Consolidated Lectures
16-Apr-20

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This book is a team effort by many good programmers, not just one person’s opinions
The rules have been widely distributed and commented upon
The rules reflect widespread and accepted practices
And no, I don’t agree with everything in the book!
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Consistent style is very important
Most times, you will enter an ongoing project, with established style rules
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Follow them even if you don’t like them
Don’t try to establish “better” style rules
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It won’t work anyway
There may be reasons you don’t know about
If a project has mixed styles with no consistency, you might try to get people to agree on one
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You’re working on a large project, so you use good style...
 ...but you need a tool to help you do one little job, so you slap it together quickly
 Guess which program will be around longer and used by more people?
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Always indent statements that are nested inside
(under the control of) another statement
} if (itemCost <= bankBalance) { writeCheck(itemCost); bankBalance = bankBalance - itemCost;
} while (seconds > 0) {
System.out.print(seconds + "..."); seconds = seconds - 1;
Indentation should be consistent throughout the program
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2 to 4 spaces is usually about right
5

 Scrolling a window horizontally is a pain!
 When you print on standard paper, long lines are either cut off or wrap in bad places
 I have long used a 72 character limit
 Some editors will show you a limit line
 The book provides good advice on how to break up long lines (read it!)
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Once upon a time, you could depend on tab stops every eight character positions
Today, every editor has its own idea of where and how to set tab stops
If you change editors, your nice indentation gets ruined
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It’s worse if you use both tabs and spaces
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I have learned this one the hard way!
A hard tab is an actual tab character in your text
Good editors can be set to use soft tabs (your tab characters are replaced with spaces)
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BlueJ uses only soft tabs
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 Names should be chosen very carefully, to indicate the purpose of a variable or method
 If the purpose changes, the variable or method should be renamed
 It is worthwhile spending a little time choosing the best name
 Long, multiword names are common in Java
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Where common terminology exists, use it; don’t make up your own
 Example from the book: If your users refer to
“customers,” your program should use the name
Customer
, not
Client
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 Variables should be used for a single purpose
 Methods should do one simple, clearly defined thing
 If a descriptive name is overly long, maybe the variable or method is trying to serve too many purposes
10

 It is common practice to use i as the index of a forloop, j as the index of an inner loop, and k as the index of a third-level loop
 This is almost always better than trying to come up with a meaningful name
 Example:
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} for (int i = 1; i <= 10; i++) { for (int j = 1, j <= 10; j++) {
System.out.println(" " + (i * j));
}
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 Method variables may be given short, simple names, if:
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The purpose of the variable is obvious from context, and
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The variable is used only briefly, in a small part of the program
 But never use meaningless names for class or instance variables
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 If variables have no special meaning, you can use names that reflect their types
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For example, if you are writing a general method to work with any strings, you might name them string1
, string2
, etc.
 Alternatively, you can use very short names
 s
, t
, u
, or s1
, s2
, etc. are often used for Strings
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 p
, q
, r
, s are often used for booleans w
, x
, y
, z are often used for real numbers
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 Despite the cutesy name, this rule is important
 In more primitive languages, names were often limited to 8 or so characters
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This led to names like maxVolum and lngPlyng
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The usual rule was to leave out vowels, starting from the right
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Such names are harder to read and to remember
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 Rule 18: Capitalize the first letter of each word, including the first:
PrintStream
,
Person
,
ExemptEmployee
 Rule 19: Use nouns to name classes:
ExemptEmployee
,
CustomerAccount
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Classes are supposed to represent things
 Rule 20: Use adjectives to name interfaces:
Comparable
,
Printable
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Interfaces are supposed to represent features
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 Rule 25: Capitalize the first letter of each word except the first: total
, maxValue
 Rule 26: Use nouns to name variables: balance
, outputLine
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Variables are supposed to represent values
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 Rule 22: Capitalize the first letter of each word except the first: display
, displayImage
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Methods are capitalized the same as variables
 Rule 23: Use verbs when naming methods: displayImage
, computeBalance
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Methods are supposed to do something
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In names, write acronyms such as GUI and API as
Gui and
Api
Examples: setDstOffset , displayAsHtml , loadXmlDocument
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Since capital letters are used to separate names, this rule helps avoid confusion
Sun’s APIs don’t always follow this convention
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A constant is an identifier whose value, once given, cannot be changed
Constants are written with the keyword final
, for example:
 final int FIVE = 5;
 final float AVOGADROS_NUMBER = 6.022E23;
Rule 31: Constants are written in ALL_CAPITALS , with underscores between words
Exception: color names, such as
Color.pink
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Colors were defined before conventions were established
However, Java 1.4 adds properly capitalized names for colors, such as
Color.PINK
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“Standard” (C-style) comments:
/* ... */
One-line and end-line comments:
// a one-line comment is on a line by itself x = 0; // an end-line comment follows code
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All of the above are “internal” comments, seen only by someone looking at your code
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Internal comments are only for maintainers
But avoid things that would embarrass you to a user!
Documentation (javadoc) comments: /** ... */
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These are meant to be seen by the entire world!
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Documentation comments are not covered in this series of slides
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Rule 36: Use “standard” ( /*...*/ ) comments to comment out code without removing it .
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This is a quick way to comment out and uncomment code
This rule isn’t actually appropriate for us
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BlueJ’s comment and uncomment commands make it easier to use one-line (
//...
) comments
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Standard comments cannot be nested, so it’s tricky commenting out code with comments
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One-line comments don’t have this problem
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 Rule 59: Add internal comments only if they will aid in understanding your code.
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Don’t repeat the javadoc comments
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Don’t put in comments to explain things that are obvious from the code
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Don’t put in irrelevant or useless comments
// Go Cubs!!!!
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Always put /* ... */ comments before the code they describe, never after the code
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 Rule 37: Use one-line comments to explain implementation details.
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One-line comments are also good for writing reminders for yourself about things you still need to work on
// These assertions should be replaced by Exceptions
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I like to use one-line comments to tell what the next several lines of code are going to do
// Put this Vehicle in a random location
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 Rule 61: Avoid the use of end-line comments.
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This rule is largely to prevent overly long lines
 But Rule 62 says: Explain local variable declarations with an end-line comment.
 int edgeDistance; // distance to the nearest edge
 And Rule 64 says: Label closing braces in highly nested control structures.
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} // end switch
} // end if
} // end for j
} // end for i
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Better yet, avoid highly nested control structures
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I also find end-line comments useful for an else that is a long way from its if
:
 if (distance > 5) {
}
... a lot of code in between ...
} else { // distance <= 5
...
But now that we have assert statements, this is even better:
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...
else { assert distance <= 5;
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 Rule 63: Establish and use a set of keywords to flag unresolved issues.
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I personally like to use
$$
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// $$ the canvas isn't being redrawn properly
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More specific flags are likely to be used in large projects
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// $$ DLM: Problem #1403; Level: Urgent
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 Rule 65: Add a “fall-through” comment between two case labels of a switch statement, if no break statement separates those labels.
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The switch statement is so badly designed that forgetting the break is a common error
To keep an intentionally missing break from being
“corrected,” add a comment
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 Sometimes you intentionally use a loop with an empty statement body
 Rule 66: Label empty statements.
while ((c = reader.read()) == space) ;
// Empty body
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This is because the semicolon is small and easy to overlook
 I prefer a different solution: use an empty block as the statement body while ((c = reader.read()) == space) { }
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 Rule 60: Describe why the code is doing what it does, not what the code is doing.
 Another way of saying this is:
Comments should not echo code.
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Here’s a typical example of a bad comment: count = 0; // set count to zero
 You should assume that anyone reading your internal comments knows some Java!
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 Rule 34: Use the active voice, and omit needless words
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// zero out the array
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// each of the elements of the array is set to
// zero by the following loop
 Writing comments is still writing --all the rules for good writing apply to comments
 Best reference: The Elements of Style , by Strunk and White
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We sometimes put in debugging statements that we plan to remove afterwards
Simple trick: start these “temporary” statements in the first column, so you can find them easily boolean legalLocation(int row, int col) {
System.out.println("In legalLocation: " + row + " " + col); return row >= 0 && row < numRows && column >= 0 && column < numCols;
}
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