Flow of Control

1. Flow of Control Chapter 3 Part 3 Edited by JJ Shepherd

2. Switch Statement

3. The switch Statement • The switch statement is a mutltiway branch that makes a decision based on an integral (integer or character) expression. • Java 7 allows String expressions • In other words you switch on integers, characters, or strings • The switch statement begins with the keyword switchfollowed by an integral expression in parentheses and called the controlling expression.

4. The switch Statement • A list of cases follows, enclosed in braces. • Each case consists of the keyword case followed by • A constant called the case label • A colon • A list of statements. • The list is searched for a case label matching the controlling expression.

5. The switch Statement • The action associated with a matching case label is executed. • If no match is found, the case labeled default is executed. • The default case is optional, but recommended, even if it simply prints a message. • Repeated case labels are not allowed.

6. The switch Statement • Syntax switch (Controlling_Expression) { case Case_Label: Statement(s); break; case Case_Label: … default: … }

7. The switch Statement • The action for each case typically ends with the word break. • The optionalbreakstatement prevents the consideration of other cases. • The controlling expression can be anything that evaluates to an integral type.

8. switch to if-else Conversion int a = keyboard.nextInt() switch(a) { case 1: System.out.println(“one”); break; case 2: System.out.println(“two”); break; default System.out.println(“What?”); break; }

9. switch to if-else Conversion int a = keyboard.nextInt() if(a == 1) { System.out.println(“one”); } else if(a == 2) { System.out.println(“two”); } else { System.out.println(“What?”); }

10. Enumerations

11. Enumerations • Consider a need to restrict contents of a variable to certain values • An enumeration lists the values a variable can have • Enumerations are good for using words instead of numbers to represent related values. Makes code more readable. • Exampleenum MovieRating {E, A, B}MovieRating rating;rating = MovieRating.A;

12. Enumerations • Now possible to use in a switch statement

13. Enumerations • An even better choice of descriptive identifiers for the constantsenum MovieRating {EXCELLENT, AVERAGE, BAD}rating = MovieRating.AVERAGE;case EXCELLENT: ...

14. Example!

15. Summary You have learned about Java branching statements. You have learned about the type boolean.