders jdt -> IJavaElement compiler -> compiler internal

cu -> compilationUnit -> preferred compilationUnit (no abbrev)

Private class variables must not have any field prefix or suffix.

class Person
{
  private String name; // NOT private String _name;
  // NOT private String fName;
// NOT private String name_;
  ...
}

void setName(String name)
{
  this.name = name; // NOT name_= name;
}

To eliminate misinterpretations qualify field puts with this. and use the same names. Use IDE highlighting settings to make more visible on which kind of variable you are working.

TODO

Generic variables should have the same name as their type.

void setTopic(Topic topic) // NOT: void setTopic(Topic value)
  // NOT: void setTopic(Topic aTopic)
  // NOT: void setTopic(Topic t) 

void connect(Database database) // NOT: void connect(Database db)
  // NOT: void connect(Database oracleDB)

Reduce complexity by reducing the number of terms and names used. Also makes it easy to deduce the type given a variable name only. If for some reason this convention doesn't seem to fit it is a strong indication that the type name is badly chosen.

Non-generic variables have a role. These variables can often be named by combining role and type:

Point startingPoint, centerPoint;
Name loginName;

All names should be written in English.

English is the preferred language for international development.

Variables with a large scope should have long names, variables with a small scope can have short names

Scratch variables used for temporary storage or indices are best kept short. A programmer reading such variables should be able to assume that its value is not used outside a few lines of code. Common scratch variables for integers are i, j, k, m, n and for characters c and d.

The name of the object is implicit, and should be avoided in a method name.

line.getLength(); // NOT: line.getLineLength();

The latter might seem natural in the class declaration, but proves superfluous in use, as shown in the example.

Specific Naming Conventions

The terms get/set must be used where an attribute is accessed directly.

employee.getName();
employee.setName(name);

matrix.getElement(2, 4);
matrix.setElement(2, 4, value);

Common practice in the Java community and the convention used by Sun for the Java core packages. Getters should not change the internal state of the object. Exceptions may be lazy initializers. Getter should actually return something :-)

NOTE: this is a pure GET. No real computation effort needed.

is prefix should be used for boolean variables and methods.

isSet, isVisible, isFinished, isFound, isOpen

This is the naming convention for boolean methods and variables used by Sun for the Java core packages. Using the is prefix solves a common problem of choosing bad boolean names like status or flag. isStatus or isFlag simply doesn't fit, and the programmer is forced to chose more meaningful names.

Setter methods for boolean variables must have set prefix as in:

void setFound(boolean isFound);

There are a few alternatives to the is prefix that fits better in some situations. These are has, can and should prefixes:

boolean hasLicense();
boolean canEvaluate();
boolean shouldAbort = false;

The term compute can be used in methods where something is computed.

valueSet.computeAverage();
matrix.computeInverse()

Give the reader the immediate clue that this is a potential time consuming operation, and if used repeatedly, he might consider caching the result. Consistent use of the term enhances readability.

The term find can be used in methods where something is looked up.

vertex.findNearestVertex();
matrix.findSmallestElement();
node.findShortestPath(Node destinationNode);

Give the reader the immediate clue that this is a simple look up method with a minimum of computations involved. Consistent use of the term enhances readability.

The term initialize can be used where an object or a concept is established.

printer.initializeFontSet();

The American initialize should be preferred over the English initialise. Abbreviation init should be avoided.

The use of initializeXYZ() in constructors to initialize complex fields is preferred over direct field initalizations.


Set<Statements> supportedCompletionRequests;
  // NOT Set<Statements> supportedCompletionNodes = createSupportedCompletionRequest()

public CallsCompletionEngine(..) {
  ...
  initializeSuportedCompletionRequests();
}

private void initializeSuportedCompletionRequests() 
{
  supportedCompletionRequests = Sets.newHashSet();
  supportedCompletionRequests.add(CompletionOnMemberAccess.class);
  supportedCompletionRequests.add(CompletionOnMessageSend.class);
  supportedCompletionRequests.add(CompletionOnQualifiedNameReference.class);
  supportedCompletionRequests.add(CompletionOnSingleNameReference.class);
}

JFC (Java Swing) and SWT variables should be suffixed by the element type.

widthScale, nameTextField, leftScrollbar, mainPanel, fileToggle, minLabel, printerDialog

Enhances readability since the name gives the user an immediate clue of the type of the variable and thereby the available resources of the object.

Plural form should be used on names representing a collection of objects.

Collection<Point> points;
int[] values;

Enhances readability since the name gives the user an immediate clue of the type of the variable and the operations that can be performed on its elements.

numberOf prefix should be used for variables representing a number of objects.

numberOfPoints, numberOfLines

Note that Sun use num prefix in the core Java packages for such variables. This is probably meant as an abbreviation of number of, but as it looks more like number it makes the variable name strange and misleading. If "number of" is the preferred phrase, numberOf prefix can be used instead of just n. num prefix must not be used.

Iterator variables should be called it

for (Iterator it = points.iterator(); i.hasNext(); )
{
  ...
} 

for (int i = 0; i < numberOfTables; i++)
{
  ...
}

Complement names must be used for complement entities.

 
get/set, add/remove, create/destroy, start/stop, insert/delete,
increment/decrement, old/new, begin/end, first/last, up/down, min/max,
next/previous, old/new, open/close, show/hide, suspend/resume, etc.

Reduce complexity by symmetry.

Abbreviations in names should be avoided.

computeAverage(); // NOT: compAvg();
ActionEvent event; // NOT: ActionEvent e;
catch (Exception exception) { // NOT: catch (Exception e) {

There are two types of words to consider. First are the common words listed in a language dictionary. These must never be abbreviated. Never write:

cmd instead of command
comp instead of compute
cp instead of copy
e instead of exception
init instead of initialize
pt instead of point
etc.

Then there are domain specific phrases that are more naturally known through their acronym or abbreviations. These phrases should be kept abbreviated. Never write:

HypertextMarkupLanguage instead of html
CentralProcessingUnit instead of cpu
PriceEarningRatio instead of pe
etc.

TODO: cu, exception changed

Negated boolean variable names must be avoided.

bool isError; // NOT: isNoError
bool isFound; // NOT: isNotFound

The problem arise when the logical not operator is used and double negative arises. It is not immediately apparent what !isNotError means.

Associated constants (final variables) should be prefixed by a common type name.

final int COLOR_RED = 1;
final int COLOR_GREEN = 2;
final int COLOR_BLUE = 3;

This indicates that the constants belong together, and what concept the constants represents.

An alternative to this approach is to put the constants inside an interface effectively prefixing their names with the name of the interface:

interface Color
{
  final int RED = 1;
  final int GREEN = 2;
  final int BLUE = 3;
}

=== Exception classes should be suffixed with Exception. ===
<pre>class AccessException extends Exception{...}

Exception classes are really not part of the main design of the program, and naming them like this makes them stand out relative to the other classes. This standard is followed by Sun in the basic Java library.

Statements

Package and Import Statements

The package statement must be the first statement of the file. All files should belong to a specific package.

The package statement location is enforced by the Java language. Letting all files belong to an actual (rather than the Java default) package enforces Java language object oriented programming techniques.

=== The import statements must follow the package statement. import statements should be sorted with the most fundamental packages first, and grouped with associated packages together and one blank line between groups.

import java.io.IOException;
import java.net.URL;

import java.rmi.RmiServer;
import java.rmi.server.Server;

import javax.swing.JPanel;
import javax.swing.event.ActionEvent;

import org.linux.apache.server.SoapServer;

The import statement location is enforced by the Java language. The sorting makes it simple to browse the list when there are many imports, and it makes it easy to determine the dependiencies of the present package The grouping reduce complexity by collapsing related information into a common unit.

Your IDE supports you on this. Check out your settings.

Imported classes should always be listed explicitly.

import java.util.List;      // NOT: import java.util.*;
import java.util.ArrayList;
import java.util.HashSet;

Importing classes explicitly gives an excellent documentation value for the class at hand and makes the class easier to comprehend and maintain.

Your IDE will always keep the import list minimal and up to date - if you enable this feature in your preferences.

Classes and Interfaces

Class and Interface declarations should be organized in the following manner:

Class/Interface documentation.
class or interface statement.
Class (static) variables in the order public, protected, package (no access modifier), private.
Instance variables in the order public, protected, package (no access modifier), private.
Constructors.
Methods (in order they are used in code AKA vertical density).

Reduce complexity by making the location of each class element predictable.

Methods

Method modifiers should be given in the following order:

<access> static abstract synchronized <unusual> final native

The <access> modifier (if present) must be the first modifier.

public static double square(double a);  // NOT: static public double square(double a);

access is one of public, protected or private while unusual includes volatile and transient. The most important lesson here is to keep the access modifier as the first modifier. Of the possible modifiers, this is by far the most important, and it must stand out in the method declaration. For the other modifiers, the order is less important, but it make sense to have a fixed convention.

Types

Type conversions must always be done explicitly. Never rely on implicit type conversion.

 floatValue = (int) intValue; // NOT: floatValue = intValue;

By this, the programmer indicates that he is aware of the different types involved and that the mix is intentional.

Array specifiers must be attached to the type not the variable.

 int[] a = new int[20];   // NOT: int a[] = new int[20]

The arrayness is a feature of the base type, not the variable. It is not known why Sun allows both forms.

Variables

Variables should be initialized where they are declared and they should be declared in the smallest scope possible.

This ensures that variables are valid at any time. Sometimes it is impossible to initialize a variable to a valid value where it is declared. In these cases it should be left uninitialized rather than initialized to some phony value.

Variables must never have dual meaning.

Enhances readability by ensuring all concepts are represented uniquely. Reduce chance of error by side effects.

Class variables should never be declared public.

The concept of Java information hiding and encapsulation is violated by public variables. Use private variables and access functions instead. One exception to this rule is when the class is essentially a data structure, with no behavior (equivalent to a C++ struct). In this case it is appropriate to make the class' instance variables public [2].

Arrays should be declared with their brackets next to the type.

double[] vertex;  // NOT: double vertex[];
int[]    count;   // NOT: int    count[];

public static void main(String[] arguments)

public double[] computeVertex()

The reason for is twofold. First, the array-ness is a feature of the class, not the variable. Second, when returning an array from a method, it is not possible to have the brackets with other than the type (as shown in the last example).

Variables should be kept alive for as short a time as possible.

Keeping the operations on a variable within a small scope, it is easier to control the effects and side effects of the variable.

Loops

Only loop control statements must be included in the for() construction.

sum = 0;                       // NOT: for (i = 0, sum = 0; i < 100; i++)
for (i = 0; i < 100; i++)                sum += value[i];
  sum += value[i];
Increase maintainability and readability. Make a clear distinction of what controls and what is contained in the loop.
50. Loop variables should be initialized immediately before the loop.
isDone = false;           // NOT: bool isDone = false;
while (!isDone) {         //      :
  :                       //      while (!isDone) {
}                         //        :
                          //      }

The use of do-while loops can be avoided.

do-while loops are less readable than ordinary while loops and for loops since the conditional is at the bottom of the loop. The reader must scan the entire loop in order to understand the scope of the loop. In addition, do-while loops are not needed. Any do-while loop can easily be rewritten into a while loop or a for loop. Reducing the number of constructs used enhance readability.

The use of break and continue in loops should be avoided.

These statements should only be used if they prove to give higher readability than their structured counterparts.

Conditionals

Complex conditional expressions must be avoided. Introduce temporary boolean variables or selfexplaining methods instead.

bool isFinished = (elementNo < 0) || (elementNo > maxElement);
bool isRepeatedEntry = elementNo == lastElement;
if (isFinished || isRepeatedEntry) {
  :
}


// NOT:
if ((elementNo < 0) || (elementNo > maxElement)||
     elementNo == lastElement) {
  :
}


// even better:
if (isFinished(..) || isRepeatedEntry(..)) {
  :
}

By assigning boolean variables to expressions, the program gets automatic documentation. The construction will be easier to read, debug and maintain. Using methods that reveal the intension of these checks should be preferred over use of temporary variables!

The nominal case should be put in the if-part and the exception in the else-part of an if statement.

boolean isOk = readFile(fileName);
if (isOk) {
  :
}
else {
  :
}

Makes sure that the exceptions does not obscure the normal path of execution. This is important for both the readability and performance.

The conditional should be put on a separate line enclosed by curly brackets.

if (isDone)
{       // NOT: if (isDone) doCleanup();
  doCleanup();
}

This is for debugging purposes. When writing on a single line, it is not apparent whether the test is really true or not. Also the usage of curly brackets ensure that no statements accidentally fall out of an if branch:

if (isDone)       
  doCleanup();
  unregisterListener(); // unregister will always be called - even if !isDone

Executable statements in conditionals must be avoided.

InputStream stream = File.open(fileName, "w");
if (stream != null) {
  :
}

// NOT:
if (File.open(fileName, "w") != null)) {
  :
}

Conditionals with executable statements are simply very difficult to read. This is especially true for programmers new to Java.

Miscellaneous

The use of magic numbers in the code should be avoided. Numbers other than 0 and 1 can be considered declared as named constants instead.

private static final int  TEAM_SIZE = 11;
:
Player[] players = new Player[TEAM_SIZE]; // NOT: Player[] players = new Player[11];
If the number does not have an obvious meaning by itself, the readability is enhanced by introducing a named constant instead.
58. Floating point constants should always be written with decimal point and at least one decimal.
double total = 0.0;    // NOT:  double total = 0;
double speed = 3.0e8;  // NOT:  double speed = 3e8;

double sum;
:
sum = (a + b) * 10.0;

This emphasize the different nature of integer and floating point numbers. Mathematically the two model completely different and non-compatible concepts.

Also, as in the last example above, it emphasize the type of the assigned variable (sum) at a point in the code where this might not be evident.

Floating point constants should always be written with a digit before the decimal point.

double total = 0.5;  // NOT:  double total = .5;

The number and expression system in Java is borrowed from mathematics and one should adhere to mathematical conventions for syntax wherever possible. Also, 0.5 is a lot more readable than .5; There is no way it can be mixed with the integer 5.

Static variables or methods must always be refered to through the class name and never through an instance variable.

 Thread.sleep(1000);    // NOT: thread.sleep(1000);

This emphasize that the element references is static and independent of any particular instance. For the same reason the class name should also be included when a variable or method is accessed from within the same class.

Default interface implementations can be prefixed by Default.

class DefaultTableCellRenderer> implements TableCellRenderer{...}

It is not uncommon to create a simplistic class implementation of an interface providing default behaviour to the interface methods. The convention of prefixing these classes by Default has been adopted by Sun for the Java library.

Singleton classes should return their sole instance through method getInstance.

 
class UnitManager
{
  private final static UnitManager instance_ = new UnitManager(); 

  private UnitManager() {...} 

  public static UnitManager getInstance() // NOT: get() or instance() or unitManager() etc.
  {
    return instance_;
  }
}

Common practice in the Java community though not consistently followed by Sun in the JDK. The above layout is the preferred pattern.

Classes that creates instances on behalf of others (factories) can do so through method new[ClassName]

class PointFactory
{
  public Point newPoint(...)
  {
    ...
  }
}

Indicates that the instance is created by new inside the factory method and that the construct is a controlled replacement of new Point().

Consider static factory methods instead of constructors

Advantages:

One advantage of static factory methods is that, unlike constructors, they have names.
A second advantage of static factory methods is that, unlike constructors, they are not required to create a new object each time they’re invoked.
A third advantage of static factory methods is that, unlike constructors, they can return an object of any subtype of their return type.

Disadvantages:

The main disadvantage of providing only static factory methods is that classes without public or protected constructors cannot be subclassed.
A second disadvantage of static factory methods is that they are not readily distinguishable from other static methods.

Follow a set of conventions when using them:

valueOf - Returns an instance that has, loosely speaking, the same value as its parameters. Such static factories are effectively type-conversion methods. Example: String.valueOf(boolean);
of - A concise alternative to valueOf, popularized by EnumSet.
getInstance - Returns an instance that is described by the parameters but cannot be said to have the same value. In the case of a singleton, getInstance takes no parameters and returns the sole instance.
newInstance - Like getInstance, except that newInstance guarantees that each instance returned is distinct from all others.
getType - Like getInstance, but used when the factory method is in a different class. Type indicates the type of object returned by the factory method.
newType - Like newInstance, but used when the factory method is in a different class. Type indicates the type of object returned by the factory method.
create[SomeSuffix] - Like newType, but may perform some special initializations on the returned objects. Example: Type.createWithDefaultResolver(...);

Public methods may delegate work to private/protected do[MethodName] methods and enclose their invocation with try/catch

public void append(..)
{
  try
  {
    doAppend(..);
  } 
  catch (Exception e)
  {
    logAppendFailedError(e);
  }
}

Sometimes the code to execute may throw exceptions which should be catched and not rethrown. Also subclasses may reimplement some behavior of the algorithm. To ensure consistency with the API one may delegate to a do[MethodName]() method and make the public method final. This way the superclass can ensure some consistency independent of actual subclasses executed.

Functions (methods returning an object) should be named after what they return and procedures (void methods) after what they do.

Increase readability. Makes it clear what the unit should do and especially all the things it is not supposed to do. This again makes it easier to keep the code clean of side effects.

List of accepted acronyms

cu: Abbreviation for Compilation Unit. Although accepted the usage of compilationUnit should be preferred over cu.
ast: Abbreviation for Abstract Syntax Tree.
jdt: Abbreviation for Java Development Tools - also used if IJavaElements are used to make clear the difference to code recommenders or ast constructs with similar names.
rec: Abbreviation for Recommenders. Typically used as prefix if objects of similar names are used in the same context. Example: jdtCu vs. recCu

Layout and Comments

Layout

Code Recommenders provides a code formatter template for Eclipse which must be used by all committers. It's located in the releng project.

Comments

Most conventions on comments are enforced by the code formatter template of the code recommenders project. Thus just a few general notes on comments here.

Tricky code should not be commented but rewritten.

In general, the use of comments should be minimized by making the code self-documenting by appropriate name choices and an explicit logical structure.

All comments should be written in English.

In an international environment English is the preferred language.

Use // for all non-JavaDoc comments, including multi-line comments.

// Comment spanning
// more than one line.

Since multilevel Java commenting is not supported, using // comments ensure that it is always possible to comment out entire sections of a file using /* */ for debugging purposes etc.

The declaration of anonymous collection variables should be followed by a comment stating the common type of the elements of the collection.

private Multimap<String /* simple class name*/, String /*list of potentially matching full qualified class names*/> nameIndex;

Without the extra comment it can be hard to figure out what the collection consist of, and thereby how to treat the elements of the collection. In methods taking collection variables as input, the common type of the elements should be given in the associated JavaDoc comment. Whenever possible one should of course qualify the collection with the type to make the comment superflous:

Something left over?

Send comments to recommenders-dev@eclipse.org

@@ Line 643: / Line 643: @@
 ;rec
 :Abbreviation for ''Recommenders''. Typically used as prefix if objects of similar names are used in the same context. Example: jdtCu vs. recCu
+= Layout and Comments =
+== Layout ==
+Code Recommenders provides a code formatter template for Eclipse which must be used by all committers. It's located in the releng project.
+== Comments ==
+Most conventions on comments are enforced by the code formatter template of the code recommenders project. Thus just a few general notes on comments here.
+=== Tricky code should not be commented but rewritten. ===
+In general, the use of comments should be minimized by making the code self-documenting by appropriate name choices and an explicit logical structure.
+=== All comments should be written in English. ===
+In an international environment English is the preferred language.
+=== Use // for all non-JavaDoc comments, including multi-line comments. ===
+<pre>
+// Comment spanning
+// more than one line.
+</pre>
+Since multilevel Java commenting is not supported, using // comments ensure that it is always possible to comment out entire sections of a file using /* */ for debugging purposes etc.
+=== The declaration of anonymous collection variables should be followed by a comment stating the common type of the elements of the collection. ===
+private Multimap<String /* simple class name*/, String /*list of potentially matching full qualified class names*/>  nameIndex;
+Without the extra comment it can be hard to figure out what the collection consist of, and thereby how to treat the elements of the collection. In methods taking collection variables as input, the common type of the elements should be given in the associated JavaDoc comment.
+Whenever possible one should of course qualify the collection with the type to make the comment superflous:

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