SWE 510: Object Oriented Programming in Java Branching Mechanism This slide set was compiled from the Absolute Java textbook slides (Walter Savitch) and the instructor’s class materials. SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java Flow of Control Branching mechanisms if-else if switch (break) Looping mechanisms while do while for Boolean expressions evaluate to either true or false and decide which branch the control should go to if the control should stay in a loop SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java if-else Statement Prev_Statement Syntax Previous_Statement if ( Boolean_Expression ) Yes_Statement else No_Statement Next_Statement Examples if ( time < limit ) System.out.println( “You made it” ); System.out.println( “You missed the deadline” ); if ( side1 + side2 > side3 && side2 + side3 > side1 && side3 + side1 > side2 ) System.out.println( “Forms a triangle” ); System.out.println( “Does not form a triangle” ); Boolean Expression? true Yes_Statement false No_Statement Next_Statement SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java Omitting the else Part Prev_Statement Syntax Previous_Statement if ( Boolean_Expression ) Yes_Statement Action_Statement Examples if ( weight > ideal ) calorieAllotment = calorieAllotment - 500; if ( mph > 60 ) System.out.println( “Too fast” ); Boolean Expression? true Action_Statement false Next_Statement SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java Compound Statements Each Yes_Statement and No_Statement branch of an if-else can be a made up of a single statement or many statements Syntax if ( Boolean_Expression ) { Yes_Statement1; Yes_statement2; ...; } else No_Statement1; No_Statement2; Example if ( myScore > yourScore ) System.out.println( “I win!” ); wager += 100; System.out.println( “I wish these were golf scores” ); wager = 0; Yes_Statement1 Yes_Statement2 … Boolean Expression? true false No_Statement1 No_Statement2 … SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java Nested Statements if-else statements and if statements both contain smaller statements within them Example if ( side1 == side2 ) { System.out.println( “Isoceles” ); if ( side2 == side3 ) System.out.println( “Equilateral” ); } Equivalent if ( side1 == side2 ) System.out.println( “Isoceles” ); if ( side1 == side2 && side2 == side3 ( System.out.println( “Equilateral” ); SWE 510: Object Oriented Programming in Java

Multiway if-else Statement Syntax if (Boolean_Expression_1) Statement_1 else if (Boolean_Expression_2) Statement_2 else if (Boolean_Expression_n) Statement_n else Statement_For_All_Other_Possibilities Example if ( testScore >= 95 ) grade = ‘A’; else if ( testScore >= 85 ) grade = ‘B’; else if ( testScore >= 75 ) grade = ‘C’; else if ( testScore >= 65 ) grade = ‘D’; grade = ‘F’; System.out.println( “grade = ” + grade ); Expression_1? Statement_1 Expression_2? Statement_2 Expression_n? Statement_n Other_Statement SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java What’s Redundant? Improve Textbook p101’s code if ( netIncome <= 15000 ) tax = 0; else if ( ( netIncome > 15000 ) && ( netIncome <= 30000 ) ) tax = 0.05 * ( netIncome – 15000 ); else { fivePercentTax = 0.05 * 15000; tenPercentTax = 0.10 * ( netIncome – 30000 ); tax = fivePercentTax + tenPercentTax; } true netIncome <= 15000 Tax = 0 false true netIncome <= 30000 Tax = 0.05 * … false Tax = 0.05 * …+ 0.10 * ….; SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java switch Statement The switch statement is the only other kind of Java statement that implements multiway branching When a switch statement is evaluated, one of a number of different branches is executed Syntax switch (Controlling_Expression) { case Case_Label_1: Statement_Sequence_1 break; case Case_Label_2: Statement_Sequence_2 case Case_Label_n: Statement_Sequence_n default: Default_Statement Sequence } Must be a constant: char, int, short, or byte Controlling_Exp Label_1? true Statement_1 false Label_2? Statement_2 Label_n? Statement_n default_Statement Optional but recommended Executed in none of label_1 ~ n SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java Example 1 (Textbook p103) int vehicleClass; double toll; ...; switch ( vehicleClass ) { case 1: System.out.println( “Passenger car.” ); toll = 0.50; break; case 2: System.out.println( “Bus.” ); toll = 1.50; case 3: System.out.println( “Truck.” ); toll = 2.00; default: System.out.println( “Unknown vehicle class!” ); } A controlling expression must return char, int, short, or byte. Case labels must be a constant. Recommended to detect error cases. SWE 510: Object Oriented Programming in Java

Example 2 (java.sun.com tutorial) A controlling expression must return char, int, short, or byte. class SwitchDemo { public static void main(String[] args) { int month = 8; switch (month) { case 1: System.out.println("January"); break; case 2: System.out.println("February"); break; case 3: System.out.println("March"); break; case 4: System.out.println("April"); break; case 5: System.out.println("May"); break; case 6: System.out.println("June"); break; case 7: System.out.println("July"); break; case 8: System.out.println("August"); break; case 9: System.out.println("September"); break; case 10: System.out.println("October"); break; case 11: System.out.println("November"); break; case 12: System.out.println("December"); break; default: System.out.println("Invalid month."); break; } Case labels must be a constant. Recommended to detect error cases. SWE 510: Object Oriented Programming in Java

switch Statement without breaks Syntax switch (Controlling_Expression) { case Case_Label_1: Statement_Sequence_1 case Case_Label_2: Statement_Sequence_2 break; case Case_Label_m; Statement_Sequence_m case Case_Label_n: Statement_Sequence_n default: Default_Statement Sequence } Controlling_Exp Label_1? true Statement_1 false Label_2? Statement_2 Label_m? Statement_m Label_n? Statement_n Default_stmt SWE 510: Object Oriented Programming in Java

Example 3 (java.sun.com tutorial) class SwitchDemo2 { public static void main(String[] args) { int month = 2; int year = 2000; int numDays = 0; switch (month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: numDays = 31; break; case 4: case 6: case 9: case 11: numDays = 30; case 2: if ( ((year % 4 == 0) && !(year % 100 == 0)) || (year % 400 == 0) ) numDays = 29; else numDays = 28; default: System.out.println("Invalid month."); } System.out.println("Number of Days = " + numDays); SWE 510: Object Oriented Programming in Java

PITFALL: Forgetting a break class SwitchDemo2 { public static void main(String[] args) { int month = 2; int year = 2000; int numDays = 0; switch (month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: numDays = 31; case 4: case 6: case 9: case 11: numDays = 30; case 2: if ( ((year % 4 == 0) && !(year % 100 == 0)) || (year % 400 == 0) ) numDays = 29; else numDays = 28; default: System.out.println("Invalid month."); } System.out.println("Number of Days = " + numDays); Compiler does not complain about no breaks. Control continues down to the next case. SWE 510: Object Oriented Programming in Java

SWE 510: Object Oriented Programming in Java Conditional Operator A notational variant on certain forms of the if-else statement Also called the ternary operator or arithmetic if Syntax ( Boolean_Expression ) ? Yes_Expression : No_Expression; // if Boolean_Expression is true, evaluate Yes_Expression, // otherwise evaluate No_Expression, and finally return the // resulted value. Example max = ( n1 > n2 ) ? n1 : n2; Equivalent if ( n1 > n2 ) max = n1; else max = n2; SWE 510: Object Oriented Programming in Java