Flow of Control

1. Flow of Control IST 311 / MIS 307

2. Control Structures • Sequence: one after the other • Selection: selects a path based upon action • Iteration: repetition

3. Selection • Simple if Statement • Multiwayif / elseStatement • Nested if / else • switch Statement • Alternative way to write a multiway selection structure • Involves a test of equality • Logical expression being tested must be a primitive integral type byte, short, int, char

4. Selection • switch executes as follows: • Integral expression is evaluated • Control passes to the statements following the case label whose value equals the integral expression • If no cases match, control passes to the default clause • All statements are executed up to the break statement

5. Selection int m = 2; switch (m) { case 1: System.out.println (“m = 1”); break; case 2: System.out.println (“m = 2”); break; case 3: System.out.println (“m = 3”); break; default: System.out.println(“default case”); }

6. Control Structures • Sequence: one after the other • Selection: selects a path based upon action • Iteration: repetition

7. Iteration / Repetition • Repeats a statement or sequence of statements • Counting Loop • for • Conditional Loop • while • do-while

8. Iteration / Repetition • Counter-Controlled Loop • Know exactly how many times to repeat the loop beforehand for ( initializer; loop entry condition; updater) { for loop body; }

9. Iteration / Repetition int k; for (k = 0; k < 5; k++) { System.out.println (“Howdy”); } System.out.println(“k = “ + k);

10. Iteration / Repetition • Infinite Loops • Loops execute while the loop entry condition remains true • Infinite loops occurs when the loop entry condition never becomes false for (k = 0; k < 5; k--) • When program generates output, loop is obvious • When no output, program will appear to freeze

11. Iteration / Repetition • Nested Loop for (row = 1; row <= 4; row++) { for (col = 1; col <= 9; col++) { System.out.print (col * row + “\t” ); } System.out.println ( ); }

12. Iteration / Repetition • Conditional Loops initializer statement; while ( loop entry condition) { loop body; updater statement; }

13. Iteration / Repetition while (n != 1) { System.out.print (n + “ “); if (n % 2 == 0) n = n / 2; else n = 3 * n + 1; } System.out.println (n);

14. Iteration / Repetition • Conditional Loops initializer statement; do { loop body; updater statement; } while ( loop entry condition);

15. Control Structures • Sequence: one after the other • Selection: selects a path based upon action • Iteration: repetition

16. Static Methods • static – means that only one copy of the variable or method is created, whether or not the class in which it occurs is instantiated • static elements are underlined in UML

17. Math Class • java.lang.Math class provides common mathematical functions like: • double pow (double x, double y) • double random( ) • long round (double x) • double sqrt (double x) • All Math methods are static class methods and are invoked through the class name answer = Math.sqrt(9.0); • Included implicitly in all Java programs

18. Generate Random Numbers • Math.random( ) – used to generate random value from 0 to 1 (0 to 0.99999999) • Given the same seed value, Math.random( ) will generate the same sequence of numbers every time. • Number generated is type double • Use a scaling factor to establish the range of numbers to be generated

19. Generate Random Numbers • int num1 = (int)(Math.random( ) * 10); • Generate numbers from 0 to 9

20. javadoc

21. Comments • Should be used to improve readability of code

22. Comments • C-style comments /* multiline comment */ // single line comment • Java documentation format: /** ….. */ • Uses the “javadoc.exe” file

23. Java Documentation Tool • javadoc tool • Generates HTML pages that describe: • Public and protected classes • Inner classes • Interfaces • Constructors • Methods • Fields • Online documentation for Java library classes