Wyo Area High School Java Coding Standards

Wyomissing Area High School
Java Language Coding Guidelines
adapted from Appendix A1 of Big Java by Cay Horstmann

While the coding style guidelines below will be enforced on graded programming assignments in this course, another set of popular and worthwhile guidelines is Oracle's own set found here http://www.oracle.com/technetwork/java/codeconv-138413.html

This coding style guide is a simplified version of one that has been used with good success both in industrial practice and for college courses.

A style guide is a set of mandatory requirements for layout and formatting. Uniform style makes it easier for you to read code from your instructor and classmates. You will really appreciate that if you do a team project. It is also easier for your instructor and your grader to grasp the essence of your programs quickly.

A style guide makes you a more productive programmer because it reduces gratuitous choice. If you don't have to make choices about trivial matters, you can spend your energy on the solution of real problems.

In these guidelines, several constructs are plainly outlawed. That doesn't mean that programmers using them are evil or incompetent. It does mean that the constructs are not essential and can be expressed just as well or even better with other language constructs.

If you already have programming experience, in Java or another language, you may be initially uncomfortable at giving up some fond habits. However, it is a sign of professionalism to set aside personal preferences in minor matters and to compromise for the benefit of your group.

These guidelines are necessarily somewhat dull. They also mention features that you may not yet have seen in class. Here are the most important highlights:

Tabs are set every three spaces.
Variable and method names are lowercase, with occasional upperCase characters in the middle. Some call this the interCap method for naming variables. For example, a proper variable name is numStudents rather than NumStudents or num_students or numstudents.
Class names start with an uppercase letter. For example, a class name BankAccount rather than bankAccount should be used.
Constant names are UPPERCASE, with an occasional UNDER_SCORE. For example, BANK_FEE is a good constant name rather than BANKFEE or bankFee.
There are spaces after keywords and surrounding binary operators.
Curly braces must line up vertically with a whole line occupied by a curly brace as in

while (num < 100)
{
   num++;
}

rather than

while (num < 100) {
   num++;
}

or

while (num < 100)
{  num++;
}

or

while (num < 100) {  num++;  }
No magic numbers may be used. You should use constants where appropriate.
Every method, except for main and overridden library methods, must have a comment.
At most 30 lines of code may be used per method.
No continue or break is allowed.
All non-final variables must be private.

A1.2 Source Files

Each Java program is a collection of one or more source files. The executable program is obtained by compiling these files. Organize the material in each file as follows:

package statement, if appropriate
import statements
A comment explaining the purpose of this file
A public class
Other classes, if appropriate

The following header comment should be in the format recognized by the javadoc utility. Start with a /**, and use the @author tag:

/**

 * THE NAME OF THE CLASS

 * @author YOUR NAME AND CLASS PERIOD

 */

Example

/**

 * ASCIIArt

 * @author John Doe Per 1

 */

A1.3 Classes

Each class should be preceded by a class comment explaining the purpose of the class.

First list all public features, then all private features.

Within the public and private section, use the following order:

Constructors
Instance Methods
Static Methods
Instance Fields
Static Fields
Inner classes

Leave a blank line after every method.

All non-final variables must be private. (However, instance variables of a private inner class may be public.) Methods and final variables can be either public or private, as appropriate.

All features must be tagged public or private. Do not use the default visibility (that is, package visibility) or the protected attribute.

Avoid static variables (except final ones) whenever possible. In the rare instance that you need static variables, you are permitted one staticvariable per class.

A1.4 Methods

Every method (except for main) starts with a comment in javadoc format.

/**
   Convert calendar date into Julian day.
   Note: This algorithm is from Press et al., Numerical Recipes
   in C, 2nd ed., Cambridge University Press, 1992
   @param day day of the date to be converted
   @param month month of the date to be converted
   @param year year of the date to be converted
   @return the Julian day number that begins at noon of the
   given calendar date.
*/
public static int dat2jul(int day, int month, int year)
{ 
   . . .
}

Methods must have at most 30 lines of code. The method signature, comments, blank lines, and lines containing only braces are not included in this count. This rule forces you to break up complex computations into separate methods.

A1.5 Variables and Constants

Do not define all variables at the beginning of a block:

{  
   double xold; // Don't
   double xnew;
   boolean more;
   . . .
}

Define each variable just before it is used for the first time:

{ 
   . . .
   double xold = Integer.parseInt(input);
   boolean more = false;

   while (more)
   {  
      double xnew = (xold + a / xold) / 2; // OK
      . . .
   }
   . . .
}

Do not define two variables on the same line:

int dimes = 0, nickels = 0; // Don't

Instead, use two separate definitions:

int dimes = 0; // OK
int nickels = 0;

with each declaration statement having its own type. Do not use use this format

int dimes = 0,  // Don't
    nickels = 0;

In Java, constants must be defined with the keyword final. If the constant is used by multiple methods, declare it as static final. It is a good idea to define static final variables as private if no other class has an interest in them.

Do not use magic numbers! A magic number is a numeric constant embedded in code, without a constant definition. Any number except -1, 0, 1, and 2 is considered magic:

if (p.getX() < 300) // Don't

Use final variables instead:

final double WINDOW_WIDTH = 300;
. . .
if (p.getX() < WINDOW_WIDTH) // OK

Even the most reasonable cosmic constant is going to change one day. You think there are 365 days per year? Your customers on Mars are going to be pretty unhappy about your silly prejudice. Make a constant

public static final int DAYS_PER_YEAR = 365;

so that you can easily produce a Martian version without trying to find all the 365s, 364s, 366s, 367s, and so on, in your code.

When declaring array variables, group the [] with the type, not the variable.

int[] values; // OK
int values[]; // Ugh--this is an ugly holdover from C

A1.6 Control Flow

A1.6.1—The if Statement

Avoid the "if ... if ... else" trap. This is sometimes called the dangling else error. The code

if ( ... )
   if ( ... ) ...;
else ...;

will not do what the indentation level suggests, and it can take hours to find such a bug. Always use a pair of curly braces { ... } with EVERY if statement and every else clause:

if ( ... )
{  

   if ( ... )
   {
      ...;
   }

}
else 
{
   ...;
}

A1.6.2—The for Statement

Use for loops only when a variable runs from somewhere to somewhere with some constant increment/decrement:

for (int i = 0; i < a.length; i++)
{
   System.out.println(a[i]);
}

Do not use the for loop for weird constructs such as

for (a = a / 2; count < ITERATIONS; System.out.println(xnew))
   // Don't

Make such a loop into a while loop. That way, the sequence of instructions is much clearer.

a = a / 2;

while (count < ITERATIONS) // OK
{  . . .
   System.out.println(xnew);
}

A1.6.3—Nonlinear Control Flow

Avoid the switch statement, because it is easy to fall through accidentally to an unwanted case. Use if/else instead.

Avoid the break or continue statements. Use another boolean variable to control the execution flow.

A1.6.4—Exceptions

Do not tag a method with an overly general exception specification:

Widget readWidget(Reader in)
   throws Exception // Bad

Instead, specifically declare any checked exceptions that your method may throw:

Widget readWidget(Reader in)
   throws IOException, MalformedWidgetException // Good

Do not "squelch" exceptions:

try
{ 
    double price = in.readDouble();
}
catch (Exception e)
{} // Bad

Beginners often make this mistake "to keep the compiler happy". If the current method is not appropriate for handling the exception, simply use a throws specification and let one of its callers handle it.

A1.7 Lexical Issues

A1.7.1—Naming Convention

The following rules specify when to use upper- and lowercase letters in identifier names.

All variable and method names and all data fields of classes are in lowercase (maybe with an occasional upperCase in the middle); for example, firstPlayer.
All constants are in uppercase letters with underscore characters used to separate two or more words; for example, CLOCK_RADIUS rather than clockRadius or CLOCKRADIUS.
All class and interface names start with uppercase letter and are followed by lowercase letters with each word, after the first word, beginning with a capital letter; for example, BankTeller rather than bankteller, BankTeller, or bank_teller.

Names must be reasonably long and descriptive. Your program is considered to be self-documenting if its variable names are descriptive. Use firstPlayerinstead of fp. No drppng f vwls. Local variables that are fairly routine can be short (ch, i) as long as they are really just boring holders for an input character, a loop variable, and so on. Also, do not use ctr, c, cntr, cnt, c2 for variables in your method. Surely these variables all have specific purposes and can be named to remind the reader of them (for example, current, next, previous, result, . . . ).

A1.7.2—Indentation and White Space

Use tab stops every three columns. That means you will need to change the tab stop setting in your editor!

Use blank lines freely to separate parts of a method that are logically distinct.

Use blank lines above and below all if statements, loops, methods, and other structures. You must even use blank lines around nested loop and if statements as in

if (num > 1)
{ 
                       // blank line here
   if (num < 3)
   {
      System.out.println(2);
   }
                       // blank line here
}

Use a blank space around every binary operator (except the ++ and -- operators):

x1 = (-b - Math.sqrt(b * b - 4 * a * c)) / (2 * a); // Good
x1=(-b-Math.sqrt(b*b-4*a*c))/(2*a);//Bad

Leave a blank space after (and not before) each comma or semicolon. Do not leave a space before or after a parenthesis or bracket in an expression. Leave spaces around the ( . . . ) part of an if, while, for, or catch statement.

Every line must fit on 80 columns. If you must break a statement, add an indentation level for the continuation:

a[n] = ..................................................
   + .................;

Start the indented line with an operator (if possible).

If the condition in an if or whilestatement must be broken, be sure to brace the body in, even if it consists of only one statement:

if ( .........................................................
   && ..................
   || .......... )
{  
   . . .
}

If it weren't for the braces, it would be hard to separate the continuation of the condition visually from the statement to be executed.

A1.7.3—Braces

Opening and closing braces must line up vertically:

while (i < n)
{   
   System.out.println(a[i]);                   
   i++;
}

Some programmers don't line up vertical braces but place the { behind the key word:

while (i < n) { // DON'T
   System.out.println(a[i]);
   i++;
}

Doing so makes it hard to check that the braces match.

A1.7.4—Unstable Layout

Some programmers take great pride in lining up certain columns in their code:

firstRecord = other.firstRecord;
lastRecord  = other.lastRecord;
cutoff      = other.cutoff;

This is undeniably neat, but the layout is not stable under change. A new variable name that is longer than the preallotted number of columns requires that you move all entries around:

firstRecord = other.firstRecord;
lastRecord  = other.lastRecord;
cutoff      = other.cutoff;
marginalFudgeFactor = other.marginalFudgeFactor;

This is just the kind of trap that makes you decide to use a short variable name like mff instead.

When using /* ... */ comments, don't "beautify" them with additional asterisks:

/* comment—don't do this
 * more comment
 * more comment
 */

It looks neat, but it is a major disincentive to update the comment. Some people have text editors that lay out comments. But even if you do, you don't know whether the next person who maintains your code has such an editor.

Instead, format long comments like this:

/*
   comment
   more comment
   more comment
*/

or this:

/*
comment
more comment
more comment
*/

These comments are easier to maintain as your program changes. If you have to choose between pretty but unmaintained comments and ugly comments that are up to date, truth wins over beauty.