1Lecture Set #3:Conditional and Iterative StructuresControl Structures if branching if / else branching logical operators nesting of control structures proper indenting and spacing conventions java identifier naming conventions named constants while loop do-while loop for loopCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)Control Flow and Conditionals Control flow: the order in which statements are executed General rule: top to bottom Several Control Structures that change that Conditional statements: permit control flow to be dependent on (true/false) conditions if if-elseCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)if and if-elseThe if and if-else statements should have the following form: if (condition) {statements; } tests the condition if true statement is done; otherwise it is skipped if (condition) {statements1; } else { statements2; } tests the condition if true, statements1 is done; otherwise statements2 is doneCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)2Java and White Spacehttp://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.htmlCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)You can add: carriage returns, spaces, tabswherever you want in JavaProperly used, this makes your program easier to read and understandLogical OperatorsUsed for forming more complex conditions. “and” &&if ( temp >= 97 && temp <= 99 ) {System.out.println( “Patient is healthy” );} “or” ||if ( months >= 3 || miles >= 3000 ) {System.out.println( “Change your oil” );} “not”: !if ( ! phone.equals( “301-555-1212” ) ) {System.out.println( “Sorry, wrong number” );}CMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)Blocks What happens?if (i > 10) i = 10; saturate = true; Desired: both i, saturate are set only when i > 10 Actual: only the i=10 statement is dependant Only one statement can be associated with if The saturate assignment statement is not part of the if Blocks solve this problemCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)3Blocks What happens?if (i > 10) i = 10; saturate = true; elsek = 100; Desired: both i, saturate are set only when i > 10 Actual: syntax error Only one statement can be associated with if The saturate assignment statement is not part of the if The else can’t find the if it belongs to Blocks solve this problem alsoCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)What Blocks Are Blocks are sequences of statements “glued together” into one Form:{<statement 1>;<statement 2>;…} Example:if (i > 10) {i = 10;saturate = true;} else {i = i+1;} if, if-else, {…} are statement constructors They take statement(s) and convert them into a new statement Implications: if statements, etc. can also appear inside (“be nested within”) one anotherCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)blockblockIssues with if-else Nested If/Elses can be Ugly and Confusing! indent and block carefully The “Dangling Else” Problem Java rule: else is associated with “innermost” possible if Cascading Elses WE WILL USE { … } FOR ALL IF, IF-ELSE, IF-ELSE-IF, STATEMENTSCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)4In Projects You must use meaningful variable names it must tell the purpose of that variable – what it is meant to hold it can not have so much abbreviation that only you can read it You must use Java convention indenting and brace placement the indenting show the purpose in nesting with braces in the “Java determined” places with respect to the lines of code Java convention of capitalization of identifiers variables and methods start with lower case classes and interfaces start with upper case variables, methods, classes and interface use camelCase constants are all uppercase with underscores between words You must have “Fully Blocked” if statements and looping structures You must have all lines less than or equal to 80 columns of text You must use "named constants" for any literal values that will not change during program execution.CMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)Named Constants If same value should be used in several places, how to ensure consistency? i.e. Check on temperature may be performed more than once i.e. Same prompt might be printed in several places final int MAX_OK_TEMP = 99; Just like a regular variable declaration/initialization, except… Special term final Necessity of initial value Any valid variable name will work, but convention is to use all capitals Difference from non-final variables: assignment attempt leads to error! literals (= named values)e.g.if (temp >= 212 || temp <= 32) …if (temp >= BOILING || temp <= FREEZING)e.g.System.out.print (“Enter integer: “);System.out.print (PROMPT);CMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)Naming Rules and Conventions What is legal for variable names? Letters, digits, $, _ Can’t start variable name with digit Avoid reserved words Avoid names starting or ending with $ or _ Use camelCase: Variables & Methods use lower-case for first letter Classes/Interfaces use upper-case for first letter Naming Conventions: Standards developed over time.Variables and methods: Start with lowercase, and use uppercase for each new word:dataList2 myFavoriteMartian showMeTheMoneyClass names: Start with uppercase and uppercase for each new word:String JOptionPane MyFavoriteClassNamed constants (variables whose value never changes): All uppercase with underscores between words:MAX_LENGTH DAYS_PER_WEEK BOILING_POINT Make variable names not too long, not too short Bad: crtItm Bad : theCurrentItemBeingProcessed Good : currentItemCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)5Meaningful Variable Names Choose names for your variables to reflect their purpose not their type Make it readable to someone else Help prevent mistakes in order of the relational operatorsCMSC 131 Fall 2010 Jan Plane and Ben Bederson (adapted from Bonnie Dorr)BadGoodtypedValue == 5menuOption ==
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