1. Switch statement

2. Problem
Write a program that inputs dates in the form month day year (ex ) and outputs the date in the form: 13-jun-1988.
Note: Days are in the range Months are in the range

3. Problem Steps: 1. prompt for a date 2. read the date 3. echo the input
4. convert the date
5. output the converted date

4. Problem /* File: Convert.java Author: George J. Grevera, Ph.D.
Date: today
Description:
This program inputs dates in the form month/day/year (ex. 6/13/1988) and outputs the date in the form: 13-jun Note: Days are in the range Months are in the range */
import java.util.Scanner;
public class Convert {
public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
//read the date
//echo the input
//convert the date
//output the converted date
in.close(); }

5. public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
//read the date
//echo the input
//convert the date
//output the converted date
in.close(); }

6. public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
//echo the input
//convert the date
//output the converted date
in.close(); }

7. public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
//echo the input
//convert the date
//output the converted date
in.close(); }

8. int month = in.nextInt(); int day = in.nextInt();
public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
//convert the date
//output the converted date
in.close(); }

9. //echo the input public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
//convert the date
//output the converted date
in.close(); }

10. System.out.println( "You entered m=" + month
public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
System.out.println();
System.out.println( "You entered m=" + month
+ " d=" + day + " y=" + year );
//convert the date
//output the converted date
in.close(); }

11. Run: Enter date --> 12 1 2008 You entered m=12 d=1 y=2008
public static void main ( String s[] ) { Scanner in = new Scanner( System.in ); //prompt for a date System.out.print( "Enter date --> " ); //read the date int month = in.nextInt(); int day = in.nextInt(); int year = in.nextInt(); //echo the input System.out.println(); System.out.println( "You entered m=" + month + " d=" + day + " y=" + year ); //convert the date //output the converted date in.close(); }
Run:
Enter date -->
You entered m=12 d=1 y=2008

12. //convert the date public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
System.out.println( “\nYou entered m=" + month
+ " d=" + day + " y=" + year );
//convert the date
//output the converted date
in.close(); }

13. //convert the date String ms; public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
in.useDelimiter( "[/,\n, ,\t]" );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
System.out.println( “\nYou entered m=" + month
+ " d=" + day + " y=" + year );
//convert the date
String ms;
//output the converted date
in.close(); }

14. //convert the date String ms; if (month==1) ms = "jan"; …
public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
in.useDelimiter( "[/,\n, ,\t]" );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
System.out.println( “\nYou entered m=" + month
+ " d=" + day + " y=" + year );
//convert the date
String ms;
if (month==1)
ms = "jan"; …
//output the converted date
in.close(); }

15. //convert the date String ms; if (month==1) ms = "jan";
public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
in.useDelimiter( "[/,\n, ,\t]" );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
System.out.println( “\nYou entered m=" + month
+ " d=" + day + " y=" + year );
//convert the date
String ms;
if (month==1)
ms = "jan";
else if (month==2)
ms = "feb"; …
else if (month==12)
ms = "dec";
else
ms = "???";
//output the converted date
in.close(); }

16. public static void main ( String s[] ) {
Scanner in = new Scanner( System.in );
in.useDelimiter( "[/,\n, ,\t]" );
//prompt for a date
System.out.print( "Enter date --> " );
//read the date
int month = in.nextInt();
int day = in.nextInt();
int year = in.nextInt();
//echo the input
System.out.println( “\nYou entered m=" + month
+ " d=" + day + " y=" + year );
//convert the date
String ms = "???";
if (month==1)
ms = "jan";
else if (month==2)
ms = "feb"; …
else if (month==12)
ms = "dec";
//output the converted date
System.out.println( day + "-" + ms + "-" + year );
in.close(); }
We have checked the month. Additionally, we could check for reasonable days and years.

17. Once again, recall the date format conversion problem…
Write a program that inputs dates in the form month day year (ex ) and outputs the date in the form: 13-jun-1988.
Note: Days are in the range Months are in the range
How did we convert the month from an integer to a string (6 to “jun”)?

18. How did we convert the month from an integer to a string (6 to “jun”)?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” );
else if (month==3)
System.out.print( “mar” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “invalid month” );

19. Introducing the switch statement
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:
statement_sequence_default }

20. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
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:
statement_sequence_default }

21. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
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:
statement_sequence_default }

22. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case case_label_1:
statement_sequence_1
break;
case case_label_2:
statement_sequence_2 …
case case_label_n:
statement_sequence_n
default:
statement_sequence_default }

23. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case case_label_1:
statement_sequence_1
break;
case case_label_2:
statement_sequence_2 …
case case_label_n:
statement_sequence_n
default:
statement_sequence_default }

24. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
statement_sequence_1
break;
case case_label_2:
statement_sequence_2 …
case case_label_n:
statement_sequence_n
default:
statement_sequence_default }

25. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
statement_sequence_1
break;
case case_label_2:
statement_sequence_2 …
case case_label_n:
statement_sequence_n
default:
statement_sequence_default }

26. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
statement_sequence_1
break;
case 2:
statement_sequence_2 …
case case_label_n:
statement_sequence_n
default:
statement_sequence_default }

27. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
statement_sequence_1
break;
case 2:
statement_sequence_2 …
case case_label_n:
statement_sequence_n
default:
statement_sequence_default }

28. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
statement_sequence_1
break;
case 2:
statement_sequence_2 …
case 12:
statement_sequence_n
default:
statement_sequence_default }

29. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
statement_sequence_1
break;
case 2:
statement_sequence_2 …
case 12:
statement_sequence_n
default:
statement_sequence_default }

30. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
statement_sequence_2 …
case 12:
statement_sequence_n
default:
statement_sequence_default }

31. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
statement_sequence_2 …
case 12:
statement_sequence_n
default:
statement_sequence_default }

32. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
System.out.print( “feb” ); …
case 12:
statement_sequence_n
default:
statement_sequence_default }

33. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
System.out.print( “feb” ); …
case 12:
statement_sequence_n
default:
statement_sequence_default }

34. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
System.out.print( “feb” ); …
case 12:
System.out.print( “dec” );
default:
statement_sequence_default }

35. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
System.out.print( “feb” ); …
case 12:
System.out.print( “dec” );
default:
statement_sequence_default }

36. How can we use the switch instead?
if (month==1)
System.out.print( “jan” );
else if (month==2)
System.out.print( “feb” ); …
else if (month==12)
System.out.print( “dec” );
else
System.out.print( “bad month” );
switch (month) {
case 1:
System.out.print( “jan” );
break;
case 2:
System.out.print( “feb” ); …
case 12:
System.out.print( “dec” );
default:
System.out.print(“bad month”); }

37. switch notes
Unlike if, the controlling expression must evaluate to int, char, short, byte.
switch (52+7/n) { is fine if n is an int
switch (s) { is not fine if s is a String
switch (d) { is not fine if d is a double

38. switch notes
You can’t repeat a case label.
case 7 :
blah;
break; …

39. switch notes
Multiple statements may be associated with a case w/out the need for a block.
case 17 :
blah1;
blah2;
blah3;
break;
The default case is optional.

40. switch notes The case labels must be constants.
case “fred” : is not OK
case : is not OK
case d : is not OK (even if d is an int)

41. switch notes
Don’t forget the break! Unexpected things may happen. The following is perfectly fine but may not be what you intended:
case 992:
case -1:
System.out.println( “here” );
case 57:
System.out.println( “there” );
System.out.println( “everywhere”);
break;

42. Multiway if-else Statement
if (Boolean_Expression)
Statement_1
else if (Boolean_Expression)
Statement_2
else if (Boolean_Expression_n)
Statement_n
else
Statement_For_All_Other_Possibilities
. . .

43. The 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
The choice of which branch to execute is determined by a controlling expression enclosed in parentheses after the keyword switch
The controlling expression must evaluate to a char, int, short, or byte

44. The switch Statement
Each branch statement in a switch statement starts with the reserved word case, followed by a constant called a case label, followed by a colon, and then a sequence of statements
Each case label must be of the same type as the controlling expression
Case labels need not be listed in order or span a complete interval, but each one may appear only once
Each sequence of statements may be followed by a break statement ( break;)

45. The switch Statement There can also be a section labeled default:
The default section is optional, and is usually last
Even if the case labels cover all possible outcomes in a given switch statement, it is still a good practice to include a default section
It can be used to output an error message, for example
When the controlling expression is evaluated, the code for the case label whose value matches the controlling expression is executed
If no case label matches, then the only statements executed are those following the default label (if there is one)

46. The switch Statement
The switch statement ends when it executes a break statement, or when the end of the switch statement is reached
When the computer executes the statements after a case label, it continues until a break statement is reached
If the break statement is omitted, then after executing the code for one case, the computer will go on to execute the code for the next case
If the break statement is omitted inadvertently, the compiler will not issue an error message

47. The switch Statement 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 }
//Show Demo program
. . .