Style About the book n n This book

Style

About the book n n 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! 2

Rule 1: Adhere to the style of the original n n Consistent style is very important Most times, you will enter an ongoing project, with established style rules n n n Follow them even if you don’t like them Don’t try to establish “better” style rules n It won’t work anyway n 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 3

Rule 3: Do it right the first time n n n 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? 4

Rule 5: Indent nested code n n Always indent statements that are nested inside (under the control of) another statement if (item. Cost <= bank. Balance) { write. Check(item. Cost); bank. Balance = bank. Balance - item. Cost; } while (seconds > 0) { System. out. print(seconds + ". . . "); seconds = seconds - 1; } Indentation should be consistent throughout the program n 4 spaces has become more-or-less standard 5

Rule 6: Break up long lines n n n 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 Various suggestions: n n n Break after, not before, operators Line up parameters to a method Don’t indent the second line of a control statement so that it lines up with the statements being controlled 6

Rule 8: Don’t use “hard” tabs n n n 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 n n It’s worse if you use both tabs and spaces 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) n Blue. J uses only soft tabs; Eclipse can do either 7

Rule 9: Use meaningful names n n n 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 Eclipse makes it very easy to rename things 8

Rule 10: Use familiar names n n 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 9

Rule 11: Question excessively long names n n n 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

Meaningful names: exceptions I n n n 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: n for (int i = 1; i <= 10; i++) { for (int j = 1, j <= 10; j++) { System. out. println(" " + (i * j)); } } 11

Meaningful names: exceptions II n Method variables may be given short, simple names, if: n n n The purpose of the variable is obvious from context, and The variable is used only briefly, in a small part of the program But never use meaningless names for fields (class or instance variables) 12

Rule 28: Use standard names for “throwaway” variables n If variables have no special meaning, you can use names that reflect their types n n For example, if you are writing a general method to work with any strings, you might name them string 1, string 2, etc. Alternatively, you can use very short names n n n s, t, u, or s 1, s 2, etc. are often used for Strings p, q, r, s are often used for booleans w, x, y, z are often used for real numbers 13

Rule 12: Join the “vowel generation” n In more primitive languages, names were often limited to 8 or so characters n n This led to names like max. Volum and lng. Plyng The usual rule was to leave out vowels, starting from the right Such names are harder to read and to remember Do not leave out vowels, or otherwise unusual abbreviations, in Java! 14

Naming classes and interfaces n n Rule 18: Capitalize the first letter of each word, including the first: Print. Stream, Person, Exempt. Employee Rule 19: Use nouns to name classes: Exempt. Employee, Customer. Account n n Classes are supposed to represent things Rule 20: Use adjectives to name interfaces: Comparable, Printable n Interfaces are supposed to represent features 15

Naming variables n n Rule 25: Capitalize the first letter of each word except the first: total, max. Value Rule 26: Use nouns to name variables: balance, output. Line n Variables are supposed to represent values 16

Naming methods n Rule 22: Capitalize the first letter of each word except the first: display, display. Image n n Methods are capitalized the same as variables Rule 23: Use verbs when naming methods: display. Image, compute. Balance n Methods are supposed to do something 17

Rule 13: Capitalize only the first letter in acronyms n n In names, write acronyms such as GUI and API as Gui and Api Examples: set. Dst. Offset, , display. As. Html, , load. Xml. Document Since capital letters are used to separate names, this rule helps avoid confusion Sun’s APIs don’t always follow this convention 18

Naming constants n n A constant is an identifier whose value, once given, cannot be changed Constants are written with the keyword final, for example: n n final int FIVE = 5; final float AVOGADROS_NUMBER = 6. 022 E 23; Rule 31: Constants are written in ALL_CAPITALS, with underscores between words Exception: color names, such as Color. pink n n Colors were defined before conventions were established However, Java 1. 4 adds properly capitalized names for colors, such as Color. PINK 19

Kinds of comments n n “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 n All of the above are “internal” comments, seen only by someone looking at your code n Don’t overcomment; not every line needs a comment! n Internal comments are only for maintainers n But avoid things that would embarrass you to a user! n Documentation (javadoc) comments: /**. . . */ n n These are meant to be seen by the entire world! Documentation comments are not covered in this series of slides 20

Which kind of internal comment? n Rule 36: Use “standard” (/*. . . */) comments to comment out code without removing it. n n However, this assumes you are using a simple text editor, because it saves typing // over and over again This is a bad rule if you are using a decent IDE n Standard comments cannot be nested, so it’s tricky commenting out code with comments n n One-line comments don’t have this problem Both Blue. J and Eclipse make it very easy to use one-line (//. . . ) comments 21

Explaining the code I n Rule 59: Add internal comments only if they will aid in understanding your code. n n n Don’t repeat the javadoc comments Don’t put in comments to explain things that are obvious from the code Don’t put in irrelevant or useless comments n n // Go Red Sox!!!! Always put /*. . . */ comments before the code they describe, never after the code 22

Explaining the code II n Rule 37: Use one-line comments to explain implementation details. n n 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 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 23

End-line comments I n Rule 62: Explain local variable declarations with an end-line comment. n n n int edge. Distance; // distance to the nearest edge But don’t let your lines get too long And Rule 64 says: Label closing braces in highly nested control structures. n n } // end switch } // end if } // end for j } // end for i Better yet, avoid highly nested control structures 24

End-line comments II n I also find end-line comments useful for an else that is a long way from its if: n n if (distance > 5) {. . . a lot of code in between. . . } else { // distance <= 5. . . } But now that we have assert statements, this is even better: n . . . else { assert distance <= 5; . . . } 25

Flagging unresolved issues n n Rule 63: Establish and use a set of keywords to flag unresolved issues. Eclipse uses these three (you can add more): n n n TODO for things you would like to do in the future FIXME for things which are broken and you need to fix, but you aren’t working on at the moment XXX for things that are arguably broken and you need to think about some more before you do anything 26

Intentionally missing break n Rule 65: Add a “fall-through” comment between two case labels of a switch statement, if no break statement separates those labels. n n 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 27

Label empty statements n n Sometimes you intentionally use a loop with an empty statement body Rule 66: Label empty statements. while ((c = reader. read()) == space) ; // Empty body § This is because the semicolon is small and easy to overlook n I prefer a different solution: use an empty block as the statement body while ((c = reader. read()) == space) { } 28

Don’t repeat the code n n 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. n n 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! 29

Use the active voice n Rule 34: Use the active voice, and omit needless words n n // zero out the array // 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 30

Debugging statements n n 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 legal. Location(int row, int col) { System. out. println("In legal. Location: " + row + " " + col); return row >= 0 && row < num. Rows && column >= 0 && column < num. Cols; } n Another option: n final boolean debugging = true; . . . if (debugging) System. out. println(. . . ) 31

The End 32

The End 33