1. switch Statement

2. Objectives: Learn the syntax for switch statements
Another objective is to discuss team development and illustrate software reusability in the context of a simple but realistic case study, the Craps applet.

3. The switch Statement switch case default break switch (variable) {
case value1:
...
break;
case value2:
default: }
Reserved words
switch case
default
break
There is a legend in software folklore that a missing break in a program caused the whole telephone grid of New York to go down, costing millions of dollars. You have to be careful about breaks; they are among the many opportunities to make a stupid mistake not caught by the compiler. Attention to detail is key.
Don’t forget breaks!

4. The switch Statement (cont’d)
switch (num) {
case 1:
System.out.println ("Buckle your shoe");
break;
case 2:
... }
This is simply a special case of a case without a break. Case 1 "falls through" to Case 2.

5. The switch Statement (cont’d)
The same case can have two or more labels. For example:
switch (num) {
case 1:
case 2:
System.out.println ("Buckle your shoe");
break;
case 3:
... }
This is simply a special case of a case without a break. Case 1 "falls through" to Case 2.

6. Top Down Design

7. Top-Down Design (cont’d)
Write a program that reads a simple equation from the keyboard in the form [a + b].
Only four symbols will be used: + - * /
Solve the equation and display the results on the console screen.

8. Top-Down Design (cont’d)
Start JCreator.
Open the file “Lab11.java”.
Lab11.java is in your Lab11 folder.

9. Top-Down Design (cont’d)
The “big problem” is defined in the main method.

10. Top-Down Design (cont’d)
import java.text.DecimalFormat; import java.util.Scanner; public class Lab11 { public static void main(String[ ] args) for (int i = 0; i < 3; i++) Lab11 lab = new Lab11( ); lab.input(); // Enter data from the kybd lab.process(); // Perform the calculation lab.output( ); // Display output }

11. Top-Down Design (cont’d)
We need four instance fields to solve the problem.

12. Top-Down Design (cont’d)
public class Lab11 { private double a; private double b; private char symbol; private double solution; public static void main(String[] args) for (int i = 0; i < 3; i++) Lab11 lab = new Lab11( ); lab.input(); // Enter data from the kybd lab.process(); // Perform the calculation lab.output( ); // Display output }

13. Top-Down Design (cont’d)
input(), process() and output( ) are the smaller parts of the problem.

14. Top-Down Design (cont’d)
input( )

15. Top-Down Design (cont’d)
public void input() { Scanner reader = new Scanner(System.in); System.out.print("Enter an expression in the form [a + b]: "); a= reader.nextDouble(); symbol = reader.next().charAt(0); b= reader.nextDouble(); }

16. Top-Down Design (cont’d)
output( )

17. Top-Down Design (cont’d)
public void output() { DecimalFormat df = new DecimalFormat("#.#"); System.out.println(df.format(a) + " " + symbol + “ " + df.format(b) + " = " + df.format(solution)); }

18. Top-Down Design (cont’d)
process( )

19. Top-Down Design (cont’d)
public void process() { switch (symbol) { case '+': solution = a + b; break; case '*': solution = a * b; case '-': solution = a - b; case '/': solution = a / b; }

20. Top-Down Design (cont’d)
Run The Program:
Enter an expression in the form [a + b]:
35 / 6
35 / 6 = 5.8
Enter an expression in the form [a + b]:
= 42.5

21. Questions?

22. Java Begin Lab 11 Object Oriented Programming
The material in this chapter is not tested on the AP CS exams.

23. Top-Down Design (cont’d)
import java.util.Scanner; public class Lab11A { public static void main(String[ ] args) for (int i = 0; i < 3; i++) Lab11A lab = new Lab11A( ); lab.input(); // Enter data from the kybd lab.output( ); // Display output }

24. Top-Down Design (cont’d)
import java.util.Scanner; public class Lab11A { private int age; public static void main(String[ ] args) for (int i = 0; i < 3; i++) Lab11A lab = new Lab11A( ); lab.input(); // Enter data from the kybd lab.output( ); // Display output }

25. Top-Down Design (cont’d)
public void input() { Scanner reader = new Scanner(System.in); System.out.print("Enter a person’s age (Between 10 & 25): "); age = reader.nextInt(); }

26. Lab 11A – output() public void output() { switch (age) {
case 13: System.out.println("Teenager!");
break;
case 16: System.out.println("Keys, please?");
case 18: System.out.println("Rise to vote, sir!");
case 21: System.out.println("Full adult privileges");
default: System.out.println("Too young to do anything."); }

27. “Full Adult Privileges!”
Lab 11A – output()
Cover all ages from
10 to 25.
Ages 21 – 25
should all say
“Full Adult Privileges!”
public void output() {
switch (age) {
case 13: System.out.println("Teenager!");
break;
case 16: System.out.println("Keys, please?");
case 18: System.out.println("Rise to vote, sir!");
case 21: System.out.println("Full adult privileges");
default: System.out.println("Too young to do anything."); }