Interview Fundas

" Tabs are set every three spaces.
" Variable and method names are lowercase, with occasional upperCase characters in the middle.
" Class names start with an Uppercase letter
" Constant names are UPPERCASE, with an occasional UNDER_SCORE.
" There are spaces after keywords and surrounding binary operators.
" Braces must line up horizontally or vertically.
" No magic numbers may be used.
" 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.

1.2 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 comment explaining the purpose of this file should be in the format recognized by the javadoc utility. Start with a /**, and use the @author and @version tags:

/**
Classes for user login.
@author Kislay Komal
@version 1.01 2006-03-31
*/

1.3 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:
1. Constructors
2. Instance Methods
3. Static Methods
4. Instance Fields
5. Static Fields
6. 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 static variable per class.

1.4 Methods

" Every method (except for main) starts with a comment in javadoc format.
/**
Validate for login details
@param String userId
@param String password
@return a boolean value
*/
public static boolean loginValidate(String userId, int password)
{
. . .
}
" 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.

1.5 Variables and Constants

" Do not define all variables at the beginning of a block:
{
double price; // Don't
double discount;
boolean creditCard;
. . .
}
Define each variable just before it is used for the first time:
{
. . .
double price = Integer.parseInt(input);
boolean creditCard = false;
while (creditCard)
{
double discount = (price + a / price) / 2; // OK
. . .
}
. . .
}
" Do not define two variables on the same line:
int day = 0, hours = 0; // Don't
Instead, use two separate definitions:
int day = 0; // OK
int hours = 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[]; // Not OK

1.6 Control Flow

1.6.1 The if Statement

" Avoid the "if ... if ... else" trap. 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 an extra pair of { ... } when dealing with "if ... if ... else":
if ( ... )
{
if ( ... ) ...;
} // {...} are necessary
else ...;

if ( ... )
{
if ( ... ) ...;
else ...;
} // {...} not necessary, but they keep you out of trouble

1.6.2 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);
}

1.6.3 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.

1.6.4 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.

1.7 Lexical Issues

1.7.1 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 (maybe with an occasional UNDER_SCORE); for example, CLOCK_RADIUS.
" All class and interface names start with uppercase and are followed by lowercase letters (maybe with an occasional UpperCase letter); for example, BankTeller.
" Names must be reasonably long and descriptive. Use firstPlayer instead 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 counter, 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 etc).

1.7.2 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 a blank space around every binary operator:
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.
if (x == 0) y = 0;

f(a, b[i]);
" 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 while statement 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.

1.7.3 Braces

" Opening and closing braces must line up, either horizontally or vertically:
while (i < n) { System.out.println(a[i]); i++; }

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.

1.7.4 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 pre-allotted 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.
" Do not use // comments for comments that extend for more than two lines. You don't want to have to move the // around when you edit the comment.
// comment - don't do this
// more comment
// more comment
" Use /* ... */ comments 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 un-maintained comments and ugly comments that are up to date, truth wins over beauty.