Alice in Action with Java

Alice in Action with Java Chapter 10 Flow Control in Java

Objectives • Learn how to use the ifstatement • Learn how to use the switchstatement • Learn how to use the whileloop • Learn how to use the forloop • Learn how to use the doloop Alice in Action with Java

Flow Control In Java • Purpose of using selective and repetitive execution • Implement methods that produce complex behaviors • Selective flow control statements: if and switch • Repetitive flow control statements: while, for, do Alice in Action with Java

Selective Execution • Directing flow based on the value of a condition • Two statements that provide selective execution • if statement: general-purpose selection structure • switch statement: multi-branch selection structure Alice in Action with Java

Java’s if Statement • General-purpose selection structure • Selects from one or more groups of statements • The else portion of the if statement is optional • One-branch if: envisioned as branching flow • Two-branch if: flow follows one of two branches Alice in Action with Java

Java’s if Statement (continued) Alice in Action with Java

Java’s if Statement (continued) • Pattern for Java’s if statement: if(Condition)Statement1[else Statement2] • Condition: any boolean expression • Statementi: set of Java statements within { } • Brackets are optional if only one statement is in path • Multi-branch ifstatements (aka if-else chain) • Flow can move along multiple paths • Nest additional if statements in the else clause Alice in Action with Java

Java’s if Statement (continued) Alice in Action with Java

Alice in Action with Java

Repetitive Execution • Program execution flows sequentially by default • if and switch perform statements selectively • Repetitive execution: control flows in loops • Three repetition statements: while, for, and do Alice in Action with Java

Java’s while Statement • Used for processing a series of values • Input loops: read and process a series of values • Sentinel-controlled input loops • Utilize a sentinel (invalid value) to falsify a condition • Problem: extract the initials in a name • Members implemented in the Initialsclass • Instance variables called myName and myInitials • Constructor to initialize the instance variables • Methods to return myName and myInitials Alice in Action with Java

Java’s while Statement (continued) • General pattern for Java’s while statement while(Condition)Statement • Statementcomprises one or more statements • Curly braces ({ }) required with multiple statements • How it works • Condition is evaluated • If true • Statement is executed • Go back to evaluate the Condition • If false • Go to next statement in program Alice in Action with Java

while Statement Flow Alice in Action with Java

String Tokenizer • StringTokenizerclass:used to splitStrings • Overview of the Initials class constructor • String argument (name) is passed to constructor • Instance variables are initialized • StringTokenizer object called names is initialized • names and while loop are used to extract initials Alice in Action with Java

Initials class Alice in Action with Java

Java’s for Statement • Repetition structure for solving counting problems • Counting input loop • Simpler design than the sentinel-controlled input loop • Provides repetition when number of inputs is fixed • Illustration: computing the city’s air pollution index • A for loop counts from 1 to NUM_READINGS • Each iteration gets a reading and adds it to sum • After loop terminates, index is computed and output • Java’s for loop is very flexible • Example: the Java for loop can count down Alice in Action with Java

Counting Up Alice in Action with Java

NinetyNineBottles Alice in Action with Java

Nested Loops • TextGraphics class illustrates nested for loops • Understanding drawBox()in TextGraphicsclass • Method takes two arguments for height and width • Outer forloop counts the rows (builds the height) • Inner forloop prints asterisk symbol through width • General pattern for Java’s for loop for (InitialExpr; Condition; ChangeExpr) Statement • Curly braces ({ }) required with multiple statements • Scope of loop control variable goes to end of loop only Alice in Action with Java

TextGraphics Alice in Action with Java

for Statement Flow Alice in Action with Java

Post-Test Loop • In while and for statements, the condition is evaluated before the loop body is executed • Sometimes you have code that needs to get executed at least once • Execute the body • Evaluate the condition • Example GuessingGame • The do-while statement can be used in this case Alice in Action with Java

Java’s do Statement • Pattern for Java’s do statement: do Statement while(Condition); • Loop provides one-trip behavior with posttest condition • You must type a semicolon after the condition • How it works • Statement is executed • Condition is evaluated • If true, go back and execute statement • If false • Go to next statement in program Alice in Action with Java

do Statement Flow Alice in Action with Java

Choosing the Right Loop • Solving a problem with fixed counting • Recommendation: use the for loop • Solving a problem without fixed counting • If one-trip behavior is needed, use a do loop • If zero-trip behavior is needed, use a while loop Alice in Action with Java

Alice in Action with Java

Java’s switch Statement • Objective: create a PetLicense class • Instance variables used in PetLicense class • chartype namedmyCode stores license code • doubletype namedmyFee stores license fee • Constructor for a PetLicenseobject • Takes a single chartype argument • Uses multi-branch if to select appropriate fee • If data is valid, instance variables are initialized • If data is invalid, an error message is displayed • switch: concise alternative to the multi-branch if Alice in Action with Java

Java’s switch Statement • Pattern for Java’s switch statement switch(IntegerCompatibleExpression){ CaseList1 StatementList1 ... CaseListN StatementListN default: StatementListN+1 } • The condition is an integer-compatible expression • Each case corresponds to a literal value • The use of default statement optional • Use of breakstatement below a case is recommended • PetLicense class meets criteria for use of switch Alice in Action with Java

Nested switch Statements • Oneswitch statement can be nested within another • A nested switch statement is used in TShirt class Alice in Action with Java

Summary • By default, program execution flows sequentially • Selective execution: directing flow based on the value of a boolean condition • ifstatement: general-purpose selection structure • switchstatement: structure designed for certain types of multi-branch selection • Repetitive execution: performing the same group of statements while a condition is true Alice in Action with Java

Summary (continued) • whileloop: provides fixed and indefinite looping • Infinite loop: fails to terminate due to a faulty or missing condition • forloop: counter-controlled loop that exhibits zero-trip behavior • doloop: repetition structure that provides one-trip behavior through the use of a posttest condition • java.util.Random: class used to generate pseudo-random numbers Alice in Action with Java

Alice in Action with Java