It's no coincidence that network computers, the Internet and Java have emerged simultaneously as trends in computing - all are "open" technologies that have democratized and universalized the sharing of information. Because it can run on any platform, the 100 per cent Pure Java environment promises to liberate MIS managers from relying on specific, proprietary technologies, including those from the Microsoft and Intel world - software programs no longer need to be written for a specific server or client.

According to a report from Redwood City, CA-based Zona Research, Java: Markets, Opportunities and Trends, 97 per cent of corporations will be using Java for server-based applications within the next two years. In fact, Java has been the fastest growing language/technology in the history of the computer industry.

Network computers free users from using specific desktop devices to access corporate information, PC-style applications and the Internet. Since the storage and processing of data is done at the server level, the expense and complexity of operating systems and microprocessors in network clients becomes more manageable - and less of an issue. Employees don't need to troubleshoot PC problems themselves and MIS managers can more easily manage the network.

The Internet is a kind of glue that connects servers and NCs - it's useful as a communications medium and as a way to distribute Java applets. Like Java and NCs, the Internet is universal - it can be accessed from any platform.

Although NCs can access personal productivity applications from a Windows server, Java software will give many former "greenscreen" users another way to perform functions previously limited to those with PCs - calendaring, word processing, spreadsheets, browsers, groupware and more - without having to take on the overhead of managing a PC. And this new style of server-delivered applications can be used by everyone in the organization, on any system - existing PCs, workstations or NCs.

With Java, IT departments can distribute software programs that can run on any system, from the largest enterprise server to the smallest PC server. And Java allows us to deliver new applications across a diverse range of clients, including PCs, NCs, mobile PCs, mobile NCs, PDAs and digital telephones. Programmers can break up "fat client" software applications into smaller pieces and store them on a central server. The NC user taps only the portions of a program needed to perform a function, while other software functions reside on the server.

When it comes to personal productivity programs, approximately 80 per cent of workers use only 20 per cent of a word processing application. But a Java word processing application divides the functions in a way that makes the most sense - simple typing, highlighting paragraphs or outlining words in bold can be performed at the NC level, while spell-checking can be done at the server level where dictionaries and large databases are stored.

Because all application-specific codes are stored and managed on centralized servers, Java can help reduce development costs, increase a company's return on IT investment and extend the reach of existing products. Other cost savings come in the form of reduced maintenance and fewer software and hardware compatibility problems.

The beauty of NCs is that they allow users to access all kinds of information, such as data residing on the Internet and corporate intranets. Many companies planning to reduce their paper environment and distribute information more quickly and pervasively can now store corporate documents and databases on an intranet. A company's return on investment increases dramatically as its intranet performs more functions and provides more information to users, according to Zona Research - dynamic access to corporate databases leads to an average return on investment of 64 per cent. Users no longer need a complex operating system on their desktops to access a few simple applications and the Internet.

Howie Hunger is director of channels and marketing, IBM Network Computer Division, based in Somers, NY.

Table of Content

• 1 Introduction
  • 1.1 Layout of theRecommendations
  • 1.2 Recommendations Importance
• 2 General Recommendations
• 3 Naming Conventions
  • 3.1 General Naming Conventions
  • 3.2 Specific naming Conventions
• 4 Files
• 5 Statements
  • 5.1 Package and Import Statements
  • 5.2 Classes and Interfaces
  • 5.3 Methods
  • 5.4 Types
  • 5.5 Variables
  • 5.6 Loops
  • 5.7 Conditionals
  • 5.8 Miscellaneous
• 6 Layout and Comments
  • 6.1 Layout
  • 6.2 White space
  • 6.3 Comments
• 7 References

1 Introduction

This document lists Java coding recommendations common in the Java development community.

The recommendations are based on established standards collected from a number of sources, individual experience, local requirements/needs, as well as suggestions given in [1], [2], [3], [4] and [5].

There are several reasons for introducing a new guideline rather than just referring to the ones above. Main reason is that these guides are far too general in their scope and that more specific rules (especially naming rules) need to be established. Also, the present guide has an annotated form that makes it far easier to use during project code reviews than most other existing guidelines. In addition, programming recommendations generally tend to mix style issues with language technical issues in a somewhat confusing manner. The present document does not contain any Java technical recommendations at all, but focuses mainly on programming style.

While a given development environment (IDE) can improve the readability of code by access visibility, color coding, automatic formatting and so on, the programmer should never rely on such features. Source code should always be considered larger than the IDE it is developed within and should be written in a way that maximize its readability independent of any IDE.

1.1 Layout of the Recommendations.

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:

Example if applicable

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.

1.2 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.

2 General Recommendations

3 Naming Conventions

3.1 General Naming Conventions

mypackage, com.company.application.ui

Line, AudioSystem

line, audioSystem

MAX_ITERATIONS, COLOR_RED

  int getMaxIterations() // NOT: MAX_ITERATIONS = 25
  {
    return 25;
  }

getName(), computeTotalWidth()

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

class Person
{
  private String  name_;
  ...
}

  void setName (String name)
  {
    name_ = name;
  }

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

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

  Point  startingPoint, centerPoint;
  Name   loginName;

fileName; // NOT: filNavn

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

3.2 Specific Naming Conventions

employee.getName();
matrix.getElement (2, 4);
employee.setName (name);
matrix.setElement (2, 4, value);

isSet, isVisible, isFinished, isFound, isOpen

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

valueSet.computeAverage();
matrix.computeInverse();

vertex.findNearestVertex();
matrix.findMinElement();

printer.initializeFontSet();

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

Collection points;  // of Point
int[]      values;

nPoints, nLines

tableNo, employeeNo

while (Iterator i = points.iterator(); i.hasNext(); ) {
  :
}

for (int i = 0; i < nTables; i++) {
  :
}

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

computeAverage();  // NOT: compAvg();
ActionEvent event; // NOT: ActionEvent e;

boolean isError; // NOT: isNotError
boolean isFound; // NOT: isNotFound

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

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

class AccessException
{
  :
}

class DefaultTableCellRenderer 
  implements TableCellRenderer
{
  :
}

4 Files

Point.java

totalSum = a + b + c +
           d + e;

function (param1, param2,
          param3);

setText ("Long line split" +
         "into two parts.");

for (tableNo = 0; tableNo < maxTable;
     tableNo += tableStep)

5 Statements

5.1 Package and Import Statements

import java.io.*;
import java.net.*;

import java.rmi.*
import java.rmi.server.*;

import javax.swing.*;
import javax.swing.event.*;

import org.linux.apache.server.*;

5.2 Classes and Interfaces

5.3 Methods

5.4 Types

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

5.5 Variables

float  x, y, z;
float  revenueJanuary, revenueFebrury, revenueMarch;

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

public static void main (String[] arguments)

public double[] computeVertex()

5.6 Loops

sum = 0;                   // NOT: for (i=0, sum = 0; i < 100; i++)
for (i = 0; i < 100; i++)  //        sum += value[i];
  sum += value[i];

boolean isDone = false; // NOT: isDone = false;
while (!isDone) {       //       :
  :                     // while (!isDone) {
}                       //   :
                        // }

5.7 Conditionals

if ((elementNo < 0) || (elementNo > maxElement)|| 
    elementNo == lastElement) {
  :
}

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

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

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

file = openFile (fileName); // NOT: if ((file = openFile (fileName)) != null) {
if (file != null) {         //        :
  :                         //      }
}    

5.8 Miscellaneous

private static final int  TEAM_SIZE = 11;
:
Player[] players = new Player[TEAM_SIZE]; // NOT: Player[] players = new Player[11];

double total = 0.0;    // NOT:  double total = 0;
double speed = 3.0e8;  // NOT:  double speed = 3e8;


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

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

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

6 Layout and Comments

6.1 Layout

for (i = 0; i < nElements; i++)
  a[i] = 0;

while (!isDone) {
  doSomething();
  isDone = moreToDo();
}

while (!isDone)
{
  doSomething();
  isDone = moreToDo();
}

while (!isDone)
  {
    doSomething();
    isDone = moreToDo();
  }

class SomeClass extends AnotherClass
  implements SomeInterface, AnotherInterface
{
  ...
}

public void someMethod ()
  throws SomeException
{
  ...
}

if (condition) {
  statements;
}

if (condition) {
  statements;
}
else {
  statements;
}

if (condition) {
  statements;
}
else if (condition) {
  statements;
}
else {
  statements;
}

  if (condition) {
    statements;
  } else {
    statements;
  }

for (initialization; condition; update) {
  statements;
}

for (initialization; condition; update)
  ;

while (condition) {
  statements;
}

do {
  statements;
} while (condition);

switch (condition) {
  case ABC :
    statements;
    // Fallthrough
  case DEF :
    statements;
    break;
  case XYZ :
    statements;
    break;
  default :
    statements;
    break;
}

try {
  statements;
}
catch (Exception exception) {
  statements;
}

try {
  statements;
}
catch (Exception exception) {
  statements;
}
finally {
  statements;
}

if (condition) 
  statement;

while (condition)
  statement;

for (initialization; condition; update)
  statement;

6.2 White Space

a = (b + c) * d;               // NOT: a=(b+c)*d
while (true) {                 // NOT: while(true) ...
doSomething (a, b, c, d);      // NOT: doSomething (a,b,c,d);
case 100 :                     // NOT: case 100:
for (i = 0; i < 10; i++) {     // NOT: for(i=0;i<10;i++){

doSomething (parameter); // NOT: doSomething(parameter);
doSomething();           // OK

Matrix4x4 matrix = new Matrix4x4();

double cosAngle = Math.cos (angle);
double sinAngle = Math.sin (angle);  

matrix.setElement (1, 1,  cosAngle);
matrix.setElement (1, 2,  sinAngle);
matrix.setElement (2, 1, -sinAngle);
matrix.setElement (2, 2,  cosAngle);

multiply (matrix);

TextFile  file;
int       nPoints;
double    x, y;

if      (a == lowValue)    compueSomething();
else if (a == mediumValue) computeSomethingElse();
else if (a == highValue)   computeSomethingElseYet();

value = (potential        * oilDensity)   / constant1 +
        (depth            * waterDensity) / constant2 +
        (zCoordinateValue * gasDensity)   / constant3;

minPosition     = computeDistance (min,     x, y, z);
averagePosition = computeDistance (average, x, y, z);

switch (value) {
  case PHASE_OIL   : phaseString = "Oil";   break;
  case PHASE_WATER : phaseString = "Water"; break;
  case PHASE_GAS ; : phaseString = "Gas";   break;
}

6.3 Comments

// Comment spanning
// more than one line

while (true) {       // NOT: while (true) {
  // Do something    //      // Do something
  something();       //        something();
}                    //      }

private Vector  points_;    // of Point
private Set     shapes_;    // of Shape

7 References

[1] Code Complete, Steve McConnel - Microsoft Press

[2] Java Code Conventions
http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html

[3] Netscape's Software Coding Standards for Java
http://developer.netscape.com/docs/technote/java/codestyle.html

[4] C / C++ / Java Coding Standards from NASA
http://v2ma09.gsfc.nasa.gov/coding_standards.html

[5] Coding Standards for Java from AmbySoft
http://www.ambysoft.com/javaCodingStandards.html