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Penn CIT 591 - Beginning Style

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Beginning StyleBe consistent!Do it right the first timeIndent nested codeBreak up long linesDon’t use “hard” tabsUsing spacesUse meaningful namesMeaningful names: exceptions IMeaningful names: exceptions IIMeaningful names: exceptions IIINaming classes and interfacesNaming variablesNaming methodsNaming constantsCorrect style made easyThe EndJan 14, 2019Beginning Style2Be consistent!Most times, you will enter an ongoing project, with established style rulesFollow them even if you don’t like themIn this course you will be working in teams with various other peopleWe’ll all use the same set of style rules3Do it right the first timeYou only write code once, but you read it many times while you’re trying to get it to workGood style makes it more readable and helps you get it right!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?4Indent nested codeAlways indent statements that are nested inside (under the control of) another statementif (itemCost <= bankBalance) { writeCheck(itemCost); bankBalance = bankBalance - itemCost;}The open brace always goes at the end of a lineThe matching close brace lines up with the statement being closedIndentation should be consistent throughout the program4 spaces has become more-or-less standard5Break up long linesKeep your lines short enough to be viewed and printedMany people use 72 or 80 character limitsSuggestions on where to break a long line:It’s illegal to break a line within a quoted stringBreak after, not before, operatorsLine up parameters to a methodDon’t indent the second line of a control statement with a long test so that it lines up with the statements being controlled6Don’t use “hard” tabsA hard tab is an actual tab character in your textIt tells the program to go to the next tab stop (wherever that is)Not every program puts tab stops in the same placeIf you use hard tabs to indent, sooner or later your nice indentation will be ruinedGood editors can be set to use soft tabs (your tab characters are replaced with spaces)When you hit the tab key, the editor puts spaces into your file, not tab charactersWith soft tabs, your indentation is always safeBlueJ uses only soft tabs7Using spacesUse spaces around all binary operators except “dot”: if (n > 1 && n % 2 == 1) n = 3 * n + 1; Do not use spaces just within parentheses: if ( x < 0 ) x = -x; // don’t do thisUse a space before and after the parenthesized test in a control statement: if (x < 0) {...} while (x < 0) {...}Do not use a space between a method name and its parameters; do put a space after each comma: int add(int x, int y) {...} a = add(3, k);8Use meaningful namesNames should be chosen very carefully, to indicate the purpose of a variable or methodIf the purpose changes, the name should be changedSpend a little time to choose the best name for each of your variables and methods!Long, multiword names are common in JavaHowever, if a name is too long, maybe you’re trying to use it for too many purposesDon’t change the name, separate the purposesDon’t abbreviate namesBut very common abbreviations, such as max for “maximum”, are OK9Meaningful names: exceptions IIt is common practice to use i as the index of a for-loop, 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:for (int i = 1; i <= 10; i++) { for (int j = 1, j <= 10; j++) { System.out.println(" " + (i * j)); }}10Meaningful names: exceptions IILocal variables in methods may be given short, simple names, if: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) or classes or methods11Meaningful names: exceptions IIIIf variables have no special meaning, you can use names that reflect their types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p, q, r, s are often used for booleansw, x, y, z are often used for real numbers12Naming classes and interfacesCapitalize the first letter of each word, including the first word: PrintStream, Person, ExemptEmployeeUse nouns to name classes: ExemptEmployee, CustomerAccountClasses are supposed to represent thingsUse adjectives to name interfaces: Comparable, PrintableInterfaces are supposed to represent features13Naming variablesCapitalize the first letter of each word except the first: total, maxValueUse nouns to name variables: balance, outputLineVariables are supposed to represent values14Naming methodsCapitalize the first letter of each word except the first: display, displayImageMethods are capitalized the same as variablesUse verbs when naming methods: displayImage, computeBalanceMethods are supposed to do something15Naming constants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;Constants are written in ALL_CAPITALS, with underscores between words16Correct style made easyIn Eclipse, go to Window  Preferences  Java  Code Style  Formatter, and under Select a profile: choose Java conventions [built-in]Select some or all of your code and choose Source  Format17The End“Where a calculator on the ENIAC is equipped with 18000 vacuum tubes and weighs 30 tons, computers of the future may have only 1000 vacuum tubes and perhaps weigh 1½ tons.” —Popular Mechanics, March


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